If there was a hormone in your body whose chief job was to make you feel hungry, most of us probably wouldn't be too keen on it. (I don't know about you, but having a healthy appetite has never been a problem for me.) But if there was a hormone that decreased our appetites, we'd order buckets of it!
Leptin is a hormone, made by fat cells, that decreases your appetite. Ghrelin is a hormone that increases appetite, and also plays a role in body weight.
Levels of leptin -- the appetite suppressor -- are lower when you're thin and higher when you're fat. But many obese people have built up a resistance to the appetite-suppressing effects of leptin, says obesity expert Mary Dallman, PhD, from University of California at San Francisco.
Here's what we know so far about the "hunger hormones" and what we can do to help control our appetites.
What We Know About Ghrelin
Ghrelin, the appetite increaser, is released primarily in the stomach and is thought to signal hunger to the brain. You'd expect the body to increase ghrelin if a person is undereating and decrease it if they are overeating. Sure enough, ghrelin levels have been found to increase in children with anorexia nervosa and decrease in children who are obese.
German researchers have suggested that ghrelin levels play a big role in determining how quickly hunger comes back after we eat. Normally, ghrelin levels go up dramatically before you eat; this signals hunger. They then go down for about three hours after the meal.
But some researchers believe that ghrelin is not as important in determining appetite as once thought. They think that its role in regulating body weight may actually be a more complex process.
What We Know About Leptin
Of the two hormones, leptin -- the appetite suppressor -- appears to be the bigger player in our bodies' energy balance. Some researchers think that leptin helps regulate ghrelin.
Leptin helps signal the brain that the body has enough energy stores such as body fat. But many obese people don't respond to leptin's signals even though they have higher levels of leptin.
In general, the more fat you have, the more leptin is in your blood. But the level varies depending on many factors, including when you last ate and your sleep patterns.
A study showed that rats that were given doses of leptin ended up eating less, but this effect lasted only about two weeks. It seems that the rats developed a resistance to leptin's appetite-cutting effects.
How to Control Hunger Hormones
Are there ways to control our "hunger hormones," and thus rein in our appetites? Possibly -- by avoiding high-fat foods.
When we eat, messages go out to various parts of our bodies to tell us we've had enough. But when we eat fatty meals, this system doesn't work as well, says Dallman. Eating fat tends to lead to eating more calories, gaining weight, and storing fat, Dallman says. Researchers have seen some of these effects after only three days of a high-fat diet.
But researchers have shown that either a diet rich in either "good" carbohydrates (like whole grains) or a diet high in protein suppresses ghrelin more effectively than a diet high in fat.
Something that might help (and certainly won't hurt) is to get enough sleep! In a study of 12 young men, sleep deprivation was associated with an increase in ghrelin levels, appetite, and hunger compared with when they slept 10 hours a night.
All in all, this adds to the huge amount of evidence showing that avoiding a high-fat diet is one of the keys to maintaining a healthy weight.