Our Evolutionary Partners Like us, most of our food plants are relative newcomers to the earth. Life arose about 4 billion years ago, but flowering plants have been around for only about 200 million years, and dominant for the last 50 million. An even more recent development is the "herbaceous" habit of life. Most food plants are not long-lived trees, but relatively small, delicate plants that produce their seeds and die in one growing season. This herbaceous habit gives plants greater flexibility in adapting to changing conditions, and it has worked to our advantage as well. It allows us to grow crops to maturity in a few months, change plantings from year to year, rapidly breed new varieties, and eat plant parts that would be inedible were they toughened to endure for years. Herbaceous plants became widespread only in the last few million years, just as the human species was emerging. They made possible our rapid cultural development, and we in turn have used selection and breeding to direct their biological development. We and our food plants have been partners in each other's evolution. Like us, most of our food plants are relative newcomers to the earth. Life arose about 4 billion years ago, but flowering plants have been around for only about 200 million years, and dominant for the last 50 million. An even more recent development is the "herbaceous" habit of life. Most food plants are not long-lived trees, but relatively small, delicate plants that produce their seeds and die in one growing season. This herbaceous habit gives plants greater flexibility in adapting to changing conditions, and it has worked to our advantage as well. It allows us to grow crops to maturity in a few months, change plantings from year to year, rapidly breed new varieties, and eat plant parts that would be inedible were they toughened to endure for years. Herbaceous plants became widespread only in the last few million years, just as the human species was emerging. They made possible our rapid cultural development, and we in turn have used selection and breeding to direct their biological development. We and our food plants have been partners in each other's evolution.

Definitions We group the foods we obtain from plants into several loose categories.

Fruit and Vegetable Apart from such plant seeds as wheat and rice, which are described in chapter 9, the most prominent plant foods in our diet are fruits and vegetables. Apart from such plant seeds as wheat and rice, which are described in chapter 9, the most prominent plant foods in our diet are fruits and vegetables. Vegetable Vegetable took on its current sense just a few centuries ago, and essentially means a plant material that is neither fruit nor seed. So what is a fruit? The word has both a technical and a common meaning. Beginning in the 17th century, botanists defined it as the organ that develops from the flower's ovary and surrounds the plant's seeds. But in common usage, seed-surrounding green beans, eggplants, cuc.u.mbers, and corn kernels are called vegetables, not fruits. Even the United States Supreme Court has preferred the cook's definition over the botanist's. In the 1890s, a New York food importer claimed duty-free status for a shipment of tomatoes, arguing that tomatoes were fruits, and so under the regulations of the time, not subject to import fees. The customs agent ruled that tomatoes were vegetables and imposed a duty. A majority of the Supreme Court decided that tomatoes were "usually served at a dinner in, with, or after the soup, fish, or meat, which const.i.tute the princ.i.p.al part of the repast, and not, like fruits, generally as dessert." Ergo tomatoes were vegetables, and the importer had to pay. took on its current sense just a few centuries ago, and essentially means a plant material that is neither fruit nor seed. So what is a fruit? The word has both a technical and a common meaning. Beginning in the 17th century, botanists defined it as the organ that develops from the flower's ovary and surrounds the plant's seeds. But in common usage, seed-surrounding green beans, eggplants, cuc.u.mbers, and corn kernels are called vegetables, not fruits. Even the United States Supreme Court has preferred the cook's definition over the botanist's. In the 1890s, a New York food importer claimed duty-free status for a shipment of tomatoes, arguing that tomatoes were fruits, and so under the regulations of the time, not subject to import fees. The customs agent ruled that tomatoes were vegetables and imposed a duty. A majority of the Supreme Court decided that tomatoes were "usually served at a dinner in, with, or after the soup, fish, or meat, which const.i.tute the princ.i.p.al part of the repast, and not, like fruits, generally as dessert." Ergo tomatoes were vegetables, and the importer had to pay.

The Key Distinction: Flavor Why do we customarily prepare vegetables as side dishes to the main course, and make fruits the centerpiece of the meal's climax? Culinary fruits are distinguished from vegetables by one important characteristic: they're among the few things we eat that we're meant to eat. Many plants have engineered their fruits to appeal to the animal senses, so that animals will eat them and disperse the seeds within. These fruits are the natural world's soft drinks and candies, flashily packaged in bright colors, and test-marketed through millions of years of natural selection. They tend to have a high sugar content, to satisfy the innate liking for sweetness shared by all animals. They have a p.r.o.nounced and complex aroma, which may involve several hundred different chemicals, far more than any other natural ingredient. And they soften themselves to an appealingly tender, moist consistency. By contrast, the plant foods that we treat as vegetables remain firm, have either a very mild flavor - green beans and potatoes - or else an excessively strong one - onions and cabbage - and therefore require the craft of the cook to make them palatable. Why do we customarily prepare vegetables as side dishes to the main course, and make fruits the centerpiece of the meal's climax? Culinary fruits are distinguished from vegetables by one important characteristic: they're among the few things we eat that we're meant to eat. Many plants have engineered their fruits to appeal to the animal senses, so that animals will eat them and disperse the seeds within. These fruits are the natural world's soft drinks and candies, flashily packaged in bright colors, and test-marketed through millions of years of natural selection. They tend to have a high sugar content, to satisfy the innate liking for sweetness shared by all animals. They have a p.r.o.nounced and complex aroma, which may involve several hundred different chemicals, far more than any other natural ingredient. And they soften themselves to an appealingly tender, moist consistency. By contrast, the plant foods that we treat as vegetables remain firm, have either a very mild flavor - green beans and potatoes - or else an excessively strong one - onions and cabbage - and therefore require the craft of the cook to make them palatable.

The very words fruit fruit and and vegetable vegetable reflect these differences. reflect these differences. Vegetable Vegetable comes from the Latin verb comes from the Latin verb vegere, vegere, meaning to invigorate or enliven. meaning to invigorate or enliven. Fruit, Fruit, on the other hand, comes from Latin on the other hand, comes from Latin fructus, fructus, whose cl.u.s.ter of related meanings includes gratification, pleasure, satisfaction, enjoyment. It's the nature of fruit to taste good, to appeal to our basic biological interests, while vegetables stimulate us to find and create more subtle and diverse pleasures than fruits have to offer. whose cl.u.s.ter of related meanings includes gratification, pleasure, satisfaction, enjoyment. It's the nature of fruit to taste good, to appeal to our basic biological interests, while vegetables stimulate us to find and create more subtle and diverse pleasures than fruits have to offer.

Herb and Spice The terms The terms herb herb and and spice spice are more straightforward. Both are categories of plant materials used primarily as flavorings, and in relatively small amounts. Herbs come from green parts of plants, usually leaves - parsley, thyme, basil - while spices are generally seeds, bark, underground stems - black pepper, cinnamon, ginger - and other robust materials that were well suited to international trade in early times. The word are more straightforward. Both are categories of plant materials used primarily as flavorings, and in relatively small amounts. Herbs come from green parts of plants, usually leaves - parsley, thyme, basil - while spices are generally seeds, bark, underground stems - black pepper, cinnamon, ginger - and other robust materials that were well suited to international trade in early times. The word spice spice came from the medieval Latin came from the medieval Latin species, species, which meant "kind of merchandise." which meant "kind of merchandise."

