Diets high in saturated fat and refined sugar lead people on the path to obesity, while also changing their brains, which may provoke overconsumption of those same foods and make losing weight very challenging.


"It is a vicious cycle that may explain why obesity is so difficult to overcome," said Terry Davidson, director of American University's Center for Behavioral Neuroscience and a professor of psychology at AU.

The Lays potato chip company points out the challenge obese individuals face in their slogan, "Betcha can't eat just one!", describing how hard it is to say no to high calorie foods.

Research published last month in The American Journal of Clinical Nutrition indicated that overweight and obese kids are more likely to overeat even when they are not hungry.

Impaired Memory Seen in Overweight Rats

Davidson, previously with Purdue University, published his work in Physiology & Behavior where he explained his investigation on the hippocampus (area of the brain which controls memory and learning).

Trained rats that were given limited access to low-fat "lab chow" were tested on two problems. One which allowed Davidson and his team to observe the animals' hippocampal-dependent learning and memory abilities, and one which did not.

The rats were divided into two groups after the training was finished. Unlimited access to the low-fat lab chow was given to half the rats, while the other half was given unlimited access to high-energy food (high in calories and saturated fat- the most unhealthy fat, and is even linked to cardiovascular disease and some cancers).

All of the rats were given the same two problems a second time. On the hippocampal-dependent learning and memory test, the rats that became obese from the high-energy diet performed much worse compared to those that were not obese. On the other test, both groups of rats performed equally.

All of the rats' blood-brain barriers (a tight network of blood vessels keeping the brain safe) were analyzed.

The team administered a dye to all the subjects that does not freely cross the blood-brain barrier into the hippocampus. They discovered that the obese rats' blood-brain barriers had been impaired after permitting a significantly greater amount of the dye than the non-obese rats permitted.

Surprisingly, the non-obese rats group consisted of rats from both groups. However, the researchers believe this is not due to certain ones having a fast metabolism.

"The rats without blood-brain barrier and memory impairment also ate less of the high-energy diet than did our impaired rats," Davidson explained. "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."

Obesity Might be Linked with Cognitive Decline

Since memories are suppressed by the hippocampus, assuming that these findings can be applied to humans, it could be because the hippocampus's ability to suppress unwanted thoughts (about high-calorie foods) is affected by diet high in saturated fat and sugar.

This would increase obese people's chances of consuming fatty foods, not allowing them to control themselves to stop eating.

"What I think is happening is a vicious cycle of obesity and cognitive decline," Davidson revealed. "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."

These results coincide with previous research that had found a link between human obesity in middle age and a higher chance of developing Alzheimer's disease and other cognitive dementias.

Davidson explained:

"We are trying to figure out that link. We have compelling evidence that overconsumption of a high fat diet damages or alters the blood-brain barrier. Now we are interested in the fact that substances that are not supposed to get to the brain are getting to it because of this breakdown. You start throwing things into the brain that don't belong there, and it makes sense that brain function would be affected."

Winning the Battle of the Bulge IS Possible

Many obese individuals believe that losing weight and becoming healthy is close to impossible. Although it may require a ton of hard work or even surgery, there is evidence showing it is possible to win the battle of the bulge.

The popular reality show "The Biggest Loser", in which fitness trainers and health professionals work together to help overweight people drastically change their bodies and health, has had great success in helping people lose excessive amounts of weight.

Some overweight celebrities have shown it is possible by undergoing gastric bypass surgery. For example, Randy Jackson from "American Idol" underwent the surgery and lots 114 lbs, and Roseane Barr, actress on the television show "Roseanne", underwent the surgery and lost almost 200 lbs.

However, in order for these people to keep the weight off, they need to change their lifestyle into a permanent, healthy one. The struggle becomes a lifelong battle, which Davidson believes is the result from permanent changes in the brain.

Davidson concluded:

"I do think it [the damage] becomes permanent, but I don't know at what point it becomes permanent. Other research has found that obese people and formerly obese people have weaker hippocampal activity when consuming food than do people who have never been obese. Just because you lose the weight doesn't mean you regain the brain function. This could help explain why it is so difficult for formerly obese people to keep the weight off."

Written by Sarah Glynn