The whiff of a sizzling burger, the sight of an oozing slice of pizza, the scent of a freshly baked cake; it’s often not easy to turn down such decadent, tempting treats. But even if you boast strong willpower, it turns out that a common substance in our diet could be worsening our hankerings for calorie-rich foods: fructose.

According to a new study on humans, compared with glucose, consuming the sugar fructose increases the brain’s response to mouthwatering images of scrumptious foods, makes us hungrier and leads to greater cravings for food.

While it may be easy to demonize fruit from these findings since some can possess large amounts of fructose, we shouldn’t use this study as an excuse to not eat it. Fruit is stuffed with lots of healthy things, like vitamins and fiber, which are lacking in sugary, processed foods and fizzy drinks. Instead, we should watch our overall intake of sugar and reduce our consumption of things like fruit juice, full-fat soda, candy and cake.

“The best way to reduce fructose intake is to decrease the consumption of added sugar sweeteners, which are the main source of fructose in the American diet,” said study author and research leader Kathleen Page.

This latest study was prompted by previous work that suggested that consuming fructose results in a weaker suppression of appetite than glucose. Although both sugars, their fate is different in the body. Glucose, which is found in almost every carbohydrate-containing food, is the primary energy source for most of our cells. When consumed, it triggers the release of insulin by the increase, which informs the brain that we have just had a meal. Fructose, which is sweeter than glucose, is a simple sugar found in fruit, honey and vegetables. Importantly, fructose does not stimulate the release of insulin.

To tease apart further differences in consuming these two different sugars, researchers from the University of Southern California enrolled a small group of volunteers—24 young men and women—into their study. These healthy adults were called in on two separate mornings before breakfast, and were provided with a cherry-flavored drink laced with sugar; once with glucose, once with fructose. Neither the researchers nor the participants knew which one they were drinking.

After a short period of time, volunteers were asked to rate their hunger and blood was drawn to monitor hormone levels. Next, to investigate brain activity, they were placed inside an MRI machine whilst being presented with images of either high-calorie foods or random objects. For the final part of the investigation, volunteers were offered a tough choice: a monetary reward later on down the line, or an immediate edible reward.

As described in Proceedings of the National Academy of Sciences, compared to glucose, consuming fructose resulted in a smaller increase in insulin levels, but a greater brain response to images of food in a region known to be involved in reward processing, the orbital frontal cortex. This increase in activity could indicate that, relative to glucose, fructose could promote feeding behaviors.

In support of this, participants also reported feeling hungrier after consuming fructose; so hungry that they were more likely to give up an offer of cash in the future in favor of an immediate, high-calorie food reward.

Although further research is warranted, the findings do seem to support prior observations that glucose is better at suppressing appetite than fructose, and that they may therefore evoke different feeding responses.

[Via University of Southern California, PNAS, NY Times and BBC News]