15 June 2017

Could your breakfast cloud your judgment?

People's decision-making may be influenced by the amounts of carbohydrates and protein contained in their breakfast.


Will that be eggs or cereal? Choose carefully; your decision should be based on more than just what you feel like eating.

A new study suggests that people's decision-making is often influenced by the amount of carbohydrates and protein contained in their breakfast.

Breakfast literally means to break the fast after a long night's sleep. Health24 previously reported that breakfast is a crucial meal needed to refuel the body and the brain with nutrients and energy.

Eating breakfast has shown to improve mental alertness and physical performance.

Specifically, the study participants were more likely to reject an unfair financial offer if they'd filled up on carbs that morning. But if they'd eaten a lower-carb, higher-protein breakfast, they were more apt to take the money instead of having nothing.

High levels of tyrosine

The study did point to a potential explanation, according to researcher Soyoung Park, of the University of Luebeck, in Germany.

After the high-carb breakfast, she explained, 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".

And changes in tyrosine correlated with changes in people's decision-making, Park said.

"I doubt we can draw any conclusion on how to best manage our social interactions with food," said Dr Luca Giliberto, a neurologist at Northwell Health Neuroscience Institute, in Manhasset, New York.

Brain's 'reward system'

A lower-carb/protein-rich meal might allow for higher levels of tyrosine – possibly "reinforcing the (brain's) reward pathway", Giliberto noted.

That, in turn, might make a person more accepting of an "unfair decision", he added.

But the study leaves open many questions, Giliberto said: For one, it's not clear what people's usual diets were – which would influence their short-term response to a high- or lower-carb meal.

Simon Young is professor emeritus of psychiatry at McGill University in Montreal. He has studied the effects of diet on the brain and behaviour, and he also said the new findings have to be taken with a grain of salt.

Young pointed to a number of limitations: The study tested only a small group of men; it used one lab-based measure of behaviour – known as the "Ultimatum Game"; and the meals were not as tightly controlled as they could be.

The two breakfasts, Young noted, also differed in fat. "So are we looking at an effect of carbohydrates, fat or protein?" he said. Young also said the behaviour changes can't be definitely pinned on tyrosine.


"This is an interesting study, but it's very preliminary," Young said. "There need to be larger, better-designed studies, with a broader range of measures."

The study was published in Proceedings of the National Academy of Sciences.

A well-balanced diet

To Park, the message is that the foods we eat may affect not only our physical health, but our "social decisions" as well. She sounded a cautionary note about diets that shun any nutrient, like low-carb diets.

"I think it's really important to have a well-balanced diet, and not get stuck on any one nutrient," Park said.

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