For weight loss and CV risk, cutting down the carbs was more effective than limiting fat intake in a randomized trial….
At 12 months, individuals on a low-carbohydrate diet had lost 5.3 kg (11.7 lb), while those on a low-fat diet with similar caloric value had lost 1.8 kg (3.9 lb), for a mean difference of -3.5 kg, or 7.7 lb (95% CI minus 5.6-minus 1.4, P=0.002), according to Lydia Bazzano, MD, PhD, of Tulane University in New Orleans, and colleagues.
Participants also had significantly greater increases in HDL cholesterol, with a mean difference of 7 mg/dL (95% CI 3-11, P<0.001), along with a greater decrease in the ratio of total to HDL cholesterol, with a mean difference of -0.44 (95% CI minus 0.71-minus 0.16, P=0.002).
Previous studies on low-carbohydrate diets and cardiovascular risk have had conflicting results and were limited by a lack of population diversity and the inclusion primarily of patients with the metabolic syndrome or diabetes.
To assess the effect of the diet in a broader population, Bazzano and colleagues enrolled 148 individuals whose mean age was 47 and whose mean body mass index was 35 kg/m2. More than 85% were women, and half were black.
At baseline, none had cardiovascular disease (CVD), kidney disease, or diabetes, and they were not allowed to take prescription weight-loss drugs.
Half were randomized to a diet limiting digestible carbohydrates to less than 40 grams per day, and the others to a diet in which less than 30% of energy intake was in the form of fats and 55% was from carbohydrates.
Both groups were provided with detailed dietary information. All participants met with a dietitian individually each week for the first month and then regularly in small group counseling sessions for the duration of the study.
Adherence to the diet was assessed in two 24-hour dietary recalls at 3, 6, and 12 months, in which participants reported food consumption for the previous day.
Throughout the study, physical activity and caloric intake were similar in the two groups — the 12-month average caloric content of the low-carb and low-fat diets was 1,448 and 1,527 calories, respectively — and approximately 80% of participants in both groups completed the yearlong trial.
Numerous parameters showed greater benefits for the low-carbohydrate diet. The mean difference in fat mass decrease at 12 months was -1.5% (95% CI minus 2.6-minus 0.4, P=0.011), and the mean difference in increased lean mass was 1.7% (95% CI 0.6-2.8, P=0.003).
Triglyceride levels fell in both groups, but more so in the low-carbohydrate group, with a mean difference of -14.1 mg/dL (95% CI minus 27.4-minus 0.8, P=0.038).
"A major concern that has been frequently raised about low-carbohydrate diets is their potential to elevate LDL cholesterol levels, an established risk factor for CVD," the researchers noted. However, in this study both groups had decreases in LDL cholesterol that did not differ significantly.
C-reactive protein levels also decreased more in the low-carbohydrate group, but glucose levels and blood pressures didn’t show significant decreases in either group.
Finally, the 10-year Framingham risk score for coronary heart disease was significantly lower at 12 months in the low-carbohydrate group, with a mean difference of -1.4% (95% CI minus 2.1%-minus 0.6%, P<0.001).
William E. Downey, MD, director of interventional cardiology and chair of the secondary prevention task force, Carolinas HealthCare System in Charlotte, N.C., who was not involved in the study, added that, "For a number of years, a host of outlets have been touting the low carbohydrate diet as a successful way to weight loss." "What has been the big concern is that often that diet is relatively high in fat and the question has been, is there a tradeoff with respect to cardiovascular outcomes?"
In an interview Dr. Downey added that, "While this trial didn’t look specifically at outcomes, they did look in a very rigorous way at changes in cholesterol, changes in CRP and inflammatory markers, changes in blood pressure, all those things that we think are tightly linked to outcomes."
That the current study was a randomized trial makes the findings far more credible. The study authors noted that most findings were similar for white and black participants, with the exception of a slightly greater increase in HDL for blacks on the low-fat diet.
"Our study found that a low-carbohydrate diet induced greater weight loss and reductions in cardiovascular risk factors at 12 months than a low-fat diet among black and white obese adults who did not have diabetes, CVD, or kidney disease at baseline," Bazzano and colleagues wrote.
"Restricting carbohydrates may be an option for persons who are seeking to lose weight and reduce cardiovascular risk factors and should be studied further," they concluded.
- Note that this small randomized trial demonstrated that a low-carbohydrate diet was superior to a low-fat diet in terms of weight loss at 1 year.
- Be aware that dietary adherence was assessed by self-report.