The food you eat does more than provide energy. It can have a dramatic effect on your body's ability to fight off heart disease, cancer, diabetes, high blood pressure, stroke, and weak bones.
With remarkable consistency, recent research has found that a diet high in plant-based foods -- fruits, vegetables, dried peas and beans, grains, and starchy staples such as potatoes -- is the body's best weapon in thwarting many health-related problems. These foods work against so many diseases that the same healthy ingredients you might use to protect your heart or ward off cancer will also benefit your intestinal tract and bones.
Here's what is currently known about these different disease-fighting foods.
Preventing cancer is a compelling reason to load up your cart in the produce department. Scientists have recently estimated that approximately 30 to 40 percent of all cancers could be averted if people ate more fruits, vegetables, and plant-based foods and minimized high-fat, high-calorie edibles that have scant nutritional value. Up to 70 percent of cancers might be eliminated if people also stopped smoking, exercised regularly, and controlled their weight.
In the past, researchers had linked fat consumption with the development of cancers, but they currently believe that eating fruits, vegetables, and grains may be more important in preventing the disease than not eating fat. "The evidence about a high-fat diet and cancer seemed a lot stronger several years ago than it does now," says Melanie Polk, a registered dietitian and director of nutrition education at the American Institute for Cancer Research.
Although scientists are still not certain about the specifics, they're beginning to close in on the healthful constituents of plant-based foods. In particular, they're looking closely at two components --antioxidants and phytochemicals.
Antioxidants. The antioxidants (carotenoids, such as beta carotene and lycopene, and vitamins C and E) found in fruits, vegetables, and other plant-based foods fight free radicals, which are compounds in the body that attack and destroy cell membranes. The uncontrolled activity of free radicals is believed to cause many cancers.
The carotenoids, in particular, which give fruits and vegetables their bright yellow, orange, and red colors, are now gaining recognition for their nutritional worth. Numerous studies have extolled the virtues of lycopene (the carotenoid that makes tomatoes red) in preventing prostate cancer. One such study at Harvard University found that men who include tomato products in their meals twice a week could reduce their risk of developing prostate cancer by one-third compared with men who never touch tomatoes.
Other lycopene-rich foods, such as watermelon, red grapefruit, and guava, are now piquing the interest of researchers. Watermelon not only yields more lycopene per serving (15 mg in 11/2 cups) than raw tomatoes (11 mg per 11/2 cups), but it's also a rich source of vitamins A and C.
Can watermelon help reduce the incidence of cancer? No one knows for sure because there haven't been sufficient studies. "We assume that we'll see benefits," says Penelope Perkins-Veazie, Ph.D., a research scientist with the USDA's Agricultural Research Service. Researchers there plan to compare people who eat watermelon with those who eat processed tomatoes -- because cooking enhances lycopene absorption -- to see which group absorbs more lycopene. (A 11/2 cup serving of tomato sauce packs 53 mg of lycopene.)
Phytochemicals. The phytochemicals present in fruits and vegetables protect the body by stunting the growth of malignant cells. Phytochemicals, naturally occurring substances, include indoles in cabbage or cauliflower, saponins in peas and beans, and isoflavones in soy milk and tofu. Investigators have only an inkling of how many phytochemicals exist and how they work. They are confident, however, that you can get a basketful of anti-cancer nutrients by mixing and matching at least five servings a day of fruits and vegetables with seven or more starchy or protein-rich plant foods such as grains, peas and beans, and potatoes.
Supplements can help you get some of the benefits of these substances, but they are no replacement for real food. "When you take a supplement, you're getting specific vitamins and minerals, but not the thousands of phytochemicals that might be present in fruits and vegetables," says registered dietitian Amy Jamieson of The Cleveland Clinic Foundation in Ohio. "If you eat a sweet potato with its skin, which is a great source of both beta carotene and fiber, you'll consume at least 5,000 phytochemicals that aren't present in a beta carotene supplement. That's a really important difference."Although the food you eat affects every system in your body, your digestive tract bears the initial brunt of your choices. To keep it running smoothly and disease-free, aim for a diet high in fiber. Unfortunately, most Americans eat only about half the 20 to 35 grams they need each day, even though fiber is readily available in raw and cooked fruits and vegetables, as well as in grain products such as breads, cereals, pasta, and rice.
Fiber comes in two forms, soluble and insoluble. Soluble fiber, found in fruits, vegetables, brown rice, oats, and barley, lowers blood cholesterol levels and slows the entry of glucose into the bloodstream, an important factor in preventing or controlling diabetes. Insoluble fiber, found mainly in whole grains, fruit and vegetable peels, high fiber cereals, and wheat and corn bran, keeps your digestive tract in order. Insoluble fiber soaks up water, adding the bulk that pushes possible cancer-causing substances (carcinogens) out of the intestine.
Fiber's presumed power of protecting against colorectal cancer has received a lot of publicity. This type of cancer is probably the most significant diet-related disorder of the digestive tract and the third leading cause of cancer deaths among both men and women. For years, health experts have speculated that a high-fat, low-fiber diet encourages the production and concentration of carcinogens in the colon, but that fiber-rich food clears them out. Yet the research remains controversial. "A diet high in fiber is almost always one that is, at the same time, low in fat," says Bennett E. Roth, M.D., a gastroenterologist at the University of California, Los Angeles School of Medicine. "So it may be that it's the reduction in fat that's beneficial rather than the fiber itself. But that issue hasn't been resolved yet."
