Energy restrictive diets are not effective at causing long term sustainable fat loss in the majority of individuals with obesity. This is because obesity is a disease caused not by eating too much food, but by eating the wrong types of food. In particular the typical Western diet, which is devoid of meaningful levels of essential and plant nutrients, particularly fibre, is a cause of insulin resistance, and it is this dysfunction which drives obesity. Associated with the insulin resistance is leptin resistance, and this is problematic because the afferent signal informing the hypothalamus of the current fat reserves becomes muted and as a result the central nervous system is misinformed as to the true extent of these reserves. One of the main problems of energy restrictive diets is that withdrawal of calories under such conditions leads to counterregulatory mechanisms to prevent fat loss, due to the presence of the leptin resistance. Once such counterregulatory mechanism is a catabolism of skeletal muscle, something which adversely affects muscle function.
The adverse effects of energy restriction on skeletal muscle function are well known. For example, in one study1, researchers assessed the skeletal muscle function in obese patients following an energy restrictive diet and period of fasting. Force contraction of the skeletal muscle of the subjects increased following two weeks of consuming a 400 kcal diet compared to the subjects normal measurements when eating maintenance calories. In addition, the time to relaxation for the muscle slowed, suggesting a detrimental change to skeletal muscle function. Both of these changes persisted following a two week fasting phase. The fatigability of the muscle increased with the low calories diet and this decline in endurance continued to deteriorate during the subsequent fasting phase. Refeeding reversed the detrimental changes to muscle function and the values trended back towards baseline readings suggesting that the higher calorie intake was returning correct muscle function to the subjects.
These results therefore suggest that energy restrictive diets have detrimental effects on muscle function. This is interesting because there is an inverse association between physical activity and body weight. It has generally been assumed that the cause of this association is the laziness on the part of the individual, the result of the laziness being the increase in body weight. However, evidence in the nutritional literature does not support this claim. These results suggest that muscle function deteriorates with energy restriction, and this sheds new light on the association between body weight and physical activity. Overweight individuals are far more likely to be on an energy restrictive diet that normal weight individuals. If muscle function does deteriorate with energy restriction, this could explain the inverse association between body weight and physical activity. The loss of muscle function seen on energy restrictive diets likely comes from the loss of skeletal muscle that accompanies calorie restriction.
Dr Robert Barrington’s Nutritional Recommendation: Energy restriction is not a successful strategy to employ in body fat loss. While energy restriction causes weight loss, much of that weight is skeletal muscle and this is likely why muscle function deteriorates with low calorie diets. High quality diets without energy restriction are the only sustainable answer to obesity and the weight gain caused by the typical Western diet.
RdB
