A one-week controlled diet and exercise intervention significantly improves insulin sensitivity without changes in plasma adiponectin concentrations in young non-Hispanic white and Mexican American adults
Date
2010
Authors
Botero, Maria Fernanda, author
Melby, Chris, advisor
Allen, Kenneth, committee member
Hickey, Matthew, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Background: Hypoadiponectinemia (low levels of adiponectin in blood) has been linked to insulin resistance and type 2 diabetes (T2D). In the USA, the prevalence of these latter two conditions is higher in Mexican Americans (MA) when compared to Non-Hispanic Whites (NHW). Variations in plasma adiponectin concentrations may partially contribute to differences in insulin resistance and T2D prevalence rates between adults of these two ethnic groups. Also, plasma adiponectin concentrations in MA and NHW adults may respond differently to a diet and exercise intervention. Objectives: 1. To determine whether or not pre-intervention fasting plasma adiponectin concentrations differ between sedentary, non-obese MA and NHW adults; 2. To determine if a combined one-week exercise and diet intervention (controlled low-saturated fat, low-sugar, high-fiber diet) improves both plasma adiponectin concentrations and insulin sensitivity in both NHW and MA adults; 3. To determine if changes in insulin sensitivity are associated with changes in circulating adiponectin concentrations. Methods: During the pre-study phase, volunteers underwent all initial screening tests. Eligible participants [n= 37; (20 NHW; 9 males, 11 females and 17 MA; 4 males, 13 females aged 18-40 years), fasting blood glucose < 126 mg/dl, blood pressure < 140/90 mm Hg, BMI < 30 kg/m2] continued with a 7-day baseline period, in which they were asked to maintain their regular food intake and their usual low level of exercise. A 3-hour intra-venous glucose tolerance test (IVGTT) for the measurement of insulin sensitivity was performed at the end of this period, as well as measurement of fasting plasma adiponectin. The intervention phase started immediately the day after and ended 7 days later. Subjects consumed a diet that was rich in vegetables, fruits, dietary fiber, and lean proteins and low in saturated fat and refined carbohydrates. Study investigators prepared all foods which were provided to participants. Subjects also exercised on a stationary cycle ergometer for 6 out of the 7 days of the intervention (40-45min/session at 65%V02 max). At the end of the intervention, 16-17 hours after the last exercise bout, plasma adiponectin was again measured and another IVGTT was performed. Dependent variables were analyzed using a 2 X 2 repeated measures ANOVA. Results: Insulin action, determined by the 3-h insulin area under the curve (IAUC) in response to glucose infusion, improved significantly (p<0.05) in response to the intervention (IAUC µU*min/L pre, post: MA = 2297, 1635; NHW = 1794, 1210). At baseline, plasma adiponectin levels were not significantly different between NHW and MA adults (NHW= 11.42 mµ/ml, MA= 11.17 mµ/ml) and there were no significant changes in adiponectin in response to the intervention in either group. Conclusion: A one-week diet and exercise intervention significantly improved insulin action in both MA and NHW adults, but changes in circulating adiponectin were not observed. Thus, the improvement in insulin sensitivity in response to a short-term diet/exercise intervention was disassociated from any changes in circulating adiponectin.