The Skinny on the Low-Carb Craze

Diet and Fatness in America

The 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."

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.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.

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."


Politi: "food industry makes it difficult for even the well-informed consumer to make healthy choices" Photo: Les Todd


"It's going to be a tremendous expense for us as a society," he adds. "It will affect us in terms of productivity. People who are sick and unhappy don't function as well. And as these children become obese, their own children are set up. The likelihood that a child will have weight problems is 80 percent if both parents are obese."

How to stop or, better yet, reverse America's obesity epidemic? For nutritionists and obesity experts, that's the $64,000 question. The late Robert Atkins, who dedicated his life to creating a dieting empire, blamed carbohydrates. Deprive the body of carbs, he preached, and your body will enter a fat-burning state called ketosis that will shed pounds.

Eric Westman, an associate professor of medicine at Duke, didn't buy Atkins' weight-loss sermon and, after reading his best-selling book, Dr. Atkins' New Diet Revolution, was convinced the Atkins plan had little scientific merit. "It's a very slick book, written to sell books," he says. Westman even advised his overweight patients against trying Atkins, warning them that the added fat that accompanied their high-protein regime would raise their cholesterol and triglyceride readings. But when three former patients disregarded his advice and returned to his office in 1997 trimmer and with improved triglyceride and cholesterol readings, Westman figured he had to learn more.

"So I wrote Atkins a letter and basically told him, 'Your ideas are intriguing, but where are your data?' " Not long after that, Westman received a surprise telephone call from the diet guru himself. After listening to Westman's complaint about the lack of medical data on low-carb diets, Atkins agreed to finance a study at Duke to determine whether the changes Westman had seen in his former patients would also show up in a randomized clinical trial.

Westman and his colleague, William Yancy, an assistant professor of medicine at Duke, published the results of their first low-carb study in the July 2002 issue of the American Journal of Medicine. They put fifty obese patients on a very low carbohydrate diet--amounting to some 25 grams per day, or about two cups of salad and one cup of a low-carbohydrate vegetable such as broccoli or cauliflower--for six months. The result: Some 80 percent of the patients lost an average of 10 percent of their body weight, or about 20 pounds.

"The most counterintuitive thing was that their cholesterol levels did not get worse, even though they could eat an unlimited amount of meat and eggs," says Westman. "Their LDL, or bad cholesterol, on average, did not get worse, and their triglycerides went down a lot. Their HDL, the good cholesterol, went up. This was interesting. So we went back to the Atkins Center and said, 'You need to fund a randomized clinical trial, because some of these people had been on the Atkins diet before and knew it would work.' "

That follow-up study, involving 120 obese patients randomly assigned for six months to either the traditional low-fat diet recommended by the American Heart Association or the Atkins plan, produced a few other surprises. The study, published in the May 18, 2004 issue of the Annals of Internal Medicine, found that low-carb dieters not only lost more weight than the low-fat dieters--an average of twenty-six pounds compared with fourteen pounds--they also lost more body fat, lowered their triglyceride levels, and raised their HDL more than the low-fat group. "The mechanism for the weight loss seems to be a reduction in calories," says Yancy. "There might be some other things that are contributing slightly, such as the thermic effect of food; that is, the body actually wastes energy when it eats, and a high- protein diet might increase that effect. But I think it's really that people are reducing their caloric intake. And the interesting thing is that people seemed to do that on their own. They said it was different from other diets because they weren't hungry all the time. We had a lot of people who said they didn't eat as many meals because they just weren't hungry for lunch or breakfast."

"The current paradigm explaining why this diet works is: It's higher protein, and protein is satisfying," adds Westman. "What most people who haven't studied this diet don't understand is that there is also an appetite suppression. It can't be the protein if you haven't eaten anything and you're not hungry. So the unknown question is, What causes the appetite suppression with people on this diet?"

Westman and Yancy's results parallel two other studies published in the past year that found low-carb diets to be at least as effective in losing weight as low-fat diets, for at least the first six months. But whether low-carb dieters regain their weight and whether these individuals suffer any medical problems when they continue their diets beyond six months remain open questions. "No one really knows," says Westman. "There are people who have done the diet for years, but not in a large enough number and not with monitoring to know that they're healthy by all of the parameters that we can measure. In both of these studies, I closed up shop after six months and told the patients, 'I'm not even sure you should be on this diet.'"

As a practical matter, both Westman and Yancy counsel their overweight patients not to go low-carb for longer than six months. And when restricting carbs, the researchers insist that dieters be monitored by a physician, particularly if they have diabetes or high blood pressure. "This really shouldn't be your first method of losing weight," advises Westman. "But over the last six months, I've come to the conclusion that if you've tried other ways of losing weight unsuccessfully and if obesity is your main problem, then this is a viable option with monitoring. The times are changing quickly, and a lot of it has to do with ongoing research."

That revisionist view on low-carb diets, combined with heightened public interest in Atkins, South Beach, and other low-carb regimes, prompted Eisenson and Politi to begin last fall what they call a "moderate low-carb diet" at the Duke Diet & Fitness Center. About 30 percent of the center's overweight patients now choose this diet, in which 35 percent of their calories come from carbs, 30 percent from protein, and 35 percent from fat.

"We've found that a lot of our clients who pick that option do extremely well," says Politi. "It's a diet that includes whole foods. They can eat fruit, which is very nutritious and shouldn't be eliminated from the diet as some low-carb diets recommend, and good grains--those high in fiber and not processed, such as oatmeal, sweet potato, corn, and peas. It's a good ratio of nutrients for people who are not very physically active. And, as they lose weight and become more active, I think it would be okay for them to eat 55 to 60 percent of their calories from carbohydrates, as the major health organizations recommend."

