The Frontal Cortex

Calories are Rewarding

Last night, while stuck in an airport (the inevitable delay), I decided to get a Wendy’s milkshake. Not a particularly noteworthy decision – when traveling, I like to subsist entirely on fast food – but it occurred to me, while standing in line, that I wasn’t actually hungry. At all. (I’d just finished a greasy combo meal.) So why was I lining up to pay $4 for ice cream? Over at Mind Matters, we’re discussing a new paper that sheds some light on the issue. The problem turns out to involve the dopamine reward pathway (not so surprising), which responds not just to the delicious taste of a milkshake but to the caloric energy in the food. As a result, we still like to eat, even when the hypothalamus is sated:

Although the hypothalamus will direct intake based on the metabolic value of the food–when you’re very hungry, you seek out food with lots of calories–it remains to be determined whether the dopamine reward system can also sense a food’s energy content. In other words, does the dopamine system care about calories, or is it just concerned with taste and pleasure? Neuroscientist Ivan de Araujo and colleagues at Duke University, explored this question by using a line of mice genetically engineered to lack a functional receptor essential for detecting the taste of sweetness. In these mice, any change in reward behavior cannot be due to food palatability or the sensation of sweetness. If these mice prefer sweetness, thus, it is because sweeter foods have more calories, implying that there is something inherently rewarding about the consumption of calories.

In the first set of behavioral experiments, the authors showed that the genetically altered mice were completely insensitive to the “sweet” rewarding properties of sucrose (table sugar) and showed no preference for sucrose compared with water. In contrast, control mice without the genetic mutation strongly preferred the sucrose solution.

The scientists then exposed the different strains of mice to a “conditioning protocol” in which the rodents received alternating access to water or sucrose for six days. During these conditioning sessions, the genetically altered mice were able to associate the sweet solutions with caloric load post-ingestion, as the sugar water has more calories than plain water. Interestingly, both strains of mice now consumed significantly more sucrose. Although the genetically altered mice couldn’t taste the sweetness, they learned to prefer the sweeter water. This finding suggests that mice without functional sweet taste receptors were able to detect the reinforcing caloric properties of sucrose in the absence of sweet taste receptors. There seems to be something inherently pleasurable about ingesting food that contains calories.

As a critical control, the experiments were then repeated with sucralose (a.k.a. Splenda), an artificial sweetener that tastes sweet but contains no calories. Although normal mice consumed more sucralose than water during the conditioning period–they still preferred the sweet taste–the genetically altered mice did not.

Read the whole thing.

Comments

  1. #1 sarcastico
    October 4, 2008

    Yo, dude. It’s a milkshake at an airport. Unless you are angling for an Ig Nobel, you are putting way too much thought into it. Wendy’s, Steak and Shake, and DQ all spend millions on advertising. None of their commercials mention dopamine reward pathways. There is a reason for that. It’s a milkshake. At an airport!

  2. #2 Donna B.
    October 4, 2008

    I could live my whole life without having a milkshake at any of those places you mention, or anything else they sell.

    Is there any milk present at all? Isn’t it flavored frozen plastic bits? Little taste, less satisfaction.

    Hamburgers, steaks. They are cheaper and better tasting prepared at home… calorie wise, I suspect at-home preparation is better too.

    Not to mention the better control one has at home over portion size. And it’s easier to safely save leftovers for another meal. That bit of steak and broccoli? mmm… fried rice the next day.

    Plus, one is tempted to always have salad greens ready to serve and/or cook.

    I’m overweight, obese probably. I am now even more picky about what food I eat because I had a stomach-limiting surgery years ago. I can’t afford to eat bad stuff because there isn’t room for good stuff.

    I’m paying for the decision to have that surgery with fatigue, weakness, muscle and hair loss, vitamin deficiency (I’ve fixed that, but I was a little late with it), bowel problems, two hernias (requiring additional surgery) and very little lasting weight loss. It wasn’t worth it for 50 lbs. before my body “re-set” it’s set point.

    All those problems and I’m still fat. I’d still be fat (likely fatter) but I’d be healthier if I hadn’t had the surgery.

    If there is an obesity epidemic (I’m not entirely convinced there is) I wonder if it is not a result of artificial sweeteners and fad diets so prevalent in the last 40 years or so.

  3. #3 Sincerity
    October 5, 2008

    What an enjoyable and interesting post! I too enjoy the occasional Wendy’s milk shake. Interesting to think that I may like them for more than just a sweet treat. :)

  4. #4 Julie Stahlhut
    October 5, 2008

    There’s something about being stuck in an airport that makes me want to consume every overpriced empty calorie in the place. I think the inherent crushing boredom of the situation has something to do with it, since in day-to-day life I’m pretty good at resisting the urge to pig out on sugar and grease in chain restaurants, even if I’m under stress at the time.

    Things have gotten a bit better since I started carrying a pair of headphones so that I can distract myself by watching comedy shows on my computer while waiting in airports. I’m beginning to wish that, like my husband, I’d opted for an iPhone so as to have actual prepaid surfing flexibility, but even the sedentary act of watching the whole first season of Metalocalypse for the fifteenth time is probably healthier than running loose with a credit card in a doughnut shop.

  5. #5 Ally Reeves
    October 5, 2008

    I’m in the midst of making an artwork a day based on things that pour into my Google reader. Today’s material came from your “Calories are Rewarding” article. Thanks for the insight and inspiration!

  6. #6 Gina Pera
    October 7, 2008

    It seems that people who live in a state of denial — meaning their neurocognitive deficits impair self-observation as well as the ability to link cause with consequences, etc — can be the most confident and optimistic.

    And somehow I think that someone who “can’t blink” might also lack brain power in that function called remorse or conscience. Seems connected.

  7. #7 Gina Pera
    October 7, 2008

    Darn, the post changed on me! Obviously, that comment was for another post.

  8. #8 Jessica
    November 3, 2008

    Isn’t it possible that the mutated mice were simply loading up on calories? It would seem that mice would eat whatever they could find whenever they could find it. That would make sense to me as far as evolutionary instinct; they would want to load up on energy, not knowing when it will be provided to them next. Perhaps drinking the sucrose told their bodies that they were being fed, and not that they were being pleased by sweet tasting, high-calorie water.

  9. #9 jack green
    March 22, 2011

    The post seems doesn’t match you!