DEAR DR. BLONZ: I continue to read about fasting and cleansing and their ability to release toxins that have built up in the body. Is there a difference of opinion among professionals in nutrition about the release of toxins in this way? Do you see any potential here? -- S.E., Arizona

DEAR S.E.: The concept of the "release of toxins" during a fasting or cleansing routine is dubious. Many of the arguments are either theoretical ("I think it might work") or anecdotal ("some tried it and thought it worked for them"). To this, we add the fact that there is little if any data or evidence in the journals to support the efficacy of these procedures. As they should, science-trained professionals tend to reject concepts where there is a lack of objective evidence.

Some connect how they feel during fasting/cleansing as an affirmation that their body is casting off toxins. This can be misleading as the lack of food can cause these same sensations. Consider that the body's priorities undergo a massive shift when it stops eating. In some cases, symptoms of chronic ailments might abate, especially those that might be due to previous poor eating habits, food-related allergies or sensitivities. But there is no reason to assume that these feelings are due to actual healing or a removal of toxins.

There is an ongoing dynamic turnover of most cells in the body; they tend to be continually broken down and remade. While all this is going on, the body acts to eliminate whatever toxins it can. While it might seem reasonable to think that fasting might hasten the rate at which toxins are shed, the opposite might actually be the case. Some toxins get stored in the body's adipose (fat) tissue, and during a fast, the body's fat stores are used to supply needed energy. This can actually increase the toxins roaming around the body, but the rate at which the body detoxifies does not increase. When this happens, the body can experience untoward effects from the increasing blood levels of the noxious agents. And then, the lack of food might hamper the immune system at it attempts to detoxify and eliminate.

Some cleansing products claim that the toxins build up in the intestines and colon, and by using cleansing laxatives and stimulants, you force those stubborn toxins out of the body. Consider that the cells that comprise the lining of the intestines are shed periodically, which means that the lining of your intestine changes from month to month. This places on dubious footing the concept that caked-on toxins are able to hang around and wreak havoc with your health. It also casts doubt on the efficacy of the "cleanse."

If there is a potential benefit to these processes, it might be that they can serve as a jump-start to a lifestyle change. One could use a fast or a cleanse to, in effect, cast off the past and change to a more healthful lifestyle, physically, emotionally and spiritually. The fast or cleanse can serve as a time of contemplation, where one considers the status quo and redefines the new quest for a quality of life.

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 dangerous are the nitrates that are in hot dogs, ham, sausages and deli meats? How do they differ from those found in vegetables? Are they all carcinogens that have to be actively avoided to reduce the risk of cancer? -- F.G., Berkeley, Calif.

DEAR F.G.: Your question involves both nitrates and nitrites; the two are related, but there are important differences.

Nitrites: Food processors use nitrites as preservatives in cured and smoked meat products such as bacon, sausage, smoked and deli meats. These are all meats that tend to be stored under refrigeration for a number of days, and without an appropriate preservative such as sodium nitrite, there's a relatively high risk of botulism -- an often-fatal food poisoning. Nitrites, themselves, represent a risk as they can form cancer-causing chemicals called nitrosamines. These compounds can form when a nitrite (either sodium nitrite or potassium nitrite) reacts with protein at a high cooking temperature. The principle here is that with the exception of freezing or high-temperature cooking, there's no safe way to protect against botulism in a low-acid food such as a cured meat.

Nitrates: Nitrates occur naturally in several vegetables including turnip greens, beets, celery, rhubarb, spinach, radish, parsley and lettuce. They represent less of a risk than nitrites, but a nitrate can be converted to a nitrite in the stomach. This means that nitrosamines can theoretically form in the stomach when you eat a nitrate-containing vegetable and a protein food at the same meal. The important difference is that antioxidant nutrients can help limit nitrosamine formation, and these nutrients, such as vitamin C, E or antioxidant phytochemicals, tend to be found in nitrate-containing foods.

By contrast, in cured meat products such as bacon or sausage, all the ingredients needed to form nitrosamines are in the same package and the nitrosamines can be formed before you eat. In weighing the relative risk from botulism against the presence of the nitrite preservative, scientists decided that if you're going to eat cured or smoked meats, the use of nitrate preservatives is an acceptable risk.

Because there is some risk involved, nitrite preservatives are not permitted in baby foods.

Although most smoked and cured meats contain sodium or potassium nitrite, you can find nitrite-free meat products either as locally made, short shelf-life products, or in the freezer case where the low temperature can effectively inhibit bacterial growth.

A prudent approach is to limit your intake of nitrite-containing cured and smoked meats. If you enjoy these foods, see if a nitrite-free brand is available. You could also look for a product that contains sodium ascorbate (a salt of vitamin C), sodium erythorbate or vitamin E; these antioxidants can help limit nitrosamine formation. Another option is to make sure you have antioxidant-rich foods at the same meal as the nitrite-containing meats. A salad with the meal, some peppers or vegetables on the sandwich, and fruits as dessert are all additions that could help blunt the potential risk.

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 am in high school, and want to put on weight so I can play football. I recently shot up a number of inches in height, but my weight proportion has not kept up. I have always been in the backfield, and now I lift weights four mornings a week and take physical conditioning. I have been eating and eating but it does not seem to help me bulk up the way I would like. Could you recommend a supplement? -- F.F., Chicago

DEAR F.F.: There is a limit to what one can do, as growth in height does not always parallel the increase in weight. Then there is the overriding influence of one's genetic predisposition. If most of your family members are tall and thin, it will lessen the odds of you becoming a 250-pound running back. This is not to say you are without any remedies, but they might not provide the exact results you hope for.

A well-balanced diet, along with weight-lifting and conditioning programs, are important adjuncts to any weight-gain program. If you wanted to gain one pound a week, this would involve taking in 500 calories a day above your normal caloric intake. There are weight-gain milkshake products that can help accomplish this, but be advised that studies have found that the body does not always gain as expected. You are not the first to face this dilemma. Remaining athletic might mean playing a different position, or even a different sport, that fits your new body type.

DEAR DR. BLONZ: I am a woman, and my hair is thin and subject to frequent breakage. Someone suggested Norwegian kelp. Will this nutrient remedy my symptoms and stimulate hair growth? -- T.T., San Diego

DEAR T.T.: Kelp, a vegetable that grows in the sea, is touted primarily for its iodine content, but it also contains potassium, calcium, magnesium and sodium. Iodine is an essential mineral that plays a role in the manufacture of the thyroid hormones that help regulate the body's metabolism. Dry, coarse, breaking hair and hair loss are among the symptoms of inadequate thyroid hormone (hypothyroidism), so perhaps that was the connection that your adviser was thinking of.

It is unclear whether kelp is the answer to your problem. Iodine is plentiful in the ocean but is not well-distributed on land. Foods containing iodine are limited to seafoods, crops grown in coastal areas, and dairy or meats from animals that have grazed on feed containing iodine. The Daily Value for iodine is 150 micrograms -- a trace amount. It's rare for anyone eating a varied diet today to suffer from an iodine deficiency.

One's genetic background, certain health conditions and medications can all have a range of influences on how the hair looks and behaves. The quality of your diet is also a player. I would take a look at what you have been eating and aim for a good mix of fruits, greens and grains as these provide the essential vitamins and minerals. I would also have a regular intake of seafood, or other sources of essential fatty acids. But irrespective of what one eats, the hair will always be greatly influenced by environmental factors and the hair products and treatments one uses. A knowledgeable hairstylist might be able to recommend products well-suited to your particular situation.

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.