Overloaded: How Every Aspect of Your Life is Influenced by Your Brain Chemicals

by Ginny Smith

There is currently only one really effective treatment for obesity: bariatric (or weight loss) surgery. This can take a number of forms, but all aim to reduce the capacity of the stomach, so people feel full more quickly. This can be done by placing a silicone band around the stomach to squeeze it closed at the top (gastric band); putting a balloon inside to take up space; or cutting away part of the stomach (gastric bypass or gastric sleeve). After surgery, patients will feel full when eating very small amounts of food, restricting their intake and causing weight loss. But this isn’t the full story. People and rats who have had the surgery could just eat more often to overcome their smaller stomach – but they don’t. This seems to be because rearranging the digestive tracts changes the release of hormones. After surgery, there is an increase in satiating chemicals like peptide YY, which activate the ‘don’t eat’ network in the hypothalamus, and a decrease in the hunger hormone ghrelin. These changes work together to help people feel full and therefore eat less. Studies have also found that gastric bypass increases the calories burned by rats, meaning they need 40 per cent more food than control animals to maintain the same body weight. We don’t yet understand how this happens, but again, it might be linked to those neurons in the hypothalamus. The surgery seems to reset the set point of the animal, so its body then does everything it can to reach and maintain its new, lower...