adipostat

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A hypothetical mechanism which keeps the level of body fat of most people within a narrow range despite considerable variations in dietary fat intake and physical activity. It is thought that some people may become obese because of a malfunction in the adipostat, but this hypothesis has not gained general support in the scientific community.

Three mechanisms for an adipostat have been proposed. The first proposal likens the adipostat to a thermostat. When fat stores exceed genetically determined limits, the adipostat switches on metabolic processes (called futile cycles) that convert excess fat into heat. Conversely, when fat stores run low, the adipostat switches off the futile cycles. Thus fat stores are regulated by the adipostat increasing or decreasing fat metabolism. The second proposal is that a hormone is released from adipose tissues affecting the appetite control centre in the brain. The third proposal is that the activity of special, metabolically active fatty tissue (see brown fat) increases when fat stores exceed the normal level, increasing heat output and burning off the excess fat.

A mechanism that works like a thermostat, keeping an individual's amount of body fat within a narrow range despite considerable variations in diet and activity. The adipostat is thought to consist of a complicated network of brain cells, hormones, and organs that regulate body weight. Researchers at the Oregon Health Science University have identified two neuronal pathways in the hypothalamus that might be the neuronal basis. One pathway, called the NPY/GRP, stimulates feeding; the other pathway, called the MSH, inhibits feeding and is involved in the maintenance of metabolic rates. See also set point theory.