0355 The Effect of Low-Carbohydrate Hypocaloric Diets on Exercise Tolerance of Sedentary Obese People

The purpose of the outlined project is to examine how low-carbohydrate hypocaloric diets affects exercise tolerance in sedentary obese subjects and investigate possible ways to counteract potentially accelerated fatigue development. These findings may inform future guidelines for optimal strategies to combine weight loss diets and exercise. Obesity is one of the major health concems world-wide and is associated with multiple co-morbidities including type 2 diabetes and cardiovascular disease. Key aspects are the combination of inactive lifestyles and food overconsumption facilitated by nutrient-dense easily accessible sources. Moreover, inactivity per se is associated with disease and increased mortality leading to substantial costs for the public health care system. To induce weight loss and simultaneously achieve the full health-related rewards, hypocaloric diets combined with exercise are the first line management strategies. In this regard, low-carbohydrate hypocaloric diets are very popular, although the superionty combined with other hypocaloric strategies has been questioned. More so, the combination of a low-carbohydrate hypocaloric diet and physical activity may induce accelerated fatigue development due to reduced muscle glycogen stores. This may in faet decrease the physical capacity and reduce the ability to engage in a successful weight loss program combining diet and physical activity. Especially the ability to engage in exercise of high intensity may be reduced by low carbohydrate availability due the preference of carbohydrate as a fuel at increased intensities. Accordingly, our research group has recently observed a substantial augmented rating of perceived exertion during high-intensity exercise in moderately trained subjects with lowered muscle glycogen stores. Despite the widespread application of low-carbohydrate diets, the effeets on physical capacity, rating of perceived exertion during exercise and voluntary exercise patterns are largely unexplored in sedentary obese subjects. Moreover, the effect of the macronutrient composition of the diet is not thoroughly examined and neither potential adaptation over time. Thus, the sparse previous literature is equivocal with findings of ~20% reduced time-to-exhaustion even during low-intensity exercise after one, but not six weeks of a low-carbohydrate diet, ~50% reduced time to exhaustion during moderate intensity exercise after one as well as six weeks of diet change, but no performance alterations after eight weeks of intervention in a third, larger sample sized study. In one of these investigations, increasing the carbohydrate content, but maintaining the same calorie deficit reversed a reduced physical capacity, whereas no effect of dietary composition has also been demonstrated. Moreover, the findings of an initially reduced performance after short-term exposure, but not necessarily after long duration exposure has led to suggestions of metabolic adaptations over time that improves the ability to rely on fat as a fuel and engage in exercise despite reduced muscle glycogen stores. However, many questions remain unanswered and methodological constraints such as low sample sizes, a lack of control of the diet, simplistic testing procedures and absence of multiple assessment time points are prevalent. Thus, the aim of the present project is to provide novel evidence for the effects of low-carbohydrate hypocalorie diets on exercise capacity and perceived exertion during different types of exercise, the effects on voluntary exercise patterns and potential effects of manipulating the macronutrient composition of a hypocalonc diet (e. g. increasing the carbohydrate content) or supplementing with carbohydrate mouth-rinse acutely during exercise. The results of the present project will result in improved guidelines for how to combine exercise and hypocaloric diet regimens and increase the probability of successful and sustained engagement.