An apple slice turns brown. Fish becomes rancid. A cut on your skin is raw and inflamed. All of these result from a natural process called oxidation. It happens to all cells in nature, including the ones in your body.

To help your body protect itself from the rigors of oxidation, Mother Nature provides thousands of different antioxidants in various amounts in fruits, vegetables, whole grains, nuts, and legumes. When your body needs to put up its best defense, especially true in today's environment, antioxidants are crucial to your health.

Here's how oxidation works. As oxygen interacts with cells of any type - an apple slice or, in your body, the cells lining your lungs or in a cut on your skin -- oxidation occurs. This produces some type of change in those cells. They may die, such as with rotting fruit. In the case of cut skin, dead cells are replaced in time by fresh, new cells, resulting in a healed cut.

This birth and death of cells in the body goes on continuously, 24 hours a day. It is a process that is necessary to keep the body healthy. "Oxidation is a very natural process that happens during normal cellular functions," researcher Jeffrey Blumberg, PhD, professor of nutrition at Tufts University in Boston, tells WebMD.

Yet there is a downside. "While the body metabolizes oxygen very efficiently, 1% or 2% of cells will get damaged in the process and turn into free radicals," he says.

"Free radicals" is a term often used to describe damaged cells that can be problematic. They are "free" because they are missing a critical molecule, which sends them on a rampage to pair with another molecule. "These molecules will rob any molecule to quench that need," Blumberg says.

The Danger of Free Radicals

When free radicals are on the attack, they don't just kill cells to acquire their missing molecule. "If free radicals simply killed a cell, it wouldn't be so bad… the body could just regenerate another one," he says. "The problem is, free radicals often injure the cell, damaging the DNA, which creates the seed for disease."

When a cell's DNA changes, the cell becomes mutated. It grows abnormally and reproduces abnormally -- and quickly.

Normal cell functions produce a small percentage of free radicals, much like a car engine that emits fumes. But those free radicals are generally not a big problem. They are kept under control by antioxidants that the body produces naturally, Blumberg explains.

External toxins, especially cigarette smoke and air pollution, are "free radical generators," he says. "Cigarette smoke is a huge source of free radicals." In fact, our food and water also harbor free radicals in the form of pesticides and other toxins. Drinking excessive amounts of alcohol also triggers substantial free radical production.

Free radicals trigger a damaging chain reaction, and that's the crux of the problem. "Free radicals are dangerous because they don't just damage one molecule," Blumberg explains. "One free radical can set off a whole chain reaction. When a free radical oxidizes a fatty acid, it changes that fatty acid into a free radical, which then damages another fatty acid. It's a very rapid chain reaction."

These external attacks can overwhelm the body's natural free-radical defense system. In time, and with repeated free radical attacks that the body cannot stop, that damage can lead to a host of chronic diseases, including cancer, heart disease, Alzheimer's disease, and Parkinson's disease.

Oxidative damage in skin cells is caused by cumulative sunlight. But if free radicals are in an internal organ - for example, if asbestos is in your lungs -- it stimulates free radical reactions in lung tissue. "Cigarette smoke has active free radical generators," says Blumberg. That's why stopping smoking is the biggest step anyone can take to preserving their health.

In the 21st century, people need to get more antioxidants in their diet to offset all these assaults, he says. "These toxins are ubiquitous in the environment. If you live in a city, you breathe the air. The oxidative burden [on the body] is much, much, much higher than it was 200 years ago. It's a fact of modern life, so we have to take that into consideration."

When you follow the USDA's advice to eat multiple servings of fruits and vegetables, you're compensating for the effects of environmental toxins. Your body simply doesn't produce enough antioxidants to do all that, says Blumberg.

What exactly do they do? Antioxidants work to stop this damaging, disease-causing chain reaction that free radicals have started. Each type of antioxidant works either to prevent the chain reaction or stop it after it's started, Blumberg explains.

"For example, the role of vitamin C is to stop the chain reaction before it starts," he says. "It captures the free radical and neutralizes it. Vitamin E is a chain-breaking antioxidant. Wherever it is sitting in a membrane, it breaks the chain reaction."

Flavonoids are the biggest class of antioxidants. Researchers have identified some 5,000 flavonoids in various foods, Blumberg tells WebMD. Polyphenols are a smaller class of antioxidants, which scientists often refer to as "phenols." (Terms like phytonutrient and phytochemical are more generic terms that researchers sometimes use to describe nutrients and chemicals in plants.)

"We have clear science about antioxidants, that our bodies need a Natural Antioxidant Defense Network, for lack of a better term," Blumberg says. "Just like a country needs a military system, the human body needs defense workers at all levels -- lieutenants, corporals, generals, staff sergeants - in the form of antioxidants."

The body needs a mix of vitamins and minerals, such as vitamins A, C, E, and beta-carotene, to neutralize this free radical assault.

"We can't rely on a few blockbuster foods to do the job," says Blumberg. "You can't eat nine servings of broccoli a day and expect it to do it all. We need to eat many different foods. Each type works in different tissues of the body, in different parts of cells. Some are good at quenching some free radicals, some are better at quenching others. When you have appropriate amounts of different antioxidants, you're doing what you can to protect yourself."

Multivitamins and vitamin supplements can provide the body with an antioxidant boost. Yet getting too much of some supplements, like vitamin E, can be harmful. Fruits, vegetables, whole grains, legumes, and nuts contain complex mixes of antioxidants, and therein lies the benefit of eating a variety of healthy foods, says Blumberg.

Researchers continue delving into the mysteries of fruits and vegetables, identifying the complex antioxidants they contain. Quercetin, luteolin, hesperetin, catetchin, even (-)-epigallocetechin are some of the stars they have found -- the blockbuster flavonoids in our foods.

"Sure, you can live your whole life without getting epicatechin 3-gallate, a flavonoid found in huge quantities in green tea," says Blumberg. "But if having it in your diet promotes better health, why not try it?"

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SOURCE: Jeffrey Blumberg, PhD
Tufts University, Boston.