Despite the fact that we consider them vegetables, capsic.u.m "peppers," pea pods, cuc.u.mbers, and even corn kernels are actually fruits: plant parts that originate in the flower's ovary and surround one or more seeds.

Plant Foods Through History How long has the Western world been eating the plant foods we eat today, and in the way that we eat them? Only a very few common vegetables have not not been eaten since before recorded history (the relative newcomers include broccoli, cauliflower, brussels sprouts, celery). But it was only with the age of exploration in the 16th century that the variety of foods we now know became available to any single culture. In the Western world, fruit has been eaten as dessert at least since the Greeks; recognizable salads go back to the Middle Ages, and boiled vegetables in delicate sauces to 17th-century France. been eaten since before recorded history (the relative newcomers include broccoli, cauliflower, brussels sprouts, celery). But it was only with the age of exploration in the 16th century that the variety of foods we now know became available to any single culture. In the Western world, fruit has been eaten as dessert at least since the Greeks; recognizable salads go back to the Middle Ages, and boiled vegetables in delicate sauces to 17th-century France.

Prehistory and Early Civilizations Many plants came under human cultivation by the unsophisticated but slowly effective means of gathering useful plants and leaving a few seeds in fertile refuse heaps. Judging from archaeological evidence, early Europeans seem to have relied on wheat, fava beans, peas, turnips, onions, radishes, and cabbage. In Central America, corn, beans, hard squashes, tomatoes, and avocados were staples around 3500 Many plants came under human cultivation by the unsophisticated but slowly effective means of gathering useful plants and leaving a few seeds in fertile refuse heaps. Judging from archaeological evidence, early Europeans seem to have relied on wheat, fava beans, peas, turnips, onions, radishes, and cabbage. In Central America, corn, beans, hard squashes, tomatoes, and avocados were staples around 3500 BCE BCE, while Peruvian settlements relied heavily on the potato. Northern Asia started with millets, cabbage relatives, soybeans, and tree fruits in the apple and peach families; southern Asia had rice, bananas, coconuts, yams, cabbage relatives, and citrus fruits. Indigenous African crops included related but distinct millets, sorghum, rice, and bananas, as well as yams and cowpeas. Mustard seed flavored foods in Europe and in Asia, where ginger may also have been used. Chilli "pepper" was probably the chief spice in the Americas.

By the time of the earliest civilizations in Sumer and Egypt about 5,000 years ago, most of the plants native to that area and eaten today were already in use (see box, p. 250). Trade between the Middle East and Asia is also ancient. Egyptian records of around 1200 BCE BCE doc.u.ment huge offerings of cinnamon, a product of Sri Lanka. doc.u.ment huge offerings of cinnamon, a product of Sri Lanka.

Greece, Rome, and the Middle Ages With the Greeks and Romans we begin to see the outlines of modern Western cuisine. The Greeks were fond of lettuce, and habitually ate fruit at the end of meals. Pepper from the Far East was in use around 500 With the Greeks and Romans we begin to see the outlines of modern Western cuisine. The Greeks were fond of lettuce, and habitually ate fruit at the end of meals. Pepper from the Far East was in use around 500 BCE BCE and quickly became the most popular spice of the ancient world. In Rome, lettuce was served at both the beginning and end of meals, and fruit as dessert. Thanks to the art of grafting growing shoots from desirable trees onto other trees, there were about 25 named apple varieties and 35 pears. Fruits were preserved whole by immersing them, stems and all, in honey, and the gastronome Apicius gave a recipe for pickled peaches. From the Roman recipes that survive, it would seem that few foods were served without the application of several strong flavors. and quickly became the most popular spice of the ancient world. In Rome, lettuce was served at both the beginning and end of meals, and fruit as dessert. Thanks to the art of grafting growing shoots from desirable trees onto other trees, there were about 25 named apple varieties and 35 pears. Fruits were preserved whole by immersing them, stems and all, in honey, and the gastronome Apicius gave a recipe for pickled peaches. From the Roman recipes that survive, it would seem that few foods were served without the application of several strong flavors.

When the Romans conquered Europe they brought along tree fruits, the vine, and cultivated cabbage, as well as their heavy spice habit. Sauce recipes from the 14th century resemble those of Apicius, and the English lettuce-free salad would also have been quite pungent (see box, p. 251). Medieval recipe collections include relatively few vegetable dishes.

New World, New Foods Plants - and especially the spice plants - helped shape world history in the last five centuries. The ancient European hunger for Asian spices was an important driving force in the development of Italy, Portugal, Spain, Holland, and England into major sea powers during the Renaissance. Columbus, Vasco da Gama, John Cabot, and Magellan were looking for a new route to the Indies in order to break the monopoly of Venice and southern Arabia on the ancient trade in cinnamon, cloves, nutmeg, and black pepper. They failed in that quest, but succeeded in opening the "West Indies" to European exploitation. The New World was initially disappointing in its yield of sought-for spices. But vanilla and chillis quickly became popular; and its wealth of new vegetables was largely adaptable to Europe's climate: so the common bean, corn, squashes, tomatoes, potatoes, and sweet chillis eventually became staple ingredients in the new cuisines of the Old World. Plants - and especially the spice plants - helped shape world history in the last five centuries. The ancient European hunger for Asian spices was an important driving force in the development of Italy, Portugal, Spain, Holland, and England into major sea powers during the Renaissance. Columbus, Vasco da Gama, John Cabot, and Magellan were looking for a new route to the Indies in order to break the monopoly of Venice and southern Arabia on the ancient trade in cinnamon, cloves, nutmeg, and black pepper. They failed in that quest, but succeeded in opening the "West Indies" to European exploitation. The New World was initially disappointing in its yield of sought-for spices. But vanilla and chillis quickly became popular; and its wealth of new vegetables was largely adaptable to Europe's climate: so the common bean, corn, squashes, tomatoes, potatoes, and sweet chillis eventually became staple ingredients in the new cuisines of the Old World.

