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Say 'Aaah' | On Nutrition

Weighing In on the Role of Calcium

July 02, 2001|AMANDA URSELL

The battle to beat the nation's growing obesity rate continues to challenge individuals and health experts alike. While short-term diets tempt us with their quick-fix promises and pharmaceutical companies invest billions in drugs to dampen hunger or speed metabolism, nutritionists are investigating how certain foods affect body weight. Among their discoveries is that calcium may play a key role.

Research published in the April issue of the International Journal of Obesity found that higher intakes of calcium were associated with lower body fat measurements in preschool children. The study of 53 children was conducted by nutritionists from the University of Tennessee. It followed findings last year by Michael Zemel, a nutrition professor at the university, who found a similar relationship when he analyzed government survey data tracking food intakes and body composition.

This potential link between calcium and weight has gained momentum in scientific circles, with other researchers reexamining studies originally conducted to determine the effect of calcium on bone health. Reviewing five such studies involving a total of 780 women, Dr. Michael Davies of Creighton University in Omaha, Neb., found that low dietary calcium was again associated with significantly higher body weights.

It is all very well having these "associations," but an explanation is needed of how and why they may exist. Through laboratory work carried out on human fat cells, Zemel and his colleagues have come up with one possible explanation.

Researchers already knew that eating a diet low in calcium tends to increase levels of vitamin D and parathyroid hormone, or PTH, in the blood. What Zemel showed was that, when raised, these substances increase calcium concentrations in human fat cells, which encourages them to store more fat. Furthermore, in studies on mice, which are genetically predisposed to obesity, they discovered that high-calcium diets raised body temperature and reduced fat accumulation; low-calcium diets lowered body temperature and increased fat accumulation.

Davies speculates that our bodies may be affected by changing calcium levels because of an evolutionary mechanism designed to help us through times of food shortages. The primitive human diet, Davies says, had more calcium than today's modern diet. It is feasible, he proposes, that low-calcium intakes helped regulate fat storage. When there was less food available, we had less calcium and were better able to hang on to what then would have been considered life-sustaining fat stores. Today, with our relatively low calcium intakes, these mechanisms may be predisposing us to fat storage.

Of course, individual calorie consumption and exercise levels still play the most important role in determining weight.

What the research could suggest, however, is that the well-documented tendency to cut calcium-rich dairy products such as milk from our diets when attempting to lose weight may be contributing to the frequent failure of weight-loss regimens.

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Amanda Ursell, a dietitian, is a London-based freelance journalist who writes about food and nutrition. Her column appears twice a month. She can be reached at http://amanda@ursell.com.

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