Hormonal and Metabolic Determinants of Energy Expenditure in Humans
The regulation of energy expenditure (Fig. 1) has been intensively investigated for many decades (for a review compare [1–4]). Traditional components of the metabolic rate are the resting metabolic rate (RMR), diet-induced thermogenesis (DIT) and the thermic effect of exercise (TEE). These components differently contribute to total daily energy expenditure (EE). In an individual with a relatively sedentary lifestyle about 70%–75% of EE is due to RMR, 10% to DIT and 10%–20% is used in physical activities. From a regulatory point of view RMR, DIT and TEE are considered separatable entities. Body cell mass, a familial trait, nutritional status and thyroid state are considered to be the major determinants of RMR. The importance of sympathetic nervous activity, different neuropeptides and corticosteroids in regulating RMR is not well defined in humans. DIT varies and is therefore responsive to food intake, the amount of calories supplied, the calorie mix of the diet, substrate transport and metabolism. Substrate processing and storage are affected by several hormones such as insulin. In addition to nutritional and hormonal factors several drugs and acute cold exposure increase DIT. TEE depends on the type and amount of physical work and can also be influenced by drugs like nicotine and proximity to meals.
KeywordsThyroid Hormone Sympathetic Nervous Activity Rest Metabolic Rate Negative Energy Balance Total Daily Energy Expenditure
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