From Heartwire
Fran Lowry
August 12, 2010 (Philadelphia, Pennsylvania) — Low-carbohydrate and low-fat diets coupled with comprehensive behavioral coaching in a randomized trial were similarly effective for weight reduction, while HDL-cholesterol levels ended up higher with the low-carb approach, researchers report in the August 3, 2010 issue of the Annals of Internal Medicine [1].
Lead author Dr Gary D Foster (Temple University, Philadelphia, PA) told heartwire that for him, the weight-control message "is that patients should probably be less concerned about whether the diet is high in this or low in that and more concerned with using behavioral strategies, like keeping track of what they eat, to help them adhere to healthy eating habits."
In the multicenter study that randomized 307 persons to follow one or the other diet, both groups achieved about 11% weight loss at six months and a total of 7% at 24 months; both changes were significant.
Both diets were also associated with increased HDL-cholesterol, but the increase was significantly higher for those on the low-carb diet.
Because weight loss itself affects HDL concentrations but was the same in both groups, Foster and his colleagues write, "we were able to determine that a low-carbohydrate diet has greater beneficial long-term effects on HDL-cholesterol concentrations than a low-fat diet."
Behavioral Training Allowed for Better Comparisons
It had been unclear whether low-carb or low-fat diets were better for weight loss, with only some studies finding in favor of the low-carb approach, at least in the short term. The problem was, these studies were of short duration, with only one lasting a year, and none included a comprehensive behavioral-treatment program. These studies also had very limited assessments of other health factors, such as the effect on bone-mineral density, muscle mass, cardiovascular risk factors, and general symptoms, Foster explained.
"We wanted to first of all do a long-term study of low-carbohydrate diets and examine these other factors. We also wanted to include a fair amount of behavioral support. The idea was that we would produce the largest possible weight loss with both diets because we would facilitate adherence, and that way we could better test any positive or adverse consequences of both diets," he said.
The 153 participants in the low-carb group followed guidelines set out in Dr Atkins' New Diet Revolution [2]. For the first 12 weeks, they were told to limit carbohydrate intake to 20 g per day in the form of low-glycemic-index vegetables. After this, they could gradually increase their intake of carbohydrates by 5 g per day per week by adding more vegetables, a limited amount of fruits, and later small quantities of whole grains and dairy products until a stable and desired weight was achieved.
"The focus for this group was on limiting carbohydrate intake and to eat foods rich in fat and protein until they were satisfied," Foster noted.
The 154 participants assigned to the low-fat diet limited their energy intake to 1200 to 1500 kcal per day for women and 1500 to 1800 kcal per day for men, with approximately 55% of calories from carbohydrate, 30% from fat, and 15% from protein. "The focus for the low-fat group was on decreasing fat intake, and limiting overall energy intake in the form of calories per day was the primary behavioral target," Foster explained.
All participants attended sessions in groups of 8 to 12 once a week for the first 20 weeks. The sessions, which tapered to every other week for the next 20 weeks and then to every other month for the remainder of the two-year study, taught such strategies as keeping a food diary, limiting places and activities associated with overeating, increasing physical activity, recovering from overeating episodes, and reversing small weight gains.
Along with the similar one-year and two-year losses in average weight, there were no differences in body composition or bone-mineral density between the groups at any time during the study. For both groups, the change from baseline in hip and spine bone-mineral density was 1.5% or less at six, 12, and 24 months. For body composition, both groups experienced 5% reductions in lean mass and 11% to 20% reductions in fat mass.
HDL Rose Twice as High With the Low Carb Diet
An advantage for the low-carb diet over the low-fat diet with respect to HDL concentrations was seen at all time points, Foster said. Plasma HDL increased by about 20% at six months in the low-carb group. This persisted throughout the study and was more than double the rise observed in the low-fat-diet group. The increase in HDL was similar to that obtained with nicotinic acid, "the most effective HDL-raising pharmacologic intervention currently available," he noted.
"Everybody in the study did better in terms of their cardiovascular disease risk factors because they lost weight," he said, but the only significant difference was in HDL levels. "So it wasn't bad to be in the low-fat group for HDL. You still went up, but you went up even more if you were on the low-carb diet," Foster said.
Symptoms of bad breath, hair loss, constipation, and dry mouth were greater in the low-carb-diet group but, except for constipation, the differences disappeared after six months.
Dr Ronald Goldberg (University of Miami, FL), not an investigator with the study, said its behavior-modification program makes it less likely that the results obtained will be generalizable to other settings. "There really wasn't much advantage for the low-carb over the low-fat diet except for HDL. It seemed that what really mattered was the behavior-modification program, which was pretty robust. It might be hard to put that into practice in a typical community setting."
He added that the use of the behavioral intervention leveled the playing field between the two diets. "There is no question that it eliminated differences in adherence. There had been some evidence that people on low-carb diets adhere better, particularly in the short term, but by adopting a behavioral-intervention approach, the study authors were able to equalize the two groups, at least in their level of physical activity, attendance at meetings, and this kind of thing."
Weight Loss With Both Diets "Impressive"
Goldberg remarked that the observed sustained weight loss on both diets was impressive, as was the substantial 20% increase in HDL. "Raising HDL is not something that is easy to do in medicine."
The fact that this study looked at bone loss is also noteworthy, he commented. "This is the first study [of its kind] to look at bone. There has been a concern, particularly for low-carbohydrate diets, that there might be an excess of bone loss in the long term. Here, they show a slight reduction in bone density that was similar in both groups. The loss was very modest, and that was reassuring."
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