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MIT Doctor Offers Dietary Guidance

By Anirban Nayak

Health Reporter

David Diamond, MD, doctor of internal medicine at the MIT Health Department, says that Americans tend to eat too much meat and not enough vegetables, fruits, and whole grains.

While he admits that meat is an excellent source of protein and should be consumed in moderate amounts (4 to 6 ounces per day), Dr. Diamond contends that plant foods should constitute the foundation of our diet.

This is because plant foods are rich in many of the vitamins and minerals essential to our body. In addition, unlike many meat products, plant foods contain no cholesterol and are usually low in saturated fat -- two substances when consumed in excess can raise blood cholesterol levels which, in turn, can increase risk for cardiovascular diseases.

In one such disease, atherosclerosis, cholesterol and fatty deposits clog arteries and obstruct blood flow. Because blood delivers oxygen and other nutrients to tissues and organs throughout our body, atherosclerosis can have many adverse effects, including numbness and dizziness, severe chest pains (angina pectoris), and even heart attacks and strokes.

Another reason plant foods are healthful is that they provide fiber -- a substance that our body cannot digest but helps us maintain regularity. In addition, the soluble fiber in oat bran is thought to reduce blood cholesterol levels by manipulating bile acid metabolism.

While it has been well established that a low-fat, fiber-rich diet can reduce the risk of cardiovascular disease, there is some evidence suggesting that such a diet may also help prevent some types of cancer.

Many studies have examined the relationship between diet and colon cancer. Despite some inconsistent results, the data taken as a whole indicate that colon cancer incidence is less frequent in populations consuming a diet high in fiber and low in total fat.

How such a diet might help prevent colon cancer is not known. However, in his book Cancer of the Colon, Rectum, and Anus, Alfred Cohen, MD, professor of surgery at the Cornell University School of Medicine, speculates on two ways fiber may reduce colon cancer risk.

First, by decreasing the time for food to transit the digestive tract, fiber might reduce the time of contact between the intestinal wall and carcinogens. Second, by absorbing water, it may also dilute and thereby weaken some of these cancer causing agents.

The National Cancer Institute recommends that we consume 20 to 30 grams of fiber per day. (However, a sudden drastic increase in fiber intake or consumption exceeding 30 grams per day can cause rumbling, bloating, diarrhea and may interfere with the body's ability to absorb vitamin B-12).

Vegetables and fruits also contain substances called antioxidants, which many believe help fight against cancer. Beta carotene (in carrots, sweet potatoes, and pumpkins), vitamin C (in citrus fruits), and vitamin E (in wheat germ, green vegetables, nuts, and seeds) are three antioxidants. These substances deactivate free radicals -- carcinogens that damage the genes regulating cell division.

Recently, scientists have identified several other chemicals in plant foods. Among them is sulforaphane, a constituent of broccoli and cauliflower.

Research at the Johns Hopkins University has shown a correlation between high sulforaphane consumption and reduced tumor growth in laboratory rats. However, whether this chemical has anti-cancerous effects in humans is not known.

While health experts urge Americans to eat more vegetables, fruits, and whole grains, they also emphasize the importance of a balanced diet, which includes meat and dairy products. Eating a variety of foods helps our body obtain all necessary nutrients.

However, since meat and dairy foods often contain too much fat, experts encourage the choice of leaner cuts of meat and low-fat milk and its products when possible.

In addition, Dr. Diamond says that fish and white meat (chicken and turkey) usually contain less saturated fat, which is the least salutary kind of fat, than red meat (beef). He also recommends that we limit our consumption of egg yolks since they are very high in cholesterol.

A general guideline for healthful eating is embodied in the food pyramid developed by the US Department of Agriculture. It assigns larger areas to those foods that we should consume more and smaller spaces to those that we should eat less.

In addition to the food pyramid suggestions, nutritionists advise that no more than 30 percent of the calories that we consume daily should come from fat. For obese individuals or those with high blood cholesterol levels, the recommended percentage might be even lower.

For more information on a nutrition program that is best for you, contact your primary care physician.