Outpouring of Evidence

What if there were a drink that could boost the effectiveness of a standard weight-loss diet, perhaps by as much as 50%? What if this drink could make you burn fat faster and store it slower? And what if this potion, also available in a variety of other forms, wasn’t the get-rich-quick dream of an infomercial pitchman or Internet scamster but the pet project of some respectable scientists?

Then would you drink your milk?

Yes, milk--that bland, blah beverage you may have stopped drinking years ago. A growing body of scientific evidence strongly suggests that frequent consumption of milk--or yogurt or hard cheeses, such as cheddar--is one of the habits that separate the svelte from the stocky. If researchers are right, America’s growing girth may be due, at least in part, to the fact that many of us have lost the milk habit: four out of 10 adults consume less than a glass a day.

Weight control isn’t the only boon dairy products have to offer. Most of us learned as children that milk is a nutritional powerhouse--a great source of protein, vitamins and essential fatty acids. But research in recent years points to milk and some other dairy products as potent disease-fighters, as well.

The benefits range from the pedestrian (milk consumption lowers the risk of kidney stones, for instance) to the possibly lifesaving (dairy products may play a role in preventing stroke and even some forms of cancer).

So what do you get if you get milk--or yogurt or hard cheese? (Cottage cheese tends to get left off scientists’ list of preferred dairy products because it’s relatively low in calcium; cream cheese and ice cream get omitted for more obvious reasons.) The list starts, of course, with the familiar, heard-it-before ability to protect against osteoporosis. Familiar or not, that protection can make a vast difference in the way someone lives his or her later years and how many of those years there are. The debilitation resulting from a hip fracture is a common cause of death.

The key to protection is calcium; it takes pounds of the mineral to build a skeleton, yet most Americans fall woefully short of recommended intakes. The average middle-aged woman gets just half of what official guidelines say she should. In the past decade or so, 50 out of 52 studies have shown that increased calcium intake--via dairy products, calcium-fortified foods or calcium supplements--protects the bones, either by making them denser and stronger in the first place or by protecting against the loss of density that generally occurs with age.

Chances are, the bone benefits come as no surprise to you. More startling is the notion that regular servings of dairy products can lower blood pressure--a worthy goal, because high blood pressure increases the risk of stroke, heart attack and a variety of other deadly problems.

The question of just what kind of diet is best to prevent or manage high blood pressure is a controversial one among scientists these days. It’s a matter of public policy that restricting salt intake is crucial, but some scientists say that policy was adopted before all the evidence was in and has been cast into some doubt by more recent data.

Certainly, people with heart failure or serious kidney disease should keep salt intake low, says Dr. David McCarron, professor of medicine at the University of Oregon Health Sciences University, who has researched hypertension for decades. But, he says, the most important aspect of the diet for most Americans who want healthy blood pressure is its mineral content. And dairy products are where Americans get their minerals.

“We’ve got data from Russia, we’ve got data from all over the European countries, from China, Japan, the Philippines, Hawaiian populations, Puerto Rican populations, and here in the United States from blacks and whites,” McCarron says. “Those people who report the richest dairy product intakes have the lowest blood pressures in their societies. That’s in the literature and there’s just essentially no debate about it.”

Of course, scientists can go only so far in drawing cause-and-effect conclusions from data on people’s eating habits and the rate at which they develop a disease.

For one thing, it’s possible that people who eat loads of dairy products also do other things that lower their blood pressure. But dairy products also played a role in the highly regarded DASH (Dietary Approaches to Stop Hypertension) trial. In one of the DASH studies, 459 adults were given a typical U.S. diet--high in fat, low in fiber and minerals--for three weeks. They then were switched to either a diet high in fruits and vegetables or to the DASH diet, which was low in saturated and total fat, and rich in fruits, vegetables and low-fat dairy products.

While the fruit and veggie diet brought blood pressure down a bit, the DASH diet did a better job, bringing systolic pressure down by 5 millimeters of mercury and diastolic down by 3 millimeters. For people with mild hypertension, the dairy-rich DASH diet was as effective as treatment with an antihypertensive drug.

Dr. Frank Sacks, a Harvard Medical School researcher and one of the DASH investigators, says he doesn’t believe that the three daily servings of non-or low-fat dairy products were a crucial part of the DASH diet. Nor, he says, do his colleagues. Much more than dairy makes the difference between the fruit and vegetable diet and the DASH diet, he points out.

DASH also includes more vegetables and fish, less meat and saturated fat, and fewer snacks and sweets. And there’s no way of knowing whether one of these, or a combination, or some unknown factor is actually responsible for the blood pressure benefit.

Perhaps just two things are clear when it comes to dairy and hypertension. First, resolution of this argument seems unlikely to come soon. And second, if you’re inclined, adding dairy foods to your menu won’t hurt you.

At least, they won’t hurt your blood pressure. There is, however, a possible risk that has some researchers a bit nervous about people consuming large quantities of milk and cheese.

The problem isn’t with the hormone known as BST, or bovine somatotropin, sometimes given to dairy cows to increase their milk production. Studies have found no ill effects come from drinking milk produced by BST-goosed cows. That makes sense, considering that the hormone is digested before it has a chance to get into the bloodstream.

