The secret to avoiding weight gain may be residing on the top of your tongue. According to a new German study, obese children have less sensitive taste buds than kids of normal weight, and that may drive them to eat more.
The investigators tested the taste sensitivity of 200 children between the ages of 6 and 18, half of whom were obese. By placing special taste strips on the children's tongues they were able to measure their response to each of the five taste sensations – sweet, sour, salty, bitter and umami (savory) -- at four different levels of intensity.
Obese children had a much harder time than their slimmer peers identifying the different tastes, especially salty, bitter and umami. They also struggled to detect the difference between salty and sour, and between salty and umami.
Girls and older children who were thin had, in general, the most finely tuned taste buds. And, while both obese and normal-weight children correctly identified all the differing levels of sweetness, obese kids rated three out of the four intensity levels lower than kids of normal weight.
At this point scientists don't know whether a sluggish sense of taste leads to overeating or if excess weight somehow diminishes the taste buds' abilities. Robin Dando, a professor in the food and science department at Cornell University in Ithaca, N.Y., said he thinks it may be a little of each.
"It could be a cause and an effect at the same time," he said. "Obese people may taste differently, but also their taste ability is contributing to their obesity."
Dando, whose own research examines the physiology of taste receptors, said we are all born with distinct taste sensitivities and preferences that are influenced by age, sex and experience. Both taste and obesity may also be shaped by hormonal fluctuations. This "hormonal fingerprint," as Dando calls it, might be different for obese and lean people.
For example, the hormone leptin is associated with hunger, fat storage and the ability to taste sweet things. Obese people may be less sensitive to its daily cycles. Also, if the level of insulin circulating in the blood stream remains consistently elevated for long periods of time, as it does in many obese people, it could weaken the cells' receptors to the hormone, which in turn could mute taste sensitivity.
Dr. Stephen Cook, associate professor at the Golisano Children's Hospital, at the University of Rochester, said he thought obese kids might also become over-habituated to taste over time. "They may get so used to certain flavors, they need to consume them at an ever-increasing threshold to notice their taste," he said.
This isn't the first study to look at the connection between taste ability and weight. Previous research has suggested that people with a heightened sensitivity to the various taste sensations tend to eat less, possibly because they get more flavor in every bite, while people who overindulge simply may not taste food as keenly as others do. In 2010, for example, Australian researchers found those with higher sensitivity to the taste of fat tended to eat fewer fatty foods overall and had lower body mass indexes.
Russell Keats, the lead author of the Australian study and an associate professor at Deakin University in Victoria, said this latest study has some issues. "The number [of subjects] is small, taste strips are not a great method to indicate taste function, and identification of taste may be related to other cognitive issues rather than anything to do with taste function," he said.
Cook said it's possible the results might change if the same study looked at American children, who are used to eating more highly processed foods than their European counterparts. "Since they have different exposures, I'm not sure the results would be the same."
Still, Dando said the work is interesting. It's not yet known whether the taste buds can be retrained to do a better job but if they can, he thought it might possibly lead to some new weight loss therapies down the road. Instead of counting calories, perhaps dieters could concentrate on eating more mindfully and getting a bigger taste hit per bite.