Fructose May Make Us Crave High-Calorie Foods. But There’s A Bigger Issue.
Fructose has, in recent years, become almost another f-word to avoid using, as it’s been implicated in certain health concerns, from metabolic problems to impaired cognitive function. Now, a new study in Proceedings of the National Academy of Sciences finds that fructose may “make” the brain find high-calorie foods more appealing. In fact, so seductive are high-calorie foods after a person drinks a serving of fructose-infused water, apparently, that he or she will even give up monetary rewards in favor of the prospect of unhealthy foods. Many of the previous fructose-and-the-brain studies have been done in rodents, so it’s noteworthy, if slightly disconcerting, to know that humans, too, seem to respond differently to fructose. This doesn’t mean we should avoid fructose completely – perhaps just to look out where it comes from – and some experts don’t think the issue is worth making much of anyway.
The team from the University of Southern California had people drink 10-oz servings of cherry-flavored water into which was dissolved 75 grams of either fructose or glucose. The researchers also asked them to rate how appealing they found pictures of different foods or other items, before and after the sugar treatment. They also measured insulin levels, as well as leptin and ghrelin, the hormones responsible for hunger and satiety. Finally, the team scanned the participants’ brains to see which areas were more or less active during all this.
It turned out that fructose produced a lower rise in insulin than did glucose – and it promoted different areas of the brain to “light up” in response to the high-calorie food pictures. The orbitofrontal cortex was more active in the fructose group, which the authors say is significant since it’s implicated in reward processing, as was the visual cortex when the participants viewed pictures of food. The hunger and satiety hormones weren’t any different between the two groups. But what was different was the fact that people who’d consumed fructose were much more likely to reject a future monetary reward in favor of a present offering food than were the glucose drinkers.
Since insulin influences not only how the body responds to sugar, but also how the brain responds, the results might be important: They suggest that if fructose doesn’t trigger a robust enough insulin response, the brain may not “realize” it’s been fed, so continues seeking food.
“Glucose is the main sugar circulating in our bloodstream,” says study author Kathleen A. Page, “and it’s the sugar used to fuel all of the cells in our body, including our brain. Fructose, on the other hand, is mainly processed in the liver, and very little fructose actually reaches the brain. In addition, fructose fails to stimulate hormones, like insulin, that let the brain know that you’re full.”
The moral of the story may not be to avoid fructose at all costs. It may just be to get it from the appropriate sources. A 10-oz glass of cherry-flavored sugar-water is very different from eating an apple or even a bunch of grapes – but it’s not so different from drinking a glass of fruit juice, sports drink, or soda. Soda in particular has no redeeming qualities like vitamins or minerals. And at least as important, any kind of sugary liquid doesn’t have the solid components of food, like fiber, that slows sugar absorption. So the sugar in fruit juice and soda is processed by the body at breakneck speed, leading to a quick spike (and subsequent drop) in blood sugar, rather than a slow, steady rise associated with eating actual fruit.
But much of this we already know. “I think this is relatively unimportant, since most of the sugar in the food supply is a combination of fructose and glucose,” says David L. Katz, of the Yale University Prevention Research Center. “This may indicate that the use of pure glucose as a sweetener has advantages, but that practice is rare. Sucrose, or table sugar, is a mix of glucose and fructose; and so is high-fructose corn syrup, albeit a different mix. Sweeteners in general stimulate appetite. This has long been known, and is exploited by the food industry.” Katz also points to Michael Moss’ piece in the Times a couple years back, which outlines the new science of designing the most addictive food possible. There may be little incentive for food makers not to use fructose, or any sugar for that matter, since it keeps us coming back for more.
So the real moral might be just to eat more natural foods, and worry less about what kind of added sugar is in our foods and drink – we shouldn’t be eating these anway. In other words, if we’re really eating healthy, that question should be moot. “Eat more food direct from nature,” says Katz, “less sweetened food, and avoid soda altogether – and that strategy will far outweigh the differential health effects of different kinds of sugar.”
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Source: Forbes
