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Obesity causes inflammation, which reduces the number of taste buds on the tongue – thereby dulling taste, according to new research presented in the journal PLoS Biology.

The experiments showed that mice who were fed more fat and grew larger also developed 25 percent fewer taste buds.

“We have analyzed the effects of obesity on taste buds and demonstrate that mice consuming a high-fat diet quickly become obese and display a pronounced loss of taste buds when compared to littermates sustained on a healthy diet,” write the scientists from Cornell University.

Each taste bud in a mouse is a heterogeneous mix of as many as 100 cells including cells that provide structural support, others that detect sweet and bitter tastes, and still others that form synapses to respond to sour taste.

The mice were subjected to eight weeks of strictly controlled diet. One group was fed nearly 60 percent fat in their diet, while the other group had a mere 14 percent allotment of fat as part of their diet.

At the end of the two months, the mice were weighed, killed, and their tongues were taken for analysis. The taste buds were counted and sized, and the RNA was extracted and assessed.

The obese mice had only three-quarters of the taste buds their diet-restricted counterparts did, the scientists counted.

Further investigation determined that obesity causes inflammation that promotes the creation of signaling cytokines – especially tumor necrosis factor alpha (TNFα). This signaling pathway increased the level of TNFα around the taste buds, report the scientists. The rate of apoptosis, a programmed kind of cell death, increased – which led to a decrease in the number of progenitor cells that are necessary to form the taste buds.

The effect is a kind of vicious cycle – and could translate to overweight humans, add the investigators.

“A loss of input from taste buds would likely encourage overconsumption to compensate for this depressed input, as has been observed when blocking input from sweet taste receptors in a human population, resulting in a drive for more highly sweetened (and thus higher-calorie) stimuli,” they write.

The team also tested this inverse relationship by genetically engineering another set of mice. The deletion of the TNFα allowed mice to preserve their taste buds intact – despite gorging themselves on a high-fat diet. On the other hand, injecting TNFα directly into the tongues of thinner mice also reduced taste buds – even though the rodents didn’t have the body bulk, according to the paper.

“These results may point to novel therapeutic strategies for alleviating taste dysfunction in obese populations,” added Robin Dando, one of the Cornell authors.

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