Is it possible that one of my favorite food groups -- milk and milk products -- not only provides crucial nutrients but can also help people maintain and lose weight? The answer, while not yet conclusive, looks encouraging. New studies are finding that calcium, particularly when in milk products, may help shed unwanted pounds and body fat.
This is doubly important news because many people slash milk products from their diets to lose weight. The research is showing that move is not only a mistake for your bones, blood pressure and overall health (which nutrition experts have been saying for years), it may also make weight loss more difficult.
Uncovering the calcium-weight loss connection was, like many scientific discoveries, a case of serendipity. In the 1980s, scientists researching the positive effects of calcium on blood pressure found that people on higher-calcium diets not only lowered their blood pressure but also lost weight. The connection wasn't taken seriously at the time. But when large government- funded studies found links between calcium intake and body weight, researchers decided it was worth looking into.
Since 2000, observational and clinical studies of men, women and children have consistently shown that people eating diets containing calcium's recommended dietary allowance of 1,000 to 1,300 milligrams per day have lower body weights and lower body fat. In fact, it's been calculated that with 300 more milligrams of calcium daily, adults will weigh about seven pounds lighter than they would without the calcium.
All of the biological mechanisms aren't completely understood. But, after many years of animal studies, the scientists, led by Michael Zemel, director of the Nutrition Institute at the University of Tennessee, have formulated the primary reason for this weight loss. When there isn't enough calcium in the diet, the body responds by releasing hormones to help conserve as much calcium as possible for critical bodily functions (heartbeat, for one). One of these hormones, calcitriol, tells arterial muscle to contract, which increases blood pressure. But calcitriol also acts on fat cells.
"Calcitriol sends the fat cells a message to start making more fat and sends another message to slow down the process of fat breakdown and oxidation," says Zemel, co-author of "The Calcium Key" (Wiley, 2004). Since high calcium levels have been the norm through evolution, the body assumes that food is scarce and conserves when calcium is low in the diet.
The result is that we become more efficient at storing calories as body fat, so when we cut calories to lose weight, a low-calcium diet makes it harder to break down body fat. Higher-calcium intakes (in which the body senses, rightly or wrongly, that there is plenty of food around) cause lower calcitriol levels and increased fat breakdown. So weight loss is harder for people who don't consume enough calcium, which is the case for average Americans, most of whom consume only half the daily calcium requirement.
In the first human clinical study of the calcium-weight loss connection, Zemel and his colleagues found that the amount of calcium and its food source made a huge difference in weight loss results.
In the study published in Obesity Research in April, three groups of people ate low-calorie diets containing 35 percent fat, 49 percent carbohydrates and 16 percent protein. The first group, which ate 400 to 500 milligrams a day of calcium (an amount of calcium typical for many Americans and less than the minimum requirement) lost an average of 15 pounds in six months.
While eating the same diet with an additional 800 milligrams of calcium from a supplement, the second group lost 19 pounds. But while eating a diet high in milk products containing about 1,200 milligrams of dietary calcium per day (not from a supplement), the third group lost 24 pounds. Fat loss followed a similar pattern. The people on the high-dairy diet lost a higher percentage of body fat, maintained more lean muscle and (a finding that surprised the researchers) lost more belly fat, known as a risk factor for diabetes and heart disease. In fact, the high-dairy group significantly improved its insulin sensitivity, but it isn't known whether that was a dairy effect or the result of the weight loss, which alone improves insulin sensitivity.
Why milk products produced more loss in weight and body fat than calcium supplements isn't completely understood. But there are some theories. For example, milk products have many biologically active compounds, similar to the phytochemicals in plants, which work synergistically to produce a more powerful effect than a single compound, like calcium alone. And milk products also contain unusually high levels of an amino acid (the building block of protein) called leucine.
"Leucine plays a unique role in stimulating protein synthesis and is very important for maintaining lean muscle mass, especially during weight loss," says Donald Layman, protein researcher and professor of nutrition at the University of Illinois, Urbana-Champaign. "If you eat a higher-protein diet, with high levels of leucine coming from dairy products, during weight loss you'll lose 80 percent body fat as opposed to the usual 60 percent body fat."
Until more human clinical research can verify these findings, remember that calcium or milk products alone won't cause you to lose weight. Calories still count. But while this research is being verified, it can only help to consume three milk servings a day. Studies show people who consume more milk products have diets higher in many beneficial nutrients such as calcium, protein, Vitamins A and D, riboflavin, phosphorous, potassium and magnesium.
Katherine Tallmadge is a Washington nutritionist and author of "Diet Simple" (Lifeline Press, 2004). Send e-mails to her at email@example.com.