Evidence suggest that increases in body fat are caused by a reduction in the sensitivity of the insulin system, which in turn is caused by poor diet. Low quality foods, particularly refined grain and refined sugars devoid of fibre, overload the circulatory system and consequently cells, with nutrients, and this leads to the nutrient overload syndrome. This describes the effect whereby excess nutrients stimulate the energy production pathways and this generates free radicals which in turn result in a the inhibition of the insulin signal system in cells. In addition, certain fatty acids such as trans fats, as well as a lack of essential nutrients and antioxidants, causes further deterioration of the insulin system by fostering an environment of oxidative stress and metabolic disruption. The decrease in insulin system is the primary driver of weight gain and reversing this insulin resistance is the only way to cause successful long term weight loss. The insulin sensitising effects of high quality diets and exercise explain their fat loss effects.
However, despite voluminous literature clearly showing a link between insulin sensitivity and fat gain, the current mainstream view that energy restriction is a desirable solution to lose weight. Such energy restriction often involves a reduction in food intake in combination with an increase in exercise. However, the failure rate for such regimens is high, and this is because energy restriction causes muscle loss, and this muscle loss decreases the resting metabolic rate. Energy restriction and exercise therefore adds a layer of metabolic disruption on top of an underlying insulin insensitive state, and this can have severe consequences for weight loss effort, making it difficult to lose body fat in the long term. Skeletal muscle loss is perhaps the most detrimental aspect of low energy exercise regimens, and the basis of the recommendation to perform resistance training to improve body composition. Resistance training can build muscle and improve insulin sensitivity, and this improves body composition.
However, for resistance training to be effective there must be a positive nitrogen balance, which requires a high intake of protein. In addition, building skeletal muscle is an anabolic activity and requires energy, and so energy intake must also be positive. Restricting energy intake and performing resistance training is counter productive, as evidenced by the literature. For example, in one study, researchers assessed the effects of resistance training on obese individuals in addition to energy restriction1. While the subjects lost weight, they also lost muscle, negating the purpose of the resistance training. The subjects in this study were elderly men and women, and so their adaptation may not have mirrored exactly that seen in younger individuals. However, these data support other studies showing that exercise in combination with energy restriction causes a deterioration of body composition through a reduction in muscle mass. It is also worth noting that muscle loss is associated with mortality in the elderly.
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