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Recent Research
Dietary Fat and Carbohydrates Differentially Alter Insulin Sensitivity During Caloric Restriction
Kirk E et al.
Gastroenterology 2009; 136: 1552-1560
A study to determine the effects of acute and chronic calorie restriction with either a low-fat, high-carbohydrate (HC) diet, or a low-carbohydrate (LC) diet on hepatic and skeletal muscle insulin sensitivity. Subjects (22 obese adults) were randomised to either an HC (>180 g/d) or LC (<50 g/d) energy deficit diet. A euglycaemic-hyperinsulinaemic clamp, muscle biopsies and magnetic resonance spectroscopy were used to determine insulin action, cellular insulin signalling and intrahepatic triglyceride (IHTG) content before, after 48 hours, and after approx. 11 weeks (7% weight loss) on the specified diet. Weight loss after completing the diet was similar in both groups. The time taken to achieve 7% weight loss was not different between the groups. Changes in fat mass and fat free mass were not different between the groups. Both diets produced a progressive reduction in IHTG: the relative decrease in IHTG was three times greater in the LC group, compared to the HC group at 48 hours, but was not different after 11 weeks. There was a significant difference in the decrease in plasma glucose between groups after 48 hours and a significant difference in plasma insulin concentration after 7% weight loss. The decrease in HOMA-IR was greater in the LC than the HC group after 48 hours and 7% weight loss (P<0.05). Both diets increased hepatic insulin sensitivity, but the improvement was greater in the LC group (P<0.05). Glucose Ra (rate of appearance) was not different between groups, but there was a decline in basal glucose Ra in both groups; the decline was significantly greater in the LC group than the HC group. Brief calorie restriction and minimal weight loss primarily affects the liver, whereas longer calorie restriction and moderate weight loss primarily affects skeletal muscle.
June 2009
