Despite promising new studies, concerns abound over high-fat diets
One in six U.S. households includes a low-carbohydrate dieter, according to an ACNielsen poll conducted earlier this year. Until last October, Jody Gorran of Delray Beach, Fla., was among them. Despite having followed a sensible, low-fat diet most of his life, Gorran says that by his 50s, "middle-age spread" was developing. So, he decided to try a new diet. Picking up a book by Robert Atkins, Gorran embraced the low-carb lifestyle and avoided foods containing sugars and starches. For 2 1/2 years, he says, he lost weight, felt great, and bragged about his diet to anyone who would listen.
That was until Gorran experienced chest pain last fall, and an X-ray scan of his heart showed 99 percent blockage in a coronary artery that had been clear a few months before he started on the Atkins diet. Gorran underwent balloon angioplasty to clear the artery, and then on May 26, he filed suit against the Atkins company and Atkins' estate. The Atkins diet "gave me heart disease," he claims.
Gorran, a millionaire businessman, isn't asking for much money, and he pledges that anything he receives will go to charity. He says he mainly wants to force labels onto Atkins products that low-carb diets can cause heart disease in susceptible individuals.
Today, sellers everywhere hawk low-carbohydrate products, including low-carb beer, bread, ice cream, and, yes, potatoes (see Science News Online, Food for Thought, 6/19/04: Coming Soon—Spud Lite). Cardiologist Atkins jump-started the movement in the early 1970s with research on weight-loss benefits from diets extremely low in sugars and starches but rich in proteins and fats.
This year, a spate of studies comparing low-carb versus low-fat diets has confirmed that unrestricted-calorie, high-fat, high-protein eating can trim a person's weight at least as much as low-fat, restricted-calorie dieting does. Several of the studies also highlight other apparent benefits from carbohydrate restriction.
However, a few studies have turned up evidence of problems, including the one that Gorran experienced. Many physicians now conclude that although low-carbohydrate diets—such as the Atkins and the Zone diets—are proving powerful weight-loss tools, they aren't for everyone. These health professionals argue that such plans should be adopted only under the guidance of a physician.
A few physicians go so far as to argue that low-carb diets aren't for anyone. They say that short-term weight loss isn't worth the potential long-term risks. They also worry that the low-carb mantra sends children a message that undermines healthy eating styles.
Carbohydrates are the sole source of health-promoting fiber and can be a primary source of vitamins, minerals, antioxidants, and high-quality protein, notes David L. Katz, director of Yale University's Prevention Research Center in Derby, Conn. Not all carbs are bad, he says.
Whole grains and most produce items have been recognized as beneficial foods. Yet Katz finds that all too many seemingly smart low-carb dieters have come to fear even the most health-promoting carbohydrates.
Two studies in the May 18 Annals of Internal Medicine highlight advantages of a low-carbohydrate diet over low-fat eating. In each study, obese participants received eating plans and ongoing counseling about health and exercise.
One report offers new data from an Atkins Foundation–funded, 6-month study of 120 individuals (SN: 2/8/03, p. 88: Dietary Dilemmas) at Duke University in Durham, N.C. People eating the low-carb diet lost 85 percent more weight and were less likely to drop out of the program than were people eating low-fat fare.
In fact, notes study leader William S. Yancy Jr., even though the low-carb diet didn't impose a calorie restriction on the Atkins group, those people took in 40 fewer calories per day, on average, than low-fat dieters did. This suggests that low-carb foods are more satisfying. Not surprisingly, Yancy says, "we often hear patients say, 'I'm not hungry on this diet.'"
Moreover, people on the Atkins diet increased their blood concentrations of beneficial high-density-lipoprotein (HDL) cholesterol by 5.5 percent; low-fat dieters' HDL counts, in contrast, fell 1.6 percent.
Another blood measure also favored low-carb dieters. Elevated triglycerides—fats in the blood—are a potent risk factor for heart disease. Atkins dieters dropped their serum-triglyceride concentrations by 47 percent, compared with just a 14 percent drop in the low-fat group.
