Word: leptin
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...wrong time might affect the body's ability to maintain its energy balance," he explains, meaning that our body starts to use its calories differently than it normally would. That in turn could cause fluctuations in numerous hormones, including an increase in ghrelin and a decrease in leptin - the two key hormones that govern appetite and satiety. The hunger hormone ghrelin, which is produced by the stomach, sends a "feed me" message to the brain; leptin, the satiety hormone, signals the brain to stop eating. (See a special report on the science of appetite...
...while these hormones have been successfully manipulated in lab mice to prompt weight gain or loss, the same has not been true in humans. Experiments in which obese human patients were injected with leptin have failed, because the metabolic pathways that control hunger and fullness in people are far more complex than they are in mice. Knocking out one of, say, 50 such pathways through drug treatment just means the other 49 will eventually pick up the slack, says Dr. George Fielding, a bariatric surgeon at the NYU Program for Surgical Weight Loss...
...guide energy use by all the body's other cells. Normally this regulation of cellular fueling is maintained by a well-balanced relay of metabolic signals. As food calories are absorbed, the pancreas secretes insulin, which prompts the liver to convert sugars into fat. Fat cells then release leptin, a hormone that puts the brakes on eating. Leptin does this by passing along the message that the body is satisfied with the deposit of calories it has received...
Karsenty became intrigued by the relationship between fat and bone after showing in 2002 how leptin, a hormone secreted by fat cells, influences bone formation. Leptin is best known as a regulator of body weight and appetite. Karsenty reasoned that if fat influences bone, then the reverse must be true. And, he says, there was another clue to the relationship: "We were using the observation that obese people are [relatively] protected from osteoporosis...
...point theory argue that everyone's body is biologically programmed to stay around a certain weight and will fight attempts at maintaining a weight more than 2-3 kg below that set point. Given less food than it's used to and responding to a drop in leptin, a hormone produced by fat cells, the body clicks into survival mode, slowing metabolism to save energy and triggering cravings for high-kilojoule foods. Now what may be looming for the dieter is months or years of fluctuating weight, possible use of potentially dangerous weight-loss pills, a heightened risk of binge...