The medical profession’s advice to overweight patients used to be straightforward: Eat less, exercise more. Today scientists know it’s not that simple. The body monitors—and defends—its energy stores with an arsenal of potent molecules. One of these is the so-called hunger hormone, ghrelin, perhaps the most powerful appetite stimulant yet discovered. In June researchers at UCLA reported how exposure to ghrelin could help explain why some of us consistently overeat.
Endocrinologist Julio Licinio and his team compared amounts of ghrelin and two other hormones in blood samples drawn from five lean and five obese men every seven minutes for 24 hours. Levels of ghrelin spiked at night, researchers found, but the increase was lower in obese men. Licinio said he “expected to see elevated concentrations in those patients. But it may be that something is overriding ghrelin in obese persons. They may have developed biological mechanisms that make them resistant to their own hormones.”
There’s ample precedent. Mice born without the ability to make leptin, a hormone that suppresses appetite, eat without restraint and become obese. Once the hormone is injected regularly, their appetites lessen, and the fat melts away. But most overweight people, researchers have found, make plenty of leptin. For some reason, they become insensitive to it.
The pattern of ghrelin’s secretion, says Licinio, also may play a role in obesity. His study suggests that lean people sleep through the period in which their ghrelin is released, while the overweight may be more exposed during waking hours, when they are likely to react by eating.
Solving this biochemical puzzle will not be easy, but there are few more important areas of medical research. Nearly one-third of American adults are obese, and the epidemic is spreading. The World Health Organization has even coined a new word for it: globesity.