The National Cancer Institute's National Cancer Polyp Prevention Trial, for example, failed to find a lowered incidence of colorectal polyps among more than 2,000 participants on a high-fiber diet. Critics have pointed out, however, that the study lasted only three to four years, while colon cancer takes decades to develop. Thus, the effect of a high-fiber diet wasn't yet apparent. In addition, they note, while polyps are a risk factor for colorectal cancer, most of them do not become malignant.
"Most research supports the protective effect of a diet high in fruits, vegetables, beans, and grains," says Polk, citing the American Institute for Cancer Research's own 1997 report, "Food, Nutrition and the Prevention of Cancer: A Global Perspective," which reviewed 4,500 international studies before coming to this conclusion.No other part of your body benefits more from good dietary choices than your cardiovascular system. What you eat, and choose not to eat, has a dramatic effect on your risk for heart disease and stroke.
Saturated fat, found mostly in meat and full-fat dairy products, is the major culprit in raising blood cholesterol, the main ingredient of artery-clogging plaque. Overindulging in these foods raises the risk of developing heart disease. But you can lower this risk by shifting the emphasis so that nutrient- and fiber-rich foods such as fruits, vegetables, and grains make up approximately two-thirds of what you eat each day.
Plant-based foods provide complex carbohydrates as well as vitamins and minerals. And they contain very little fat. Because they're rich in indigestible fiber, they take up space in the intestines, which can help you control your appetite -- and your weight.
These foods have another advantage. "When you look at non-drug alternatives to reduce cholesterol," says registered dietitian Linda Van Horn, Ph.D., of Northwestern University Medical School in Chicago, "you find that a high-fiber component to a low-fat diet is very effective." Soluble fiber, in particular, has a direct bearing on the body's production, regulation, and elimination of cholesterol. Although the reasons aren't entirely clear, it may be that soluble fiber combines with intestinal fluids to form a gel that binds to fat or prevents it from being absorbed into the bloodstream. Whatever the reason, it does work. One study found that by increasing the amount of soluble fiber they ate, people with Type 2 diabetes decreased their cholesterol levels by almost 7 percent. Other studies show that simply adding two servings a day of oats or other cereals high in soluble fiber can reduce cholesterol levels by almost 3 to 4 percent in people without diabetes. These two servings represent only a small portion of the recommended six to 11 daily servings of bread, cereals, grains, and pasta.
While fiber is the most important dietary adjunct in controlling blood cholesterol, fiber-rich foods contain other nutrients, including antioxidants and phytochemicals, which researchers believe also deter the buildup of plaque in arteries. But the mechanism is unclear. "Is it the nutrients in these foods that have a positive effect, or is it that the more of them you eat, the less fat-laden food you consume?" asks Alice H. Lichtenstein, D. Sc., of the USDA Human Nutrition Research Center at Tufts University in Boston. "We don't know the answer right now, but it's probably a combination of both."
What is clear is that you can eat a heart-healthy diet and still include some fat. "We've made people aware of cholesterol and fat," says Sayed F. Feghali, M.D., a cardiologist at the Texas Heart Institute in Houston. "There's no question that saturated fat is the villain when it comes to cholesterol buildup in blood vessels. But we need some fat. We cannot function on a zero-fat diet."
So be judicious in your choices. Restrict meat and dairy products to less than 10 percent of your daily calories. Try poultry, dried beans, eggs, and nuts for protein and energy. Soy products, when substituted for animal protein, show promise in reducing LDL ("bad") cholesterol. Substitute heart-healthy monounsaturated oils, such as olive, canola, and peanut, for saturated and hydrogenated fats.
Also, watch out for the words "hydrogenated" or "partially hydrogenated" on baked goods and snack foods. They indicate that otherwise heart-healthy unsaturated fat has been manipulated so that oils that would normally be liquid at room temperature stay solid. The process yields trans fats, which raise both total and LDL cholesterol.
Finally, don't be so preoccupied with fat that you lose sight of calories. It's too many calories that add unwanted weight, which can put a strain on your heart. If you're stumped about striking a reasonable dietary balance, check out the eating plans of the American Heart Association (www.americanheart.org).The road to strong bones is paved with calcium-rich food. Leafy green vegetables and low-fat dairy products are excellent sources of calcium, the mineral that puts stiffness into your skeletal system and keeps your bones from turning rubbery and fragile.
Your body uses calcium for more than keeping your bones strong. Calcium permits cells to divide, regulates muscle contraction and relaxation, and plays an important role in the movement of protein and nutrients inside cells. If you don't absorb enough from what you eat to satisfy these requirements, your body will take it from your bones. Because your body doesn't produce this essential mineral, you must continually replenish the supply. Even though the recommended daily amount is 1,200 mg, most adults don't eat more than 500 mg.
One reason may have been the perception that calcium-rich dairy products were also loaded with calories. "In the past, women, in particular, worried that dairy products were high in calories," says Letha Y. Griffin, M.D., of Peachtree Orthopaedics in Atlanta. "But today you can get calcium without eating any high-fat or high-calorie foods by choosing skim milk or low-fat yogurt." Also, low-fat dairy products contain phosphorous and magnesium and are generally fortified with vitamin D, all of which help your body absorb and use calcium.
If you find it difficult to include enough calcium in your diet, ask your doctor about supplements. They're a potent way to get calcium as well as vitamin D and other minerals. But there's a downside. If you rely on pills in lieu of a calcium-rich diet, you won't benefit from the other nutrients that food provides. Getting the recommended vitamin D may be easy, since your body makes the vitamin when your skin is exposed to the sun's rays.