David Brill
Weight loss diets which promote one particular food group may not be the best way to shed the kilos, a recent study suggests.
In one of the longest trials of its kind, US researchers found that there was ultimately little difference in weight loss whether diets emphasized carbohydrates, protein or fat.
Nor did waist circumferences differ significantly after 2 years of following the diets, the study of 811 overweight adults showed.
"This is important information for physicians, dieticians and adults, who should focus weight loss approaches on reducing calorie intake," said lead author Professor Frank Sacks, Harvard School of Public Health, US.
Participants were randomized to one of four diets. The compositions varied, but all targeted a 750 kcal decrease in daily intake. [N Engl J Med 2009;360(9):859-73]
Weight loss peaked at 6 months – when participants had lost an average of 6 kg, or 7 percent of their initial weight. Weight regain began after 12 months: those who completed the study had lost an average of 4 kg at its conclusion.
The researchers also found that people who attended the most group counseling sessions lost the most weight – an average of 0.2 kg per weekly session.
"These findings suggest that continued contact with participants to help them achieve their goals may be more important than the macronutrient composition of their diets," said Sacks.
Singapore’s Health Promotion Board (HPB) welcomed the study as an informative, but not definitive, addition to the literature.
“The study was limited in that the differences in the macronutrient content of the different diets was not as substantial as originally planned, hence the resultant diets did not fully replicate the macronutrient distribution of popular ‘low-carb’ or low-fat diets,” said Mr. Benjamin Lee, manager and nutritionist, adult health division, HPB.
The HPB advocates a holistic approach to weight loss including exercise and stress management, added Lee. Specific dietary recommendations are to focus on calorie reduction while maintaining a diet which covers four food groups: rice and alternatives, fruit, vegetables, and meat and alternatives (including dairy foods).
Ms. Jamie Liow, a nutritionist and member of the Singapore Nutrition and Dietetics Association, said that carbohydrate intake is typically a concern among Asians who diet.
“Most would either have a low-carbohydrate, high-protein diet, or no carbohydrates at all. Crash dieting seems to be popular among younger girls as well,” she said.
Liow also emphasized the importance of getting nutrients from “a whole spectrum of foods,” adding that doctors should refer their patients to dieticians for specific advice on the best way to lose weight.
The four diets tested by Sacks et al. comprised: 20 percent fat, 15 percent protein and 65 percent carbohydrate; 20 percent fat, 25 percent protein and 55 percent carbohydrate; 40 percent fat, 15 percent protein and 45 percent carbohydrate; or 40 percent fat, 25 percent protein and 35 percent carbohydrate.
The lowest-fat and the highest-carbohydrate diets brought about the greatest reduction in LDL cholesterol levels, whereas the lowest-carbohydrate diet yielded the biggest increase in HDL cholesterol. Triglyceride levels dropped similarly for all diets.
Dieters were also encouraged to exercise for 90 minutes per week, and received weekly group counseling sessions and 8-weekly individual sessions.
Despite this intensive encouragement, dieters did not meet their nutrient intake targets when questioned at 6 months and 2 years. This appears to be a common problem in weight-loss trials, say the authors, noting that many previous studies have also found that adherence declines after a few months.
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