Effects of restrained eating behaviour on insulin sensitivity in normal-weight individuals

Restrained eating behaviour has been linked to abnormalities in metabolic and endocrine functions. However, the impact of restraint on fasting insulin and glucose plasma levels and insulin sensitivity remains controversial. Moreover, the few postprandial studies to date are limited by an inappropriate sampling time frame and a low "net" energy and carbohydrate load. The aims of this study are to assess the role of dietary restraint on fasting and postprandial plasma levels of insulin, glucose, triacylglycerol (TAG) and non esterified fatty acids (NEFA) in healthy volunteers with a normal and stable body weight and to determine whether the effect of restraint on the plasma levels of the previous hormones/metabolites is load dependent. Normal-weight participants (21 women and 12 men) were classified as restrained/unrestrained based on the restraint scale of the Three Factor Eating Questionnaire-18R and Dutch Eating Behaviour Questionnaire. The impact of restraint on the plasma levels of different hormones/metabolites was measured, in response to a 500 kcal and 1000 kcal breakfast, using a randomised crossover design. Restraint was associated with lower fasting insulin plasma levels (P<0.05) and a lower insulin (P<0.015) and glucose (P<0.05) plasma levels in the postprandial state, but did not impact on TAG or NEFA. Moreover, restrained eaters showed a better fasting (P<0.05) and postprandial insulin sensitivity (P<0.01). Restrained eating behaviour has, therefore, a significant impact on both fasting and postprandial glucose metabolism, being associated with increased insulin sensitivity. These findings suggest the need for adjusting for restraint level in studies where glucose metabolism is a major outcome.