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3 Nonessential Substances Involved in Nutrition Nutrients play essential roles in the biochemical machinery of all cells, but thousands of other substances in plant foods are also beneficial to mammals despite the fact that they are not essential parts of cellular biochemistry. These optional dietary substances, called phytochemicals, were first recognized in the late twentieth century and their significance is poorly under- stood. A few phytochemical-like substances are also found in meat and dairy products. Many of these nonessential sub- stances function as antioxidants. Others stimulate the immune system or the production of detoxification enzymes; modulate hormones or gene expression; or act as antibacterial, antifun- gal, or antiviral agents. Some are pigments that plants produce to limit damage by sunlight. In humans, phytochemicals seem to help protect against heart disease, cancer, hypertension, and many other major and minor disorders. They are probably widely distributed in all plants, including fruits (in particular, berries and melons), vegetables, whole grains, beans, nuts, and seeds, as well as in plant extracts such as tea, wine, and coffee. Nutraceuticals Nutrients, conditional nutrients, and phytochemicals collec- tively have been called nutraceuticals, which may be defined as substances considered to be a food, or part of a food, that pro- vide health benefits, including the prevention and treatment of disease. Some organizations promote research and develop- ment of nutraceutical supplements, and they seek a potentially separate legal status for them that would be intermediate between nutrients and pharmaceuticals. Foods and Nutrition Because of the biochemical unity of living organisms, all whole foods (those that have not undergone processing that greatly alters their nutritional value) contain a wide assortment of the nutrients needed by humans and other mammals. Thus, diets derived from a variety of whole foods tend to supply adequate amounts of all nutrients. Guided in part by some innate, evolu- tionarily ingrained abilities to select proper kinds and amounts of various whole foods, animal species survive without scien- tific nutritional knowledge. However, experience shows that suboptimal nutrition is commonplace in nature, and nutrition can always be improved. Probably all foods contain small amounts of naturally occur- ring toxins and antinutrients, some of which are deactivated by cooking. These compounds are directly harmful to organisms or interfere with their use of consumed nutrients. The possible roles of these minor components in nutrition are generally only dimly perceived. Their amounts seem mostly insignificant, and some may play useful roles. For example, dietary fiber is known to reduce the availability of some minerals, yet its presence in all plant foods is considered valuable. For modern humans, the problems of suboptimal nutrition have increased with the advent and extensive consumption of technologically derived, refined foods. In industrialized nations, more than half of the dry weight and energy content of food supplies derives from purified sugars, separated fats, alcohol, and milled grains. These nonwhole foods have lost most or all of the nutrients present in the whole foods from which they derive. Although they are manufactured in a wide variety of ap- pealing products that satisfy hunger, their excessive use facili- tates various kinds of malnutrition and overconsumption that do not occur readily with whole foods. Modern dietary guide- lines and nutrition education focus substantially on partially replacing nonwhole foods with whole grains, legumes, low-fat meats and dairy products, fish, vegetables, fruits, and nuts that retain their natural biochemical unity. Relationship of Nutrition and Disease One of the bases for interest in nutrition is the fact that indi- viduals who have differing genetic makeups have differing nutritional needs. For this reason, various human ills may arise because the individuals concerned do not get all of the nutri- ents in amounts compatible with their own distinctive require- ments. Every cell and tissue in the body requires continued adequate nutrition in order to perform its functions properly. A multitude of functions, involving the production of specific chemical sub- stances (hormones and prostaglandins, for example) and the regulation of numerous processes, are performed by cells and tissues. It is therefore clear that improper nutrition may pro- duce or contribute to almost every type of illness. Nutritional and medical investigations are yielding important advances in the use of improved nutrition to prevent, cure, and ameliorate disease and illness. For example, diet composition has been linked to obesity, heart disease, cancer, diabetes, hypertension, osteoporosis, kidney stones, and other prominent maladies. Obesity has long been considered a simple result of excessive consumption of energy and fat, compounded by insufficient exercise. However, this concept is evolving. Although fat con- sumption has decreased in recent decades, the consumption of nonwhole foods has continued, and rates of obesity and Nutrition (continued) + ward ' s science