Politi and Eisenson, however, don't think people should adopt low-carb as a lifestyle, especially if they are active and are simply looking to lose five or ten extra pounds. "Low fat is an all-inclusion diet," Politi says. "Low carb is a diet in which a lot of important foods are not allowed. The restrictive diets are not the ones that are normally successful for the long haul. So I'm skeptical that low-carb diets are going to solve the obesity problem. That said, I strongly believe that there is no diet that fits everyone. And I think our major health organizations need to come up with different diet recommendations, depending on whether we're young and more active or older and more sedentary."

One useful outcome of the current low-carb craze is that people are now paying more attention to limiting their refined carbs, eating more vegetables and other complex carbohydrates, and avoiding overindulging in foods just because they're low in fat.

Medical professors Westman, left, and Yancy: their studies showed low-carb dieters lost more than low-fat dieters

Medical professors Westman, left, and Yancy: their studies showed low-carb dieters lost more than low-fat dieters. Photo:Les Todd

"We had people in our studies tell us that they are eating more vegetables on the Atkins diet," says Yancy. "It's because people have concentrated so much on starches and carbohydrates. When those are taken out of the picture, they have only meat, eggs, and vegetables as an option, and so they end up eating more vegetables."

"The USDA food pyramid emphasized eating too many carbohydrates," Politi says, noting that a revised food pyramid due out in 2005 is expected to change that. "People who are obese and not very active don't need to eat a lot of carbohydrates. It wasn't helpful to recommend that everyone indiscriminately eat six to eleven servings of grains and starches every day. For someone who is very active, it's fine. But for an obese individual, it's just too many every day."

But Politi is also concerned about the other end of the spectrum: those thin, healthy individuals in the grocery line with baskets of low-carb snacks and foods, cutting back on their carb intake in the mistaken belief that it will improve their health. "If you're not overweight, it's not a good idea to cut down on carbohydrates, because carbohydrates are the best fuel that your body can use to generate the energy you need on a daily basis for metabolic function and physical activity. Carbohydrate foods are also high in fiber, vitamins, and minerals, which are important essential nutrients, so they have to be part of a well-balanced diet. Limiting carbohydrates should only be an option for people who are obese and having difficulty moving."

If you're not overweight, but insist on going low carb, the Duke experts have strict guidelines for their patients, to avoid the dehydration and nutrient deficiencies that come with a diet high in protein. "If a person approaches me with a low-carbohydrate diet and says they've tried the other diets and it wasn't effective for them for some reason, then I would be agreeable to them trying a low-carbohydrate diet," says Yancy. "But I would monitor them closely, check their cholesterol, counsel them to drink plenty of water and take a multivitamin every day, and teach them how to systematically add back vegetables and other carbohydrates to their diet."

Yancy and Westman also warn dieters not to go overboard on low-carb, high-protein bars and snacks. Yancy thinks the explosion of low-carb convenience foods on supermarket shelves may prove detrimental to low-carb dieters, just as the no-fat Snackwells snacks were to low-fat adherents. "I really see them as a double-edged sword," he says. "They could make it easier for people to stick with the diet. But, now that people have more options, it might turn out that they just eat more calories, and the diet might be less effective. Low-carb manufacturers are learning how to make their snacks taste better. And when they taste better, people tend to eat more."

"The main difference between protein bars and real food is that there are sugar alcohols in these products, and it might be a more concentrated source of protein than you get from a chicken breast," says Westman. "If people just eat those foods and they don't reduce their calorie intake--which is how low-carb diets work--then they won't lose weight."

Eisenson doesn't believe low-carb snacking or dieting will be medically detrimental for the typical healthy consumer, just expensive--foods high in protein and fat are higher in price. (They're also less environmentally friendly, points out Politi, because a given serving of meat and dairy exacts a higher toll on our environment than, say, fruits, breads, and vegetables.)

"I may sound a little cynical," adds Eisenson, "but I don't think most [consumers] are going to do low-carb for very long. In our society, we like quick solutions and, in my experience, a lot of people play with low-carb, but they don't really understand it. They go out and buy low-carb products, but they don't adhere diligently to it. A fairly significant percentage of them tire of it. They get to the point where they feel too deprived, and they give up. So I don't know how much medical harm we're really going to see. We're probably going to see more harm to their pocketbooks."

It's no surprise, then, that food manufacturers see big bucks in the low-carb trend and are spending millions in infomercials and low-carb advertising supplements to pump up sales of low-carb fare. Some of these products, such as low-carb colas, with half as much sugar as regular sodas, have nutritionists shaking their heads.

"I really think it's a shame our food industry is so aggressive," adds Politi. "It has manipulated the low-carb idea by saying, Don't eat rice, potatoes, pasta, and bread, but eat the low-carb pasta and low-carb bread. It's unfortunate for the health-conscious consumer, because we're getting away from eating more wholesome foods, which I think would help our health in the long run."

"I'm hoping that people will see that low-carb diets are not the magic bullet. The epidemic of obesity that we're seeing in this country is going to be really difficult to tackle. We need to have more time to cook for our children," she says. "If children are raised on healthy food, they are naturally going to choose that food. But if children are always brought to McDonald's and Burger King because their parents don't have time to cook, it's really going to be hard for them to be healthy consumers later in life. If schools keep providing Pizza Hut and sodas, it's going to be really hard for our children to make good choices. The food industry is just so powerful, but I'm hoping that education and awareness will counterbalance this difficult environment that all of us live in."

McDonald, a former science writer for The Chronicle of Higher Education, is director of science communications for the University of California, San Diego. He is certified by the American Council on Exercise as a personal trainer and teaches wellness classes.

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