As the low-carb food craze—propelled by high-profile diets such as Atkins and South Beach —becomes increasingly mainstream, it is difficult to find a grocery store, let alone a health-food store, without a selection of "carb aware," "carb fit," or "low-carb lifestyle" products promising all the taste of regular cookies, pastas, and cereals, with fewer grams of now-suspect carbohydrates. Even chain restaurants such as T.G.I. Friday's, Bennigan's, and Ruby Tuesday have begun to offer low-carb options. And a new survey by equity researchers at Morgan Stanley suggests that fully 22 percent of American adults are trying to limit their carbohydrate intake at least somewhat (though according to the survey the numbers may have dipped slightly in recent months).
Among the most famous adherents to the South Beach diet is Bill Clinton, whose recent heart surgery prompted questions about the safety of low-carb regimens (though Clinton's lifelong penchant for junk food was well-noted, too). The highly publicized death of Robert Atkins, who developed the Atkins diet, also fueled the controversy. (Though Atkins died after slipping on ice in Manhattan, his medical history was scrutinized, somewhat viciously, for evidence of heart disease.) The intensity of the debate has been such that many Americans, including those who've tried low-carb diets, have begun to wonder: What are the health consequences of these plans? Are they in fact an effective way to keep weight off long-term? And what about the recent explosion of low-carb products and marketing claims—how do they impact dieters?
As most Americans know by now, a low-carb diet is one that limits intake of foods such as pasta, potatoes, rice, and bread in favor of foods such as meats, chicken, seafood, and salads. The idea is that many carbohydrates—especially those with high glycemic indices such as bread or white rice—cause a rapid increase in blood glucose levels, which in turn causes the pancreas to release insulin. Insulin then works to lower blood sugar by signaling the body to convert excess glucose to fat; this dip in blood sugar also triggers a new wave of hunger. By contrast, meals high in fats and proteins are said to create a feeling of satiety (the mechanism here is not fully understood, but the less rapid fluctuations in blood glucose levels associated with fats especially may play a role).
When Atkins published his first diet book in the 1970s, there was widespread concern about the long-term health consequences of his program, particularly for the heart. Atkins' original plan placed no restrictions either on total caloric intake or on the consumption of saturated fats, which are strongly associated with artery-clogging LDLs, the low-density lipoproteins also known as "bad cholesterol." In classic Atkins, dieters were permitted unlimited eggs, butter, cheese, and red meat, as long as they restricted their daily intake of carbohydrates. A more recent carb-conscious program, the South Beach diet, introduced by cardiologist Arthur Agatston, has been less galling to physicians because it does limit saturated fats, and also encourages the consumption of some "good" carbohydrates, including most fruits, later in the diet. It is in fact much closer to the conventional wisdom offered by nutritionists. (For a detailed comparison of Atkins and South Beach, click here.) Some doctors and nutritionists still worry, though, that higher fat intake over time will increase an adherent's risk of cardiovascular disease. There is also concern that higher protein consumption places a strain on the kidneys; one study has shown that for people who already have kidney problems, high-protein diets may hasten slightly a decline in renal function. These are important considerations that may not be fully addressed until longer-term research is completed.
These concerns aside, several recent studies, which followed patients for up to one year, offer a fairly positive and consistent view of low-carb dieting. A handful of papers published in the last two years suggest that patients on low-carb regimens—defined as diets that restricted carbs to fewer than 20 grams or fewer than 30 grams per day, depending on the study—lost more weight during the first six months than did their counterparts on reduced-fat plans. (Weight loss generally leveled off after the first six months.) Surprisingly, members of the low-carb groups also tended to have better blood lipid profiles at the six-month and one-year marks: They showed greater decreases in blood triglycerides, which are a risk factor for heart disease, as well as greater increases in HDLs, high-density lipoproteins or "good cholesterol," which helps to prevent the arteries from clogging. (Neither total cholesterol nor LDL levels rose significantly in either group.) While blood lipids are not the only heart disease risk factor—and many researchers would like to see whether low-carb adherents in fact have higher rates of cardiovascular disease later in life—recent studies have gone a long way toward reassuring skeptics. "One can no longer dismiss low-carbohydrate dieting as fad," asserted an overview published this summer in Journal Watch Cardiology. Low-carb diets may also offer benefits for people with diabetes. (For details, click here.) For a variety of reasons, then, many academic physicians have come to like—or are at least reluctant to dismiss—the low-carb approach.
Yet in true American fashion, we have taken this craze to its illogical extreme, creating all manner of low-carb products, including pastas, cereals, chocolate bars, brownies, and ice cream. In other words, instead of cutting out refined sugars and flours and moving toward more of a "whole foods" approach—which is what these diets implicitly (or explicitly) encourage—we have managed to spawn yet another generation of packaged, artificial foods. This is precisely what happened with the low-fat food boom in the '80s and '90s, which promised a dietetic alternative to every conceivable high-fat snack food and dessert. Indeed, many of the same physicians who tout the health benefits of low-carb diets worry that the sheer availability of low-carb options will confuse and mislead many dieters.
