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The Brain Factor in Obesity and Weight Control

Obesity shrinks the brain, cheat days lead to bingeing, and raiding the frig during the night is worse than you think

Weight control authorities typically focus on calorie intake and energy expenditure. That’s important, of course, but brain response to what and when we eat may be an under-appreciated factor. New studies suggest that the brain shrinks in response to obesity and overweight, becomes stressed in response to diet cycling, and adds to fat stores in response to eating at irregular times. Understanding these issues help us become smarter eaters. 

The first study involves brain size and structure. Featured in UCLA Healthy/Years newsletter (December 2009), it was published online August 6, 2009, in the journal Human Brain Mapping.

Obesity and Brain Structure

Researchers have long known that obesity and overweight are associated with heart and circulatory problems that increase the risk of mental decline. To learn more about the process, Paul M. Thompson, MD, a professor of neurology at UCLA, and a team of researchers used sophisticated brain imaging techniques to explore whether obesity is associated with brain shrinkage. What they found is troubling--and motivating.

Thompson's team compared the brains of healthy individuals in their 70s who were obese (14), overweight (51), and normal bodyweight (29). They found significant brain shrinkage in the obese and overweight participants. Obese individuals, on average, had eight percent less brain tissue than normal weight individuals, while overweight subjects had four percent less tissue. Importantly, the areas of brain shrinkage control critical functions, such as attention, planning, memory, and movement.

“The brains of obese people looked 16 years older than those who were lean, and overweight subjects looked eight years older,” Dr. Thompson told the UCLA newsletter. That’s a big difference and puts them at “much greater risk of Alzheimer’s and other diseases that attack the brain,” he warned.

Happily, Thompson also gave this hopeful assessment: “You can greatly reduce your risk for Alzheimer’s if you can eat healthily and keep your weight under control.”

The next two studies will help us do that.

Diet Switching Triggers Stress

“Backsliding is OK,” I wrote in Ripped 2. “It takes the pressure off. In fact, an occasional eating splurge is a good idea….If I have my fling occasionally, I’m happy to go back to my regular eating pattern the next day.”

That’s true. A little backsliding has helped me stay on track. But I should have put more emphasis on the occasional part. Many readers interpret what I wrote to mean “every weekend.” That’s not what I meant. When Matt was small, we’d go to the ice cream shop from time to time. It was a father-son thing; we had a good time.

I have never made a habit of splurging. As the next study shows, that would be a bad idea. 

The study, led by Eric Zorrilla, PhD, and Pietro Cottone, PhD, was published November 9, 2009, in Proceedings of the National Academy of Sciences (PNAS).

Drs. Zorrilla, Cottone and their colleagues put rats on two different eating regimens. One group was fed alternating cycles of food; five days of regular lab chow and two days of sugary sweet-tasting chow. The other group, the control group, was fed only regular lab chow. Both groups were allowed to eat as much as they wanted. 

What happened is interesting and instructive.

The two groups showed strikingly different patterns of behavior. The diet-cycled rats put less effort into obtaining the previously acceptable regular chow, ate less of it, and were more likely to shy away from anxiety-provoking situations. When they returned to a diet of sweet food, their anxiety-related behaviors returned to normal, but they ate more than they needed. The control group showed no change in behavior and eating patterns. 

“We found that rats cycled in this way…begin to binge on the sweet food, stop eating their regular food, and show withdrawal-like behaviors often associated with drug addicts,” Dr. Zorrilla explained. The control group showed no addictive behavior.

“Our research suggests that this eating pattern leads to a vicious cycle,” Dr. Cottone added. “The more you cycle this way, the more likely it is you cycle again. Having a ‘free day’ in your diet schedule is a risky habit. 

Investigating further, the researchers began to look at involvement of the brain stress system. They found that rats cycling between regular and sweet food began to produce a stress-related substance known as hypothalamic corticotrophin-releasing factor (CRF). Significantly, CRF is produced by a part of the brain involved in drug dependence.

The diet-cycling group on normal chow produced five times as much CRF as the control group. Significantly, CRF returned to normal when the cycling rats returned to sweet food. Switching from sweet to regular food increased stress, and cycling back to sweet food relieved stress. The rats were hooked on the sweet chow. Like a drug addict denied a fix, they experienced withdrawal when they cycled back to regular chow.

“Our findings suggest that intermittently eating sweet food changes the brain’s stress system so that you might feel stressed, even though nothing that terrible has happened,” Dr. Zorrilla said. The control group was perfectly content eating regular chow.

“The findings suggest that frequent dieting with frequent relapse is worse than dieting by itself,” said Dr. Cottone. Similarly, regular cheat days are likely to encourage compulsive eating.

Don’t become a junk food junky on weekends. Stick with healthy food most of the time and you’ll be more comfortable—and leaner.

Finally, let’s look at a surprising downside of mid-night bingeing.

Brain Clock Adds Pounds

A friend of ours used to duct tape the refrigerator closed to keep him from eating during the night. I thought that was overkill, but a new study has made me think again. Researchers are finding that timing of food intake may play a significant role in weight gain.

A Northwestern University study, reported in the November 2009 issue of Obesity, found that feeding nocturnal mice a high fat diet only during daylight hours caused them to gain significantly more weight anticipated. It’s the equivalent of our friend ripping the duct tape off and eating in the middle of the night.  

“One of our research interests is shift workers, who tend to be overweight,” said lead author Deanna M. Arble, a doctoral student at the Northwestern Center for Sleep and Circadian Biology. “Their schedules force them to eat at times that conflict with their natural body rhythms. This was one piece of evidence that got us thinking—eating at the wrong time of day might be contributing to weight gain. So we started our investigation with this experiment.” 

Over a six-week period, two groups of mice, both nocturnal, consumed the same high-fat diet and were equally active. The only difference was feeding time. One group was fed during normal sleeping hours (during the day) and the other was fed during the night when they were normally active. They were not allowed to eat at other times.

The difference in weight gain was remarkable. The mice fed during normal sleeping hours (daylight hours) gained more than twice as much, 48 percent compared to 20 percent for those fed during the night, their natural hours of wakefulness. (Like humans, both groups overate on high fat food.)

“How a person gains weight is very complicated, but it clearly is not just calories in and calories out,” said Fred W. Turek, professor of neurobiology and director of the Center for Sleep and Circadian Biology. “We think some factors are under circadian control. Better timing of meals…could be a critical element in slowing the ever-increasing incidence of obesity.” 

Calories do count, but it appears that timing of meals may be a bigger factor than previously thought in regulating energy use. We don’t understand the underlying molecular mechanisms, but it appears that eating at the wrong time can lead to surprising weight gain. Common sense tells us that eating in the middle of the night is not a good idea. Now we know it’s a really bad idea.

In my experience, a planned bedtime snack helps tame the appetite until breakfast. It keeps me out of the frig during the night even better than duct tape.

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As always, I have summarized and simplified. Many more details can be found in the reports of these studies.

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