Eggs and avocado on toast
A high-protein breakfast might make you more accepting of others. Katherine Lim / Flickr

Having a high-protein breakfast might put you in a better mood for the morning, a new study finds.

We all know that a good breakfast sets you up for the day. But exactly what you eat for breakfast could put you in a better or worse mood, finds a study published in the journal PNAS.

The study of 111 people found that eating lots of protein made them more likely to accept an unfair offer they took part in a couple of hours later. They were given either a rather large high-protein or an equally large high-carb breakfast. They had to eat it all, and once they had digested they took part in the 'Ultimatum Game'.

This game is a favourite tool of psychologists. In it, one person – in this case the experimenter – offers the other to split a sum of cash, for example, "£5 for me and £5 for you". If the second person – the study participant – accepts the offer, they split the cash. If they reject the offer, no one gets any money.

On a high-protein breakfast, people were more likely to accept what they saw as an unfair bid, say £2 for them while their partner keeps £8. On a high-carb breakfast, they weren't having any of it, and were much more likely to say no.

"When they reject the £2, no one gets any money. So they're punishing the other person, and rejecting their own money. After all, £2 is better than nothing," study author Soyoung Park of the University of Lübeck, Germany, told IBTimes UK.

"It had a striking effect and it also strengthens the idea of the importance of a balanced diet."

While the study was only of breakfast, having a high-protein or high-carb lunch or dinner could have similar effects, Park said.

"We had to do this with the breakfast because there's a greater chance that people have not eaten anything before," she said. "I can imagine it also works after lunch and dinner but then was not possible to control for what they have eaten before."

The findings have implications for school meals as well as for adults' awareness of the importance of a healthy diet.

"Our kids in kindergarten or at school might receive a meal that may not be balanced.

"What this study is showing is that a simple meal that we all eat normally has such a big influence on our behaviour. If you imagine that we eat three times a day – it is actually a very large intervention in our lives."