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Ask Dr. Weil: Role of hormones in cancer of prostateAsk Dr. Weil: Online courses available for nutrition educationAsk Dr. Weil: Boost resistance to upper-respiratory infectionAsk Dr. Weil: Enlarged breasts in boys resolved oils Ask Dr. Weil by Andrew Weil : A new slant on carpal tunnel Ask Dr. Weil by Andrew Weil : Mineral-based makeup appears to be safe to use Ask Dr. Weil: Anti-inflammatory food pyramid on Web site Ask Dr. Weil by Andrew Weil : No reason to doubt lycopene benefits Ask Dr. Weil: There's no proof that chaparral cleanses toxins Ask Dr. Weil by Andrew Weil : Ayurvedic cleansing rids the body of toxins

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Q I haven't heard anything about MSG lately. Is it harmful or not?

A Probably not, although some people are sensitive to monosodium glutamate (MSG), a flavor enhancer used in Asian foods as well as in a wide range of commercially prepared foods. MSG is a salt of glutamic acid, one of the amino-acid building blocks of protein. Many foods naturally contain free glutamates — these include fresh tomatoes, tomato paste and Parmesan cheese. In the traditional cuisine of East Asia, glutamate-rich foods such as seaweeds and mushrooms have long been used to add a deep savory flavor to soups and sauces.

Purified, crystalline MSG became available in 1909 and was patented and marketed by a Japanese company. Shortly thereafter, Asian cooks began to add it to their dishes. Glutamic acid and its salts, including MSG, stimulate a particular taste receptor, the one responsible for the so-called "fifth taste" (in addition to sweet, sour, salty and bitter). The official name for the receptor and taste is umami, a Japanese word meaning "meaty" or "savory." The company that patented MSG almost a century ago, Ajinomoto ("essence of taste"), built its fortune on this compound. Aji-No-Moto-USA was established in 1958, when pure MSG appeared in groceries here under the catchy brand name "Accent."

The first report that set off alarms about MSG was a letter by a physician published in the New England Journal of Medicine in 1968. The writer observed that after eating Chinese food he developed numbness at the back of the neck, flushing, general weakness and heart palpitations. He called this reaction "Chinese restaurant syndrome" and blamed it on MSG, which Chinese cooks often use with abandon. The syndrome starts 15 to 20 minutes after eating MSG-rich dishes, lasts about two hours and ends without a hangover.

That report stimulated much research on MSG, but overall the studies have produced no evidence linking MSG with any serious reactions. A comprehensive review of the scientific data conducted from 1992 to 1995 by the Federation of American Societies for Experimental Biology (FASEB), an independent group of scientists, at the behest of the FDA, found no connection between MSG and any short- or long-term health problems. Nor did it find evidence linking MSG or other glutamates to Alzheimer's disease, Huntington's disease or neurodegenerative diseases, although articles in the media have suggested such a connection.

However, the FASEB review did conclude that people who eat large amounts of MSG (3 grams or more per meal) on an empty stomach and people with severe and poorly controlled asthma can develop such symptoms as numbness, burning sensation, tingling, facial pressure or tightness, chest pain, headache, nausea, rapid heartbeat, drowsiness and weakness. Note that 3 grams is a lot of MSG. The amount in a typical serving of food to which MSG is added is less than 0.5 grams.

If you find that you react to foods containing MSG or glutamate, check labels carefully when shopping. The FDA requires labels to list MSG as well as other glutamic acid salts (monopotassium glutamate and monoammonium glutamate). When you're dining in Asian restaurants, ask that your food be prepared without MSG. And if you want to boost the umami component of foods naturally, try using seaweeds such as kombu and mushrooms such as shiitake in soups and stocks and sauces.

Q Is it true that caffeine can promote hair growth and could cure baldness?

A Maybe so, but don't start loading up on double espressos yet. You would have to drink an awful lot of them, and probably would be so wired that you wouldn't care about the state of your hair. The caffeine connection to hair growth comes from a small study published in the January 2007 issue of the International Journal of Dermatology, which showed that the drug can block the effects of a biochemical that damages hair follicles.

Male pattern baldness develops when hair follicles are exposed to too much dihydrotestosterone (DHT), a metabolite of the male sex hormone testosterone. High levels of testosterone are believed to cause baldness, especially if male pattern hair loss runs in the family. Overall, about 50 percent of men over the age of 50 are affected.

German researchers discovered the caffeine connection. They took scalp biopsies from 14 men in the early stages of hair loss, extracted hair follicles from the samples and put them in test tubes containing various concentrations of caffeine. After five to eight days, they found that the hairs had grown by 33 percent and 40 percent. In other test tubes, hair from follicles mixed with testosterone grew much more slowly.

The investigators suggested that caffeine might prove to be a way to stimulate hair growth in men going bald. If so, it probably would be applied to the head in a topical solution — don't imagine that you could get the same effects from drinking more coffee. Not even the most dedicated coffee aficionado could down the estimated 60 cups a day required to provide significant amounts to hair follicles.

Also, this study was small and the results will have to be confirmed by further investigations.