When Americans try to lose weight, the first thing they do is reduce their fat intake. Often, this means that they stop eating milk, cheese and other dairy products, which are thought of as high in fat. New research, however, shows that might not be a very good idea.

Not only are dairy foods high in essential nutrients such as calcium and vitamin D, but they may even help you lose, rather than gain, weight.

The key is getting enough calcium, especially calcium from dairy products, according to a new study using mice that were genetically altered to make their fat cells more like those of humans. As reported by Science News magazine, the study was presented at the Experimental Biology 2000 meeting held in San Diego in April of this year by researchers from the University of Tennessee (Knoxville).

The study found that eating a diet high in calcium influences the metabolism so that a smaller share of food energy is converted into fat. This effect was even more dramatic when the mice were given calcium in the form of dairy products. Citing a reanalysis of data collected from earlier studies of women, another scientist attending the meeting confirmed that the same process appears to take place in the human body.

Michael B. Zemel, director of the University of Tennessee's Nutrition Institute, and his team put groups of mice on a low-calorie diet for six weeks. One group ate a diet that was also deficient in calcium. This group got roughly the same amount of calcium, adjusted for species differences, that today's typical American woman consumes -- about 500 milligrams per day. This is well below the recommended daily intake of 1,200 milligrams.

This group lost eight percent of their body fat and 11 percent of their weight.

Two other groups were given the same amount of calories but more calcium. Both received the mouse equivalent of a human dose of 1,600 mg calcium per day. One group was given its calcium in the form of a supplement; and the other in the form of nonfat dry milk.

The differences were dramatic. The mice in the supplement group lost 42 percent of their body fat and 19 percent of their weight. Those in the dry milk group lost 60 percent of their body fat and 25 percent of their weight.

As Zemel explained, these differences occurred even though all of the groups got the same exercise, the same amount of calories, and the same mix of dietary fat, protein and carbohydrates.

Why have the weight-loss benefits of calcium never been noticed in human beings? According to endocrinologist Robert P. Heaney of Nebraska's Creighton University, they may actually have been. When he first saw preliminary data from the studies done by Zemel's group, he decided to take another look at data from five calcium-supplement trials he had conducted on humans. "In all five," Heaney says, "we found a significant weight effect that we had ignored." These data, to be published soon, show that women consuming the least calcium weighed the most.

TheDoctor's, Robert Russell, M.D., Professor of Medicine and Nutrition at Tufts University School of Medicine and Associate Director of the Jean Mayer USDA Human Nutrition Research Center on Aging, welcomed the new findings, saying that Americans consume far too little dairy foods. "Unfortunately, milk and milk products have gotten a bad reputation due to their high saturated fat content," he explained, "However, these products are wonderful concentrated sources of calcium and vitamin D. The saturated fat problem can be gotten around by drinking skim or 1% milk rather than whole."

Dairy products also suffer from a bit of a PR problem. "Milk has had a 'baby-food image,' Russell says, "although the milk mustache advertisements have helped somewhat to dispel this notion."

"Other people avoid milk because of real or perceived lactose intolerance, although double-blinded studies have shown that this is more often imagined than real. That is, objective testing (for lactose maldigestion) often shows that people who believe themselves to be lactose intolerant are, in fact, not."

Russell's concern that Americans do not get enough calcium is shared by other researchers who attended a symposium on calcium supplementation at the Experimental Biology meeting.

Symposium chair and Tufts University endocrinologist Bess Dawson-Hughes, M.D., cited data that shows the importance of building strong bones by consistently getting enough calcium from early childhood on through adulthood. Recent studies confirm that calcium helps build strong bones, but also show that the positive effects quickly disappear if people stop taking in enough calcium.

"Meeting the calcium requirement," Dawson-Hughes concluded, "should be a lifetime commitment."

Reviewed by: Robert M. Russell, M.D.