It seems like an easy fix for weight loss: eat better, exercise, and the pounds will just come off. But as obesity becomes a greater and greater problem for the United States and countries worldwide, the solution for weight loss is not so simple. And, while it is possible for obese and overweight people to win the battle of the bulge (as evidenced by NBC's weight-loss program "The Biggest Loser" and countless celebrities' gastric bypass surgery), successful weight loss tends to occur with lifestyle changes.

According to a new study, the reason for failed weight-loss attempts may lie in the fact that unhealthy diets may physically change the brain in order to make weight loss more difficult. The study was conducted by Terry Davidson, now the Director of American University's Center for Behavioral Neuroscience, and colleagues at Purdue University in Indiana.

The research indicates that diets high in saturated fat and refined sugar, which can leave consumers prone to obesity, re-wires the brain to fuel overconsumption of such foods and to make weight loss close to impossible. The research focused on the hippocampus, which is the part of the brain responsible for memory and learning. The researchers trained mice to perform two exercises, one that tested learning and memory that was dependent on the hippocampus and one that tested learning and memory that did not rely on that region of the brain.

During the training process, all of the mice were given a low-fat diet. After training was completed, the mice were divided into two groups. One group had unlimited access to the low-fat foods, while the other had unlimited access to a diet high in fat and calories. A significant amount of mice exposed to the high-energy diet became obese.

Then the mice were tested again on the two exercises. On the hippocampus-dependent task, the obese mice did significantly worse than their non-obese counterparts. On the task that did not rely on the hippocampus, both groups performed the same.

Researchers also examined the blood-brain barrier in the mice. The blood-brain barrier is a membrane that is responsible for controlling what gains access to the brain. They found that the blood-brain barrier of obese mice let items through much more easily than the barriers of the non-obese mice.

While the obese mice all came from the high-energy diet, non-obese mice came from both groups. The researchers found that it was not a high metabolism that kept mice slim even while eating a diet high in fat and calories, but that these mice simply ate less than their non-obese peers. That ability also saved their brains too, allowing them to perform as well on the memory task as their peers who ate a low-energy diet. "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. The researchers' findings may explain why human families, for example, with access to the same foods may have obese and thin members.

The study suggests that people who eat a diet high in saturated fats and refined sugar may have impacted the hippocampus's ability to suppress unwanted thoughts that would cause them to stop at reasonable servings of food. The study also seems to confirm a link that previous research has found between obesity in middle age and cognitive dementia and Alzheimer's disease later in life.

"I do think [the damage] becomes permanent, but I don't know at what point it becomes permanent," Davidson said in a statement. "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."

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