A new study shows that overweight adolescents lose more weight on a diet low in carbohydrates than on a diet low in fats--and that they maintain an acceptable lipid profile. Investigators assigned about half of a group of 30 overweight 12- to 18-year-olds to a very low carbohydrate diet. For the first two weeks, the diet comprised no more than 20 g of carbohydrate a day; for the balance of the 12-week study period, carbohydrate was increased to 40 g/d. No limit was placed on consumption of protein, fat, or total calories. Meanwhile, the low-fat (control) group was asked to eat a diet that contained less than 40 g/d of fat, with five servings of starch, plus as much fat-free dairy foods, fruits, and vegetables as they wanted. Participants in both groups were asked to take nutritional supplements to ensure that they consumed recommended dietary allowances of vitamins and minerals.
At the end of 12 weeks, participants in the low-carbohydrate group had lost a mean weight of 9.9 kg, compared with a mean weight of 4.1 kg in the low-fat group. Similarly, the average decline in body mass index was 2.4 kg/[m.sup.2] in the low-carbohydrate group and 1.2 kg/[m.sup.2] in the low-fat group. No adverse effects on lipid parameters were seen in either group. In the low-fat group, the level of low-density lipoprotein (LDL) cholesterol decreased significantly; in the low-carbohydrate group, the level of non-high-density lipoprotein cholesterol (which includes triglycerides, LDL, and intermediate-density lipoprotein) improved greatly--reflecting, in part, a drop in the triglyceride level.
On average, adolescents in the low-carbohydrate group consumed more calories than youngsters in the low-fat group. Not surprisingly, the low-carbohydrate group ate significantly more fat and far less carbohydrate than the low-fat group; the low-carbohydrate group also ate more saturated fat and more cholesterol--much more of these macro-nutrients than recommended. The most common side effects...