t is believed by a great many people that exercise causes weight loss in the overweight. This is thought to be so self evident that questioning such an idea is looked upon with derision. However, the scientific literature does not support the hypothesis that exercise is beneficial to overweight individuals. In fact many studies show that dietary intervention is just as beneficial as dietary intervention combined with exercise, in terms of causing body composition changes. For example, in a recent study published in the American Journal of Clinical Nutrition1, overweight women were assigned to an exercise and diet group, or a diet only group in order to cause weight loss. However, after the one year follow up, the diet only group had lost more weight than the diet and exercise combination group, supporting the contention that it is dietary changes that cause weight loss, and not exercise.
Another interesting observation is that weight loss attributed to forced calories restriction is often no such thing. It again appears self evident that reducing calories intake is a cause of weight loss. However, calories restriction often involves reductions in the intakes of sugar within the diet, and as sugar is the real cause of obesity, it is actually the sugar restriction that is the cause of the weight loss and not the overall calories restriction. Evidence for this viewpoint comes from studies investigating body fat loss through improvements in diet quality. Many studies have reported improvements in body composition through addition of high quality diets such as the Mediterranean diet with no calorie restriction. In addition, low carbohydrate diets also cause weight loss without calorie restriction confirming that it is sugar and refined carbohydrate restriction that is the cause of weight loss, not calories restriction
The fact that exercise is ineffective at causing weight loss suggest that lack of exercise is not the cause of the weight gain in obesity. Further, the evidence that sugar restriction causes weight loss infers that sugar consumption is a contributory factor in obesity. In fact, fructose is now implicated in the development of mammalian insulin resistance, and it is this insulin resistance that is the likely cause of metabolic syndrome and abdominal obesity. Fructose can only be metabolised in the liver of mammals and high intakes cause liver overload and increase production of lipids through de novo lipogenesis. These lipids accumulate in skeletal muscle and liver cells were they cause peripheral and central insulin resistance. Exercise is not effective at reducing weight gain because it does not address the cause of the weight gain, that is the consumption of sugar.
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