The Metabolic and Reproductive Effects of Whole Grains and High Fiber Foods in Metabolic Syndrome and Polycystic Ovary Syndrome
Open Access
- Author:
- Katcher, Heather Ilene
- Graduate Program:
- Integrative Biosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 11, 2007
- Committee Members:
- Penny Margaret Kris Etherton, Committee Chair/Co-Chair
Richard Scott Legro, Committee Chair/Co-Chair
Michael Henry Green, Committee Member
Peter J Gillies, Committee Member
Ian Alexander Simpson, Committee Member - Keywords:
- metabolic syndrome
weight loss
whole grains
c-reactive protein
testosterone
fiber
polycystic ovary syndrome - Abstract:
- Two studies were conducted to evaluate the metabolic and reproductive effects of whole grains and high-fiber foods in metabolic syndrome and polycystic ovary syndrome. Insulin resistance is implicated in the pathology of both metabolic syndrome and polycystic ovary syndrome, and both conditions are associated with elevated levels of cardiovascular disease risk factors. Given the similar etiology of metabolic syndrome and polycystic ovary syndrome, whole grains and high fiber foods have been recommended for both conditions because they lower the glycemic response and improve insulin sensitivity. However, there is limited evidence from clinical trials as to the effectiveness of whole grains and high-fiber foods in the dietary treatment of these conditions. The purpose of the two clinical trials I conducted was to determine if including whole grains and high fiber foods in the diet reduces cardiovascular disease risk in metabolic syndrome, and lowers testosterone levels in polycystic ovary syndrome. In the first study, obese men and women (25M, 25F) with metabolic syndrome were randomized to receive dietary advice to either avoid whole grain foods or to have all of their grain servings from whole grains for 12 weeks. All other dietary advice to achieve weight loss was the same for both groups. A fasting blood draw, 2-hour oral glucose tolerance test (OGTT), dual energy x-ray absorptiometery (DXA) scan, and biometric measurements were done at the beginning and end of the 12-week diet period. Body weight decreased 3.7 ± 3.5 kg or 3.5% in the whole grain group (P<0.001) and 5.3 ± 5.2 kg or 4.8% in the refined grain group (P<0.001) (n.s. between groups). Waist circumference and body fat percentage also decreased in both groups from baseline (P<0.02). Despite a similar decrease in body weight, CRP levels decreased 38% in the whole grain group, but were unchanged in the refined grain group (P=0.007 between groups). There were no other significant differences between groups with respect to changes in biometric measurements, lipids and lipoproteins, glucose tolerance, markers of inflammation and fibrinolysis, and sex hormones. Participants in the whole grain group but not the refined grain group increased their intake of dietary fiber and magnesium, and decreased their intake of saturated fat compared with baseline (P<0.05). Participants in both groups reported a greater overall satisfaction with their diet compared with baseline (P < 0.001), rated a greater sense of having a healthy lifestyle (P < 0.001), and considered their families to be more approving of their diet (P < 0.001). In addition, participants in the refined grain group had a lower preoccupation with food compared with baseline (P = 0.002) and participants in the whole grain group rated their meal planning and preparation as more difficult (P = 0.006). The aim of the second study was to determine if varying meal composition affects postprandial testosterone levels in women with PCOS. I evaluated changes in testosterone, sex hormone binding globulin (SHBG), glucose, and insulin levels following a high-fat, Western meal (62% fat, 24% carbohydrate, 1g fiber) and a low-fat, high-fiber meal (6% fat, 81% carbohydrate, 27g fiber) in 15 women with PCOS using a randomized, 2x2 crossover design with a 7-day washout period. Blood samples were collected at baseline and at 30 minutes and every hour after each meal for six hours. Testosterone levels decreased 27% within two hours after both meals (P<0.001). However, the testosterone level and the free androgen index remained below pre-meal values for four hours after the low-fat, high-fiber meal (P <0.004) and for six hours after the high-fat, Western meal (P <0.004). Insulin levels were almost 2 fold higher at 30, 60, and 120 minutes after the low-fat, high-fiber meal compared with the high fat, Western meal (P <0.03). Glucose levels also were higher at 30 and 60 minutes after the low-fat, high-fiber meal compared with the high-fat, Western meal (P<0.003). The findings from these two studies demonstrate that whole grains and high fiber foods have metabolic and reproductive effects in metabolic syndrome and polycystic ovary syndrome. The results from the first study demonstrate that weight loss can be achieved with a diet high in whole grains, similar to a conventional hypocaloric diet with refined grains, but there may be additional benefits to the cardiovascular risk profile. Specifically, I observed a reduction in c-reactive protein, an independent risk factor for cardiovascular disease, in participants consuming whole grains but not refined grains. The finding of a prolonged reduction in postprandial testosterone levels following a high-fat, Western meal compared with a low-fat, high-fiber meal indicates that diet plays a role in the regulation of testosterone levels in women with PCOS, and that diet composition may be an important consideration in the treatment of hyperandrogenism in PCOS. Future studies examining larger cohorts for longer periods are necessary to determine the long-term health benefits of whole grains and high-fiber foods in metabolic syndrome and polycystic ovary syndrome.