Effects of whole and refined grains in a weight-loss diet on markers of metabolic syndrome in individuals with increased waist circumference: a randomized controlled-feeding trial

Abstract

BACKGROUND: Higher whole-grain (WG) intake is associated with a lower prevalence of metabolic syndrome (MetS); however, there is inconsistent clinical evidence with regard to the benefit of WGs compared with refined grains (RGs) on MetS. OBJECTIVE: We hypothesized that consuming WGs in the place of RGs would improve MetS criteria in individuals with or at risk of MetS. DESIGN: A randomized, controlled, open-label parallel study was conducted in 50 overweight and obese individuals with increased waist circumference and one or more other MetS criteria. Participants consumed a controlled weight-loss diet containing either WG or RG (control) products for 12 wk. Body composition, MetS criteria and related markers, and plasma alkylresorcinols (compliance marker of WG intake) were measured at baseline and at 6 and 12 wk. A subgroup (n = 28) underwent magnetic resonance imaging to quantify subcutaneous and visceral adipose tissue (AT). RESULTS: Baseline variables were not significantly different between groups; however, the RG group tended to have higher triglycerides and lower high-density lipoprotein (HDL) cholesterol (P = 0.06). Alkylresorcinols increased with consumption of the WG diet and did not change with consumption of the RG diet (time × treatment, P < 0.0001), which showed dietary compliance. There were no differences in anthropometric changes between groups; however, weight, body mass index, and percentage of body AT decreased at both 6 and 12 wk (P < 0.05), and reductions in percentage of abdominal AT occurred by 6 wk and did not change between 6 and 12 wk (P = 0.09). Both glucose (P = 0.02) and HDL cholesterol (P = 0.04) were lower with the consumption of the WG compared with the RG diet. However, when noncompliant individuals (n = 3) were removed, the glucose effect was stronger (P = 0.01) and the HDL-cholesterol effect was no longer significant (P = 0.14). CONCLUSIONS: Replacing RGs with WGs within a weight-loss diet does not beneficially affect abdominal AT loss and has modest effects on markers of MetS. WGs appear to be effective at normalizing blood glucose concentrations, especially in those individuals with prediabetes.