ISSN No. 1606-7754                   Vol.15 No.2  August 2007

A tepary bean diet and exercise delays indices of type 2 diabetes in female fa/fa rats
Carol D. Rodgers1, Pam E. Burch2, Jaci L. VanHeest3, K. Suzuki4, Chantal T. Bussiere1, Rachel A. Schemmel4
College of Kinesiology, University of Saskatchewan, Saskatoon, Canada1, Department of Kinesiology, Michigan State University, USA2, Department of Kinesiology, University of Connecticut, USA3, Department of Food Science and Human Nutrition, Michigan State University, USA4

Abstract

Legumes have been shown to protect against the development of type 2 diabetes (T2D). Previous work has focused on the impact of legumes on the glycemic index with little attention given to other physiological changes. Considerable evidence also demonstrates that exercise is beneficial for diabetic individuals. This study sought to determine the individual and synergistic effects of a legume diet and exercise on indices of T2D and tested the hypothesis that the synergy of these factors would protect against typical changes in glycemic hormones and lipids across the weight gain and insulin resistant stage of development in genetically obese rats. Fatty Zucker (fa/fa) rats, 6-7 wks of age were assigned to one of four treatment groups (n = 10/group); 1) tepary bean diet and exercise [TE], 2) tepary bean diet [T], 3) control diet and exercise [CE], 4) control diet [C]. A legume diet and exercise [TE] resulted in significantly less weight gain (126 g vs. 222 g in [C]) and lower body mass compared to animals in other treatment groups. The interaction of [TE] also resulted in significantly lower serum insulin compared to [C] animals across the study period. Diet [T] alone, significantly decreased serum triglycerides and cholesterol relative to [C] animals. Our results indicate that a tepary bean diet, with exercise, can decrease typical changes in weight gain, glycemia and lipid profile in fa/fa rats. The adoption of such a program in individuals showing signs of T2D would also likely serve to protect against these physiological changes. (Int J Diabetes Metab 15: 38-45, 2007)

Key Words: Tepary bean, carbohydrate metabolism, lipids, exercise, Type 2 diabetes

Introduction

Diets high in fiber are effective for improving glucose control,1-10 lowering plasma insulin concentration6,7,10 and decreasing serum triglyceride and cholesterol concentrations1,9,11,12 in individuals with Type 2 diabetes. In humans, regular physical exercise enhances insulin sensitivity, improves glucose tolerance and decreases serum triglyceride and cholesterol concentrations in both non-diabetic13-16 and non-insulin dependent diabetic individuals (NIDDM).17 Considerable evidence also exists that demonstrates that when regular physical training is used in conjunction with dietary manipulation there is an even greater improvement in glucose tolerance than with diet alone in individuals with Type 2 diabetes.18 While we have shown previously that exercise, together with the incorporation of tepary bean into a high fat diet, attenuated weight gain, subcutaneous and visceral fat gain compared to untreated controls,19 we have yet to report the effects of this diet and exercise program on glucose and lipid metabolism.

Exercise training has been shown to be associated with improved insulin stimulated muscle glucose uptake,20-23 decreased insulin and glucose response to an oral glucose tolerance test,23,24 improved total body glucose disposal25 and decreased glycated hemoglobin.26 Also, exercise training has been shown to yield a decrease in basal blood glucose, insulin, cholesterol and triglyceride in fa/fa rats.27

To date there are no studies which have looked at the combined effect of a leguminous diet and exercise on changes in plasma insulin, glucose and lipid concentration across both the rapid weight gain phase and the insulin resistance stage of development in genetically obese rats, an animal model of human obesity and type 2 diabetes. Such an investigation is warranted since much of the rising incidence of Type 2 diabetes and obesity in many of today's population groups has also been accompanied by an increase in urbanization and a move away from the traditional active farming lifestyle; lifestyle changes that often result in a decrease in both physical activity and the consumption of traditional foods such as legumes. In many native groups, such as the Pima Indians of Arizona, who demonstrate an exceptionally high incidence of Type 2 diabetes, this change in activity pattern has also been coupled to a shift away from the traditional diet high in wild foods and fiber (wolfberries, tepary beans, prickly pears, mesquite pods, mustard seeds etc.) towards a more high-fat, fast food diet. In a recent study comparing the effect of a diet rich in traditional desert foods with a high-fat mixed diet on diabetes incidence rates and the risk of developing diabetes in this particular population, it was noted that those Pima Indians who consumed the mixed diet had a greater risk (2.5 times), and a greater crude incidence rate (63 cases per 1000 person years) of developing diabetes than those individuals who consumed the more traditional Indian diet.28 Several investigators have also proposed that these more traditional legume foods have acted as protective agents against the development of diabetes in these, and other genetically prone populations.29,30 The progressive change to a diet that is low in fiber and high in fat, particularly in these more susceptible populations, may in fact be a major contributing factor to the dramatic rise in prevalence of NIDDM over the last century.31

The hypothesis tested in this study was that the combined effect of a leguminous diet with or without exercise, compared with a purified control diet, would protect against changes in plasma insulin, glucose and lipid concentrations which are typical across both the rapid weight gain phase and the insulin resistance stage of development in genetically obese rats. The Fatty Zucker rat was chosen as the animal model for this study since it is genetically predisposed to characteristics such as hyperinsulinemia, hyperlipidemia, obesity, and insulin resistance that simulate the type 2 diabetic state in humans. Moreover, the development of these characteristics occurs in an age-dependent fashion, similar to that which is observed in humans.

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