I normally just roll my eyes when I come across diet books festooned with the word revolutionary. That expression is usually the hallmark of some gimmicky regimen that fails to reduce weight but manages to increase the author’s bank account. So it was with my usual skepticism that I began to look through The Calcium Key: The Revolutionary Diet Discovery that Will Help You Lose Weight Faster. In truth, the only reason I had any interest was because the author, Dr. Michael Zemel, is a professor in the Department of Nutrition and Medicine at the University of Tennessee, and has published numerous research papers in respected journals. He should know what he is talking about. And what he talks about is the connection between calcium intake and weight loss.
Dr. Zemel’s interest in the calcium connection was aroused in the 1980s, when scientists began to explore the link between calcium and blood pressure. It became quite clear that people who had a high calcium intake had lower blood pressure. Unexpectedly, though, the researchers also noted that high calcium intake correlated with a lower body weight. Why should this be so? Zemel decided to find out. He had no trouble enlisting a few dozen subjects for his studies, for the simple reason that the subjects were mice. But these creatures do serve as good models for humans, as far as metabolism goes. Zemel and colleagues found that a diet low in calcium causes the kidneys to release calcitriol, a form of vitamin D. Calcitriol’s role is to compensate for a low calcium intake by decreasing calcium excretion from the kidneys, increasing its absorption from the gastrointestinal tract, and stimulating its release from bones. This was no great surprise, since it was already well known that calcium is critical for heart and nerve function, and that the body has means of increasing blood levels when the diet isn’t providing enough of the mineral. What did come as a shock was the discovery that calcitriol also increased calcium absorption into fat cells, where it triggered a cascade of chemical reactions. The end result was a buildup of fat in these cells.
There seems to be a reasonable rationale for this observation. When calcium intake is low, the body assumes that there is not much food coming in. So it takes emergency measures, and starts to store fat for use during the lean times that may be approaching. A nice theory, but could it be confirmed by evidence? Once again, Dr. Zemel reached for his mice. First, the mice, specially bred to be obese, were allowed to dine until they became portly. Then they were put on a low-calorie diet, with varying amounts of calcium. With no calcium, the mice managed to lose only 8 percent of their body fat. When they were given calcium carbonate supplements (à la “Tums”), the animals managed to shed 42 percent of their body fat. But the really exciting results came with the mice that had been given high amounts of lowfat dry milk. They led the pack with a stunning 69 percent loss in body fat! Mice, though, are not humans. Would people show the same effect? There was only one way to find out.
This time, the Zemel group enlisted thirty-two obese adults and planned a randomized, placebo-controlled trial. For twenty-four weeks, the subjects were put on a diet that contained 500 fewer calories than they were accustomed to eating, but with varying amounts of calcium. One group of subjects had at most one dairy serving a day, for a total intake of 400 to 500 milligrams of calcium, a second group had the same diet but also received an 800-milligram calcium supplement, for a total of 1,200 to 1,300 milligrams of calcium, and a third group was given three low-fat dairy servings, again for a total of 1,200 to 1,300 milligrams of calcium. The results were clear: the greatest weight loss, a pound a week, was seen with the high-calcium diet. Why calcium from a dairy source should be more effective than calcium supplements is not clear. Milk is chemically complex and contains numerous compounds that can apparently enhance the “calcium effect.” Obviously, more research is needed in this area, and it will need to be supervised by scientists who do not have a financial stake in the calcium connection. In addition to profiting from his book, Dr. Zemel holds a patent on treating obesity with a high-calcium regimen.
Zemel’s results are, however, corroborated by an epidemiological study carried out at Laval University in Quebec City. Here, researchers analyzed the nutrient intake of 235 men and the same number of women over seven years, and found that a low calcium intake was associated with obesity, particularly in women. Furthermore, they found that cholesterol levels were significantly lower in people who had a high calcium intake.
Now, then, what do we take away from all this? First, when we’re dieting, we don’t take away all dairy products, as so many people try to do. But we should take away the fat from the dairy products. Low-fat dairy has as much calcium as the high-fat version, so stick to it. A couple of glasses of skim milk a day will go a long way toward satisfying the daily calcium requirement. Remember, though, that calories count! Nobody is suggesting that adding low-fat dairy products to an ordinary diet is going to shed pounds. But incorporating such into a low-calorie diet just may enhance weight loss. And it will also benefit the bones, help control blood pressure, and even reduce the risk of colon cancer. Dr. Zemel’s research may not exactly be “revolutionary,” but it may represent a small victory in the battle against the bulge.