Brain Changes in the Obese May Make it Harder to Lose WeightBeth Fontenot, MS, RD, LDN
October 11, 2012
Eating high fat junk food does more than widen your waistline. It can produce changes to your brain in the very areas that you need to call upon in order to resist eating, which may be the reason why it is so difficult for severely overweight people to lose weight and keep it off. It may also fuel further overconsumption.
A group of rats were fed a restricted amounts of low-fat feed and trained on two problems—one that tested the rats’ hippocampal-dependent learning and memory abilities and one that did not. The researchers focused on the hippocampus because one of its functions is to help consolidate new memories so they can enter long-term memory
Once the rats were trained on the two tasks, they were divided into two groups. One group was given unlimited access to low-fat feed, and the other had unlimited access to feed that was high in calories and saturated fat, the unhealthiest type of fat. Not surprisingly, most of the rats allowed unrestricted access to the high-calorie feed became obese.
When the two groups of rats were given the hippocampal-dependent learning and memory test again, those that had become obese performed much worse on than the non-obese rats did and worse than they had before being given a high-fat diet.
As they looked into why the rats' memories appeared to decline, the researchers discovered that the obese rats’ blood-brain barriers had been damaged. Injected dye was unable to easily enter the low-fat rats' brains, while the brains of the obese rats allowed a larger amount of the dye to enter into the hippocampus.
Because the hippocampus is also responsible for suppressing memories, 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. The obese rats had lost a crucial gatekeeper.
Should these findings apply to humans, it could mean that a high saturated fat diet reduces the brain's ability to suppress a desire for high-calorie food, making it more likely that a person who is obese will be less able to restrict their caloric intake. Terry Davidson, lead author and director of American University’s Center for Behavioral Neuroscience said he believes that at some point the damage becomes permanent which could help explain why it is hard for some people to lose weight and keep it off.
"What I think is happening is a vicious cycle of obesity and cognitive decline," said Davidson in a press release. "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 line up with those of other studies which found a link between human obesity in middle age and an increased likelihood of developing Alzheimer’s disease and other cognitive dementias later in life.
Not all the high-fat rats became obese, and those who were able to resist over-indulging in the high calorie diet also did not show breakdowns in the blood-brain barrier. "Our results suggest that whatever allows them to eat less and keep the pounds off also helps to keep their brains cognitively healthy," Davidson said. "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."
The study was published in the journal, Physiology and Behavior.