DEAR DR. BLONZ: I read that orange-, pink- or red-fleshed fruits and vegetables contain beta carotene, but I wonder just what it is and how it got its name. I also recall you mentioning another antioxidant category with which I am completely unfamiliar: the "flavonoids." What are they, where did they get their name, and what foods contain them? -- S.H., Poway, California

DEAR S.H.: The naming of chemical compounds is a recipe of science and folklore. The root, or family name, of compounds is often taken from the name of the plant in which it was first discovered. From that point on, naming variations tend to be based on how the structure differs from the parent compound.

In the case of beta carotene, the parent compounds are the carotenes -- a group of yellow-red pigments widely distributed in plants, but most notably present in carrots (hence the name). The "beta" is the Greek letter designation for the fact that a key structure is in the second, or beta, position. (Alpha and gamma carotene have their identifying structures in the first and third positions, respectively.)

What's unique about these colorful compounds is that oxygen tends to combine with them in preference to other compounds and bodily tissues. The fact that beta carotene is a more attractive target means that its presence can "spare" other bodily substances and tissues from being oxidized, and possibly damaged in the process. That is the essence of what it takes to be called an antioxidant.

Please understand that oxidation is not a bad thing: It is entirely essential for life, and is used to release the energy from the foods we eat. After all, we breathe to get oxygen into our body. But when oxidation takes place at the wrong place and at the wrong time, it can lead to tissue damage that causes aging and can increase our risk of heart disease, cancer, certain forms of arthritis and a host of other ailments. A diet that is rich in whole-food antioxidants can help stave off unwanted damage due to errant oxidation. Nutrients that function as antioxidants include vitamin C, beta carotene, vitamin E and selenium. And manganese, copper and zinc are constituents of superoxide dismutase, an enzyme that plays an important role in the body's antioxidant defense system.

The flavonoids are compounds that contain a particular structure called a flavone. They, like the carotenes, are color compounds and strong antioxidants. The flavonoids are widely distributed in plants, and include such compounds as quercetin (found in onions), rutin (buckwheat), the bioflavonoids (citrus fruits) and the isoflavones (soybeans).

Through the discovery of antioxidant compounds and how they work, science has provided a detailed explanation of yet another reason why whole foods are so good for us.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: Is it best to stick with foods that say "no preservatives added" on the label? -- F.F., Los Angeles

DEAR F.F.: If we only ate farm-fresh products, we would have little need for food preservation beyond a refrigerator. But most of us aren't fortunate enough to have that as an option. Instead, we have to rely on methods of food preservation designed to deal with the reality that the nutrients in foods are just as attractive to microorganisms as they are to us.

Here are some examples, many of which are based on the fact that water is as essential to spoilage organisms as it is to humans.

Drying is the most basic method, in that it removes water. Sugaring or salting work through an ionic effect that can draw water out of the spoilage organisms and prevents their growth. Freezing slows down the spoilage process by changing that water into ice crystals, which cannot be utilized by most bacteria. The canning process destroys organisms through heating, and then places food in a sealed container to prevent further contamination. Pasteurization destroys most existing spoilage organisms by heating the food to a high temperature for a short duration.

Pickling (or fermentation or culturing) leaves the food with a higher level of acid, creating an inhospitable environment for certain types of spoilage organisms. Smoking adds smoke-born chemicals to a food that help destroy potential organisms.

Finally, there is the use of chemical additives designed to either destroy spoilage organisms or inhibit their growth. Antimicrobial preservatives are special chemicals that can stop the growth of bacteria, molds, fungi and yeast that destroy food. Antioxidant preservatives prevent rancidity, "off" flavors and discoloration caused by oxidation.

Chemical preservatives get mixed reviews. Some are essentially harmless in the minute quantities used, while others have an inconsistent safety record. Nature serves as our best instructor, as many commonly used preservatives are based on natural substances.

Tocopherol (vitamin E) compounds are used in nature to protect plant seed oils, and ascorbates (vitamin C) help keep fruits and vegetables fresh. Both are natural antioxidants. Fruits, such as cranberries, raisins, prunes and citrus, contain natural acids that make effective antimicrobial agents. These compounds include citrate, propionate, benzoate, sorbate and lactate.