Vegetables, Fruits, and Spices Used in the WestMediterranean Area Natives, Used BCE BCE Vegetables 1. Mushroom 2. Beet 3. Radish 4. Turnip 5. Carrot 6. Parsnip 7. Asparagus 8. Leek 9. Onion 10. Cabbage 11. Lettuce 12. Artichoke 13. Cuc.u.mber 14. Broad bean 15. Pea 16. Olive Fruits 1. Apple 2. Pear 3. Cherry 4. Grape 5. Fig 6. Date 7. Strawberry Herbs and Spices 1. Basil 2. Marjoram 3. Fennel 4. Mint 5. Rosemary 6. Sage 7. Savory 8. Thyme 9. Anise 10. Caraway 11. Coriander 12. c.u.min 13. Dill 14. Parsley 15. Oregano 16. Bay 17. Caper 18. Fenugreek 19. Garlic 20. Mustard 21. Poppy 22. Sesame 23. Saffron Later Additions Vegetables 1. Spinach 2. Celery 3. Rhubarb 4. Cauliflower 5. Broccoli 6. Brussels sprouts Asian Natives, Brought to the West BCE BCE Fruits 1. Citron 2. Apricot 3. Peach Herbs and Spices 1. Cardamom 2. Ginger 3. Cinnamon 4. Turmeric 5. Black pepper Imported Later Vegetables 1. Yam 2. Water 3. Bamboo 4. Eggplant Fruits 1. Lemon 2. Lime 3. Orange 4. Melon Herbs and Spices 1. Tarragon 2. Mace 3. Clove 4. Nutmeg New World Natives, Imported 15th16th Centuries Vegetables 1. Potato 2. Sweet potato 3. Pumpkin 4. Squashes 5. Tomato 6. Kidney bean 7. Lima bean 8. Capsic.u.m pepper 9. Avocado Fruits 1. Pineapple Herbs and Spices 1. Allspice 2. Chillis 3. Vanilla The 17th and 18th centuries were a time of a.s.similating the new foods and advancing the art of cooking them. Cultivation and breeding received new attention; Louis XIV's orchards and plantings at Versailles were legendary. And cooks took a greater interest in vegetables, and handled them with greater refinement, in part to make the meatless diet of Lent and other Catholic fasts more interesting. France's first great culinary writer, Pierre Francois de La Varenne, chef to Henri IV, included meatless recipes for peas, turnips, lettuce, spinach, cuc.u.mbers, cabbage (five ways), chicory, celery, carrots, cardoons, and beets, as well as ordinary dishes of artichokes, asparagus, mushrooms, and cauliflower. And the recipes leave a major role for the vegetables' own flavors. Similarly, the Englishman John Evelyn wrote a book-length disquisition on salads, once again firmly based on the lettuces, and emphasized the importance of balance.

Plant Ingredients in Rome and Medieval EuropeA Roman Sauce for Sh.e.l.lfishc.u.min Sauce, for Sh.e.l.lfish: Pepper, lovage, parsley, mint, aromatic leaf [e.g., bay], malabathrum [a Middle Eastern leaf], plenty of c.u.min, honey, vinegar, liquamen [a fermented fish paste similar to our anchovy paste]. Pepper, lovage, parsley, mint, aromatic leaf [e.g., bay], malabathrum [a Middle Eastern leaf], plenty of c.u.min, honey, vinegar, liquamen [a fermented fish paste similar to our anchovy paste].- from Apicius, first few centuries CE CEMedieval Sauces, French (Taillevent, ca. 1375) and English (The Forme of Cury (The Forme of Cury , ca. 1390) , ca. 1390)Sauce Cameline, for Meats:France: Ginger, mace, cinnamon, cloves, grain of paradise, pepper, vinegar, bread [to thicken].England: Ginger, cloves, cinnamon, currants, nuts, vinegar, bread crusts.Verde Sauce:France: Parsley, ginger, vinegar, bread.England: Parsley, ginger, vinegar, bread, mint, garlic, thyme, sage, cinnamon, pepper, saffron, salt, wine.Salad and a Vegetable Compote (The Forme of Cury (The Forme of Cury , ca. 1390) , ca. 1390)Salat: Take parsley, sage, garlic, scallions, onions, leeks, borage, mints, young leeks, fennel, cress, new rosemary, purslane; wash them clean; pick them and pluck them small with your hands, and mix them well with raw oil. Lay on vinegar and salt, and serve it forth. Take parsley, sage, garlic, scallions, onions, leeks, borage, mints, young leeks, fennel, cress, new rosemary, purslane; wash them clean; pick them and pluck them small with your hands, and mix them well with raw oil. Lay on vinegar and salt, and serve it forth.Compost: Take root of parsley and parsnip, sc.r.a.pe them and wash them clean. Take turnips and cabbages pared and cut. Take an earthen pan with clean water, and set it on the fire. Cast all these things in. When they are boiled, add pears and parboil them well. Take these things out and let them cool on a fair cloth. Put in a vessel and add salt when it is cold. Take vinegar and powder and saffron and add. And let all these things lie there all night or day. Take Greek wine and honey clarified together, Lombardy mustard, and raisins, whole currants, and grind sweet powder and whole anise, and fennel seed. Take all these things and cast them together in a pot of earth, and take some when you wish, and serve it forth. Take root of parsley and parsnip, sc.r.a.pe them and wash them clean. Take turnips and cabbages pared and cut. Take an earthen pan with clean water, and set it on the fire. Cast all these things in. When they are boiled, add pears and parboil them well. Take these things out and let them cool on a fair cloth. Put in a vessel and add salt when it is cold. Take vinegar and powder and saffron and add. And let all these things lie there all night or day. Take Greek wine and honey clarified together, Lombardy mustard, and raisins, whole currants, and grind sweet powder and whole anise, and fennel seed. Take all these things and cast them together in a pot of earth, and take some when you wish, and serve it forth.

With the 19th century, English vegetable cooking became ever simpler until it almost always meant boiled and b.u.t.tered, a quick and simple method for homes and restaurants alike, while in France the elaborate professional style reached its apogee. The influential chef Antonin Careme declared in his Art of French Cooking in the 19th Century Art of French Cooking in the 19th Century (1835) that "it is in the confection of the Lenten cuisine that the chef's science must shine with new l.u.s.ter." Careme's enlarged repertoire included broccoli, truffles, eggplant, sweet potatoes, and potatoes, these last fixed (1835) that "it is in the confection of the Lenten cuisine that the chef's science must shine with new l.u.s.ter." Careme's enlarged repertoire included broccoli, truffles, eggplant, sweet potatoes, and potatoes, these last fixed a l'anglaise, dites, Mache-Potetesse a l'anglaise, dites, Mache-Potetesse ("in the English style, that is, mashed"). Of course, such l.u.s.ter tends to undermine the whole point of Lent. In his ("in the English style, that is, mashed"). Of course, such l.u.s.ter tends to undermine the whole point of Lent. In his 366 Menus 366 Menus (1872), Baron Brisse asked: "Are the meatless meals of our Lenten enthusiasts really meals of abstinence?" (1872), Baron Brisse asked: "Are the meatless meals of our Lenten enthusiasts really meals of abstinence?"

