Lead author Frederick F. Samaha, MD, chief of cardiology at the Philadelphia VA Medical Center and assistant professor at the University of Pennsylvania School of Medicine (UPSM), cautioned against discarding the low-fat approach, which has been shown to cut the risk of heart attack, but he also said more attention needs to be paid to the harmful effects on body chemistry of carbohydrate-rich diets. "There are important metabolic effects to a high-carbohydrate diet in a person who tends to overeat, and we need to take a close look at that," said Samaha.
Linda Stern, MD, co-leader of the study, said the research is among the first clinical trials of a low-carbohydrate diet in a population other than healthy volunteers. The study volunteers were severely obese--their average weight was 288 pounds--and many had conditions such as diabetes, heart disease, hypertension, high cholesterol and depression.
"Our results may be surprising to some people," said Stern, a primary care doctor with VA and clinical assistant professor of medicine at UPSM. "Diabetics in particular did very well on the low-carbohydrate diet. So, especially in the realm of lifestyle modification, we might have to broaden our horizons on what we're recommending."
In the study, 132 men and women were randomly put on either a low-fat or low-carbohydrate diet for six months. The low-carbohydrate group was told to limit carbohydrate intake to 30 grams per day. They received counseling on healthy types of fat, such as omega-3 fatty acids, but had no limit on total fat intake. The low-fat group was put on a calorie-restricted diet, with no more than 30 percent of total caloric intake from fat.
Overall, volunteers assigned to a low-carbohydrate diet lost an average of about 13 pounds, compared to 4 pounds for the low-fat group. The low-carbohydrate dieters reduced their levels of triglycerides--blood fats that, like cholesterol, may contribute to clogged arteries--by an average of 20 percent, versus 4 percent for the low-fat group. There were no significant changes in cholesterol or blood pressure levels in either group.
The authors said the study results underscore the paradox of America's fascination with low-fat eating: Americans are taking in less fat, but not losing weight or improving their cardiovascular health as a result.
"People have gotten the message loud and clear--they're restricting their fat," said Samaha. "But they're still overeating. And when they overeat carbohydrates, they remain overweight and perhaps even exacerbate the development and management of diabetes, unfavorable lipids and heart disease."
Among non-diabetic people in the study, insulin sensitivity improved for the low-carbohydrate group, but worsened somewhat for the low-fat group, possibly raising their risk of diabetes. Among diabetic participants, the low-carbohydrate dieters reduced their fasting blood-sugar levels by about 9 percent, versus only 2 percent for the low-fat dieters. Over the six-month study, seven diabetic patients in the low-carbohydrate group were able to reduce their dose of insulin or other medication to control blood sugar. In the low-fat group, one diabetic patient lowered his insulin dose and one had to begin therapy.
Samaha pointed out that even though all the study participants remained extremely overweight, those in the low-carbohydrate group significantly reduced risk factors for diabetes and heart disease: Their triglycerides dropped to normal range, and their glycemic, or blood sugar, levels approached normal. "The metabolic effects were fairly impressive," said Samaha.
The study provides some validation for the eating plan advocated by the late Dr. Robert Atkins, the well-known diet doctor who died last month. Atkins advised patients to cut down on carbohydrates, especially refined carbohydrates, and not to worry about saturated fat--butter, cream, steak--as long as they were limiting carbohydrates.
According to Stern, eating fewer carbohydrates and more protein and fat makes people feel fuller and less likely to consume extra calories. It avoids blood sugar fluctuations and the constant insulin spikes that lead to the development of insulin resistance, which sets the stage for diabetes.
Said Samaha: "There are aspects of what Dr. Atkins was saying that were not being taken seriously, and perhaps should have been. There are important risks in over-consuming carbohydrates."
A review article in the April 9 Journal of the American Medical Association, analyzing scores of studies from the past three decades, concluded there was not enough evidence to recommend for or against low-carbohydrate diets. Samaha asserted most of the studies looked at were too small to produce meaningful data, or did not compare the diet to a traditional low-fat diet. He said studies with more participants, over longer periods of time, are needed to gauge the true effects of low-carbohydrate versus low-fat eating, especially on the risk of heart attack.
The ideal approach, said the authors, may be to focus less on the proportions of fat and carbohydrate in the diet and more on the quality of foods. One reason for the apparent failure of low-fat diets, they said, is that people tend to make up for lower fat intake by eating more junk food. "People shouldn't get the message that as long they lower their fat intake they can eat all kinds of carbohydrates--candy, cookies, sugar-coated cereals, and other foods that may not be that healthful," said Samaha. He cited vegetables with a high fiber-to-carbohydrate ratio as an example of the "good" carbohydrates that should play a greater role in either low-fat or low-carbohydrate eating plans.
Stern pointed out that even the best diet must be combined with other lifestyle changes, such as increased physical activity, to combat obesity. "Half the equation is to get people to be aware of what they're eating, and to eat less," she said. "The other half is to get them to move. Any weight loss program, at the VA or elsewhere, must include a formal exercise program."
Collaborating with Samaha and Stern on the study were Dr. Nayyar Iqbal, VA and UPSM; Dr. Prakash Seshardi, UPSM; Kathryn L. Chicano, Denise A. Daily, Joyce McGrory, Terrence Williams and Monica Williams, VA; and Dr. Edward J. Gracely, Drexel University College of Medicine.
NOTE FOR REPORTERS: Study leader Frederick F. Samaha, MD, of the Philadelphia VA Medical Center, is available for press interviews. For telephone or on-site interviews, please contact Judi Cheary at 215-823-5807 (Office); 877-591-9348 (Pager) or judi.cheary@med.va.gov. For additional assistance, please contact Jim Blue at 212-807-3429 or james.blue@mail.va.gov.
Journal
New England Journal of Medicine