It is difficult for a person to lose (or gain) weight, many scientists believe, because the body has negative feedback loops that act to "defend" a particular body weight, or more accurately, the amount of adipose tissue. This regulatory system has been called an adipostat. When a person eats more than is needed to maintain the set point of adipose tissue, the person's metabolic rate increases and hunger decreases, as previously described. Homeostasis of body weight implies negative feedback loops. Hunger and metabolism (acting through food and hormones) affect adi pose cells, so in terms of negative feedback, it seems logical that adipose cells should influence hunger and metabolism.
Adipose cells, or adipocytes, store fat within large vacuoles during times of plenty and serve as sites for the release of circulating energy substrates, primarily free fatty acids, during times of fasting. Since the synthesis and breakdown of fat is controlled by hormones that act on the adipocytes, the adipocytes traditionally have been viewed simply as passive storage depots of fat. Recent evidence suggests quite the opposite, however; adipocytes may themselves secrete hormones that play a pivotal role in the regulation of metabolism.
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Metabolism. There isn’t perhaps a more frequently used word in the weight loss (and weight gain) vocabulary than this. Indeed, it’s not uncommon to overhear people talking about their struggles or triumphs over the holiday bulge or love handles in terms of whether their metabolism is working, or not.