Ghrelin, Comfort Eating, and Obesity (Part 2)

Back in the hunting-and-gathering days of humankind, the only really delicious things to eat were fruits like berries, and honey. Even those were not available at all times or in all climes. Honey and berries advertise their rewards right up front and are immediately identifiable as hedonic foods. They send out a strong “Eat Me” message.

In those days, hyperpalatable food was not a problem, and even when such an extraordinary treat was found, there was never enough of it for any one person to binge on. It wouldn’t matter how monstrous a tendency a person might have toward getting addicted to food — if there’s nothing to eat but cabbage and potatoes. Anyway, we can’t thrive on honey and berries, we need more nourishment than that.

The obvious charms of fruit are not found in, for instance, bread and meat. A sheaf of grain is not an appetizing proposition, nor is a wild pig on the hoof. The grain and the pig don’t have an irresistible appearance or fragrance until much preparation has been done. In their natural state, the basic ingredients of bread and pork chops have no shelf appeal.

So, the inherent deliciousness of the food was not enough to serve as the only “Eat Me” cue. We needed some other built-in impetus to eat, and ghrelin apparently is it. The hormone triggers the sensation we identify as hunger, reminding us to put some fuel into the tank.

From the University of Texas, and more specifically from the Southwestern Medical Center, comes news of a discovery that might lead to more questions than answers. We discussed some of Dr. Jeffrey Zigman’s previous research on what has been nicknamed the “hunger hormone.” If you’re a mouse with more than the normal amount of ghrelin, you are drawn to pleasurable, fatty foods, and you shun plain old rat chow.

Zigman, who teaches internal medicine and psychiatry, is senior author of this most recent study, and Jen-Chieh Chuang is the other member of the team. Zigman says,

This helps explain certain complex eating behaviors and may be one of the mechanisms by which obesity develops in people exposed to psychosocial stress.

The article explains further:

Dr. Zigman’s laboratory has previously shown that chronic stress also causes elevated ghrelin levels, and that behaviors generally associated with depression and anxiety are minimized when ghrelin levels rise. In mice, these stress-induced rises in ghrelin lead to overeating and increased body weight, suggesting a mechanism for the increased prevalence of weight-related issues observed in humans with chronic stress and depression.

In the laboratory setting, when mice need to be stressed for experimental purposes, they are exposed to dominant “bully” mice, which is kind of interesting, because as we know, in the human world, there is a definite link between childhood obesity and bullying.

The bottom line seems to be, if mice are altered so they can’t produce ghrelin, they don’t seek comfort food when stressed. The researchers believe this carries over to human behavior. Chronic stress causes an increase in ghrelin which causes a person to go for the chocolate-covered bacon in order to soothe the distress and feel better.

Here is some of the more technical stuff:

The study also showed that these effects of ghrelin are due to direct interaction with a subset of neurons that use catecholamines as a neurotransmitter. These include dopaminergic neurons in the brain’s ventral tegmental area, which is known to be associated with pleasure and reward behaviors… The researchers next plan to investigate the molecular mechanisms by which ghrelin acts to cause these stress-associated food-reward behaviors.

What causes an excessive amount of ghrelin to swim around in our veins? Can it be stopped at the source? Or, once it reaches the brain, can the brain counteract the “eat” message that the ghrelin conveys to it? When you’re talking molecules, you’re talking drugs. This sounds like a search for a pharmaceutical answer, a pill to prevent ghrelin from urging the stressed individual to go eat some comfort food.

It seems as if stress eating comes in two varieties. One is more passive, and the reward is attained immediately from the sweet, smooth, warm type of comfort food that just slides right down the hatch. And then there is the more active kind of stress eating that involves a lot of displacement activity — vigorous crunching, chewing, and grinding. The food has to be conquered, overcome, and subdued by muscular exertion before it can be swallowed, so there are two different rewards — the relief of the mechanical discharge of energy, along with the comfort reward of tasting and swallowing.

But some people avoid obesity and food addiction, even though their lives are very stressful. Maybe they dissipate stress through an unattractive displacement activity like nail biting, or even a healthful one like running. The trick is to find a displacement activity that causes no harm — especially one that doesn’t involve caloric intake. It seems like what we ought to be looking for are ways to cope with stress before it has a chance to get our ghrelin all stirred up.

It certainly would be unfair to label ghrelin as a childhood obesity villain because it has always been a part of us, and the childhood obesity epidemic is relatively new. But maybe something else is happening at the same time, something unprecedented that disrupts the way the body manufactures or distributes ghrelin. Maybe there is something in the water or the air, or in food additives, that messes up our hormones in ways they were never messed up before.

Your responses and feedback are welcome!

Source: “Ghrelin likely involved in why we choose ‘comfort foods’ when stressed,” Southwestern Medical Center, 06/23/11
Image by likeaduck, used under its Creative Commons license.