The Influence of Modern Technology The age of exploration and the advancement of fine cooking brought a new prominence to fruits and vegetables in Europe. Then the social and technical innovations of the industrial age conspired to make them both less available and less desirable. Beginning early in the 19th century, as industrialization drew people from the agricultural countryside to the cities, fruits and vegetables became progressively rarer in the diets of Europe and North America. Urban supplies did improve with the development of rail transportation in the 1820s, then canning at mid-century, and refrigeration a few decades later. Around the turn of the 20th century, vitamins and their nutritional significance were discovered, and fruits and vegetables were soon officially canonized as one of the four food groups that should be eaten at every meal. Still, the consumption of fresh produce continued to decline through much of the 20th century, at least in part because its quality and variety were also declining. In the modern system of food production, with crops being handled in ma.s.sive quant.i.ties and shipped thousands of miles, the most important crop characteristics became productivity, uniformity, and durability. Rather than being bred for flavor and harvested at flavor's peak, fruits and vegetables were bred to withstand the rigors of mechanical harvesting, transport, and storage, and were harvested while still hard, often weeks or months before they would be sold and eaten. A few mediocre varieties came to dominate the market, while thousands of others, the legacy of centuries of breeding, disappeared or survived only in backyard gardens. The age of exploration and the advancement of fine cooking brought a new prominence to fruits and vegetables in Europe. Then the social and technical innovations of the industrial age conspired to make them both less available and less desirable. Beginning early in the 19th century, as industrialization drew people from the agricultural countryside to the cities, fruits and vegetables became progressively rarer in the diets of Europe and North America. Urban supplies did improve with the development of rail transportation in the 1820s, then canning at mid-century, and refrigeration a few decades later. Around the turn of the 20th century, vitamins and their nutritional significance were discovered, and fruits and vegetables were soon officially canonized as one of the four food groups that should be eaten at every meal. Still, the consumption of fresh produce continued to decline through much of the 20th century, at least in part because its quality and variety were also declining. In the modern system of food production, with crops being handled in ma.s.sive quant.i.ties and shipped thousands of miles, the most important crop characteristics became productivity, uniformity, and durability. Rather than being bred for flavor and harvested at flavor's peak, fruits and vegetables were bred to withstand the rigors of mechanical harvesting, transport, and storage, and were harvested while still hard, often weeks or months before they would be sold and eaten. A few mediocre varieties came to dominate the market, while thousands of others, the legacy of centuries of breeding, disappeared or survived only in backyard gardens.

Refinements of 17th-Century Vegetable CookingChoose the largest asparagus, sc.r.a.pe them at the bottom, and wash. Cook them in some water, salt them well, and do not let them overcook. When done, let them drain, and make a sauce with some good fresh b.u.t.ter, a little vinegar, salt, and nutmeg, and an egg yolk to bind the sauce; take care that it doesn't curdle. Serve the asparagus well garnished with whatever you like.- La Varenne, Le Cuisinier francois, Le Cuisinier francois, 1655 1655...by reason of its soporifous quality, lettuce ever was, and still continues the princ.i.p.al foundation of the universal tribe of Sallets, which is to cool and refresh, besides its other properties [which included beneficial influences on "morals, temperance, and chast.i.ty"]. We have said how necessary it is that in the composure of a sallet, every plant should come in to bear its part, without being overpower'd by some herb of a stronger taste, so as to endanger the native sapor and virtue of the rest; but fall into their places, like the notes in music, in which there should be nothing harsh or grating: And though admitting some discords (to distinguish and ill.u.s.trate the rest) striking in all the more sprightly, and sometimes gentler notes, reconcile all dissonancies, and melt them into an agreeable composition.- John Evelyn, Acetaria: A Discourse of Sallets Acetaria: A Discourse of Sallets, 1699 At the end of the 20th century, several developments in the industrialized world brought renewed attention to plant foods, to their diversity and quality. One was a new appreciation of their importance for human health, thanks to the discovery of trace "phytochemicals" that appear to help fight cancer and heart disease (p. 255). Another was the growing interest in exotic and unfamiliar cuisines and ingredients, and their increasing availability in ethnic markets. Yet another, at the opposite extreme, was the rediscovery of the traditional system of food production and its pleasures: eating locally grown foods, often forgotten "heirloom" or other unusual varieties, that were harvested a matter of hours beforehand, then sold at farmers' markets by the people who grew them. Allied to this trend was the growing interest in "organic" foods, produced without relying on the modern array of chemicals for controlling pests and disease. Organic practices mean different things to different people, and don't guarantee either safer or more nutritious foods - agriculture is more complicated than that. But they represent an essential, prominent alternative to industrial farming, one that encourages attention to the quality of agricultural produce and the sustainability of agricultural practices.

These are good times for curious and adventurous eaters. There are many forgotten varieties of familiar fruits and vegetables to revive, and many new foods to taste. It's estimated that there are 300,000 edible plant species on earth, and perhaps 2,000 that are cultivated to some extent. We have plenty of exploring to do!

Plant Foods and Health Plant foods can provide us all the nourishment we need in order to live and thrive. Our primate ancestors started out eating little else, and many cultures still do. But meat and other animal foods became important to our species at its birth, when their concentrated energy and protein probably helped accelerate our evolution (p. 119). Meat continued to have a deep biological appeal for us, and in societies that could afford to feed livestock on staple grains and roots, it became the most prized of foods. In the industrialized world, meat's prestige and availability pushed grains, vegetables, and fruits to the side of the plate and the end of the meal. And for decades, nutritional science affirmed their accessory status. Fruits and vegetables in particular were considered to be the source of a few nutrients that we need only in small amounts, and of mechanically useful roughage. In recent years, though, we've begun to realize just how many valuable substances plant foods have always held for us. And we're still learning.

Essential Nutrients in Fruits and Vegetables: Vitamins Most fruits and vegetables contribute only modestly to our intake of proteins and calories, but they're our major source for several vitamins. They provide nearly all of our vitamin C, much of our folic acid, and half of our vitamin A. Each of these plays a number of roles in the metabolism of our cells. For example, vitamin C refreshes the chemical state of metal components in many enzymes, and helps with the synthesis of connective-tissue collagen. Vitamin A, which our bodies make from a precursor molecule in plants called beta-carotene (p. 267), helps regulate the growth of several different kinds of cells, and helps our eyes detect light. Folic acid, named from the Latin word for "leaf," converts a by-product of our cells' metabolism, h.o.m.ocysteine, into the amino acid methionine. This prevents h.o.m.ocysteine levels from rising, causing damage to blood vessels, and possibly contributing to heart disease and stroke.

