1. Diets containing 1000 kcal/day with varying proportions of carbohydrate (CHO) were fed to four women with simple obesity. The patients were given, in various sequences and for 8 days in each instance, diets in which 3, 6, 12, 25 or 50% of the calories were supplied by sucrose.
2. No significant difference in the rate of weight loss was found when the diets of graded CHO content were fed and mean weight loss was 1.2 kg/week.
3. The high-CHO diets were antiketogenic; there was no daily relationship between urinary ketones and sodium. The 25 and 50% CHO diets had a nitrogen-sparing effect.
4. A 1000 kcal/day diet with about a third of the calories derived from CHO leads to a useful rate of weight loss and minimum changes in body chemistry. This finding may have implications in the long-term treatment of obesity.