Study Finds Fructose Causes High-Calorie Cravings

Previous evidence has shown that all sugars are not created equal, but we haven't understood why that is. That changed last week, with the publication of a new study looking at how our brains respond to fructose and glucose, specifically in terms of appetite.

In short: Fructose causes our brains to crave high-calorie foods.

The study went as follows: 24 participants (a small sample size indeed!) ingested a beverage with fructose, and were shown images of foods while their brains were scanned. The same participants were later brought back, given a beverage with glucose, and their brains were once again scanned. The results:

What does it mean? I spoke to one of the study's authors, Kathleen A. Page.

Why were you interested in studying our brains' response to sugar?

Kathleen Page: We were interested in looking at a place in the brain called the hypothalamus that regulates our hunger, and we wanted to see how that area responded to fructose and glucose. What we found previously was that when people consume fructose, that area of the brain did not respond and people still felt hungry. But when people consumed the glucose, the activity in that region was suppressed and people reported feeling full. In this particular study, we wanted to see if there were differences between the way brain areas that regulate reward and attention and motivation for food were activated, and we also wanted to look at how people's behaviors might change as a result of drinking fructose rather than glucose.

The study used photos of food rather than actual food. Is this a normal practice?

Page: It's a pretty common paradigm that people use in neuroimaging. We expose them to food cues, in this case, to images of food, and see how their brains respond as compared to non-food images which we use as a control. What we say is that if the brain areas that control reward are responding more to the food than non-food images, they're maybe paying more attention to the food, and they have more anticipatory reward responses to the food cues. Then, to really understand how it affects behavior, we look at their behavioral past which accompanies the neuroimaging part of the study.

Are there any theories as to why our brains work this way?

Page: We've been interested in sugars for quite some time, and what we know from a number of studies is that your body processes fructose and glucose differently. So, when you consume straight glucose, the body's response is to produce hormones like insulin, and those hormones provide signals to the brain that you're full and that you've eaten. In contrast, fructose does not stimulate insulin. Also, most of the fructose in our bodies is actually extracted from the bloodstream and taken to the liver, where it's metabolized. Very little fructose circulates in our blood or reaches the brain. So, we had reasons to believe there may be differences in the signaling from the body to the brain when people consume fructose or glucose.

Is the takeaway of the study, then, to stay away from fructose?

Page: We wanted to test one variable at a time, so we wanted to study fructose and glucose separately. It's good to keep in mind that glucose and fructose are almost always together in the foods that we eat. We don't know yet how the brain is going to respond to sucrose, which is table sugar, which contains equal components sucrose and fructose. What we can say right now is that the fructose component of added sugar could be more appetite stimulating than the glucose component. Other groups have shown that the fructose component of added sugars can be processed in the liver and be made into fats. We think this adds to evidence that suggests the fructose component of added sugar are particularly damaging to our metabolic health.