Decisions best made on a full stomach

British researchers say decisions are best made on a full stomach. The scientists say a full stomach minimises hasty decisions and prevents impulsive actions.

They say this is because missing meals lowers levels of the brain chemical serotonin which plays a key role in regulating emotions such as aggression.

Serotonin keeps careless and impulsive behaviour in check and low levels of the brain chemical may mean emotions overrule and bad decisions are made.

The scientists, from Cambridge University, made the association between the chemical serotonin and decision making after examining how a group of men and women reacted to being treated unfairly.

The team manipulated serotonin levels in twenty volunteers who were asked to take part in a game.

The game involved one person offering another a smaller share of some money - if the offer was accepted, both players were paid their share - but if it was rejected, neither player received anything.

The researchers say in normal circumstances a sense of resentment at being treated unfairly provokes players into rejecting up to a third of low offers, even though it means they will get nothing.

It appears that the satisfaction produced by denying the unfair player any cash is reward enough.

However the research team say when serotonin levels were low the number of low offers rejected increased to more than 80 per cent.

Those with lower serotonin levels were far more likely to deprive other players of money, even though they too lost out, as a way to punish the person who made the offer.

Researcher Dr. Molly Crockett says the results suggest that serotonin plays a critical role in social decision making by normally keeping aggressive social responses in check.

Dr. Crockett, says changes in diet and stress cause serotonin levels to fluctuate naturally, and it is important to understand how this might affect daily decision making.

Serotonin is synthesized from the amino acid tryptophan and plays an important role as a neurotransmitter; it helps control anger, aggression, body temperature, mood, sleep, sexuality, appetite and metabolism.

Serotonin is also found in red meat, dairy products, nuts, seeds, bananas, tuna, shellfish and soy products and is often referred to as the 'happy hormone' because of it's effects on mood.

Too little can lead to depression but too much can produce feelings of euphoria akin to being high on drugs such as ecstasy.

Commonly used antidepressants such as Prozac work by maintaining higher levels of serotonin in the brain.

Dr. Crockett says the study is one of the first to show a causal link between serotonin and impulse control.

Crockett says this is a controversial issue but because serotonin levels were directly manipulated they were able to see the effect on behaviour.

This does to some extent help to explain why some people become combative or aggressive when hungry because the essential amino acid needed for the body to create serotonin is only obtained through diet.

The researchers believe the findings could help doctors treat people with depression and anxiety disorders by teaching them ways to regulate emotions during decision making, especially in social situations.

The research is published in the journal Science.