Ghrelin, Comfort Eating, and Obesity (Part 1)

Zigman Lab YinYang

The word “fasting” may call up visions of a strict religious practice or some elaborate health-oriented routine involving a carefully calibrated number of ounces of fresh juice per day. A person might think, “I don’t know anybody who does that.”

Maybe not, but voluntarily abstention from food for a period of time is actually pretty commonplace, for spiritual or medical reasons, or even just because of a busy schedule. In fact, we all fast every night so we can get some sleep. In the morning, we terminate that condition by eating break-fast. When we fast for any reason, the body produces a hormone that reminds us to eat, so ghrelin is something we all have to deal with.

A ScienceDaily article from 2009 discusses some of Dr. Jeffrey Zigman’s previous work with Dr. Mario Perello on ghrelin and its possible implications in obesity. It says,

Scientists previously have linked increased levels of ghrelin to intensifying the rewarding or pleasurable feelings one gets from cocaine or alcohol.

The basic quest was to figure out why someone who is already full from eating a big lunch will still go ahead and top it off with dessert. The suspect was ghrelin. What they seem to be saying is that the right amount of ghrelin tells us to eat so we don’t die, but too much ghrelin tells us to eat solely for the rewards of pleasurable sensations that we can’t resist seeking.

One of the best rewards available in this hard world is the feeling of comfort and safety we get from certain foods, which is why they are called comfort foods. Warm, soft, silky, sweet, and fatty, they take us back to mother’s breast, or at least to the days of receiving nourishment through a nipple. And for most of us, those were pretty good days.

The research team trained a bunch of mice to recognize two different rooms, one which routinely contained high-fat treats with a yummy, “more-ish” appeal, rodent junk food in other words. The other room only ever contained bland chow with nutritional value, period. The mice learned and remembered which room was which.

Then, the well-nourished mice, with no legitimate reason to be hungry at the moment, were given the opportunity to go to either of those two rooms. A sensible mouse, having just eaten, doesn’t much care which of the two rooms it goes to. But if you shoot up a mouse with ghrelin, even if it’s already had a nice, adequate meal, it will make a beeline for the room where it remembers finding hyperpalatable goodies in the past.

The scientists extrapolate from this that the same thing happens to people. It may be that too much ghrelin makes us cross the line from eating to live into the territory of living to eat. It’s the difference between eating for nourishment and eating for pleasurable reward. One is a healthful response to being a living organism. The other is not inherently evil, but can easily become a very unhealthful response that threatens our existence as a living organism.

Dr. Zigman is quoted as saying:

What we show is that there may be situations where we are driven to seek out and eat very rewarding foods, even if we’re full, for no other reason than our brain tells us to.

But what tells the brain? That message is carried by ghrelin manufactured in the stomach and lower gastrointestinal tract, which arrives at the brain and says, “eat.” So… what makes ghrelin? Or, as Dr. Zigman puts it,

I am interested in learning the molecular basis for ghrelin biosynthesis and ghrelin release.

He and his various colleagues have learned a lot already. For instance, if you set out to make a lab mouse fat on purpose, that mouse needs to have intact ghrelin signaling pathways and receptors, or it’s no deal. Ghrelin has been shown to stimulate food intake, and the stimulation of food intake is exactly what some people don’t need because they are already obese or at risk of becoming so.

These excerpts are from the Zigman Lab page on its research interests:

In addition, our group has shown that ghrelin levels rise in the setting of chronic stress, and that this mechanism may influence eating behaviors as well as alterations in mood associated with stress… The exact mechanisms by which ghrelin influences these behaviors, body weight, mood and pancreatic islet function… remain to be determined… My current research focuses on gaining a better understanding of ghrelin’s roles in the regulation of body weight, the regulation of hedonic/pleasurable aspects of eating (food reward), the regulation of mood and anxiety, and the maintenance of glucose homeostasis.

In other words, ghrelin is involved with many things that obesity is also involved with, and there is a lot of cause-and-effect that needs to be sorted out. Stay tuned…

Your responses and feedback are welcome!

Source: “Why Some Continue to Eat When Full: Researchers Find Clues,” ScienceDaily, 12/08/09
Source: “Our Research Interests,” Southwestern Medical Center
Image of Zigman Lab YinYang, used under Fair Use: Reporting.

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