In the study, entitled Obesity is associated with hypothalamic injury in rodents and humans
, the researchers, lead by Dr. Michael Schwartz of the Diabetes and Obesity
Center of Excellence, University of Washington School of Medicine, used a collection of rats and mice who were genetically bred to be obese. Initially fed a regular low-fat die, the rodents were taken off that diet and placed upon a high-fat diet.
High fat diet injures rodents hypothalamus
Within 24 hours of their diet switch researchers found the rodents began to show inflammation in a part of their forebrain known as the hypothalamus. In humans as in rodents, the hypothalamus regulates the fat and energy our body burns and takes signals from fat tissue and relays them to the brain;
these signals tell the brain either we've had enough food or not had enough food.
Dr. Schwartz, quoted by Sharon Kirkey of Postmedia News
, said brain scans showed there was "direct evidence of neuron injury" and that after months on the diet there was "a loss of neurons in this hypothalamic area that's vital for body weight control." The researchers concluded that the onset of inflammation means switching to a high-fat diet is in fact "injuring the neurons that are supposed to protect them from obesity."
Obese humans: increased brain scarring
The next step for researchers was to compare brain scans of 34 humans and they found obese people had more scarring in the hypothalamus, scarring called gliosis, than did the brains of the subjects who were of normal weight. The amount of gliosis increased the larger the obese person was. "We don't know this is a cause of obesity, or a consequence of obesity," Schwartz said. "(But) it suggests that what we've seen in the mouse and rats is also occurring in the human."
This scarring is significant to weight, Dr. Schwartz said, because the scarring of the brain alters how both insulin and a hormone called leptin function in such a way that the brain gets the wrong idea about the amount of fat and energy the body has stored. Losing weight then becomes problematic because the brain is coming to conclusions about fat and energy that are misleading.
``This may help to explain why it's so hard for obese people - they can lose weight but they can't keep it off because their hypothalamus is reading them as basically weighing the right amount.''