A healthful diet gives you the nutrients you need to keep your body in top-flight condition. In addition, evidence suggests that eating well may prevent or minimize the risk of a long list of serious medical conditions, including heart disease, high blood pressure, and cancer.

This article describes what nutritionists know right now about how to use food to prevent, alleviate, or cure what ails you — with a couple of hints about what’s to come in the evolving world of medical nutrition.

Start with a definition. A food that acts like a medicine is one that increases or reduces your risk of a specific medical condition or cures or alleviates the effects of a medical condition. For example:

• Eating foods with lots of beta carotene (the natural chemical in deep yellow and dark green fruits and veggies that your body converts to vitamin A) — along with vitamin C, vitamin E, and zinc — protects your vision by reducing the risk of age-related degeneration of the macula, the organ at the back of your eye that enables you to perceive light.

• Eating foods, such as wheat bran, that are high in insoluble dietary fiber (the kind of fiber that doesn’t dissolve in your gut) moves food more quickly through your intestinal tract and produces soft, bulky stool that reduces your risk of constipation.

• Eating foods such as beans that are high in soluble dietary fiber (fiber that dissolves in your intestinal tract) seems to help your body mop up the cholesterol circulating in your bloodstream, preventing it from sticking to the walls of your arteries. This reduces your risk of heart disease.

• Eating sufficient amounts of calcium-rich foods ensures the growth of strong bones early in life and protects bone density later on.

• Eating very spicy foods, such as chili, makes the membrane lining your nose and throat weep a watery fluid that makes blowing your nose or coughing up mucus easier when you have a cold.

• Eating (or drinking) foods (or beverages) with mood-altering substances such as caffeine, alcohol, and phenylethylamine (PEA) may lend a lift when you’re feeling down or help you chill when you’re tense.

The joy of food-as-medicine is that it’s cheaper and much more pleasant than managing illness with drugs. Given the choice, who wouldn’t opt to control cholesterol levels with oats or chili (all those yummy beans packed with soluble dietary fiber) than with a drug whose possible side effects include kidney failure and liver damage?

Sometimes, a person with a life-threatening illness is frightened by the side effects or the lack of certainty in standard medical treatment. In desperation, he may turn down medicine and turn to diet therapy. Alas, doing this may be hazardous to his already-compromised health.

No reputable doctor denies the benefits of a healthful diet for any patient at any stage of any illness. Food not only sustains the body but also can lift the spirit. But although food and diet may enhance the effects of many common drugs, no one has found them to be an adequate, effective substitute for (among other medicines):

• Antibiotics and other drugs used to fight infections
• Vaccines or immunizations used to prevent communicable diseases
• Anticancer drugs

If your doctor suggests altering your diet to make your treatment more effective, your brain will tell you, Hey, that makes sense. But if someone suggests chucking your doctor and tossing away your medicine in favor of food therapy alone, heed the natural warning in your head. You know there’s no free lunch and — as yet — no truly magical food, either.