Raisin juice is a natural source of propionate, a compound used by bread makers to help slow the formation of molds. The bakers have the option of using raisin juice (natural) or adding calcium propionate (artificial) to inhibit mold in their products. In either case, these compounds and others like them are harmless at the levels used.

Some preservatives have less than glowing safety records. Among these are the sulfites and nitrites. Sulfites are effective antioxidants, but the U.S. Food and Drug Administration estimates that as many as 100,000 people in the United States react badly to sulfite preservatives. If you are among them, eating foods with sulfites might cause symptoms like headache, hives or shortness of breath. If sulfites are present, the food's label must say so.

Processors put nitrites in sausages, bacon and other cured meats because they inhibit the bacteria responsible for botulism poisoning. In the body, nitrites can be converted into nitrosamines, compounds known to cause cancer in animals. In making a choice between the possible dangers of botulism and nitrosamines, nitrite preservatives are deemed the lesser of the two dangers. Still, it makes sense to limit our consumption of nitrite-containing meats.

It is perceived as desirable for food labels to say "no preservatives added," but we should realize that not all preservatives are of concern -- especially ones based on naturally occurring substances. There's little value in keeping foods preservative-free if half the product gets discarded due to spoilage, or, worse, if you end up eating food that has already begun to spoil.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.

DEAR DR. BLONZ: How do the nutritional needs of an older athletic individual -- that's me -- differ from one who has chosen a sedentary lifestyle? My lifelong friend, who happens to be the same approximate height and weight, doesn't do much exercise, and I keep trying to encourage him to get with the program, but he doesn't see the upside. -- F.L., Walnut Creek, California

DEAR F.L.: There is a big difference in how contrasting lifestyles impact the body, so don't think that the fact that you and your friend might wear the same size clothes be viewed as a pass for his non-active lifestyle. As for nutritional requirements, those for the average older athlete will be similar to those of an individual who is sedentary, with two exceptions: water and calories. Both require a varied diet that focuses on nutrient-dense fruits, vegetables, grains, nuts, seeds and dairy products, with a modicum of high-protein foods such as fish, poultry and meat.

The body's metabolism goes through radical changes as we progress through mid-life into our senior years. The need for dietary calories decreases because of the continually decreasing calorie-burning capacity of our cells. In addition, the digestive system, through which nutrients are digested and absorbed, gradually becomes less efficient. The ability to feel thirst also tends to diminish, resulting in an inadequate water intake.

The body's skeleton shifts into "negative balance." This is where the removal of minerals, such as calcium from the bones, proceeds more rapidly than they can be replaced. The net result is a gradually weakening bone structure and an increased risk of osteoporosis. A sedentary lifestyle allows all these changes to proceed unabated. When you're active, though, the body behaves differently.

Because muscle movement is required during exercise, the calorie-burning capacity of our cells does not decrease as rapidly. The bones need to retain more strength so less of their precious minerals will be lost. The joints will tend to retain more flexibility to help support the physical activity. Circulation, needed to provide fuel to the working muscles, improves, and the heart muscle tends to remain stronger. In essence, activity, even if it's only regular daily walks, will help to keep you younger, longer.

Water is especially essential before, during and after exercise because it helps to keep the body cool via perspiration. In addition, water helps to shuttle waste products from energy production out of the body through the urine. Dehydration, even when mild, impairs performance and can cause the body to overheat and malfunction. This can be especially dangerous in the older athlete because the kidneys do not operate as efficiently. Because one's awareness of thirst can be lost during exercise, it's best to make drinking water a part of any exercise routine.

I am hopeful that your friend will be able to grasp the big picture that activity should be considered an investment that is especially important for seniors. It not only affects the quality of our day-to-day lives and capabilities, but it bolsters the resilience with which we are able to handle the inevitable curveballs that life throws our way.

Send questions to: "On Nutrition," Ed Blonz, c/o Universal Uclick, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.