Adverse effects on insulin secretion of replacing saturated fat with refined carbohydrate but not with monounsaturated fat: A randomized controlled trial in centrally obese subjects.

Current dietary guidelines recommend the replacement of saturated fatty acids (SAFAs) with carbohydrates or monounsaturated fatty acids (MUFAs) based on evidence on lipid profile alone, the chronic effects of the mentioned replacements on insulin secretion and insulin sensitivity are however unclear.

To assess the chronic effects of the substitution of refined carbohydrate or MUFA for SAFA on insulin secretion and insulin sensitivity in centrally obese subjects.

Using a crossover design, randomized controlled trial in abdominally overweight men and women, we compared the effects of substitution of 7% energy as carbohydrate or MUFA for SAFA for a period of 6 weeks each. Fasting and postprandial blood samples in response to corresponding SAFA, carbohydrate, or MUFA-enriched meal-challenges were collected after 6 weeks on each diet treatment for the assessment of outcomes.

As expected, postprandial nonesterified fatty acid suppression and elevation of C-peptide, insulin and glucose secretion were the greatest with high-carbohydrate (CARB) meal. Interestingly, CARB meal attenuated postprandial insulin secretion corrected for glucose response; however, the insulin sensitivity and disposition index were not affected. SAFA and MUFA had similar effects on all markers except for fasting glucose-dependent insulinotropic peptide concentrations, which increased after MUFA but not SAFA when compared with CARB.

In conclusion, a 6-week lower-fat/higher-carbohydrate (increased by 7% refined carbohydrate) diet may have greater adverse effect on insulin secretion corrected for glucose compared with isocaloric higher-fat diets. In contrast, exchanging MUFA for SAFA at 7% energy had no appreciable adverse impact on insulin secretion.