An experiment by a collaborative team of food scientists and psychologists suggests that the anecdotal "sugar coma" – a temporary loss of higher cognitive function from eating copious amounts of processed sweets – may be grounded in fact.

The findings, published in the journal Physiology & Behavior, could someday be added to the long list of reasons why refined sugar is bad for you.

To assess the impact of sugar on mental performance, researchers from the University of Otago, New Zealand, administered a suite of cognition tests on 49 volunteers, 20 minutes after they ingested one of three types of sugar: glucose, fructose, sucrose, or an artificial sweetener (sucralose) as a control.

Glucose and fructose are single-molecule sugars called monosaccharides, whereas sucrose, also known as table sugar, is a larger molecule composed of both glucose and fructose. The tests included three well-studied tasks known to employ the brain’s prefrontal cortex – the area associated with higher thought and problem solving.

The authors found that individual subjects scored significantly lower on the tests after they ingested a drink containing glucose or sucrose compared with when they received fructose or a placebo. The detrimental effects of these two sugars were heightened if the subject had consumed the beverage after a 10-hour fast.

“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,” study author Mei Peng told PsyPost.

Although fructose and glucose are both absorbed straight into the bloodstream from the small intestine, brain cells primarily use glucose to meet their high-energy demand. The body must break down sucrose into monosaccharides and convert the fructose molecules into glucose, before the fuel can pass through the blood-brain barrier.

Despite the brain's reliance on glucose, some recent data shows that rapid increases in blood levels can lead to cognitive deficits. People with diabetes, who experience a lifetime of unstable sugar levels, are known to have an elevated risk of dementia.

Fructose takes the longest of the three sugars evaluated to reach the brain. In this study, consuming a beverage with fructose led to similar results as those seen after the placebo drink, which contained zero sugar.

Though interesting, these findings are far from conclusive. For example, previous investigations have found that intake of glucose immediately prior to a test actually improved response time and memory in fasting adults. Additionally, the beverages used had differing caloric content, meaning the total energy levels were not standardized.

Future research assessing the short-term effects of different sugars on cognition is required before we know for certain whether a pre-exam diet of candy and soda is truly worth the litany of negative health consequences.