40000 ACTIVOS REALES

Modern society has dramatically affected how we eat. Since the introduction of TV dinners, it appears that convenience greatly influences people’s food choices. Researchers have found that monkeys or apes foraging in the wild appear to get far higher levels of many essential nutrients and beneficial phytochemicals relative to their body weight than the average American (58).

Without a doubt, vegetables can be considered more nutrient-dense (nutrient content per kilocalorie of food) than foods from other food groups. However, the phytochemicals in vegetables may provide equally important benefits for the prevention of chronic diseases like cancer and heart disease (59).

Research on the purported health benefits of vegetables focuses on two main areas of study: maintenance of gastrointestinal tract health and reduction of chronic disease risk.

A. Gastrointestinal Tract Health

The gastrointestinal tract (GI tract) is the gateway through which the body transports nutrients and phytochemicals into the circulation for delivery to body cells. A complex network of internal organs and tissues is responsible for the digestion or breakdown of food components into compounds and elements that can be absorbed into the body. In addition, the GI tract serves as a protective barrier to prevent some substances from entering the body (60).

Due to the extremely active and chemically hostile internal environment necessary to accomplish the digestive process within the GI tract, cells along the 25 – 30 feet of intestine are exposed to a great deal of chemical and physical damage. Consequently, many of these cells have only a 3 to 5 day life span. This constant turnover of GI tract cells results in continuous cellular replacement and repair of damage.

There is a significant amount of nutrient recycling from injured GI tract cells, which allows many nutrients to be digested and absorbed along with new food components. This combination of recycled and dietary nutrients is utilized to support adequate replacement of the cell lining of the GI tract.

Over the last decade there has been an increase in the number of reported cases of various gastrointestinal diseases. Two of the most common GI tract diseases are diverticulitis (inflammation of small pouches formed along the gastrointestinal tract) and gastroesophageal reflux disease (GERD), the common cause of indigestion, which causes the pain popularly called heartburn (61). In fact, GERD is so common and chronic in the United States that Prilosecw was one of the world’s top selling drugs in the year 2000.

Diverticulitis and GERD have one significant dietary factor in common. Both of these conditions appear to be related to years of inadequate dietary fiber intake (61,62). Ironically, fiber is the most abundant phytochemical in vegetables.

Vegetables contain both soluble and insoluble forms of dietary fiber. The physiological effects of these two dietary fiber types have both similarities and some significant differences.

Both soluble and insoluble fiber types hold water and create bulk inside the GI tract. Soluble fibers slow the rate of stomach emptying into the small intestine. It is thought that the stomach distension caused by fiber bulk and the slower stomach emptying produces an extended feeling of satiety after a meal (63,64). Intake of high soluble fiber also tends to decrease the overall nutrient absorption rate and may also reduce the amount of nutrients and phytochemicals absorbed. This can benefit those with problems in the management of blood glucose and may reduce the absorption of cholesterol (65). Excessively high intake of dietary fiber can interfere with the absorption of minerals.

B. Immune System Health

The immune system is part of the body’s natural defense system against disease and disease- producing conditions. Approximately 80 percent of the immune system is located directly adjacent to the gastrointestinal tract. Ordinarily, undigested food molecules, microorganisms, and many toxins cannot readily cross through the intestinal lining and do not enter the circulatory system. However, disruptions to the integrity of the GI tract can challenge the immune system beyond its capacity to maintain health (60).

C. Chronic Disease

Many phytochemicals have been associated with preventing or decreasing the incidence of disease. Disease conditions and related mechanisms that are purported to be affected by various

phytochemicals are summarized inTable 5.

No doubt there are numerous triggers in the initiation of cancer and heart disease. Although there may be many varied mechanisms of phytochemicals with anticancer and heart-promoting properties, one mechanism may be related to the antioxidant property shared by many of these compounds. The process of normal cellular metabolism produces chemicals that are reactive oxygen species like hydrogen peroxide and the superoxide anion free radical. It is thought that free radical production causes a secondary oxidative stress whenever there is an imbalance of antioxidants to oxidants. This can occur with an excess of oxidation stress or an inadequate amount of antioxidants in the diet.

Research has shown that antioxidants are involved in delaying many diseases and conditions that are associated with aging, such as cancer, heart disease, decreased immune functioning, and visual and cognitive impairment (66). A number of vitamins, minerals, and phytochemicals provide antioxidant protection in the body. On a per gram or per kilocalorie basis, vegetables contain significant amounts of antioxidants.

Dietary phytoestrogens may help reduce the risk of developing certain hormone-stimulated cancers such as breast and prostate cancers. However, much more research on this relationship is needed, since some studies indicate that phytoestrogen compounds may stimulate the progression of some types of cancer (67).

Flavonoids such as those found in onions, tea, and red wine also are under study for potential cancer prevention. The possible mechanisms of action may vary from one flavonoid to another. They may prevent cancer cell proliferation through specific enzyme inhibition (68).

V. SUMMARY

As a major category of foods, vegetables have a variety of qualities and characteristics that supports common recommendations to include them as a significant part of a balanced and varied diet. They serve as important sources of a wide variety of vitamins and minerals essential for normal human nutrition.

Vegetables supply these nutrients in forms that are generally low in energy and fat, making them more nutrient-dense than most other foods. The nutrient content of a particular vegetable can vary, with the extent dependent on the nutrient, and a variety of factors including plant genetics, agricultural factors, storage and handling, processing, packaging, and preparation. Nutrient content values in databases generally reflect averages.

The extent to which a vegetable food is a good source of a nutrient also depends on the type of processing and the bioavailability of the nutrient. In some cases, a vegetable can contain high

levels of a mineral such as calcium or iron, but the form of the mineral or interfering compounds in the vegetable allow very little of the mineral to be absorbed into the body. Some nutrients are not found in vegetables, including vitamins D and B-12 and the long-chain omega-3 fatty acids commonly found in fish oils and some species of algae.

In addition to nutrients, vegetables provide a great variety of nonnutrient chemical compounds commonly called phytochemicals. The potential benefits and risks of various phytochemicals found in vegetables represents an increasingly active area of nutrition research. The body of scientific research to date supports the inclusion of a wide variety of vegetables in the human diet for reducing the risk of developing a number of disease conditions that tend to develop with age. Additional research is needed to clarify more specific risks and benefits of various types of chemical compounds found in vegetables.

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