A slice of spectacular, possibly sugar coma-inducing cake.
A slice of spectacular, possibly sugar coma-inducing cake. Toa Heftiba / Public Domain

If you can’t resist a slice of cake or a freshly-baked cookie, then you’ve likely experienced the dreaded sugar coma phenomenon. The sluggish hangover that sometimes follows the buzz of eating sweets has been the subject of much scientific debate. Yet a new study published in Physiology & Behavior by researchers at New Zealand’s University of Otago suggests that sugar comas impair cognitive functions such as response time and attention span.

As the study’s authors note, the impact that the dietary sugars fructose (fruit sugar) and sucrose (the table sugar added to, say, coffee) have on cognitive functions receives less research and attention than glucose (the sugar your body makes from carbs). By testing out all three dietary sugars on their 49 subjects, as well as an artificial sweetener as a placebo, researchers found that both sucrose and glucose had “relatively negative effects” on their ability to complete cognitive tests such as arithmetic problems.

The reason fructose fared differently is likely because your body treats it differently. It’s metabolized in the liver and doesn’t cross the blood-brain barrier. Hence why those who had fructose performed better in cognitive tests.

Fructose, in the form of a banana.
Fructose, in the form of a banana. Mike Dorner / Public Domain

So what do these new findings mean for sugar comas? “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,” Mei Peng, one of the study’s authors, told PsyPost.

Yet in the past, studies mapping glucose’s effect on cognition, especially memory, had wildly contradictory results. A 1994 study noted that subjects who performed one of these same cognitive tests called the Stroop Task—which shows that it’s challenging to name the color of a word, such as blue, if it’s written in green ink —saw an improvement in both memory and attention if the rates of their blood glucose increased right before the test. The same experiment found that people’s ability to remember words from a list got better if they guzzled a glucose-heavy drink.

But tell that to researchers from Boston University’s School of Medicine, who wrote last year about the link between sugary drinks and preclinical Alzheimer’s Disease, which, of course, affects memory. Consuming more fructose doesn’t seem to be the answer to our sugar woes, either. A 2012 UCLA study suggested that consuming tons of fructose in the long term “alters your brain’s ability to learn and remember information.”

Still, one thing everyone can agree on, particularly in the United States, is that sugar exists in places you don’t expect. Both sucrose and high-fructose corn syrup are added to scores of food and drinks that range from ketchup to coffee creamer. The fact that people unknowingly consume huge amounts of various sugars suggests something even more pernicious: We may unwittingly experience mini-sugar comas all the time.

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