Effects of whole and refined grains on the resolution of Metabolic Syndrome and the distribution of abdominal adipose tissue in overweight and obese individuals with increased waist circumference

Open Access
- Author:
- Harris, Kristina Arline
- Graduate Program:
- Nutrition
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 18, 2012
- Committee Members:
- Penny Margaret Kris Etherton, Dissertation Advisor/Co-Advisor
Sheila Grace West, Committee Member
John Patrick Vanden Heuvel, Committee Member
Connie Jo Rogers, Committee Member
Ryan John Elias, Special Member - Keywords:
- nutrition
weight loss
obesity
whole grain
metabolic syndrome
insulin resistance - Abstract:
- Metabolic Syndrome (MetSyn) is a constellation of risk factors (excess abdominal adiposity, dyslipidemia, increased blood pressure, and hyperglycemia) that is due to the dysregulation of insulin function and excessive abdominal adiposity. Having MetSyn increases the risk of developing type 2 diabetes and cardiovascular disease. Epidemiological studies have shown that higher whole grain intakes are associated with a lower prevalence of MetSyn or MetSyn-related biomarkers. However, there is inconsistent clinical evidence regarding the benefit of whole versus refined grains on MetSyn markers. We hypothesized that including whole grains in the place of refined grains within a healthy diet would improve MetSyn markers. A randomized, controlled, open-label, parallel study was conducted in 50 overweight and obese individuals who had or were at risk for MetSyn. Participants consumed an isocaloric diet containing either whole or refined grain products for 6 weeks followed by a hypocaloric version of the same diet for 6 weeks. All foods were provided to participants daily from a metabolic kitchen. MetSyn criteria, body composition, adipokines, endothelial function, and plasma alkylresorcinols (compliance biomarker) were measured at baseline, 6 and 12 weeks. Alkylresorcinols increased by 450% (P <0.0001) on the whole grain diet and did not change significantly on the refined grain diet, indicating that the participants were compliant to their assigned diets. Fasting plasma glucose tended to decrease more on the whole grain compared to the refined grain diet (whole: -0.24, -0.10 to -0.48 mmol/L vs. refined: -0.05, 0.06 to -0.17 mmol/L, P=0.07). Prediabetes was resolved in all participants in the whole grain group (n=9/9) and in only 13% of the refined grain group (n=1/8). Weight, waist circumference, % adipose tissue (AT; body, trunk and abdomen), cholesterol (total, LDL, and HDL), and blood pressure were decreased on both diets (P <0.05). Levels of the insulin-sensitizing adipokine, high-molecular weight adiponectin, decreased during the ISO phase in both groups (whole: -543 ± 489, vs. refined: -470 ± 718 pg/mL), but increased in the whole grain group and decreased further in the refined grain group during HYPO phase (whole: 255 ± 782, vs. refined: -106 ± 712 pg/mL, P <0.05). Similar patterns were observed with total adiponectin (P<0.05). Leptin decreased more in individuals with hyperleptinemia on the whole grain diet compared to the refined grain diet (P <0.05). Most inflammatory and oxidative stress markers and endothelial function did not change; however, a surrogate marker of arterial stiffness, the augmentation index (AI), increased in both groups (whole: 4.22 ± 14.3, vs. refined; 2.26 ± 7.29, P <0.05). In sum, the improved adipokine profile may, in part, account for the improvement in fasting glucose on the whole grain diet. Furthermore, we speculate that microbial metabolism of cereal fiber in the lower intestine may be involved in improving body insulin sensitivity, specifically through the increased production of glucagon-like peptide-1, although this endpoint was not measured in the current study. Including whole grains in the place of refined grains improved glycemic control in individuals with prediabetes. Abdominal adiposity is a central criteria of MetSyn. Increased visceral adipose tissue (VAT) is associated with higher risk of developing insulin resistance and MetSyn. We explored the relationship between VAT, abdominal subcutaneous adipose tissue (ASAT), and metabolic and anthropometric measurements in a subset (n=28/60) of abdominally obese study subjects. In addition, the effects of whole and refined grains on ASAT and VAT were assessed. Interested, eligible participants underwent magnetic resonance imaging of their abdomens at 0 and 12 weeks. Axial scans at lumbar vertebrae L4-5 to L3 were manually traced to separate the AT depots. Average AT mass across all slices and sum of 3 slices around L4-5 and L3 (“segments”) were calculated. Positive correlations (Spearman) existed between ASAT and BMI (r=0.63), waist circumference (r=0.62), total (r=0.71), trunk (r=0.63) and abdominal AT (r=0.71), CRP (r=0.57), IL6 (r=0.63), and leptin (r=0.57, P<0.05), whereas VAT directly correlated with trunk AT (r=0.42), resting metabolic rate (r=0.40), insulin (r=0.37) and HOMA-IR (r=0.39, P<0.05) at baseline. Changes in ASAT correlated with changes in weight (r=0.59), BMI (r=0.61), total (r=0.41), trunk (r=0.46) and abdominal AT (r=0.44) and triglycerides (r=0.42). Changes in VAT correlated with changes in insulin (r=0.39, P<0.05) alone. Percent change from baseline in VAT correlated inversely with percent change in alkylresorcinols, a biomarker of whole grain intake (r=-0.48, P=0.01); however, this relationship was trend in raw change scores (r=-0.34, P=0.09). Only the whole grain group had a significant reduction in average VAT (refined: -14 ± 20 g, P=0.08 vs. whole: -18 ± 20 g, P=0.001), although the changes were not significantly different between the groups. Overall, the results show that VAT and insulin were strongly correlated whereas ASAT was correlated with body fatness and inflammatory markers. In conclusion, the evidence demonstrates that replacing refined grains with whole grains improves glycemic control in those with prediabetes, possibly related to improved AT function and adipokine profiles. Furthermore, we confirmed that VAT and insulin were positively correlated, suggesting that VAT plays a role in the progression of insulin dysfunction. On the other hand, the effect of whole and refined grains on the different abdominal AT depots was not elucidated and requires further research.