By contrast, average values for low-density lipoprotein (LDL) cholesterol—the bad cholesterol—remained unchanged throughout the trial among the low-carb dieters, while falling among the low-fat dieters.
In the second study, cardiologist Frederick F. Samaha of the Veterans Affairs (VA) Medical Center in Philadelphia and his colleagues followed 132 obese individuals, most of whom had diabetes or a related problem with sugar metabolism (SN: 4/8/00, p. 236: The New GI Tracts). The researchers prescribed either a low-carb or a low-fat diet to each volunteer and met regularly with the participants for 1 year. The researchers overtly encouraged adherence to the diets for only 6 months but evaluated the participants' weight loss and maintenance for the full year of this federally funded study.
Although the low-carb dieters initially shed pounds faster, they reached a plateau at 6 months. The low-fat group, however, continued to slim down after the doctors' encouragement ended, and by year-end had achieved a weight loss similar to that of the low-carb dieters.
However, other differences emerged that favored the low-carb approach. For instance, Samaha notes, among low-carb dieters with diabetes, cumulative blood-sugar control was better at both 6 months and at 1 year. Also, only low-carb dieters experienced a drop in serum-triglyceride concentrations. And HDL—good cholesterol—concentrations were stable in the blood of people limiting their carbohydrate intake, but they dropped in people on the restricted-fat diet.
Low-carb dieters' bodies also had a better response to insulin during the first half of the study, a particularly important factor in people with diabetes or poor blood sugar control. This result wasn't surprising, Samaha notes, because it's carbohydrates that ordinarily raise blood sugar and aggravate a poor response to insulin.
Samaha says that he now "would like to see a study investigating whether this diet lowers the incidence of diabetes in people who are at high risk."
In April, Jeff S. Volek of the University of Connecticut in Storrs and his colleagues presented related results supporting advantages of low-carbohydrate eating. Reporting at the Experimental Biology meeting in Washington, D.C., they offered details from a series of short-term Atkins Foundation–funded studies. Though most of their findings were consistent with what the Duke researchers reported May 18, there was one surprise. The University of Connecticut group found that low-carb dieters lost weight primarily from their trunks, where fat is typically hard to shed, rather than from arms and legs.
Volek says the result may be "clinically important because [trunk] obesity is associated with many big killers, such as heart disease and diabetes."
A contrasting view
In another presentation at the Experimental Biology meeting last April, researchers from the Oregon Health and Science University in Portland described a 6-week study comparing a low-fat diet to a low-carb regimen including the same number of calories.
Diane Stadler and her colleagues first determined how many calories obese but otherwise healthy people would eat when offered an unlimited amount of Atkins diet–approved foods. While the low-carb group continued to eat at will, the scientists fed another group the same number of calories from a low-fat, low-salt menu approved by the American Heart Association.
The researchers reported that the two groups shed equal amounts of weight. However, blood concentrations of cholesterol and other lipids improved more in the low-fat eaters. For instance, Stadler's team noted that LDL cholesterol fell an average of 16.6 milligrams per deciliter of blood in people eating the low-fat fare but increased 5.5 mg/dl in the low-carb dieters. Cholesterol advantages of the low-fat diet persisted for at least 1 year, this study found.
Stadler suspects that the LDL rise in the Atkins dieters traces to foods rich in cholesterol-elevating saturated and trans fats, which that diet permits. Many studies have correlated consumption of such fats with LDL increases.
The study reflects what Gorran experienced, as alleged in his lawsuit. The Florida man's medical records show that before going on the Atkins diet, his LDL concentration was a healthy 81 mg/dl. Shortly after changing his eating habits to favor high-protein, high-fat fare, his LDL cholesterol spiked to 138 mg/dl.
