Experts often attribute overeating to stress, sadness or the need to find pleasure in food. But according to the results of a recent study of rats published in the Journal of Neurophysiology, obesity may result from different taste perceptions in overweight individuals.
To conduct the experiment, Penn State researchers stimulated the tongues of both Otsuka Long Evans Tokushima Fatty rats and Long Evans Tokushima Otsuka rats with sucrose. Fatty rats lack CCK-1R, a receptor that makes rats feel full and when missing can cause the rat to become obese, Peter Kovacs, a post-doctoral fellow at Penn State College of Medicine, said.
The results showed that fattier rats had more salt-responsive neurons and fewer sugar-responsive neurons compared to leaner rats. Fattier rats had an overall reduced response to sugar. In obese rats, there was also a rightward shift in sucrose concentration, which shows that neurons in obese rats are more likely to respond to higher concentrations of sucrose, Kovacs said. The findings demonstrated different taste processing for sugar in obese rats, which supports the notion that taste-perception is encoded in the brain.
‘Meal size can be regulated by stop signals, and one of the most important stop signals is taste when you’re eating something that’s higher in calories or maybe sweeter,’ Kovacs said. ‘But if this process is altered, you’re not going to have a stop signal and that can lead you to desire a bigger meal.’
Remembering that rats and humans are not comparable physiologically and psychologically is very important, Andras Hajnal, an associate professor of neural and behavioral sciences at Penn State College of Medicine, said. However, humans, and rats have many commonalities when it comes to obesity ‘-‘- like obese rats eating larger meals and preferring sweeter foods, he said.
‘The obese animal brain is different from that of the lean rats, and it’s very scary to think about,’ Hajnal said. ‘They do not see or smell the same, and I think it’s very interesting that the sensory taste neuron behaves differently.’
More than 34 percent of U.S. adults ages 20 and older are obese, according to a 2006-07 survey conducted by the Centers for Disease Control and Prevention.
Though obesity can be attributed to both genetics and environment, the proliferation of the condition is likely due to changes in what we eat, Anne Wolf, a research instructor at the University of Virginia school of Medicine, said.
‘Genes haven’t changed over last 40 years, and obesity has been increasing, which signifies that the environment is changing,’ Wolf said. ‘People are taking in more snacks, more juices and more beverages that have calories, and they’re not exercising as much, so it’s contributing to a high calorie load.’
Processed foods may be the biggest reason people are obese, Kovacs said.
‘When we start eating processed foods, they have a lot of things that can send false information to the brain,’ Kovacs said. ‘If you eat a lot of artificial sweeteners then the sweet taste is not a ‘good stuff’ signal.’