he bagel section at Elisabetta Politi's neighborhood supermarket says it all. Six months ago, shelf space devoted to the onetime low-fat staple of health fanatics took up three long yards. Today, it's less than half that."People are not buying rice, bread, pasta, and bagels as much as before," observes Politi, the nutrition manager of the Duke Diet & Fitness Center. "And for the first time, they're eating more eggs. This low-carb trend has touched everybody. Even people who are not overweight have begun thinking that it's probably not a good idea to eat too many carbs."

	Measuring Mass
	Sweat Equity for Health

Walk into any supermarket these days, and it's clear we've become a low-carb nation. Products once touted as low fat have been reformulated and remarketed to appeal to our new low-carb sensibilities. Dwindling sales of bread, rice, and pasta at checkout lines are being replaced, to the glee of many food manufacturers, by sharply rising sales of much more expensive dairy products, meat snacks, and nuts. And the trend shows no signs of slowing. This year, U.S. consumers are expected to spend an estimated $30 billion on low-carb products, up from $15 billion in 2003.

Most of these new products are being marketed to the 24 million Americans now on low-carb diets and the estimated 44 million others thinking about trying one in the next year. But they're also satisfying the hunger pangs of millions of other Americans who, overweight or not, have begun cutting back their carbohydrate intake as a result of news reports and advertising blaming carbs, rather than fat, as the culprit behind our nation's steadily expanding waistlines.

Critics of the Atkins, South Beach, Zone, and other low-carb diets-- including most of the medical establishment--have long contended that most of the weight shed from these high-protein regimens is due to water loss and that the diets are medically dangerous, unsustainable, and nutritionally unsound. While they concede that a small percentage of low-carb dieters do lose weight, they argue that the vast majority end up regaining the weight they lost and more.

That mainstream view, however, is now under fire from recent clinical trials at Duke, Harvard, and other respected medical institutions, which discovered that weight losses among obese patients on Atkins and other low-carb diets are not only real, they exceed the losses on low-fat diets. While many of these studies also show no ill effects and even some improvement to cholesterol levels from Atkins-style diets, physicians wary of potential long-term effects continue to recommend that their patients go low fat or avoid staying on low-carb diets for longer than six months.

So what's the average American seeking good health--and maybe ten fewer pounds--supposed to do in light of this conflicting advice? Do we drop our low-fat diets and put the kibosh on fruit and grains? Start loading up on low-carb (hold the bun) double cheeseburgers? Politi and other health experts at Duke see a number of potential risks for consumers getting caught up in the current low-carb mania.

"We do know that if you eat fewer carbohydrates, you're going to replace them with protein and fat," she says. "And eating a high-protein diet can raise your risk of cancer. There are already some studies that have suggested that. It's definitely not good for your kidneys, because your kidneys are the only organs in your body that can break down and dispose of extra nitrogen from the protein you're eating. If you're also not eating the same amount of carbohydrate as before, you're also probably eating more fat. And we know that a diet high in saturated fats is linked with an increase in heart disease."

"There's also the concern that if you have a diet that's relatively low in fruits and vegetables and whole grains, you might be missing out on some nutritional elements that are important in reducing cancer risk," warns Howard Eisenson, a professor of medicine at Duke who directs the Duke Diet & Fitness Center. Eisenson has a long list of people he wouldn't recommend going low carb, because there are no studies on the diets' long-term health effects: pregnant women, children, the elderly, and those at risk for impaired kidney function, osteoporosis, or kidney stones.

"The decent studies on low-carb diets are in their infancy," he says, adding that he recommends the traditional low-fat diet for most patients at his center looking to lose weight. "Our low-fat diet has the greatest weight of scientific work behind it. We've been doing it for a long time. We feel most confident in this as a way of life. If you haven't tried a traditional low-fat diet in a very serious way in a well-supported setting such as this, that's our leaning."

Low fat, however, has been the mantra for the past three decades and, in case you haven't noticed, it hasn't done much to halt the supersizing of America. Nearly two in three adults across the nation are now defined as overweight, compared with less than half two decades ago, and half of those are classified as obese, with a body mass index, or BMI, of 30 or more. Among Americans, residents of North Carolina weigh in among the heaviest, with more than 21 percent of the state's adults defined as obese, compared with 13 percent in 1991. Experts cite a number of reasons to explain how we've grown so fat, so fast: declining physical activity, less cooking at home, more eating at restaurants and fast-food outlets, and increased portion sizes.

"Our society makes it really easy for us to consume more calories than we can expend," says Politi. "We're surrounded by a lot of calorically dense foods. We don't have as many opportunities to move as before. And the food industry makes it difficult for even the well-informed consumer to make healthy choices."

"You've got to eat less; you've got to exercise in moderation," says Eisenson. "That's a simple message, but apparently it's very complicated for people to apply." Another basic lesson we forgot during our past obsession with low-fat foods is that calories are calories, whether they're from carbs or fat. Many of us got caught up in what nutritionists call the "Snackwells phenomenon"--the mistaken belief that you can eat as much as you want as long as it's low in fat. "There's no doubt that low-fat diets were depriving too many dieters," says Politi. "They didn't feel satisfied. One of the big arguments against them is that when you eat more carbohydrates they enhance your appetite, because they raise your blood sugar. Then, when your blood sugar crashes, you feel like you're starving."

While we may feel starved, we're anything but. A quick glance around the mall these days underlines the fact that Americans have become the fattest people on the planet, having munched and slurped our way to a national health crisis that threatens our future economy. Earlier this year, the Centers for Disease Control and Prevention reported that obesity, which killed 400,000 Americans in 2000, may soon overtake smoking, which killed 435,000 during the same year, as the leading preventable cause of disease in the United States. Obesity and its health consequences--such as type 2 diabetes--now cost the nation $117 billion a year. And many experts fear the doubling and tripling of obesity rates for children and teens, respectively, over the past twenty years have created a health-care time bomb that will have an even more dramatic economic impact. The sad fact that some 20 to 30 percent of teens are now considered obese, compared with just 5 percent in the 1960s, suggests that the growing girth of American adults is likely to continue for many years, if not generations, unless we find ways to halt this destructive trend.

"If kids make it into their teen years obese, they've got an 80 percent likelihood of being obese as adults," says Eisenson. "And most people gain weight through adulthood, especially overweight people. So someone who starts adulthood already obese is likely to have very severe weight problems as they go through life. And we know that obesity correlates very strongly with premature death. People lose years from their life. That's the biggest thing. And even if you don't die, having high blood pressure, high cholesterol, diabetes, all those things, predispose you to having heart disease."