Nor does lactose intolerance appear to be a reason for avoiding the potential health benefits of milk. Although perhaps 30% of adult Americans lack lactase, the enzyme necessary to digest milk sugar, studies show that, thanks to microbes in the intestines, most people can consume milk, for instance, without suffering gas, cramps or diarrhea--so long as they add it to their diet gradually (over two or three weeks) and take it at meals.

Of more concern to researchers is a possible link between dairy consumption and prostate cancer. Years ago, scientists started noticing relatively high rates of that disease in populations that consumed many dairy products. The correlation has appeared in a number of studies and in a number of countries. In one recent large study, men who averaged about three servings of dairy daily had a 30% greater risk of prostate cancer than men who had half a serving a day, according to Dr. June Chan, an assistant professor of epidemiology at UC San Francisco, who led that investigation.

“We’re not recommending any dietary changes or changes in policy,” Chan says. “But we thought people should be aware of these findings because there’s always been the idea with calcium that the more, the merrier.”

The prostate cancer connection isn’t a sure thing. Dairy consumption and the disease haven’t risen and fallen in every piece of research. What’s more, in a study at Dartmouth College in Hanover, N.H., men who took calcium supplements for a few years were actually less likely to develop prostate cancer than men taking a placebo. “I don’t have a satisfying answer,” says Dr. John Baron, who led the Dartmouth study. “I would say that it’s an issue and it’s unresolved.”

The situation is all the more perplexing because there’s some fairly convincing evidence that dairy products protect against a number of other kinds of cancer. Baron’s study, for instance, was actually designed to investigate the possibility that calcium might lower the risk of colon cancer. He found that men and women who took 1,200 mg of the mineral daily had 25% fewer colon polyps--growths that can turn malignant.

Drinking plenty of milk may lower a woman’s risk of breast cancer, too. In a recent study in Norway, women who had downed three glasses of milk a day since childhood were about 40% less likely to develop the cancer by age 39 than women who never or rarely drank milk. A fatty acid found in milk, called conjugated linoleic acid, or CLA, seems to inhibit the growth of tumors in lab dishes and in animals exposed to cancer-causing chemicals, according to Gregory Miller, a senior vice president for the National Dairy Council.

The trick here is that CLA is a fat, so you won’t get much of it if you stick to 1%, and you’ll get essentially none by drinking nonfat milk. Full-fat cheese is a good source, though. And what a lovely excuse for the occasional bowl of ice cream.

Which brings us back to dairy products as an instrument of weight control.

Dr. Michael Zemel, chairman of the Department of Nutrition at the University of Tennessee in Knoxville, was one of the first researchers to stumble onto the possibility that dairy products might be good for a person’s waistline. About a decade ago he added two cups of yogurt to the daily diets of a small number of African American men with high blood pressure, to see whether a year of a calcium-enriched regime would bring their blood pressure down. It did, but he noticed something else: Their weight dropped, too, by almost 11 pounds, on average.

“It was too striking an effect not to be real,” Zemel says. “But I didn’t have an explanation for it, and I tend not to believe things I can’t explain, at least in science.”

In the years since, though, a number of studies have shown a similar effect in every age group investigated. The amount of milk a child consumes is a good predictor of his level of body fat, for instance: the more milk, the leaner the kid.

In another piece of research, college-age women who ate a fairly low-calorie, low-calcium diet gained weight over a two-year period, while others who hit the same caloric mark with a higher-calcium diet stayed steady or actually dropped pounds.

And older women are well aware of the tendency to gain weight at midlife--typically a half-pound to a pound a year, according to Dr. Robert Heaney, a nationally recognized calcium researcher at Creighton University in Omaha, Neb. “That seems inexorable,” he says. The exception in his studies was in midlife women who received 1,000 to 1,300 milligrams of calcium a day, generally from food. Their average weight gain at midlife: zero.

What’s going on? From studies of mice genetically predisposed to obesity and of fat cells in lab dishes, among other things, Zemel thinks he knows.

A low-calcium diet prompts the release of a hormone, calcitriol, that signals fat cells to make more fat and to burn less. “It’s a fairly complex set of molecular reactions,” he says, “but the bottom line is, it causes more fat to be made and less fat to be broken down. And having lots of bigger, fatter fat cells makes for bigger, fatter people.”

Fortunately, Zemel found, raising the calcium level suppresses the release of calcitriol and shifts the balance toward fat-burning. Calcium-rich foods seem to be more effective than calcium supplements.

Judging from the studies so far, it seems clear, he says, that if you’re exercising and cutting calories to lose weight, you’ll do yourself a favor by making sure your diet includes three or four servings of milk, hard cheese or yogurt a day. How big a favor? If you would have dropped a pound a week on a calcium-poor regime, adding dairy products will let you peel off a pound and a quarter or a pound and a half instead, Zemel says.

“Calories count--it would be foolish to think otherwise,” Zemel says. “At the end of the day, energy balance--calories in through food, calories out through physical activity--counts.

But to believe that’s all there is would be to believe that human beings are machines that operate at a fixed level of efficiency, and we’re not.

“What increasing dietary calcium does is make us less efficient, which in this day and age is what we want,” he says. “Increasing dietary calcium helps us waste our food energy. Instead of putting more of it into fat storage, it allows us to waste more of it in the form of heat.”