The coming of summer is wonderful for many reasons, not the least of which is the return of fresh ripe berries. Every Sunday, I hustle to my farmers market to see what is waiting for me.

There are very few foods that match the beautiful color and intense flavor of berries. And, fortunately, these fruits are nutrition superstars.

For many years, most berries were regarded as nutritionally inferior because of their lack of traditional essential nutrients such as vitamins A and C. But that was before scientists discovered the presence of large amounts of beneficial phytochemicals.

Apparently, each berry is a repository of at least 100 nutrients and phytochemicals, the plant compounds with potent powers of healing. Some of the most important phytochemicals in berries are antioxidants, powerful substances believed to reduce inflammation, improve immune function and help prevent heart disease and cancers.

Antioxidants are compounds that absorb oxygen free radicals -- molecules that cause oxidation in the body's cells. Scientists believe that these molecules cause most of the diseases of aging, such as immune system decline, arthritis, heart disease, cancer and neurological impairments affecting cognition and balance. Think of oxidation as being similar to rusting. Or imagine an apple slice turning brown. By simply adding lemon juice, an antioxidant, the apple's flesh stays fresh and prevents the browning or oxidation.

A similar thing happens in your body. Oxidation is constantly occurring in your cells because of environmental pollutants, smoking, exposure to the sun, heat generated through basic metabolic functioning, unhealthy diets and other factors. It takes a large supply of antioxidants to counter this. Berries have been found to have one of the highest antioxidant scores of all fruits and vegetables.

But there are other good reasons to eat berries. The berry family contains 300 to 400 beneficial, disease-fighting chemicals. The phytochemicals in berries, depending on the type, also stimulate the immune system, reduce inflammation, enhance cancer-fighting enzymes, positively influence hormone metabolism, have antibacterial and antiviral effects and may even reverse some aspects of brain.

The most potent berries are the more deeply colored varieties, especially blueberries and cranberries, followed by blackberries, raspberries, strawberries and cherries (not technically a berry) but all more potent than most other fruits. Their color is provided by one of the most powerful phytochemicals, called anthocyanins.

"Anthocyanins play a role in . . . protecting against cancers of the gastrointestinal tract," says Ronald Prior, nutritionist at the Arkansas Children's Nutrition Center in Little Rock. "Blackberries have been shown in animals to protect against colon and esophageal cancer." A preliminary human study found blueberries inhibited blood clotting, a risk factor in cardiovascular disease.

The anthocyanins in berries also may be responsible for improving some aspects of aging, such as memory, motor coordination, balance, vision and even symptoms of Alzheimer's disease, according to many years of animal studies. New studies with humans are offering promising results, too. At a Connecticut senior center, people who ate two cups of blueberries a day reported an increase in reaction speed, especially men. The women reported that they felt happier and had fewer aches and pains.

"Blueberries have interesting, surprising qualities," says James Joseph, director of the neuroscience lab at the USDA's Human Nutrition Research Center on Aging at Tufts University. "We're hoping foods such as blueberries can help prevent Alzheimer's disease in humans as they do in rats."

The scientists found similar effects in cranberries, which have additional phytochemicals called tannins. They may be responsible for helping to prevent urinary tract infections, stomach ulcers, gum disease and even ear infections in children. Cranberries are also effective against antibiotic-resistant bacteria -- and 20 percent of urinary tract infections are resistant to antibiotics. The tannins work by blocking the disease-causing bacteria and preventing it from adhering to human cell walls.

New research conducted at the Natural Products Utilization Research Unit of the USDA's Agricultural Research Service has found that raspberries, blueberries, cranberries and huckleberries also contain a phytochemical called resveratrol, which is thought to help prevent cancer and cardiovascular disease.

Strawberries contain large amounts of phytochemicals called ellagitannins, which are also in raspberries and blackberries. Studies at the UCLA Center for Human Nutrition found those berries are capable of inhibiting a number of key steps in the development of cardiovascular disease and may have immense potential for the prevention and treatment of heart disease and stroke. Strawberries are also high in antioxidant Vitamin C and folic acid, important in preventing birth defects.

Most of what scientists know about berries has been determined in animal studies and in labs using cell cultures. But the few human clinical studies are showing promising results. Human studies on berries are limited because they're very expensive, and as one scientist explained, "You can't patent a berry!" This means that big pharmaceutical companies are unwilling to foot the research bill. Groups such as blueberry or strawberry growers fund some, but it's up to Uncle Sam to find out if we can save millions on medications and hospitalizations by simply eating more berries.

Katherine Tallmadge is a Washington nutritionist and the author of "Diet Simple" (Lifeline Press, 2004). Send e-mails to her at food@washpost.com.