3 P52290 Turn over 9. Although these hunger and reward systems sound very different, there’s a growing awareness of how interconnected they are. Some clues come from genetics. A gene called FTO is strongly linked to weight gain, and one variant of it raises a person’s risk of becoming obese by 70 per cent. A recent study showed that such people have higher than normal levels of the hormone ghrelin, which is released by the gut, telling them they are still hungry after eating, but their reward system works differently too. MRI studies showed that this group’s brains responded differently when they were shown pictures of food: the most pronounced differences being in the reward regions. The reward pathways in the brains of obese people have also been shown to respond less strongly to food – which could be driving them to seek out even more each time. 10. More evidence of the link comes from people who have had gastric bypass surgery – which reduces the capacity of the stomach and makes food pass more quickly into the small intestine. After surgery, not only do people want to eat less, they experience a profound change in what they want to eat, finding they are drawn to much less calorie-dense foods. And brain scans of people before and after gastric bypass surgery showed altered activity in their reward centres. That contrasts with people who have a gastric band inserted. One explanation for these effects is that after a gastric bypass, food reaches the bowel much more quickly, so there’s a faster hormone response, whereas a gastric band has no effect on hormone levels. 11. “These hormones are normally released after a meal to make us feel full, but as we’re discovering, they also have effects on the way the brain works, to regulate the hedonic responses, the pleasure from food,” says Goldstone. “The bypass patient will say, ‘I’m not hungry, and I also don’t want or like the food’. The band patient will say: ‘I’m not hungry, but I could murder the chocolate cake’. ” 12. What if you could recreate these effects without the surgery? Susan Roberts, at Tufts University in Medford, Massachusetts, has designed a diet in which foods look like the kinds of calorie-dense treats people have learned to crave, but with a twist. “We basically confused people’s reward system by giving them foods that had the flavour and appearance of high-calorie foods that are easily digested, but in fact they were lower calorie, slowly digested versions,” she says. For instance, her diet includes a lower-calorie, slowly digested pizza, made with added fibre. 13. In a small trial, she scanned the brains of a group of overweight people before and after putting them on a six-month diet based on these foods. At the end of the study, the scans showed an increase in activity of reward pathways when the participants looked at pictures of healthy, low- calorie foods, compared with a group not eating the diet. Risky rewards 14. “We were effectively retraining their brains,” says Roberts. “You can think of pizza and you start craving pizza because you anticipate that rush of calories. If you eat the food and you fail to get the rush of calories, over time the reward circuitry adapts so it’s no longer expecting a great zoom of carbohydrate coming in,” she says. 15. The added fibre helped recondition cravings by making people feel full, but Roberts says it’s also important that the participants only ate when they were truly hungry, to strengthen the reward they got from the food. And if dieters cheat and tuck into old favourites, it would strengthen the old reward pathways. Roberts is now beginning two larger clinical trials, and has commercialised the diet plan.