Does Sugar Impact Brain Function?

A new study looked at how sugar impacts cognitive performance and found that glucose may reduce attention span and slow down our reaction times.

The small University of Otago study, published in the journal Physiology & Behavior, looked at 49 participants to see how three types of sugar affect cognitive function. Participants ingested glucose, fructose and sucrose. They used the artificial sweetener, sucralose, as a placebo. The researchers then looked at how each sugar impacted participant response time, performance on simple arithmetic and their ability to focus.

Not all sugars behaved the same in these tests. Participants who had glucose and sucrose seemed to perform worse than the fructose or placebo groups. 

They suspect that glucose is the culprit behind the poorer performance, because our bodies break sucrose down into glucose and fructose. That means both glucose-containing sugars were the ones that impacted brain function. Fructose doesn’t cross the blood-brain barrier, which may be why it didn’t have the same effect.

The researchers also kept an eye on blood sugar levels during the study and found that higher blood sugar levels, especially when participants had been fasting overnight, also harmed their performance on these tests.

In an interview with PsyPost, study author Mei Peng said, “Our study suggests that the ‘sugar coma’ – with regards to glucose – is indeed a real phenomenon, where levels of attention seem to decline after consumption of glucose-containing sugar.”

This isn’t the first study on how sugar impacts our brains. Our brains need glucose to function properly, but like this study, earlier research has shown that too much sugar – even glucose – can cause issues. A Harvard Medical School article on sugar and brain health points to a 2009 animal study which found that too much glucose harmed memory and cognitive function.

The University of Otago study looked at how ingesting refined sugar impacted brain function, but eating sugar isn’t the only way we feed glucose to our brains. When our bodies break down carbohydrates, glucose is one of the resulting compounds. A 2009 Live Science article explains that complex carbohydrates are the best glucose source for brain health.

That’s because our bodies break down complex carbs – like whole grains – slowly. Instead of a rush of glucose that spikes (then crashes) blood sugar levels and harms cognitive function, you get a “slow and steady” release that’s just what our brains need to thrive.