Not all sugar is alike — and our brains know it. (Getty Images)
While some experts may still disagree on whether all calories are created equal, the debate over whether all sugars are created equal is pretty settled: They’re not.
Fructose, for instance, is a simple sugar that is found in fruit, but it’s also frequently added to foods in the form of refined sugar (high-fructose corn syrup, anyone?). Glucose is also a simple sugar, but its primary task is to fuel the body through the breakdown of complex carbs.
Turns out, the brain also seems to acknowledge the differences between these two sugars, according to a new report presented earlier this week at the American College of Neuropsychopharmacology.
Researchers gave 24 young men and women a solution of fructose to drink on one occasion, followed by a solution of glucose to drink on another, while also evaluating their motivation to eat as they looked at pictures of appetizing foods. After scanning their brains using fMRI, the scientists found that loading up on fructose increased the brain’s reward circuits in response to the mere thought of noshing on something like chocolate cake. Glucose did not have this effect. The findings suggest that a fructose binge could spur you to hunger for (and perhaps eat) more.
Adding to the evidence
We’ve known for awhile these sugars affect the body and brain in different capacities. Past studies in mice have shown administering fructose directly into the brain may spur feeding behaviors, whereas glucose doled out the same way promotes satiety. Preliminary studies in humans have also indicated that glucose lowers hypothalamus activity, which generally helps us feel fuller. Fructose does not have this effect.
But while this new study is small, and research on how different simple sugars affect the brain is still in relatively early stages, it may help us further understand why we crave the way we do, sometimes even after eating, says lead author Katie Page, MD, an assistant professor of medicine at the University of Southern California Keck School of Medicine.
“We think the data supports the idea that fructose compared to glucose is less effective at suppressing the brain’s regulation of hunger and motivation for food,” she tells Yahoo Health. “It is striking that fructose and glucose — which have the same number of calories — have different effects on the brain regions that regulate appetite.”
While fructose occurs naturally in fruits, the average American diet is rife with the added form. Glucose can be found in added sugars and fruits as well, but also in the complex carbs our bodies break down slowly. “Fructose and glucose are metabolized differently in the body,” Page explains. “When we consume glucose, it causes the release of hormones that suppress hunger, but fructose doesn’t.”
So eating a slice of cake loaded with fructose doesn’t halt hunger, but rather seems to encourage it. Even the fructose in a piece of fruit might have this effect, according to the study’s theory, though fruit is also packed with filling fiber and high water content. But if you’re feeling super-hungry, a bowl of oatmeal — which supports the slow breakdown of carbs into sugar — may be the better way to go for feeling fully satisfied.
That being said, according to Lisa Moskovitz, RD, CDN, sugars might be metabolized differently, but it all is metabolized in the body at some point. Both forms will affect your blood sugar and drop the same amount of calories into your system. “Whether its fructose, sucrose, or glucose, it all can have negative consequences,” she tells Yahoo Health. “While some sugar is fine and often necessary to provide fuel and easy energy for highly active individuals, high-sugar diets have been linked to inflammation in the body, obesity, heart problems, dental cavities, and many other health risks.”
How to be smart about consuming sugar
Fructose is abundant these days, especially in the American diet, so being more cautious of its sources is key to curb cravings and disease risk. Don’t avoid fruit outright because of its fructose, as fruit provides your body with vitamins and minerals, as well as satiating fiber and water. Consume sugar in its most natural form, and beware where it may be lurking on your food label as unhealthy added sugar with names like malt syrup, corn syrup, maple syrup, honey, or molasses.
When it comes to these refined sugars, no matter which you choose to eat, “the most important thing is that it’s not a significant source of calories in your diet,” says Moskovitz. According to the American Heart Association, most adults should not consume upward of 25 to 37 grams of added sugar per day — the equivalent of six to nine teaspoons, or 100 to 150 calories.
Remember, anything in excess can be a bad thing. “The biggest takeaway here is that it is most important to limit overall sugar intake by consuming a variety of food groups,” Moskovitz says. “Balancing your plate with lean protein, high-fiber grains or starches, healthy fats, and vegetables will help keep your appetite, waistline, and overall health status in check.”
That way, you can have your cake and eat it, too — and maybe not crave too much of it.
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