November 26, 2008
Obese Rats Have Lower Taste Sensation

As measured by electrodes implanted in rat brains an obese strain of rats reacts differently to concentrations of sugar as compared to a non-obese strain.

Obesity gradually numbs the taste sensation of rats to sweet foods and drives them to consume larger and ever-sweeter meals, according to neuroscientists. Findings from the Penn State study could uncover a critical link between taste and body weight, and reveal how flab hooks the brain on sugary food.

"When you have a reduced sensitivity to palatable foods, you tend to consume it in higher amounts," said Andras Hajnal, associate professor of neural and behavioral sciences at Penn State College of Medicine. "It is a vicious circle."

Previous studies have suggested that obese persons are less sensitive to sweet taste and crave sweet foods more than lean people. However, little is known about the specific differences between obese and lean individuals in their sense of taste and the pleasure they derive from sweet foods.

Hajnal and his Penn State colleague Peter Kovacs, a post-doctoral fellow, investigated these differences by studying the taste responses of two strains -- OLETF and LETO rats.

Compared to the lean and healthy LETO rats, the taste responses in OLETF rats mirror those in obese humans. These rats have normal body weight at first, but they tend to chronically overeat due to a missing satiety signal, become obese and develop diabetes. The obese rats also show an increased preference for sweet foods and also are willing to work harder to obtain sweet solutions as a reward for their learning.

Obese rats react less to weaker concentrations of sucrose sugar but more to stronger concentrations - as compared to non-obese rats.

The researchers implanted electrodes in the rodents' brains to record the firing of nerve cells when the rats' tongues were exposed to various tastes -- salt, citric acid, plain water and six different concentrations of sucrose.

Hajnal and Kovacs specifically looked at differences in processing taste in the pontine parabrachial nucleus (PBN), a part of the brain that uses nerve cells to relay information from the surface of the tongue to the brain.

"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," explained Hajnal, whose findings appeared in a recent issue of the Journal of Neurophysiology. The response to salt was the same for both strains.

However, when the obese rats were fed a stronger concentration of sucrose, their nerve cells fired more vigorously than in the lean rats. In other words, obese rats have a weaker response to weak concentrations and a stronger response to strong concentrations.

This probably at least partially explains human obesity. If one could increase the neural response to less sugary foods while dampening the neural response to stronger sugar concentrations one could make it much easier for people to eat less food.

Share |      Randall Parker, 2008 November 26 12:11 PM  Brain Appetite

Nerissa Belcher said at November 27, 2008 4:01 AM:

Could the obese prone person's response to food also apply to other things? For example, if the same pattern were to apply to sexual behavior such a person would enjoy plain vanilla sex less than "normal" people (the neurotypicals). But, they'd enjoy extreme sexual behavior, such as BDSM, more. The advantage excessive eating has over other behaviors is the reliability of being able to engage in the behavior. I.E. it is a culturally approved excess which is one of the very few extreme behaviors the moralists have not regulated nearly out of existence nor has the US Government taxed to the point few can afford to engage in it frequently.

My guess is if the population majority would get out of the faces of the sizable minority that enjoys extreme (as defined by the neurotypicals and not by the participants) behaviors of many types we'd see less obesity and more human diversity as obese prone people found other outlets for their need for "extreme" behaviors. Gay marriage comes to mind as one example of many where supporting diversity might lower obesity. Of course if my hypothesis is correct the typical gay marriage would be more satisfactory and successful than the typical straight marriage which probably is, truth be known, why many straights will not support gay marriage.

Randall Parker said at November 27, 2008 8:03 AM:


I would not expect a desire for sex to be satisfied by food or vice versa. Sex drive is a different instinct than the desire for food. They were each selected for to perform different functions.

Also, overweight people have less energy for sex. Plus, as people get older their sex drives wane along with their hormones. They have less desire to have sex and so sex is less able to substitute for other desires.

Gay marriage: Male gay marriage is going to be extremely unstable. Look at male homosexual sex practices. There'll be exceptions. But most will be among older guys who have less sex drive and less ability to attract younger men that they find most desirable. Female gay marriage will be more stable or similarly stable than heterosexual marriage.

Neurotypicals and extremes: I really do not think there's a lot of suppression going. This isn't the 1950s. The "white male conservative oppressor overclass" argument is getting pretty tired. If you need someone to resent you'd better go back to the drawing board.

TheAbstractor said at December 1, 2008 7:05 PM:

Everyone who's fasted for several days knows that food has a much more vivid taste afterwards. My hunch is that obesity and poor taste both share correlation with overeating, and not closer causation with each other.

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