Effects of Progressive Negative Energy Balance on Glucose Tolerance, Insulin Sensitivity, and Beta-cell Function

Plain-language summary

Type 2 diabetes results from a combination of peripheral insulin resistance and beta-cell dysfunction, and manifests as fasting and postprandial hyperglycemia. In Singapore, despite the relatively low prevalence of overweight and obesity, the prevalence of type 2 diabetes is disproportionately high and is expected to double in the near future. This indicates that insulin resistance and beta-cell dysfunction are widely prevalent even among individuals who are not overweight or obese. Still, weight loss induced by a variety of ways (calorie restriction, exercise, surgery, etc.) is considered the cornerstone of diabetes treatment. This underscores the importance of negative energy balance in improving metabolic function. In fact, negative energy balance induced by calorie restriction can improve metabolic function acutely, i.e. within 1-2 days and before any weight loss occurs. Likewise, negative energy balance induced by a single session of aerobic exercise improves metabolic function over the next few days. However, the magnitude of negative energy balance that needs to be achieved in order to improve metabolic function, as well as possible dose-response relationships, are not known. Furthermore, the comparative efficacy of calorie restriction vs. exercise in improving metabolic function has never been directly assessed. Accordingly, a better understanding of the effects of acute negative energy balance induced by calorie restriction or aerobic exercise on insulin sensitivity and beta-cell function will have important implications for public health, by facilitating the design of effective lifestyle (diet and physical activity) interventions to prevent or treat type 2 diabetes. To test these hypotheses, whole-body insulin sensitivity, the acute insulin response to glucose, and the disposition index (i.e. beta-cell function), will be determined the morning after a single day of progressively increasing negative energy balance (equivalent to 20% or 40% of total daily energy needs for weight maintenance) induced by calorie restriction or aerobic exercise. Results from this project are expected to result in the better understanding of the effects of negative energy balance induced by diet and exercise on metabolic function. Therefore, this project may help in the design of effective lifestyle intervention programs for the prevention and treatment of type 2 diabetes.

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