Most of us are well familiar with the feeling of having just eaten a filling meal, but still wanting to taste something sweet.

The workings of this phenomenon have now been illuminated by an international research team led by the Max Planck Institute for Metabolic Research in Cologne, Germany.

According to their findings, it's the same nerve cells in our brain that give us a feeling of being full after a meal that also make us crave sweet things.

In the study, the researchers led by Henning Fenselau examined the response of mice to sugar, finding that mice help themselves even when they are completely full.

Brain scans showed that a specific group of nerve cells is responsible for this, as the team writes in the journal Science. These so-called POMC neurons become active as soon as the body has absorbed food.

When mice are full and eat sweets, these nerve cells not only release messenger substances that signal satiety, but also an opiate produced naturally in the body, beta-endorphins.

According to the study, this triggers a feeling of reward that causes the animals to eat even more sugar. The mechanism was triggered in the experiments when the animals only perceived sugar without eating it.

Brain scans on test subjects showed that the same brain region reacts to sugar in humans. As in mice, many opiate receptors are located in the vicinity of satiety neurons.

"From an evolutionary point of view, this makes sense: sugar is rare in nature, but it provides quick energy," study leader Fenselau says. The brain is programmed to stimulate an intake of sugar when it becomes available, he says.

The results could be significant for the treatment of obesity. Although there are already drugs that block opiate receptors in the brain, the weight loss achieved with these is less than with injections for weight loss.

Fenselau says a combination of different therapies might be useful, but cautions: "We still need to investigate this further."