The Overstimulated Brain
Dieting is hard to do. How can one resist good tasting food? But what if the food stimulates the brain itself? New research by Terry Davidson, director of American University’s Center for Behavioral Neuroscience, indicates that diets that lead to obesity—diets high in saturated fat and refined sugar—may cause changes to the brains of obese people that in turn may fuel over consumption of those same foods and make weight loss more challenging.
"It is a vicious cycle that may explain why obesity is so difficult to overcome," said Davidson, one of the authors.
A high-energy diet is one that furnishes more calories than needed for maintenance. It may be used to increase body condition, in recovery from illness and for maintenance under stressful conditions. Then again it may be used because it tastes good.
Davidson recently published his research, "The Effects of a High-Energy Diet on Hippocampal-Dependent Discrimination Performance and Blood-Brain Barrier Integrity Differ for Diet-Induced Obese and Diet-Resistant Rats," in the journal Physiology & Behavior.
For this study, Davidson and his team trained rats given restricted access to low-fat lab chow on two problems—one that tested the rats’ hippocampal-dependent learning and memory abilities and one that did not. Once the training phase completed, the rats were split into two groups: one group had unlimited access to the low-fat lab chow, while the other had unlimited access to high-energy (high-fat/calorie) food.
The high-energy food was high in saturated fat (animal fats, such as those found in cheese or meat or certain plant-based fats, such as cottonseed oil and coconut oil)—considered to be the most unhealthful dietary fat as research has linked it to cardiovascular disease and certain types of cancer.
When both groups of rats were presented the problems again, the rats that from the high-energy diet performed much more poorly than the non-obese rats did on the problem designed to test hippocampal-dependent learning and memory.
When the researchers later examined all of the rats’ blood-brain barriers, they found that the obese rats’ blood-brain barriers had become impaired as they allowed a much larger amount of a dye that does not freely cross the blood-brain barrier into the hippocampus than did blood-brain barriers of the non-obese rats.
Interestingly, the non-obese rats group included rats from both the low-fat lab chow group and the high-energy diet group. But this isn’t a matter of some rats having a super-high metabolism that allowed them eat to large amounts of the high-energy food and remain a reasonable weight.
Davidson said: "The rats without blood-brain barrier and memory impairment also ate less of the high-energy diet than did our impaired rats. Some rats and some people have a lower preference for high-energy diets. Our results suggest that whatever allows them to eat less and keep the pounds off also helps to keep their brains cognitively healthy."
The hippocampus is also responsible for suppressing memories. If Davidson’s findings apply to people, it could be that a diet high in saturated fat and refined sugar impacts the hippocampus’s ability to suppress unwanted thoughts—such as those about high-calorie foods, making it more likely that an obese person will consume those foods and not be able to stop at what would be considered a reasonable serving.
Davidson said: "The idea is, you eat the high fat/high calorie diet and it causes you to overeat because this inhibitory system is progressively getting fouled up. And unfortunately, this inhibitory system is also for remembering things and suppressing other kinds of thought interference."
As evidenced by contestants of NBC’s reality show "The Biggest Loser," formerly obese celebrities who undergo gastric by-pass surgery, and other numerous examples of extreme weight loss, it is possible for obese people to win the battle of the bulge. Unfortunately, the attempt to keep it off is, more often than not, a lifelong battle that requires permanent lifestyle changes. Davidson says this could be due in part to permanent changes in the brain.
For further information see Obese Brains.
Cake image via Wikipedia.