2 P52290 Scientific article for use with Question 7 Craving control: how food messes with your mind 1. You’ve just had a hearty lunch, but the doughnuts next to your desk are winking at you. You can’t shake the thought of what the glazed, soft dough would taste like – and know that you won’t be able to get on with your day until you have it. 2. On a basic level our relationship with food is simple – signals between the gut and the brain tell us when we’re hungry, and when we are full. But experience shows us that the drive to eat is much more tangled and irrational. Some of that is down to the reward hit – the feeling of pleasure, mediated by the brain’s reward centre – that we get from eating calorie-dense food like that glistening doughnut. Indeed, the effect of such foods has led some to liken our desire for them to drug addiction. 3. But we now know the gut itself, and also the microbes inside it, manipulate what we crave, painting a much more complex picture of the forces that determine the way we see food. Cravings could even be contagious – literally. When it comes to food, we’re not as in control as we might think. 4. “People think we have much more conscious control over our eating behaviour than we do. There’s a lot going on behind the scenes and it makes it very difficult to exert control on it,” says Tony Goldstone, an endocrinologist at Imperial College London. 5. Even so, knowing about the forces that manipulate the way we think about food opens up new ways to regain control – for instance by retraining the brain or altering our gut flora. Fresh approaches would be more sensible than just expecting people to eat better, says Goldstone: “We don’t just tell asthmatic people to breathe more.” 6. What, when and how much we eat has typically been explained by two systems, one based on hunger and one on reward. The hunger system is mediated by hormones from the gut and from fat cells, which send information to the brain via the gut’s own nervous system about when we last ate and how hungry we should feel. “We can eat very little one day, and a great deal the next, but this system works to ensure that body weight is relatively stable across the years,” says John Menzies, a neurobiologist at the University of Edinburgh, UK. 7. The reward system is more concerned with what type of food we eat. At its heart is the dopamine pathway, which seems to respond most strongly to foods that are high in fat and sugar. This is natural and necessary – it evolved to prompt us to seek out such food, helping us survive. “If we see a high-energy food, it pays to get it while it’s available – a famine may be round the corner,” says Menzies. “However, in our modern environment where food is abundant and cheap, the reward system may work against us, pushing us towards eating sweet and fatty foods even though we already have plentiful energy stores.” 8. The brain even has its own calorie counter that drives our choices without us knowing, according to a recent study. Participants were shown pictures of 50 foods and asked how many calories they thought each contained, and then invited to bid in an auction for a chance to eat the foods. Regardless of their calorie estimations, which were often inaccurate, the individuals were more likely to bid for the foods that were truly the most calorific. MRI scans showed that activity in reward regions of the brain correlated with the true calorific content of foods – the more calories, the greater the reward.