Although the Duke study had found no change in the average LDL concentration among low-carb dieters, about one-third of those participants in fact experienced increases in LDL. Most were low to modest, but "we actually pulled one person out [of the study]" in response to an LDL spike, notes study leader Yancy.
Those whose cholesterol profiles prove especially sensitive to fat intake may want to switch diets, he told Science News, or take cholesterol-lowering drugs. "We have fabulous medications now to lower a person's LDL," Yancy says.
Stadler, on the other hand, expresses concern about LDL and other indicators of heart health in low-carb dieters. She says her team has identified at least four micronutrients—folate, potassium, vitamin C, and magnesium—that protect people from heart disease but can be deficient in low-carb dieters. Her team now makes sure that all recruits to its low-carb diet studies take multivitamin and mineral supplements.
Physicians have raised concerns about the low-carb diet that haven't yet been examined systematically. For example, a medical team at the University of Missouri in Columbia suggested a link between the diet and the suspicious death 2 years ago of a 16-year-old girl. The scientists reported in the Southern Medical Journal that the seemingly healthy girl succumbed to sudden cardiac arrest at school 2 weeks after starting a low-carb diet. The death was triggered by a heart arrhythmia fostered by severe electrolyte imbalances—profoundly low blood concentrations of potassium, calcium, and possibly magnesium—that might have been caused by her change in food intake.
Another concern focuses on the kidneys, especially in people with diabetes, which itself damages those organs. Proteins contain nitrogen, which the kidneys must remove from the body. So, the extra protein typical of low-carbohydrate diets makes the kidneys work harder than normal. These diets could further damage kidneys already injured by diabetes or some other problem, notes Nathaniel Clark of the National Diabetes Association in Alexandria, Va.
While providing too much nitrogen, a low-carb diet may not deliver sufficient vitamins, particularly folate. Since the 1998 start of mandatory folate fortification of grain-based foods, which are all carbohydrates, there's been a 25 percent drop in neural tube birth defects in the United States (SN: 5/29/04, p. 349: Available to subscribers at Folate enrichment pays baby dividends). Says Randy Morris, an endocrinologist in Naperville, Ill., "My fear is that as [low-carb] diets become increasingly popular, we're going to see a reversal in the trend for decreased neural tube defects."
Katz points to several additional concerns. Fatty meals may harm people with gall bladder problems. Moreover, protein-rich diets increase acidity in the body, which the blood system neutralizes by pulling calcium out of bone. This "increases the risk of osteoporosis," Katz says.
Finally, he notes, "there have been case reports of depression tied to low-carb diets." He explains that carbohydrates in a meal normally induce insulin to trigger the delivery of tryptophan to the brain (SN: 7/8/00, p. 23: Available to subscribers at Stress-prone? Altering the diet may help). That amino acid is a building block of the mood-enhancing brain neurotransmitter serotonin.
Many physicians are concerned that low-carb diets offer an overly simplistic approach to nutrition. Yet people who read the Atkins diet book thoroughly find that there's a lot more to the doctor's approach. He advocated a laundry list of vitamin and mineral supplements to compensate for the diet's shortfalls. He also recognized that slow-to-digest, complex carbohydrates that are full of fiber shouldn't be neglected. However, such nuances may be lost, Stadler points out, when people simply skim primers on how to begin low-carb dieting—or, worse, pick up their guidance solely from friends and news clippings.
Keep in mind, she and others note, that virtually eliminating a major category of nutrients forces the body's metabolism to change—and not necessarily in predictable ways.
The best way to minimize health risks, says Alice Lichtenstein, a nutritional biochemist at Tufts University in Boston, would be to tailor low-carb diets to resemble typical heart-healthy eating plans: Include whole grains, a broad range of fruits and vegetables, legumes, fish, lean meats, and low-fat or nonfat dairy foods and minimize saturated and trans fats.
Correction: This article was incorrect in saying that the Atkins diet permits foods rich in trans fats. In fact, the diet strictly avoids trans fats.
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