They Can’t Fully Enjoy The Food They Crave

Sweets and chocolate are supposed to taste scrumptious. And the more decadent the indulgence, the more a person supposedly enjoys the act of eating. Extrapolating further, those who eat more - and therefore weigh more - must derive more pleasure from their rich treats. Yes?

No.

Recent studies have plumbed the brain chemistry behind two mirror opposites – obesity and anorexia. It turns out that individuals on both extremes of the weight spectrum do not fully enjoy tasty foods.

How can obesity and anorexia share the ascetic underpinning? To answer that, we need to consider the neurotransmitter dopamine. It’s the brain chemical that makes you feel good about eating. The more dopamine your brain cells release, the more pleasure you get from yummy food. 

Sadly, obese people have fewer dopamine receptors and therefore are less sensitive to the effects of dopamine on the reward centers of the brain. At the same time, up to half the overall population carries an alternation in the gene for a dopamine receptor, called "the Taq1A1 allele," which, incidentally, is linked to a lower number of dopamine receptors and a subpar dopamine response.

In a paper published in the journal Science, Eric Stice and colleagues at the Oregon Research Institute and the University of Oregon wanted to investigate obesity, dopamine, and feelings of reward. The researchers pumped chocolate milkshakes into the mouths of 77 female college students while imaging their brains with an MRI scanner. While some of the women were lean, others were obese. Some of these women also had the culprit alteration their Taq1A1 genes.

The researchers found that when obese women slurped away:

• The dopamine responses in the reward centers of their brains were less robust compared to that of lean women.
• Those who carried the culprit version of Taq1A1 had even more bland responses to the milkshakes.
• One year after the scanning, women with the altered Taq1A1 put on more weight than women without the genetic alteration.

Stice’s team concluded that obese people and/or those with the altered dopamine receptor gene may overindulge simply to get the same pleasure from a chocolate milkshake as compared to someone who is not obese and/or has a typical receptor gene. In other words, obese people gain weight not because they love food more but because they can’t love it enough.

On the other side of the weight spectrum, women who had recovered from anorexia were going through their own tasting, scanning experience. Psychiatrist Walter Kaye at the University of Pittsburgh and the University of California in San Diego and his colleagues pumped either plain water or sugar water into the mouths of 13 women who had recovered from anorexia and 13 women who have always eaten normally. The women sat in MRI scanners while drinking and ranking the degree of pleasure they were experiencing.

It turns out that the women in the control group enjoyed the taste of the sugar water more than the plain water. In their brains, the pleasing, sweet sensation activated the insula, a structure important for processing reward and recognizing taste. In contrast, not all of the women with histories of anorexia liked the sugar. Even among those who did, the insula did not consistently register that enjoyment, suggesting that such women lacked an ability to appreciate good tastes fully – and so eat less.

So what’s the take-home message? The brain and its reward responses play a major role in the pleasure derived from eating and, as a consequence, weight gain. In obesity, a blunted response can lead to overeating, ostensibly as compensation. In anorexia, a lack of reward from food leads to undereating; the rationale “I don’t like it so why bother” aptly sums up this phenomenon.

The studies show that so much of appetite, craving, hedonism, and addiction depends on a person’s genetic make-up and many other biological factors yet to be uncovered.