Eating a high-carb breakfast, which includes bread, cheese and milk, may help you make good decisions throughout the day, say scientists who found that people who consume a lean meal in the morning tend to accept unfair financial offers.

Researchers said that people's decision-making was often influenced by the amount of carbohydrates and protein contained in their breakfast.

The study participants were more likely to reject an unfair financial offer if they had filled up on carbs that morning. However, if they had eaten a lower-carb, higher-protein breakfast, they were more apt to accept such offers.

According to Soyoung Park from the University of Luebeck, in Germany, after a high-carb breakfast people tended to have lower levels of an amino acid called tyrosine.

Tyrosine is important in producing brain chemicals like dopamine - which is part of the brain's "reward system." Changes in tyrosine correlated with changes in people's decision-making, Park said.

In the first, Park's team had 87 college students play an online version of the Ultimatum Game. The game gives players the opportunity to either accept or reject a clearly unfair financial offer from an opponent. The catch is, if the offer is rejected, no one gets any money. So when a player makes that choice, it's seen as a form of "social punishment" for the opponent.

After playing the game, the students told the researchers what they had eaten that morning. It turned out that 53 per cent of people who had eaten a high-carb breakfast rejected unfair offers, compared with only a quarter of students who had eaten a lower-carb breakfast.

The second phase included 24 men who came to the lab for a controlled breakfast before playing the Ultimatum Game. They also had blood samples drawn over several hours.

On one day, the breakfast was 80 per cent carbs, 10 per cent protein: Bread with jam and cream cheese; milk and apple juice; and an apple and banana.

On another day, the breakfast was 50 per cent carbs and 25 per cent protein: There was bread and jam again, but also ham, yogurt, milk and a bigger slab of cream cheese.

The results were similar. The men were more likely to reject unfair offers after the high-carb breakfast.

The test included only men, Park said, because there are gender differences in metabolism that might have interfered with the results.

Even in the all-male group, people varied in their responses. Some still accepted unfair offers after having a high-carb breakfast, for instance. It would be interesting to figure out why some people were influenced by the breakfast switch, and others were not, Giliberto sai.