When it comes to hunger, eating too much and gaining weight, the stomach is not the only or even the major organ to blame.
Scientists looking for new and better ways to counter our obesity epidemic are increasingly finding how our genes, hunger and satiety hormones and brain interact to make us eat more than we should.
In most of us, most of the time, the hormones leptin and ghrelin are supposed to work in sync to suppress or signal hunger based on how well fed we are and how much fat we have circulating through us.
Ghrelin, which stimulates appetite, is secreted mostly from the lining of the stomach, and like the hunger-suppressor leptin, activates the brain’s metabolic command centre, the hypothalamus.
But a recent study by researchers at Yale University showed that both the brain and the ghrelin could be fooled.
For the study, published online in the journal Health Psychology, subjects were given a 380-calorie milkshake, but individuals were falsely told they were getting a 620-calorie “indulgent” shake or a 140-calorie “sensible” shake. Ghrelin levels were measured in both groups.
Those who thought they had consumed the high-calorie shake had a dramatically steeper drop in ghrelin levels after drinking it than did those told they had gotten the low-cal shake — their ghrelin levels scarcely moved.
“This study shows that mindset can affect feelings of physical satiety,” said Alia Crum, a psychologist and lead author of the study.
“The brain was tricked into either feeling full or feeling unsatisfied.
“That feeling depended on what people believed they were consuming rather than what they actually were consuming.”
Last winter, Baylor College of Medicine scientists reported working with mice genetically modified to lack a receptor for the ghrelin hormone.
They found this turned up the fat-burning thermostat in the animals’ bodies. In an older group of the mice, the rodents were slimmer than a control group even though they ate just as much and were no more physically active.
Still another mouse study, reported in this month’s Cell Metabolism, looked more closely at what happens inside the hypothalamus and found that when they are starved, some neurons in that part of the brain actually start eating bits of themselves, which in turn ramps up hormonal signals to start eating.
Such cellular cannibalism goes on all the time as part of the body’s natural housekeeping, but the discovery that this process also helps regulate appetite opens a new possible route for obesity-fighting drugs.
Switching to the other end of hunger signals, researchers in Europe and the U.S. studied both rats and humans that had undergone the most common type of gastric bypass surgery, which reduces the stomach to a small pouch and connects it to the middle of the small intestine.
In the Journal of Physiology published in July, researchers reported that both animal and human subjects that had this type of surgery soon became less inclined to eat high-fat foods and more likely to eat low-fat foods compared to those who had no surgery or a different type of surgery.
Researchers suspect this is the result of hormonal changes within the stomach, perhaps a protein that helps regulate blood sugar.
But the stomach doesn’t readily catch up with our heads, consumer psychologist Brian Wansink of Cornell University noted during a recent presentation before the American Psychological Association.
His studies have shown that people tend to fill — and eat more from — bigger containers, whether they’re larger-than-normal bowls or short, wide glasses rather than tall skinny ones.
In one lab study, 60 subjects came into a lab for a “free lunch” that featured 22-ounce bowls of soup — but half got soup in bowls that were secretly refilled from a pressure-released system hidden under the table.
The result: People with the bottomless bowls ate 73 per cent more than those who used regular bowls, yet when they were asked, they didn’t realize they had eaten more.
“The lesson,” Wansink said, “ is don’t rely on your stomach to tell you when you’re full. It can lie.”
Lee Bowman is a health and science writer for Scripps Howard News Service. Contact Bowman at bowmanl@shns.com