Genetic Engineering and FoodThe most far-reaching development in 20th-century agriculture was the introduction in the 1980s of genetic engineering, the technology that makes it possible to alter our food plants and animals by surgically precise manipulation of the DNA that makes up their genes. This manipulation bypa.s.ses the natural barriers between species, so theoretically a gene from any living thing, plant or animal or microbe, can be introduced into any other.Genetic engineering is still in its infancy, and to date has had a limited impact on the foods we eat. In the United States, an estimated 75% of all processed foods now contain genetically modified ingredients. But this remarkable figure is due to just three agricultural commodities - soybean, canola, and corn - all of them modified for improved resistance to insect pests or herbicides. As I write in 2004, the only other significant engineered U.S. crop is Hawaiian papaya, which is now resistant to a formerly devastating virus disease. A few other foods are processed with enzymes made in engineered microbes - for example, much cheese is coagulated with rennet made by microbes into which the cattle gene for the enzyme has been inserted. But in general, our raw ingredients remain relatively untouched by genetic engineering.This will certainly change in coming years, and not just in the West: China also has a very active program in agricultural biotechnology. Genetic engineering is the modern fruit of agriculture itself, an outgrowth of the ancient human realization that living things can be shaped to human desires. That shaping began when the first farmers selectively cultivated plants and animals that grew larger or tasted better or looked more interesting. In its own way, this simple process of observation and selection became a powerful biological technology. It gradually revealed the hidden potential for diversity within individual species, and made that potential real in the form of hundreds of distinct varieties of wheat and cattle, citrus fruits and chillis, many of which had never before existed in nature. Today, genetic engineers are exploring the hidden potential for improving a given food plant or animal not just within that species, but among all species, in the entire living world's cornucopia of DNA and its possible modifications.Genetic engineering holds the promise of bringing great improvements to the production and quality of our foods. However, like any powerful new technology, it also has the potential to cause unintended and far-reaching consequences. And as the instrument of industrial agriculture, it's likely to contribute to the ongoing erosion of traditional, decentralized, small-scale food production and its ancient heritage of biological and cultural diversity. It's important that these environmental, social, and economic issues be considered by all concerned - by the biotechnology and agriculture industries, the governments that regulate them, the farmers who plant and raise their products, the cooks and manufacturers who turn the products into something edible, and the consumers who support the whole system by buying and eating food - so that in the long run this new agricultural revolution will benefit the common good as much as possible.

Vitamins A, C, and E are also antioxidants (see below).

Phytochemicals The first edition of this book reflected the prevailing nutritional wisdom circa 1980: we should eat enough fruits and vegetables to avoid vitamin and mineral deficiencies, and to keep our digestive system moving. Period.

What a difference 20 years makes!

Nutritional science has undergone a profound revolution in that time. For most of the 20th century it aimed to define an adequate adequate diet. It determined our body's minimal requirements for chemical building blocks (protein, minerals, fatty acids), for essential cogs in its machinery (vitamins), and for the energy it needs to run and maintain itself from day to day. Toward the end of the century, it became clear from laboratory studies and comparisons of health statistics in different countries that the major diseases of the adequately nourished developed world - cancer and heart disease - are influenced by what we eat. Nutritional science then began to focus on defining the elements of an diet. It determined our body's minimal requirements for chemical building blocks (protein, minerals, fatty acids), for essential cogs in its machinery (vitamins), and for the energy it needs to run and maintain itself from day to day. Toward the end of the century, it became clear from laboratory studies and comparisons of health statistics in different countries that the major diseases of the adequately nourished developed world - cancer and heart disease - are influenced by what we eat. Nutritional science then began to focus on defining the elements of an optimal optimal diet. So we discovered that minor, nonessential food components can have a c.u.mulative effect on our long-term health. And plants, the planet's biochemical virtuosos, turn out to be teeming with trace diet. So we discovered that minor, nonessential food components can have a c.u.mulative effect on our long-term health. And plants, the planet's biochemical virtuosos, turn out to be teeming with trace phytochemicals phytochemicals - from the Greek - from the Greek phyton, phyton, meaning "leaf" - that modulate our metabolism. meaning "leaf" - that modulate our metabolism.

Antioxidants Oxidative Damage: The Price of Living One major theme in modern nutrition is the body's need to cope with the chemical wear and tear of life itself. Breathing is essential to human life because our cells use oxygen to react with sugars and fats and generate the chemical energy that keeps the cellular machinery functioning. Unfortunately, it turns out that energy generation and other essential processes involving oxygen generate chemical by-products called "free radicals," very unstable chemicals that react with and damage our own complex and delicate chemical machinery. This damage is called One major theme in modern nutrition is the body's need to cope with the chemical wear and tear of life itself. Breathing is essential to human life because our cells use oxygen to react with sugars and fats and generate the chemical energy that keeps the cellular machinery functioning. Unfortunately, it turns out that energy generation and other essential processes involving oxygen generate chemical by-products called "free radicals," very unstable chemicals that react with and damage our own complex and delicate chemical machinery. This damage is called oxidative oxidative because it usually originates in reactions involving oxygen. It can affect different parts of the cell, and different organs in the body. For example, oxidative damage to a cell's DNA can cause that cell to multiply uncontrollably and grow into a tumor. Oxidative damage to the cholesterol-carrying particles in our blood can irritate the lining of our arteries, and initiate damage that leads to a heart attack or stroke. The high-energy ultraviolet rays in sunlight create free radicals in the eye that damage proteins in the lens and retina, and cause cataracts, macular degeneration, and blindness. because it usually originates in reactions involving oxygen. It can affect different parts of the cell, and different organs in the body. For example, oxidative damage to a cell's DNA can cause that cell to multiply uncontrollably and grow into a tumor. Oxidative damage to the cholesterol-carrying particles in our blood can irritate the lining of our arteries, and initiate damage that leads to a heart attack or stroke. The high-energy ultraviolet rays in sunlight create free radicals in the eye that damage proteins in the lens and retina, and cause cataracts, macular degeneration, and blindness.

Our bodies stave off such drastic consequences by means of antioxidant antioxidant molecules, which react harmlessly with free radicals before they have a chance to do any damage to the cells' chemical machinery. We need a continuous and abundant supply of antioxidants to maintain our good health. The body does make a few important antioxidant molecules of its own, including some powerful enzymes. But the more help it gets, the better it's able to defend itself from the constant onslaught of free radicals. And plants turn out to be a goldmine of antioxidants. molecules, which react harmlessly with free radicals before they have a chance to do any damage to the cells' chemical machinery. We need a continuous and abundant supply of antioxidants to maintain our good health. The body does make a few important antioxidant molecules of its own, including some powerful enzymes. But the more help it gets, the better it's able to defend itself from the constant onslaught of free radicals. And plants turn out to be a goldmine of antioxidants.