Part of the problem is that the frenzy over limiting carbs has diverted attention from the question of calories. One of the original rationales for reduced-carb diets was that they are naturally calorie-limiting; people eat less simply because they feel more sated. (In the studies cited above, all of which predate the boom in low-carb consumer fare, this is the mechanism that seems to be at work; patients tended to limit caloric intake without being told to do so.) But as Bonnie Liebman, director of nutrition at the Center for Science in the Public Interest, told me: The reduced-carb alternatives now promoted by many chain restaurants are not necessarily low in calories. At Ruby Tuesday, for instance, the Low-Carb Steak Fajitas, Black & Bleu Burger Wrap, and Cajun Chicken Salad contain roughly 1,000 calories each—approximately half of an adult's daily caloric requirement. At grocery stores, low-carb frozen dinners and desserts often have as many calories as their traditional counterparts: a cup, say, of Breyers CarbSmart Ice Cream contains roughly 260 calories—approximately as much as Breyers original (and far tastier) ice cream. Perhaps the lessons of the low-fat food boom are instructive here: namely, that it is not possible to consume unlimited bagels, SnackWell's, and fat-free ice cream and still lose weight. Similarly, one cannot eat steak fajitas, brie, and low-carb cookies with abandon and expect a low-carb regimen to work magic (as many dieters surely realize).
Another issue is the aggressive and often misleading marketing that accompanies many low-carb products. While the FDA has provided strict guidelines for terms such as "low-fat" and "reduced-fat," it has not done so for "low-carb" and "reduced-carb." Since undefined food claims are expressly forbidden by law, one would expect the food industry to tread carefully—as indeed most companies did before early 2004. In December 2003, however, for obscure bureaucratic reasons and perhaps in response to industry pressure, the USDA, which regulates meat and poultry, including many frozen dinners, issued a policy statement specifically permitting carb-related marketing— statements such as "Carb Conscious" and "Carb Wise"—without providing any guidelines on what these terms should mean. According to Liebman, this move was interpreted by the food industry, including sectors overseen by the FDA, to mean that virtually anything goes. (It is well known that the two agencies work closely together behind the scenes and also that the FDA under the Bush administration has been slow to regulate food companies.) Suddenly the market was flooded with undefined "quasicarb" claims suggesting that a particular cereal or pasta or chocolate bar is low in carbs.
The most deceptive marketing trick has been the focus on "net carbs," a quantity often featured prominently on product labels. Net carbs (also called effective carbs or net impact carbs) means total carbohydrate content minus any carb or carblike substances that have a "minimal impact" on blood sugar—and, implicitly, on weight gain. Such substances may include fiber (found, for instance, in whole grains) as well as sweeteners called sugar alcohols. This is where things get problematic. Sugar alcohols (xylitol, maltitol, sorbitol) are structurally similar to their carbohydrate cousins but have an increased number of hydrogen atoms, which, in chemical terms, renders them "hydrogenated" or "reduced"; as a result, they are processed somewhat differently by the body. (For a complete rundown of various sugar alcohols, including some differences in absorption pathways, click here.)
Consider maltitol, one of the most popular (and, not incidentally, cheapest) sugar alcohols. Maltitol is not absorbed in the small intestine as regular carbohydrates are; instead, it passes undigested into the large intestine where it is fermented by intestinal bacteria, producing carbon dioxide, hydrogen, and small fatty acids. (This process, as well as its byproducts, can cause all manner of gastrointestinal distress.) The fatty acids are then absorbed across the lining of the large intestine into the bloodstream—and, ultimately, can be broken down for energy, stored as fat, or converted to other molecular forms, including glucose. In other words, eating maltitol can increase the amount of glucose in your bloodstream, albeit indirectly; it canraise your blood sugar—as many diabetics have now discovered. It is thus misleading to make "net carb" claims that exclude all sugar alcohols. Some experts believe that the issue is so confusing that net carb marketing in general should be prohibited. In addition, dieters might be surprised to learn that most sugar alcohols have a caloric impact that is not insignificant: While maltitol may contribute fewer calories than regular carbs do—approximately 2 kilocalories per gram rather than 4 kilocalories per gram—its caloric count is plainly not zero.
Ultimately, the more technical food claims become—the more shopping for snacks seems to resemble shopping for pharmaceuticals—the savvier we as consumers need to become. However, considering this country's tortured relationship to food, and government's stated desire to address rampant obesity, it is a shame that the FDA has not stepped in to regulate misleading claims—that it is, to use Liebman's words, "abdicating its responsibility." It is particularly ironic that this explosion of claims and products threatens to undermine the low-carb approach to dieting just as it has begun to prove itself in reliable clinical trials.