Last updated March 22, 2018 at 12:10 pm
Being overweight dulls the taste of food by changing the structure of the tongue, according to new research in mice.
Obesity affects the ability to taste food because it actually reduces the number of taste buds on the tongue, according to researchers at Cornell University.
Their work suggests that a low-grade inflammatory response to a high-fat diet causes a disruption in the balancing mechanisms of taste bud maintenance and renewal.
Previous studies have shown that weight gain can reduce taste sensitivity and that this effect can be reversed when the weight is lost again, but it’s been unclear as to why.
Taste bud cells turn over quickly, with an average lifespan of just 10 days. Each comprises 50-100 cells of three major types, which have different roles in sensing the five primary tastes (salt, sweet, bitter, sour and umami).
To explore changes in taste buds in obesity, the authors fed mice either a normal diet made up of 14 per cent fat or an obesogenic diet containing 58 per cent fat.
After eight weeks, the latter group weighted about one-third more but, surprisingly, had about 25 per cent fewer taste buds than the lean mice, with no change in the average size or the distribution of the three cell types within individual buds.
The turnover of taste bud cells normally arises from a balanced combination of programmed cell death (a process known as apoptosis) and generation of new cells from special progenitor cells. However, the researchers observed that the rate of apoptosis increased in obese mice, whereas the number of taste bud progenitor cells in the tongue declined, likely explaining the net decline in the number of taste buds.
Mice that were genetically resistant to becoming obese did not show these effects, even when fed a high-fat diet, implying that they are due not to the consumption of fat per se, but rather the accumulation of fatty tissue (adipose).
Obesity is known to be associated with a chronic state of low-grade inflammation, and adipose tissue produces pro-inflammatory cytokines – molecules that serve as signals between cells – including one called TNF-alpha.
The researchers found that the high-fat diet increased the level of TNF-alpha surrounding the taste buds, but mice that were genetically incapable of making TNF-alpha had no reduction in taste buds, despite gaining weight. Conversely, injecting TNF-alpha directly into the tongue of lean mice led to a reduction in taste buds, despite the low level of body fat.
The researchers suggest the results may point to novel therapeutic strategies for alleviating taste dysfunction in obese populations.
The paper published in PLOS Biology.