Crossed hunger signals to brain a factor in overeating


I’ve just read Joseph Conrad’s “Heart of Darkness” again. The story formed the basis for the movie “Apocalypse Now.” Disturbing questions are raised about the essence of madness and human nature.

Philosophers may conclude that we are — or are not — sinners or stained with something that draws us to the devil.

I am certain of only one thing in that regard. We do have powerful drives that compromise our expression of free will. Those cravings create most of the bad news in the weight loss story.

We have very little control over our heart rate or the moment that our gut makes an embarrassing sound. The same autonomic nervous system that controls those functions effects energy balance in our bodies.

The goal of maintaing a normal weight has become the subject of intense study. In the 1990s there was hope we had found a magical protein that hides in our fat cells and controls weight. Lots of chubby fat cells make lots of leptin. It goes to the hypothalamus in our brain.

If the system is working, our brain delivers signals that we have enough stored away and we should stop eating and do something that will burn energy, like taking a bike ride or training for a marathon.

In theory, we should be able to inject some leptin every day and watch the fat dissolve. It was tried and it didn’t work, with one exception.

Dr. Robert H. Lustig, a pediatric endocrinologist at the University of California, San Francisco, reports there are rare cases of massively obese children whose bodies can’t produce leptin. They respond dramatically to treatment.

The problem of most with obesity is that they make plenty of it, but the brain doesn’t respond. The main connection seems to be an insulin problem.

Think of it this way: You have a food pantry at home. It’s very high-tech. The pantry is connected to your favorite grocery store by telephone line. When the food reserves on the shelf get heavy enough, a message goes out and service is stopped.

Oh, darn! You came home last night. Boxes of food covered the floor, the garage and the driveway. A truck driver was dumping more in the street and asking where you want the next one.

What happened? Did the service make a mistake or did the pantry send the wrong message?

Consider another possibility, something blocked the message and the shelf didn’t know it was full.

Well, our fat sends messages to the brain. It is rare for the foul-up to occur in the message-sending component, although a brain tumor could do just that. What happens is that fat sends the information by releasing leptin, but the brain can’t see it because insulin competes for the receptor sites.

Like the delivery service that kept putting food on your doorstep, the brain never got the news and your body tells you to forget the hot-fudge sundae — just scoop fudge from jar and refuse to stop.

In order to beat this problem, we have to understand that sugar is involved in the insulin response and insulin plugs up the message center.

The leptin story helps explain what is going on, why almost everyone slips over time, and where future hope lies.

The feedback loops involve more than one chemical. If we understand the general concept, we can begin to comprehend why dieters struggle to control their waistline after months or years. They use drugs, herbs and potions and rely on anecdotes, unreliable claims by one person or a small group. We are inclined to believe a story and reject statistics. Our children suffer.

In the short term, another chemical, ghrelin, plays a role in your hunger drive. It comes from your empty stomach. There are also materials released from the small intestine. Those send a satiety indicator to your brain and help to explain the logic of eating moderately and waiting a half hour before you make a decision to add another scoop of potatoes right away and chase it with a dose of sugar.

Ghrelin, the messenger from stomach to brain, leads to one of the more controversial issues in weight management and lifestyle change. Should you skip breakfast?

A recent review of the literature challenges the importance of breakfast. The Jan. 31 New England Journal reviewed the literature on commonly held beliefs about obesity. It reported on two studies that compared groups assigned to eat or skip breakfast. There was no difference in weight loss.

Meanwhile, a study was reported the same month in the International Journal of Obesity. It looked at 420 dieters, whose food intake and activity were matched. Those who ate more of their diet late in the day had less weight loss. Lustig suggests a breakfast with high protein suppresses the ghrelin output during the day and that nighttime gorging is a common result. That may be the best answer, but some issues remain controversial.

The book, “Fat Chance,” shows that most dieters fail to maintain their weight loss by the end of two years. By nine years, the number drops below 2 percent. I’ve seen worse numbers. The criterion of being below initial weight is less stringent than “ideal” weight or proving that weight loss ever consisted of bad fat.

Data is tricky in other ways, too. A diet company may report only on people who stayed in the program. They aren’t following dropouts.

Leptin is part of the chemistry that drives our belts back to the notch we used before we dieted. We wish we didn’t have our clothier take in a couple of inches.

I’ve discussed leptin and other factors, skipping the action of cortisol, and saying very little about insulin cycling. I wanted to present an overview, not regurgitate a chemistry course or add one more diet book to the shelf.

I will address the question of whether we’ve been looking at a bogeyman created by the food-government complex, but I want to review the diet myths next time and then take a break from the obesity question.

Dr. Larry Mulkerin is a retired clinical professor. He can be reached at


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