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.

DEAR DR. BLONZ: I have an interest in "real food" supplements, specifically soy supplements, and would appreciate your opinion. You recently wrote about soy and thyroid hormones, but I am interested in soy isoflavones to help with the symptoms of menopause. I don't have much soy in my diet, and wanted to know if taking a supplement would be a good strategy. -- P.L., Chicago

DEAR P.L.: The idea of a "real food" supplement is a bit of a contradiction in terms: Nothing compares with real food. Science has only begun to identify the healthful elements in the foods we eat. Each new study can provide greater awareness about a specific component, and if the research sounds promising, it can breed interest in spinoff products in pill form.

But all this misses the "whole food" point. It is unlikely that a single element holds the key. The smart money rests with the concept that all of a food's elements working together -- that is, the whole food itself -- provides the magic. This makes perfect sense, as whole foods represent an interactive, nature-evolved system designed to survive. What's more, these systems have passed the test of time -- a critical asset when considering GMO crops, as they sidestep this process.

Now, on to the specifics of the soy isoflavones. The isoflavones are phytochemicals (phyto = plant) unique to soybeans. They have a number of abilities and are antioxidants, which may have a direct role in soy's beneficial effects.

Isoflavones have structural similarities to estrogen, but eating soy isn't like taking estrogen. The isoflavones don't function as estrogen in the human body. They only have a "weak estrogenic effect" -- only one-hundred-thousandth (1:100,000) as potent as estrogen. The build of the isoflavone is believed to play a role in some of soy's observed beneficial effects, as it may bind with the body's natural estrogen receptors in a way that lessens estrogen's negative effects. Higher levels of (human) estrogen, for example, are connected with an increased risk of certain hormone-related cancers, such as breast cancer. Studies have shown how populations eating soy-based diets have a lower incidence of breast cancer. Diets containing soy may also protect against colorectal cancer in women: A study in the February 2009 issue of the American Journal of Clinical Nutrition reported that for every 5 grams per day of soy food eaten, the risk decreased by 8 percent.

This is one reason health professionals have encouraged people to have more soy in their diets. For someone who wants soy's benefits, but is not able to have soy in her daily diet, your soy extract capsule may actually seem like a good alternative. I would tend to agree -- but with reservations.

First is the fact that soy foods offer much more than isoflavones. Soybeans contain protein, vitamins, minerals, fiber and essential fatty acids, in addition to other valuable phytochemicals. (Check the information sheet from University of California at Davis at goo.gl/0YcpKv.) If you only take the isoflavones, you miss out on other components that are likely to play a role in soy's whole-food beneficial effects.

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.