Why we can't help finishing off the whole can of Pringles Ever wondered why that single square of chocolate after dinner is never enough? Why it's impossible not to consume the whole damn slab, even to the point of nausea? Scientists no longer blame the tendency to binge on high-fat, high-sugar foods on sheer greed or lack of self-control. Rather, the urge to finish off the Pringles is now thought to be due to hedonic hunger - a powerful physiological response over which we have little control. ""People shouldn't feel guilty for not being able to resist certain foods,"" says Zoe Griffiths, a dietitian and head of public health at Weight Watchers UK. ""It's not a question of not being strong enough."" Experts believe there are two drivers behind what and how much we eat. The first, the homeostatic system, regulates appetite according to the body's need for energy. Homeostasis is controlled by communication between the brain and the digestive system: hence when we are in an energy deficit we get signals such as shakiness (caused by low blood-sugar levels), stomach rumbles and hunger pangs. But the second driver, hedonic hunger, can override the former. It is defined as a physiological response, involving the brain's ""reward centres"" to smelling, seeing and thinking about certain foods. The result is that we eat not according to energy needs, but purely for pleasure. Richard Lowe, professor of psychology at Drexel University in Philadelphia, says neuroimaging studies have shown that in the presence of high-fat, high-sugar or high salt food, areas of the brain related to pleasure ""light up"," in a similar way to the brain changes seen in drug or alcohol addicts. The release of dopamine, a chemical strongly associated with the brain's reward system, is also involved. Ghrelin is a hormone normally produced by the stomach when the body needs energy, to stimulate feelings of hunger; but scientists have found it is also released in the presence of high-fat, high-sugar foods - even when the body does not need calories.The latest studies, from Oregon Research Institute, indicate that with time, dopamine release in the presence of such foods gets stronger, but starts to decline when we actually consume them. In other words, we need more of these foods to get our ""hit"." The hedonic system is thought to have evolved from the time when humans were hunters and foragers and did not always know where the next meal was coming from. Primitive man developed the need to override homeostasis and to eat more than the body required. But today, experts believe hedonic hunger has become a liability, responsible for mounting levels of obesity. In response, Weight Watchers UK has changed its strategy to put more emphasis on how we can control our ""personal food environment"." That means taking simple steps such as not keeping cakes and biscuits on the desk in the office; or, if you have a long commute, ensuring you have healthy snacks such as fresh fruit available. ""Simply understanding about hedonic hunger seems to help people make better choices,"" says Zoe Griffiths. ""Obesity is a natural reaction to the food environment we live in. When people understand that, they feel empowered to make better food choices."" The Telegraph, London