In flies, consuming high-sugar diet reduces sensitivity to sweetness

In fruit flies fed a high-sugar diet for one week, a complex that regulates taste-related sensory neurons reprogrammed the neurons to make the flies less sensitive to sweet taste. Half of these changes were not reversed even after the flies returned to a control diet, the study shows, suggesting flies' perception of sweet taste was permanently altered. Anoumid Vaziri and colleagues suggest that these lasting changes may sway animals towards dietary habits that promote obesity. Their study focused on the epigenetic regulator Polycomb Repressive Complex 2.1 (PRC2.1), which is also found in humans. While previous research has suggested that unhealthy foods with lots of sugar, salt, and fat skew human perceptions of taste, nudging us to overindulge in them, the molecular mechanisms behind this phenomenon have been difficult to identify due to the complexity of taste in mammals. To explore these mechanisms in a simpler organism, Vaziri et al. fed Drosophila melanogaster flies either a sugary diet (30% sucrose) or a control diet (5% sucrose) for 7 days. Afterwards, they compared the flies' responses to three different concentrations of sweetness based on how far they extended their proboscises - an established proxy for taste response commonly used by fruit fly researchers - finding that flies fed the high-sugar diet showed a substantially decreased response to sweet taste compared to the control group. However, flies with mutations in one or more of the protein components of the PRC2.1 complex showed the same response to sweet taste on both diets, further indicating this epigenetic regulator's important role in dulling sugar perceptions. "The mechanisms we discovered are similar to those that lead to depression and anxiety in people that experience trauma," says Monica Dus, corresponding author of the study. "In this case, eating sugar changes the taste system so that the animal will be stuck into making unhealthy food choices, always choosing foods that have higher sugar content. Over time, this locked-in behavior will lead to weight gain, obesity, and chronic diseases."

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