Packing on pounds seems to dull people's sense of taste, and puzzled researchers turned to mice to figure out why: Obesity, they found, can rob the tongue of taste buds.
If Tuesday's findings pan out, "this could be a whole new kind of target in treating obesity," said Cornell University food scientist Robin Dando, whose lab led the research. "People don't really look at the taste bud, but it's so fundamental."
Diet, exercise and genetics are among many factors that play a role in obesity. But taste preferences influence dietary choices, and some earlier studies have suggested that obese people often taste flavors with less intensity than lean people. The theory, still unproven, is that people might make up for weakened taste by turning to higher-calorie foods or generally eating more.
Dando's team took a closer look at taste buds, those clusters of cells on the tongue that help perceive the five tastes: sweet, sour, salty, bitter and umami. They turned to lab mice, feeding them a high-fat diet that caused rapid weight gain — and then counting the taste buds in a spot on the tongue that's normally packed with them.
The obese mice wound up with 25 percent fewer taste buds than lean mice that were fed a normal diet, the researchers reported in the journal PLOS Biology.
Taste buds constantly regenerate as the 50 to 100 cells inside them mature, die off and are replaced by new ones. Taste bud cells have an average lifespan of about 10 days, and turnover of the entire taste bud takes about four weeks, explained Dando, who directs the Cornell Sensory Evaluation Facility. Both sides of that cycle were affected in the obese mice, as regular cell death sped up and resupply dropped.
Could fatty food be responsible? No, the researchers found mice genetically resistant to obesity chowed down yet didn't lose taste buds.
The remaining suspect: the chronic inflammation that obesity triggers throughout the body. Dando's team examined a common inflammatory molecule called TNF-alpha. Mice bred to be genetically incapable of making that molecule got fat but also didn't lose taste buds. But injecting that molecule directly into the tongues of lean mice resulted in faster die-off of taste bud cells, the researchers reported.
The study "does underscore the relationship between taste sensitivity and weight," said Dr. John Morton, a Stanford University bariatric surgeon who wasn't involved in the new work. "It's another reason why it's hard to lose weight."
Several years ago, Morton gave his own patients taste tests before and after stomach-shrinking surgery, and found taste perception improved as the pounds dropped.
Whatever the role of taste buds, Morton advises patients to eat mindfully — appreciating the sight and smell, and slowing down to chew 30 times before they swallow.
"You get satisfaction from food in ways other than volume," he said.