Food should make us feel satisfied, and it’s been suggested that some obese people overeat because they don’t derive as much satisfaction from food as leaner people do. Researchers at the University of Michigan (UM) wanted to use the fruit fly, a common model animal, to learn more about how sugary tastes impact food intake behaviors. They found that if fruit flies were given a diet high in sugars, the neurons in those flies initiated a cascade of events that disrupted the flies’ ability to taste something sweet. That was also associated with overeating and obesity. The work, which can help researchers learn more about how an excess of sugar contributes to weight gain, has been published in Cell Reports and is briefly outlined in the video.
This work also supports the idea that factors outside of our control can affect some overeating behaviors. Although the scientists cannot tell how satisfied the flies are after eating, the principal investigator of the study, Monica Dus, a UM associate professor of molecular, cellular, and developmental biology noted that the flies ate more when they were fed a high-sugar diet.
Fruit flies have enough in common with humans that they’re a good way to ask these questions about diet; they both have a love of fat and sugar, and after eating the substances, will produce dopamine. Many aspects of their neurobiology are similar as well. For those who wonder, the first author of the study, graduate candidate Christina May, added that fruit flies do indeed get fat.
In this work, the scientists also fed a high-sugar diet to genetically obese flies that had not eaten that type of diet before; their tastes were not altered. In another model - flies that can’t store fat, the flies remained thin after consuming the high-sugar diet, but couldn’t taste sweet stuff anymore. "That's really amazing because it tells you their ability to taste sweets changed because of what they're eating, not because they're becoming obese," explained May.
The researchers also tested sugar substitutes and found that they did not have the same impact. "We know it's something specific about the sugar in the diet that's making them lose their taste," Dus noted.
The investigators also altered taste cells in flies so they could not lose their ability to taste sugar, and these altered flies did not overeat, even when there was a lot of sugar in their food.
"This means the changes in taste, at least in flies, are pretty important to drive overconsumption and weight gain," Dus said. "Do changes in taste also play a role in the overconsumption that we see when humans and other animals find themselves in food environments high in sugar?"
Though it remains to be confirmed in humans, this work can help shed light on the molecular signals related to obesity and overeating, and how they can change based on food intake. It may be that one day, a pharmacological intervention could restore the sensation of sweetness to help reduce obesity. That would require a lot more work, of course.
If these findings are replicated in people, it may indicate that modulating dietary sugar can help control food intake, noted Dus. Sugars can be easily hidden in processed foods, she added, so it’s important to minimize our consumption.
"I think if you try to keep added sugars out of your diet, you'll probably be totally fine, you won't have problems with changing taste and overeating," May said. "All of us try to avoid the added sugars. That's important."