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Investigating slow carbs for metabolic rate

Glycemic index, glycemic load, insulin index: only one of these is widely known by the public. But when it comes to keeping weight off, does glycemic index and total carb content actually have any impact?

Study under review: Effects of carbohydrate quantity and glycemic index on resting metabolic rate and body composition during weight loss

Introduction

One of the biggest struggles for people who have lost weight is trying to keep it off. Weight regain after an initial period of loss is a highly common occurrence among dieters[1]. While there are different reasons for this weight gain, a potential contributor may be the metabolic adaptation to weight loss[2] itself. As weight loss occurs, a person will be physically moving around less mass, and therefore expending less energy. But these periods of weight loss can induce reductions in metabolic rate above and beyond what can be attributed to the weight loss alone. This is known as adaptive thermogenesis. Resting metabolic rate (RMR) is a component of energy expenditure that plays a role in adaptive thermogenesis. RMR is the amount of energy your body expends during a state of rest to keep all your organs and bodily systems functioning and, in most people, it is the biggest contributor to total daily energy expenditure.

It is plausible that dietary factors could help to prevent these reductions in RMR during weight loss. One area of research has examined carbohydrate quantity and glycemic index (GI) as a potential strategy to prevent RMR decreases. The glycemic index is a measure of how much a food will raise your blood sugar. To date, the research has been somewhat equivocal. Some studies[3] have shown benefits[4] for low-GI diets in terms of preserving RMR, but these studies did not match protein intake between intervention groups, which can confound the results. Other studies have shown[5] no weight loss difference or significant changes in RMR between diets that altered both carbohydrate content and GI level.

This study aims to further examine the effects of dietary carbohydrate content and GI on RMR adaptations and changes in body composition during and following weight loss. By isolating both the carbohydrate content and GI level in a diet, we can better tease out if either of these variables may have an RMR preserving effect. Additionally, it is not known if diets very high in carbohydrate (greater than 65%) could attenuate these outcomes. The researchers conducting this study examined four types of diets in an effort to determine their ability to attenuate reductions in RMR.

Resting metabolic rate (RMR) can become depressed during and after weight loss. It has been hypothesized that this decrease in RMR could play a role in weight regain. The effects of dietary carbohydrate content and glycemic index to preserve RMR are not well known. This trial examines four diets varying in GI and carbohydrate content to determine their influence on RMR during and after weight loss.

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