The Cause Of Obesity May Be Decreased Taste Sensitivity
Eating processed foods full of fat and sugar can decrease our sensitivity to taste, perhaps causing a vicious cycle that makes us eat more and become obese. The findings come from Penn State researchers, Andras Hajnal, associate professor of neural and behavioral sciences at Penn State College of Medicine and his colleague Peter Kovacs, a post-doctoral fellow.
Past studies show that obese people have decreased taste sensitivity to sweets. The new research studied the effects of specific taste differences that might occur between obese and lean people.
The researchers used two types of rats, the OLETF rat whose taste sensitivity is associated with that of obese people, and healthy, lean LETO rats. The OLETF rats consistently overeat, though they start out slim, due to a missing signal that tells them when achieved food satisfaction.
Dr. Hajnal explains, "When you have excess body weight, the brain is supposed to tell you not to eat more, or not choose high caloric meals… this control apparently fails and thus the obesity epidemic is rising, and we want to find out how the sense of taste drives up food intake." The scientist looked at the brain's response to various taste including six different concentrations of sucrose, salt, plain water and citric acid. They mapped the brain signals in the rats by attaching electrodes to their heads to measure the areas of the brain stimulated. They specifically looked at the area that processes signals from the tongue's surface to the brain - the pontine parabrachial nucleus (PBN).
"We found that compared to the LETO rats, the OLETF rats had about 50 percent fewer neurons firing when their tongues were exposed to sucrose, suggesting that obese rats are overall less sensitive to sucrose," explains Hajnal. When the researchers gave the rats stronger concentrations of sucrose, the PBN became more stimulated, indicating that the obese rats have less sensitivity to the taste of sweets.
Dr. Hajnal concluded, "If you sense sweetness less, you may be inclined to eat sweeter foods." Obese humans have less Dopamine, a chemical in the body that is associated with pleasure. The result may be that we eat more to compensate for lack of sensitivity to taste. He believes that high concentrations of fat and sugar found in processed foods provide constant food rewards that merely lead to a vicious cycle of overeating. "We simply start putting an extra spoonful of sugar in our coffee," rather than eating less.
Estimates show that 60% of Americans are overweight or obese. Perhaps we need to tame our taste buds so we can all enjoy the taste of fresh, unprocessed, whole foods.
The source of this research for reference is Route to obesity passes through tongue.