Some Beneficial Effects of Chemicals in Fruits and Vegetables, Herbs and SpicesThis is a very broad survey of a rich and complex subject. It's meant to give a general idea of how a variety of plant chemicals can affect various aspects of our health by a variety of means. Certain phenolic compounds, for example, appear capable of helping us fight cancer by preventing oxidative damage to DNA in healthy cells, by preventing the body from forming its own DNA-damaging chemicals, and by inhibiting the growth of already cancerous cells.Prevent oxidative damage to important molecules in body: antioxidantsEye: slow cataracts and macular degeneration slow cataracts and macular degenerationKale, many dark green vegetables (carotenoids: lutein)Citrus fruits, corn (carotenoids: zeaxanthin)Blood lipids: slow development of heart disease slow development of heart diseaseGrapes, other berries (phenolics: anthocyanidins)Tea (phenolics)General: reduce DNA damage, development of cancer reduce DNA damage, development of cancerTomatoes (carotenoids: lycopene)Carrots, other orange and green vegetables (carotenoids)Tea (phenolics)Green vegetables (chlorophyll)Broccoli, daikon, cabbage family (glucosinolates, thiocyanates)Moderate the body's inflammatory responseGeneral: slow development of heart disease, cancer slow development of heart disease, cancerRaisins, dates, chillis, tomatoes (salicylates)Reduce the body's own production of DNA-damaging chemicalsMany fruits, vegetables (phenolics: flavonoids)Broccoli, daikon, cabbage family (glucosinolates, thiocyanates)Citrus fruits (terpenes)Inhibit the growth of cancer cells and tumorsMany fruits, vegetables (phenolics: flavonoids)Soybeans (phenolics: isoflavones)Grapes, berries (phenolics: ellagic acid)Rye, flaxseed (phenolics: lignans)Citrus fruits (terpenes)Mushrooms (carbohydrates)Slow the body's removal of calcium from bonesOnions, parsley (responsible agents not yet identified)Encourage the growth of beneficial bacteria in the intestineOnion family, sunchokes (inulin)Prevent the adhesion of infectious bacteria to walls of urinary tractCranberries, grapes (phenolics: proanthocyanidins) Antioxidants in Plants Nowhere in living things is oxidative stress greater than in the photosynthesizing leaf of a green plant, which harvests energetic particles of sunlight, and uses them to split water molecules apart into hydrogen and oxygen atoms in order to make sugars. Leaves and other exposed plant parts are accordingly chock-full of antioxidant molecules that keep these high-energy reactions from damaging essential DNA and proteins. Among these plant antioxidants are the carotenoid pigments, including orange beta-carotene, yellow lutein and zeaxanthin, and the red lycopene that colors tomato fruits. Green chlorophyll itself is an antioxidant, as are vitamins C and E. Then there are thousands of different "phenolic" compounds built from rings of 6 carbon atoms, which play several roles in plant life, from pigmentation to antimicrobial duty to attracting and repelling animals. All fruits, vegetables, and grains probably contain at least a few kinds of phenolic compounds; and the more pigmented and astringent they are, the more they're likely to be rich in phenolic antioxidants. Nowhere in living things is oxidative stress greater than in the photosynthesizing leaf of a green plant, which harvests energetic particles of sunlight, and uses them to split water molecules apart into hydrogen and oxygen atoms in order to make sugars. Leaves and other exposed plant parts are accordingly chock-full of antioxidant molecules that keep these high-energy reactions from damaging essential DNA and proteins. Among these plant antioxidants are the carotenoid pigments, including orange beta-carotene, yellow lutein and zeaxanthin, and the red lycopene that colors tomato fruits. Green chlorophyll itself is an antioxidant, as are vitamins C and E. Then there are thousands of different "phenolic" compounds built from rings of 6 carbon atoms, which play several roles in plant life, from pigmentation to antimicrobial duty to attracting and repelling animals. All fruits, vegetables, and grains probably contain at least a few kinds of phenolic compounds; and the more pigmented and astringent they are, the more they're likely to be rich in phenolic antioxidants.

Each plant part, each fruit and vegetable, has its own characteristic cl.u.s.ter of antioxidants. And each kind of antioxidant generally protects against a certain kind of molecular damage, or helps regenerate certain other protective molecules. No single molecule can protect against all kinds of damage. Unusually high concentrations of single types can actually tip the balance the wrong way and cause cause damage. So the best way to reap the full benefits of the antioxidant powers of plants is not to take manufactured supplements of a few prominent chemicals: it is to eat lots of different vegetables and fruits. damage. So the best way to reap the full benefits of the antioxidant powers of plants is not to take manufactured supplements of a few prominent chemicals: it is to eat lots of different vegetables and fruits.

Other Beneficial Phytochemicals Antioxidants may be the most important group of ingredients for maintaining long-term health, but they're not the only one. Trace chemicals in plants, including herbs and spices, are turning out to have helpful effects on many other processes that affect the balance between health and disease. For example, some act like aspirin (originally found in plants) to prevent the body from overreacting to minor damage with an inflammation that can lead to heart disease or cancer; some prevent the body from turning mildly toxic chemicals into more powerful toxins that damage DNA and cause cancer; some inhibit the growth of cells that are already cancerous. Others slow the loss of calcium from our bones, encourage the growth of beneficial bacteria in our system, and discourage the growth of disease bacteria. Antioxidants may be the most important group of ingredients for maintaining long-term health, but they're not the only one. Trace chemicals in plants, including herbs and spices, are turning out to have helpful effects on many other processes that affect the balance between health and disease. For example, some act like aspirin (originally found in plants) to prevent the body from overreacting to minor damage with an inflammation that can lead to heart disease or cancer; some prevent the body from turning mildly toxic chemicals into more powerful toxins that damage DNA and cause cancer; some inhibit the growth of cells that are already cancerous. Others slow the loss of calcium from our bones, encourage the growth of beneficial bacteria in our system, and discourage the growth of disease bacteria.

The box on p. 256 lists some of these effects, and the chemicals and plants that cause them. Our knowledge of this aspect of nutrition is still in its infancy, but we know enough right now for at least one conclusion to be evident: no single fruit or vegetable offers the many kinds of protections that a varied diet can provide.

So today's provisional nutritional wisdom goes like this: fruits and vegetables, herbs and spices supply us with many different beneficial substances. Within an otherwise adequate diet, we should eat as much of them as we can, and as great a variety as we can.

Estimating Healthfulness by Eye There's a useful guideline for estimating the relative healthfulness of vegetables and fruits: the deeper its color, the more healthful the food is likely to be. The more light a leaf gets, the more pigments and antioxidants it needs to handle the energy input, and so the darker the coloration of the leaf. For example, the light-colored inner leaves of lettuce and cabbage varieties that form tight heads contain a fraction of the carotene found in the darker outer leaves and in the leaves of more open varieties. Similarly, the dark leaves of open romaine lettuce contain nearly 10 times the eye-protecting lutein and zeaxanthin of the pale, tight heads of iceberg lettuce. Other deeply colored fruits and vegetables also contain more beneficial carotenoids and phenolic compounds than their pale counterparts. Their skins are especially rich sources. Among the fruits highest in antioxidant content are cherries, red grapes, blueberries, and strawberries; among vegetables, garlic, red and yellow onions, asparagus, green beans, and beets. There's a useful guideline for estimating the relative healthfulness of vegetables and fruits: the deeper its color, the more healthful the food is likely to be. The more light a leaf gets, the more pigments and antioxidants it needs to handle the energy input, and so the darker the coloration of the leaf. For example, the light-colored inner leaves of lettuce and cabbage varieties that form tight heads contain a fraction of the carotene found in the darker outer leaves and in the leaves of more open varieties. Similarly, the dark leaves of open romaine lettuce contain nearly 10 times the eye-protecting lutein and zeaxanthin of the pale, tight heads of iceberg lettuce. Other deeply colored fruits and vegetables also contain more beneficial carotenoids and phenolic compounds than their pale counterparts. Their skins are especially rich sources. Among the fruits highest in antioxidant content are cherries, red grapes, blueberries, and strawberries; among vegetables, garlic, red and yellow onions, asparagus, green beans, and beets.

