PCRM Dietitians Respond to New Low-Carb Versus Low-Fat Diet Study
By Susan Levin, M.S., R.D.
Aug. 3, 2010
A new study on low-carb versus low-fat diets was published in the Aug. 3 issue of the Annals of Internal Medicine. In this study, a low-fat diet is defined as less than or equal to 30 percent of calories from fat. This is not what the Physicians Committee for Responsible Medicine considers a low-fat diet. This is the typical range of fat recommended for healthy people by the Dietary Guidelines and is not a therapeutic diet for prevention or reversal of disease. When diets are kept at about 10 percent of calories from fat, you see the scientifically proven benefits—including reversal and prevention of heart disease, diabetes, and cancer—found in the published studies of PCRM president Neal Barnard, M.D., and nutrition researchers Dean Ornish, M.D., and Caldwell Esselstyn, M.D.
The study’s authors admit that the low-fat group’s main focus was not to keep fats low. “Limiting overall energy intake (kcal/d) was the primary behavioral target” for this group. This is more a study of a calorie-restricted diet than a low-carb diet.
The mean body mass index (BMI) of the participants was very high, 36.1 kg/m2 (BMI > 30 is obese). Although most Americans are overweight (BMI > 25), a mean BMI of 36 is extremely high, and the results may be hard to translate into the typical population. Attrition in this study was very high, especially among the low-carb dieters. After two years, 42 percent of the low-carb dieters dropped out, compared with 32 percent of the low-fat dieters.
Among those who were left after two years, the low-fat group still managed to do better in terms of weight loss, triglyceride levels, LDL (“bad”) cholesterol levels, and total cholesterol levels. The headlines focus on how well the low-carb group did in terms of raising HDL (“good”) cholesterol levels. However, as Dr. Ornish likes to say, “You don’t need that many garbage trucks (HDL) if you don’t have that much garbage (LDL).”
I think a better title for this study would be, “Extremely obese people on calorie-restricted diets do better overall than those on low-carb diets.”
Susan Levin, M.S., R.D., is director of nutrition education for the Physicians Committee for Responsible Medicine.