Obesity Fuels Overeating
October 2, 2012

Obesity May Impair Brain And Fuel Overeating

Lee Rannals for redOrbit.com — Your Universe Online

Diets that lead to obesity may actually cause changes to the brains of obese people, making weight loss more challenging, creating a vicious cycle, according to new research published in the journal Physiology & Behavior.

Researchers found that diets high in saturated fat and refined sugar make changes to the brain that fuels over-consumption of those same foods.

During their study, the team trained rats given restricted access to low-fat "lab chow," and tested the rats' hippocampal-dependent learning and memory abilities.

Once the training phase was completed, they split the rats into two groups: one group with unlimited access to low-fat lab chow, while the other had unlimited access to high-energy food.

The high-energy food was high in saturated fat and is considered to be the most unhealthful dietary fat.

They found that those rats that became obese from the high-energy diet performed much more poorly than those non-obese rats did on the hippocampal-dependent learning and memory test.

When the researchers 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 blood-brain barriers of the non-obese rats.

The non-obese rat group included rats from both the low-fat lab chow group and the high-energy diet group.

"The rats without blood-brain barrier and memory impairment also ate less of the high-energy diet than did our impaired rats," Terry Davidson, director of American University's Center for Behavioral Neuroscience, said in a statement. "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."

If the findings apply to people, it could mean 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 food. This could inevitably make 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.

"What I think is happening is a vicious cycle of obesity and cognitive decline," Davidson said in the statement. "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."

The findings are compatible with other studies that found a link between human obesity in middle age people, and an increased likelihood of developing Alzheimer's disease and other cognitive dementias later in life.

"We are trying to figure out that link," Davidson said in the statement. "We have compelling evidence that over-consumption 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."