CHICAGO, May 8 (Xinhua) -- Researchers at the University of Michigan (UM) found that feeding fruit flies a high-sugar diet, the flies' taste neurons triggered a molecular chain-reaction that hampered their ability to taste sweets, which in turn fueled overeating and obesity.
They also found that eating sugar caused the taste changes, not the metabolic consequences of obesity or the sweet taste of food.
The researchers tested the findings in several ways. First, they fed flies that were genetically obese but never exposed to high dietary sugar, and their taste didn't change. However, when they fed sugar equivalent to a cookie to flies that are unable to store fat, they stayed thin but still lost the ability to taste sweets.
To find out if the sugar or the sweet taste of food caused taste changes, the researchers fed flies a diet similar to artificially sweetened diet soda. Only the files eating real sugar lost their sweet-tasting ability.
"We know it's something specific about the sugar in the diet that's making them lose their taste," said principal investigator Monica Dus, U-M assistant professor of molecular, cellular, and developmental biology.
The researchers identified the molecule O-GlcNAc transferase, a sugar sensor located in the flies' taste buds that keeps track of how much sugar is in the cells. OGT has previously been implicated in obesity-related conditions like diabetes and heart disease in humans.
The researchers also manipulated flies' taste cells so that even on a high-sugar diet they wouldn't lose taste, and those flies didn't overeat despite loads of sugar.
"This means the changes in taste, at least in flies, are pretty important to drive overconsumption and weight gain," Dus said.
The study not only sheds light on sugar-diet-dependent neural mechanisms of overeating and obesity, but provides a platform to study the underlying molecular mechanisms that drive changes in neural activity, said Dus.
The study also means a lot to people who are overweight, dieting or feel addicted to sugar, as flies and humans share surprising similarities: Both love sugar and fat and produce dopamine upon eating it, and the fly's brain cells use many of the same proteins and molecules humans do, for the same things.
It's possible that in the long-term, a drug or other intervention that corrects dietary sweetness and preserves the sweet taste sensation could someday help curb obesity and the associated chronic diseases, said Christina May, first author of the study and a doctoral student in Dus' lab.
In the next step, the researchers will examine sugar's impact on the brain's reward circuits to learn what causes overeating, and how sugar changes the brain on a molecular level.
The study was published on Tuesday in Cell Reports.