Comparable Weight Loss Seen with Low-Carb, Non-Restricted and Low-Fat, Calorie-Restricted Diets
New research published in the Annals of Internal Medicine compared bodyweight and metabolic outcomes when utilizing either a low-carbohydrate or low-fat diet. A similar comparison of diets has been evaluated in previous clinical studies, but during this work, led by Gary D. Foster, PhD, the research team also tracked additional outcomes such as cardiovascular risk factors, bone mineral density (BMD), and general symptoms. Over the two-year study period, 307 clinically obese participants were placed on either a calorie and dietary fat controlled diet or a low carbohydrate diet. Subjects in the study presented with a mean age of 45 years, mean body mass index (BMI) of 36, and a mean weight of 103 kg (227 lbs); two thirds of the participants were women. Researchers excluded any individuals with dyslipidemia or diabetes.
During the study individuals assigned to the low-carbohydrate diet limited intake of carbohydrates to 20 grams per day for the first 12 weeks, then increased their intake by 5 grams of carbohydrates per day for each subsequent week until a stable and desirable weight was achieved. These participants could consume as much fat and protein as desired, as limiting carbohydrates was the chief behavioral focus for the group. Participants assigned to the low-fat diet were placed on a calorie restricted intake (1,200-1,500 kcal/d for women and 1,500-1,800 kcal/d for men) with carbohydrates accounting for approximately 55% of calories, fat 30%, and protein 15%. Limiting total energy intake was the primary behavioral focus for this group.
Multiple randomized trials have revealed that low-carbohydrate diets achieve superior short-term weight loss when compared to low-fat, calorie-restricted diets, but long-term results have been diverse. In this study both diet groups achieved clinically significant and nearly identical weight loss with no statistically relevant differences in weight, body composition or bone mineral density. Weight loss averaged 11 kg (24 lbs) at one year and 7 kg (15 lbs) at two years for both groups.
The long-term results presented in this study suggest that both a low-fat, calorie controlled diet and a low-carbohydrate dietary approach may be a viable option for obesity treatment among adults. A significant difference in weight loss only occurred at the three month period, where the low-carbohydrate group averaged 9.49 kg loss compared to an 8.37 kg loss in the low-fat group. As previously mentioned, at the 24 month end-point the loss of weight did not differ between the groups.
When additional physiological outcomes beyond weight were evaluated, the groups presented with significantly different results. The low-carbohydrate diet was associated with quicker reductions in triglycerides, VLDL, and diastolic blood pressure; but the overall trends were not significantly different. Interestingly enough, a greater increase in total HDL and reduction of total cholesterol was observed with the low-carbohydrate diet, however the low-fat diet led to greater reductions of LDL cholesterol during the entire study. Of practical importance the low-carbohydrate group reported more adverse effects during the first 6-12 weeks of the study such as bad breath, hair loss, irritability, constipation, and dry mouth. Furthermore, the authors noted hypothetical concerns that the low-carbohydrate diet could lead to greater BMD loss, but this theory was not represented in the study results. It is important to note this study was conducted with obese, sedentary persons whose total energy and carbohydrate needs fall significantly below that of a physically active person. Likewise the carbohydrates used in the low-carb treatment group consisted of low glycemic index vegetables whereas carbohydrate selections were not identified for the low-fat group.
Ann Intern Med. 2010 Aug 3;153(3):147-57.
Weight and metabolic outcomes after 2 years on a low-carbohydrate versus low-fat diet: a randomized trial.
Foster GD, Wyatt HR, Hill JO, Makris AP, Rosenbaum DL, Brill C, Stein RI, Mohammed BS, Miller B, Rader DJ, Zemel B, Wadden TA, Tenhave T, Newcomb CW, Klein S.