Fiber Fiber is defined as the material in our plant foods that our digestive enzymes can't break down into absorbable nutrients. These substances therefore aren't absorbed in the small intestine, and pa.s.s intact into the large intestine, where some are broken down by intestinal bacteria, and the rest are excreted. The four main components of fiber come from plant cell walls (p. 265). Cellulose and lignin form solid fibers that don't dissolve in our watery digestive fluids, while pectins and hemicelluloses do dissolve into their individual molecules. Minor components of fiber include uncooked starch and various gums, mucilages, and other unusual carbohydrates (e.g., mushroom chitin, seaweed agar and carrageenan, inulin in onions, artichokes, and sunchokes). Particular foods offer particular kinds of fiber. Wheat bran - the dry outer coat of the grain - is a rich source of insoluble cellulose, while oat bran is a rich source of soluble glucan (a carbohydrate), and juicy ripe fruits are a relatively dilute source of soluble pectins.

The different fiber components contribute to health in different ways. Insoluble cellulose and lignin mainly provide bulk to the intestinal contents, and thus increase the rate and ease with which they pa.s.s through the large intestine. It's thought that rapid excretion may help minimize our exposure to DNA-damaging chemicals and other toxins in our foods, and the fiber materials may bind some of these toxins and prevent them from being absorbed by our cells. Soluble fiber components make the intestinal contents thicker, so that there is slower mixing and movement of both nutrients and toxins. They, too, probably bind certain chemicals and prevent their absorption. Soluble fiber has been shown to lower blood cholesterol and slow the rise of blood sugar after a meal. Inulin in particular encourages the growth of beneficial intestinal bacteria, while reducing the numbers of potential troublemakers. The details are complex, but overall it appears that soluble fiber helps protect against heart disease and diabetes.

In sum, the indigestible portion of fruits and vegetables does us good. It's a mistake to think that a juiced orange or carrot is as valuable as the whole fruit or vegetable.

Toxins in Some Fruits and Vegetables Many plants, perhaps all plants, contain chemicals meant to discourage animals from eating them. The fruits and vegetables that we eat are no exception. While domestication and breeding have reduced their toxin contents to the point that they're not generally hazardous, unusual preparations or serving sizes can cause problems. The following plant toxins are worth being aware of.

Alkaloids Alkaloids are bitter-tasting toxins that appeared in plants about the time that mammals evolved, and seem especially effective at deterring our branch of the animal family by both taste and aftereffects. Almost all known alkaloids are poisonous at high doses, and most alter animal metabolism at lower doses: hence the attractions of caffeine and nicotine. Among familiar foods, only the potato acc.u.mulates potentially troublesome alkaloid levels, which make greened potatoes and potato sprouts bitter and toxic (p. 302). Alkaloids are bitter-tasting toxins that appeared in plants about the time that mammals evolved, and seem especially effective at deterring our branch of the animal family by both taste and aftereffects. Almost all known alkaloids are poisonous at high doses, and most alter animal metabolism at lower doses: hence the attractions of caffeine and nicotine. Among familiar foods, only the potato acc.u.mulates potentially troublesome alkaloid levels, which make greened potatoes and potato sprouts bitter and toxic (p. 302).

Cyanogens Cyanogens are molecules that warn and poison animals with bitter hydrogen cyanide, a deadly poison of the enzymes that animals use to generate energy. When the plant's tissue is damaged by chewing, the cyanogens are mixed with the plant enzyme that breaks them apart and releases hydrogen cyanide (HCN). Cyanogen-rich foods, including manioc, bamboo shoots, and tropical varieties of lima beans, are made safe for consumption by open boiling, leaching in water, and fermentation. The seeds of citrus, stone, and pome fruits generate cyanide, and stone-fruit seeds are prized because their cyanogens also produce benzaldehyde, the characteristic odor of almond extract (p. 506). Cyanogens are molecules that warn and poison animals with bitter hydrogen cyanide, a deadly poison of the enzymes that animals use to generate energy. When the plant's tissue is damaged by chewing, the cyanogens are mixed with the plant enzyme that breaks them apart and releases hydrogen cyanide (HCN). Cyanogen-rich foods, including manioc, bamboo shoots, and tropical varieties of lima beans, are made safe for consumption by open boiling, leaching in water, and fermentation. The seeds of citrus, stone, and pome fruits generate cyanide, and stone-fruit seeds are prized because their cyanogens also produce benzaldehyde, the characteristic odor of almond extract (p. 506).

Hydrazines Hydrazines are nitrogen-containing substances that are found in relatively large amounts (500 parts per million) in the common white mushroom and other mushroom varieties, and that persist after cooking. Mushroom hydrazines cause liver damage and cancer when fed to laboratory mice, but have no effect in rats. It's not yet clear whether they pose a significant hazard to humans. Until we know, it's best to eat mushrooms in moderation. Hydrazines are nitrogen-containing substances that are found in relatively large amounts (500 parts per million) in the common white mushroom and other mushroom varieties, and that persist after cooking. Mushroom hydrazines cause liver damage and cancer when fed to laboratory mice, but have no effect in rats. It's not yet clear whether they pose a significant hazard to humans. Until we know, it's best to eat mushrooms in moderation.

Protease Inhibitors and Lectins These are proteins that interfere with digestion: inhibitors block the action of protein-digesting enzymes, and lectins bind to intestinal cells and prevent them from absorbing nutrients. Lectins can also enter the blood-stream and bind red blood cells to each other. They're found mainly in soy, kidney, and lima beans. Both inhibitors and lectins are inactivated by prolonged boiling. But they can survive in beans that are eaten raw or undercooked, and cause symptoms similar to food poisoning. These are proteins that interfere with digestion: inhibitors block the action of protein-digesting enzymes, and lectins bind to intestinal cells and prevent them from absorbing nutrients. Lectins can also enter the blood-stream and bind red blood cells to each other. They're found mainly in soy, kidney, and lima beans. Both inhibitors and lectins are inactivated by prolonged boiling. But they can survive in beans that are eaten raw or undercooked, and cause symptoms similar to food poisoning.

