vidence suggests that obesity is by a metabolic dysfunction of the insulin receptor that induces physiological abnormalities in lipid and glucose metabolism. These changes results in an inability of the body to correctly utilise food for work output in skeletal muscle and instead causes the energy to be stored in adipocytes, necessitating increase energy intakes to compensate. The result of this process is a decrease in the normal thermic effects of food, overeating and a lack of energy available for muscular contraction. Correction of this underlying insulin resistance is paramount in treating and curing obesity. Forced calorie restriction is ineffective at causing weight loss because it assumes that obese individuals have normal physiological responses to food. However, the blunted thermic response to food results in a considerable reduction in energy output in obese individuals when compared to lean counterparts.
Changes to the thermic effects of food in obese individuals has been documented scientifically in a number of studies. For example, researchers1 investigated the thermic response of obese and lean individuals following consumption of a standardised 720 kcal meal or after a meal supplying 35 % of the subjects resting metabolic needs. The relative load was calculated to be 752 kcal in obese individuals and 683 in lean individuals indicating that the total resting metabolic rate was larger in the obese individuals. This increase in resting metabolic rate may reflect the higher levels of fat free mass required to support extra weight. When the subjects were fed a meal, the 3 hours postprandial the energy utilisation, as calculated by the thermic effect of food minus the resting metabolic rate, was greater for the lean subjects in both the 720 kcal meal and the 35 % meal.
When expressed as a percentage of energy intake, the thermic effect of the 720 kcal and percentage meal was identical in each group. However, in both cases this value was lower for the obese subjects suggesting that defective thermogenesis might be associated with obesity. Therefore obese subjects have an increased metabolic rate but a lower thermic effect of food, but when combined total energy utilisation is lower, compared to lean individuals. This is supportive of the contention that insulin resistance diverts the energy from food to storage in adipose tissue rather than allowing oxidation in skeletal muscle. This explains the lack of energy in obese individuals that reduces physical activity, something that is portrayed as laziness by a large number of people. It also explains the increase energy intakes of overweight individuals, as compensatory eating occurs to replenish these low energy stores.
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