A study published in PLOS ONE shows that being severely overweight impaired the ability of mice to detect sweets.
The study compared 25 normal mice to 25 of their littermates who were fed a high-fat diet and became obese. To measure the animals' response to different tastes, the research team looked at a process called calcium signaling. When cells "recognize" a certain taste, there is a temporary increase in the calcium levels inside the cells, and the scientists measured this change. The researchers found that taste cells from the obese mice responded more weakly not only to sweetness but, surprisingly, to bitterness as well. Taste cells from both groups of animals reacted similarly to umami, a flavor associated with savory and meaty foods.
"Studies have shown that obesity can lead to alterations in the brain, as well as the nerves that control the peripheral taste system, but no one had ever looked at the cells on the tongue that make contact with food," said lead scientist Kathryn Medler, Associate Professor of Biological Sciences. "What we see is that even at this level—at the first step in the taste pathway—the taste receptor cells themselves are affected by obesity. The obese mice have fewer taste cells that respond to sweet stimuli, and they don't respond as well."
How an inability to detect sweetness might encourage weight gain is unclear, but past research has shown that obese people yearn for sweet and savory foods though they may not taste these flavors as well as thinner people.