Flavor Chemicals Flavor chemicals are generally consumed in only tiny amounts, but a few may cause problems when overindulged in. Safrole, the main aromatic in oil of sa.s.safras and therefore of traditional root beer, causes DNA damage and was banned as an additive in 1960 (root beer is now made with safe sarsaparilla or artificial flavorings). Myristicin, the major flavor contributor in nutmeg, seems largely responsible for intoxication and hallucinations that result from ingesting large amounts. Glycyrrhizin, an intensely sweet-tasting substance in true licorice root, induces high blood pressure. Coumarin, which gives sweet clover its sweet aroma and is also found in lavender and vanilla-like tonka beans ( Flavor chemicals are generally consumed in only tiny amounts, but a few may cause problems when overindulged in. Safrole, the main aromatic in oil of sa.s.safras and therefore of traditional root beer, causes DNA damage and was banned as an additive in 1960 (root beer is now made with safe sarsaparilla or artificial flavorings). Myristicin, the major flavor contributor in nutmeg, seems largely responsible for intoxication and hallucinations that result from ingesting large amounts. Glycyrrhizin, an intensely sweet-tasting substance in true licorice root, induces high blood pressure. Coumarin, which gives sweet clover its sweet aroma and is also found in lavender and vanilla-like tonka beans (Dipteryx odorata), interferes with blood clotting.

Toxic Amino Acids Toxic amino acids are unusual versions of the building blocks for our proteins that interfere with proper protein functioning. Canavanine interferes with several cell functions and has been a.s.sociated with the development of lupus; it's found in large quant.i.ties in alfalfa sprouts and the jack bean. Vicine and convicine in the fava bean cause a blood-cell-destroying anemia, favism, in susceptible people (p. 490). Toxic amino acids are unusual versions of the building blocks for our proteins that interfere with proper protein functioning. Canavanine interferes with several cell functions and has been a.s.sociated with the development of lupus; it's found in large quant.i.ties in alfalfa sprouts and the jack bean. Vicine and convicine in the fava bean cause a blood-cell-destroying anemia, favism, in susceptible people (p. 490).

Oxalates Oxalates are various salts of oxalic acid, a waste product of plant metabolism found in a number of foods, notably spinach, chard, beets, amaranth, and rhubarb. The sodium and pota.s.sium salts are soluble, while the calcium salts are insoluble and form crystals that irritate the mouth and digestive system. Soluble oxalates can combine with calcium in the human kidney to form painful kidney stones. In very large doses - a few grams - oxalic acid is corrosive and can be fatal. Oxalates are various salts of oxalic acid, a waste product of plant metabolism found in a number of foods, notably spinach, chard, beets, amaranth, and rhubarb. The sodium and pota.s.sium salts are soluble, while the calcium salts are insoluble and form crystals that irritate the mouth and digestive system. Soluble oxalates can combine with calcium in the human kidney to form painful kidney stones. In very large doses - a few grams - oxalic acid is corrosive and can be fatal.

Bracken-Fern Toxins Bracken-fern toxins cause several blood disorders and cancer in animals that graze on this common fern ( Bracken-fern toxins cause several blood disorders and cancer in animals that graze on this common fern (Pteridium), which is sometimes collected in the young "fiddlehead" stage for human consumption. Ostrich ferns, Matteuccia Matteuccia species, are thought to be a safer source of fiddleheads, but there's little solid information about the safety of eating ferns. It's prudent to eat fiddleheads in moderation, and to avoid bracken ferns by checking labels and asking produce sellers. species, are thought to be a safer source of fiddleheads, but there's little solid information about the safety of eating ferns. It's prudent to eat fiddleheads in moderation, and to avoid bracken ferns by checking labels and asking produce sellers.

Psoralens Psoralens are chemicals that damage DNA and cause blistering skin inflammations. They're found occasionally in badly handled celery and celery root, parsley, and parsnips, when these vegetables have been stressed by near-freezing temperatures, intense light, or infection by mold. Psoralens are absorbed through the skin during handling, or by being ingested with the vegetable, either raw or cooked. They lie dormant in skin cells until they're struck by ultraviolet rays in sunlight, which causes them to bind to and damage DNA and important cell proteins. The psoralen-generating vegetables should be bought as fresh as possible and used quickly. Psoralens are chemicals that damage DNA and cause blistering skin inflammations. They're found occasionally in badly handled celery and celery root, parsley, and parsnips, when these vegetables have been stressed by near-freezing temperatures, intense light, or infection by mold. Psoralens are absorbed through the skin during handling, or by being ingested with the vegetable, either raw or cooked. They lie dormant in skin cells until they're struck by ultraviolet rays in sunlight, which causes them to bind to and damage DNA and important cell proteins. The psoralen-generating vegetables should be bought as fresh as possible and used quickly.

In addition to their own chemical defenses, fruits and vegetables can carry other toxins that come from contaminating molds (patulin in apple juice, from a Penicillium Penicillium mold growing on damaged fruit), agricultural chemicals (pesticides, herbicides, fungicides), and soil and air pollutants (dioxins, polycyclic aromatic hydrocarbons). In general, it's thought that the usual levels of these contaminants do not const.i.tute an immediate health hazard. On the other hand, they are toxins, and therefore undesirable additions to our diet. We can reduce our intake of them by washing produce, by peeling off surface layers, and by buying certified organic produce, which is grown in relatively clean soil without the use of most agricultural chemicals. mold growing on damaged fruit), agricultural chemicals (pesticides, herbicides, fungicides), and soil and air pollutants (dioxins, polycyclic aromatic hydrocarbons). In general, it's thought that the usual levels of these contaminants do not const.i.tute an immediate health hazard. On the other hand, they are toxins, and therefore undesirable additions to our diet. We can reduce our intake of them by washing produce, by peeling off surface layers, and by buying certified organic produce, which is grown in relatively clean soil without the use of most agricultural chemicals.

Fresh Produce and Food Poisoning Though we generally a.s.sociate outbreaks of food poisoning with foods derived from animals, fruits and vegetables are also a significant source. They have caused outbreaks of nearly every major food pathogen known (see box below). There are several reasons for this. Fruits and vegetables are grown in the soil, a vast reservoir of microbes. Field facilities for the harvesting crew (toilets, wash water) and for processing and packing may not be hygienic, so the produce is easily contaminated by people, containers, and machinery. And produce is often eaten raw. Salad bars in restaurants and cafeterias can collect and grow bacteria for hours, and have been a.s.sociated with many outbreaks of food poisoning. Fruit juices, often made by crushing whole fruits, are readily contaminated by a small number of infected pieces; so fresh cider has become hard to find. Nearly all juice production in the United States is now pasteurized.

Disease Outbreaks Caused by Raw Fruits and VegetablesThis selected list demonstrates that raw produce is capable of causing a wide range of food-borne illnesses. These disease outbreaks are not common or a cause for great concern, but they do mean that produce should be prepared carefully, and ideally should be cooked for people with weak immune systems - the very young and very old and people suffering from other illnesses.

Microbe

Food Food

Clostridium botulinum

Garlic in oil Garlic in oil

E. coli

Salad bars, alfalfa and radish sprouts, melons, apple juice Salad bars, alfalfa and radish sprouts, melons, apple juice

Listeria

Cabbage (long cold storage) Cabbage (long cold storage)

Salmonella

Salad bars, alfalfa sprouts, orange juice, melons, tomatoes Salad bars, alfalfa sprouts, orange juice, melons, tomatoes

Shi