The adipokine retinol-binding protein 4 (RBP4) may contribute to the pathophysiological link between obesity and insulin resistance⁽Reference Graham, Yang and Bluher¹⁾. The aim of the present study was to investigate whether plasma RBP4 mediates the improvement in insulin sensitivity following diet-induced weight loss.

Twenty-four overweight and obese subjects without diabetes (BMI 33.6 (se 0.8) kg/m², age 39 (se 2) years) were randomly assigned to consume one of two energy-restricted diets (low-carbohydrate or low-fat; twelve subjects per group) for 8 weeks. Throughout the intervention food was provided (in pre-weighed portions) to achieve a minimum weight loss of 0.5 kg/week.

Plasma RBP4 levels were measured before and after diet-induced weight loss using a commercially-available sandwich ELISA. Insulin sensitivity and body composition were also assessed by the euglycaemic–hyperinsulinaemic clamp and dual-energy X-ray absorptiometry scan respectively.

There was no significant between-group (twelve subjects per group) difference in weight loss or insulin resistance as a result of the diet assignment. For the group as a whole (n 24), RPB4 levels did not correlate with insulin sensitivity at baseline (r 0.16, P=0.48) or after diet-induced weight loss (r 0.07, P=0.75). Weight loss (7% decrease of initial body weight; P<0.01) significantly improved insulin sensitivity (by 13%; P=0.03) and reduced plasma RBP4 levels (by 17%; P=0.03). However, there was no correlation between weight-loss induced changes in RBP4 levels and the change in insulin sensitivity or between plasma RBP4 and measures of adiposity.

In conclusion, weight loss following acute energy restriction is associated with a reduction in plasma RBP4 levels. However, the present study does not support a role for RBP4 in determining insulin resistance or influencing dietary-mediated modulation of insulin sensitivity.