A syndrome called “sugar coma” has achieved the status of urban myth. The phrase describes the cognitive price people supposedly pay if they eat too much sugar in a short period of time. The cause can be any sugary blowout from cakes to soft drinks.

I’m told that some people report a slowdown or loss of brain function, but whether these anecdotes amount to a new medical syndrome is not known.

So researchers from New Zealand decided to find out.

Four Types of Sweetener Tested

For their study, the team of psychologists and food scientists from the University of Otago, recruited 49 adults.

They were given a drink containing one of three different types of sugar: glucose, fructose (fruit sugar) or sucrose (table sugar), which is a combination of glucose and fructose. The artificial sweetener, sucralose, was used as a control.

The study was not only double-blind and placebo-controlled, but “crossed-over” (a phrase new to me). The participants were switched from one type of sugary drink to another in the course of the 16-week trial period. In addition, some of the volunteers were asked to fast for ten hours before the test.

Twenty minutes after their refreshment they were given three cognitive tests designed to work the prefrontal lobe, a part of the brain involved with attention, planning, information processing and problem solving. Besides measuring mental abilty the scientists also assayed blood glucose levels.

Glucose Reduces Attention and Response Time

The researchers found that consuming glucose or sucrose led to significantly worse performance on the tests compared to fructose or sucralose.

Participants were slower by an average of 0.2 seconds in coming up with answers to questions. This may not sound much, but it is a high percentage of the overall response time. The effect was even stronger in those who fasted because the increase in blood glucose was more marked.

The study authors concluded, “Overall, these results indicate that cognitive effects of sugar are unlikely to be mediated by the perception of sweetness. Rather, the effects are mediated by glucose.”

Lead researcher and food scientist Dr. Mei Peng commented, “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.

“While the sample size is relatively small, the effect we observe is substantial.”

Glucose and Fructose are Different

Even though glucose and fructose are both simple sugars and are absorbed via the small intestine into the bloodstream, the brain prefers to meet its high need for energy with glucose. In fact, when doctors talk about “blood sugar” it’s generally glucose they’re talking about.

Glucose and fructose are metabolized by different pathways. While glucose is transported by a protein directly to the brain, fructose is taken up by the liver. If it’s needed for energy it will be converted to glucose, otherwise it will be turned into fat.

This explains the failure of fructose to have a negative short-term impact on the brain. And that’s all this study was looking at – whether the four substances in the test strike a quick blow at cognitive ability.

Another thing to note is that it really doesn’t matter much if foods “contain” glucose because the body quickly converts most low-fiber carbs (starches) into glucose anyway. That’s why we’re often advised to avoid high-glycemic carbs – “white foods” like rice, potatoes, flour and, of course, sugar itself.

These foods aren’t much better than eating sugar right out of the sugar bowl (which I have to confess I used to do as a child.)

So is Fructose “Safer” than Cane Sugar?

Don’t take this study as a green light to consume fructose. As I said, it’s narrowly focused on one narrow issue.

Small amounts of fructose in nutrient-rich, fiber-rich fruit is consumed slowly, absorbed steadily, and causes less harm than the pure fructose molecule that’s not embedded in food. When you eat whole fruit, you’re taking in a lot besides the sugar, and this modulates your absorption of the sugar.

But when pure sucrose (cane sugar) or high-fructose corn syrup is used as an added sugar in processed foods, it’s a big driver of diabetes, cardiovascular disease and obesity.

A team of researchers at UCLA found that fructose alters several brain genes. These set off a cascade of events that damage hundreds of other genes. The sequence of events can lead to Alzheimer’s and a wide range of other diseases.

So the message is clear. To preserve brain and body function, stay away from foods containing added sugars of any kind.

  1. http://www.psypost.org/2018/01/study-suggests-sugar-coma-real-glucose-ingestion-leads-worse-cognitive-performance-50514
  2. http://www.sciencedirect.com/science/article/pii/S0031938417304328
  3. http://newsroom.ucla.edu/releases/fructose-alters-hundreds-of-brain-genes-which-can-lead-to-a-wide-range-of-diseases