Red wine polyphenols do not improve obesity‐associated insulin resistance: A randomized controlled trial

Preclinical studies have suggested that polyphenols extracted from red wine ( RWP s) favourably affect insulin sensitivity, but there is controversy over whether RWP s exert similar effects in humans. The aim of the present study was to determine whether RWP s improve insulin sensitivity in obese volunteers. Obese (body mass index >30 kg/m 2 ) volunteers were randomly allocated to RWP s 600 mg/d ( n = 14) or matched placebo ( n = 15) in a double‐blind parallel‐arm study for 8 weeks. The participants were investigated at baseline and at the end of the study. Insulin sensitivity was determined using a hyperinsulinaemic‐euglycaemic clamp ( M ‐value), a mixed‐meal test ( M atsuda index), and homeostatic model assessment of insulin resistance ( HOMA‐IR ). RWP s elicited no significant changes in M ‐value ( RWP group: median [interquartile range; IQR ] baseline 3.0 [2.4; 3.6]; end of study 3.3 [2.4; 4.8] vs placebo group: median [ IQR ] baseline 3.4 [2.8; 4.4]; end of study 2.9 [2.8; 5.9] mg/kg/min; P = .65), in M atsuda index ( RWP group: median [ IQR ] baseline 3.3 [2.2; 4.8]; end of study 3.6 [2.4; 4.8] vs placebo group: median [ IQR ] baseline 4.0 [3.0; 6.0]; end of study 4.0 [3.0; 5.2]; P = .88), or in HOMA‐IR . This study showed that 8 weeks of RWP supplementation did not improve insulin sensitivity in 29 obese volunteers. Our findings were not consistent with the hypothesis that RWP s ameliorate insulin resistance in human obesity.