Thursday, May 26, 2011

Food Reward: a Dominant Factor in Obesity, Part IV

What is Food Reward?

After reading comments on my recent posts, I realized I need to do a better job of defining the term "food reward".  I'm going to take a moment to do that here.  Reward is a psychology term with a specific definition: "a process that reinforces behavior" (1).  Rewarding food is not the same thing as food that tastes good, although they often occur together. 

Food reward is the process by which eating specific foods reinforces behaviors that favor the acquisition and consumption of the food in question.  You could also call rewarding food "reinforcing" or "habit-forming", although not necessarily in an addictive sense.  Food reward is a perfectly normal and healthy part of life, although I believe it can be harmful if it exceeds the bounds of what we're adapted to.  Food reward is essential for survival in a natural environment, because it teaches you what to eat and how to get it through a trial-and-error process. 

Researchers have demonstrated in rodents and humans that pairing a flavor with a source of calories makes us gradually enjoy the flavor more*, whether or not it remains paired to calories afterward (2, 3).  That's called a "conditioned flavor preference", and it's a simple demonstration of food reward in action.  The brain senses the ingested calories and assigns a positive reward value to the cues (flavor, location, etc.) associated with the calories, after which we'll be more likely to eat something that contains the preferred flavor.

As another example, rats prefer to hang around a place where they have repeatedly received rewarding food (4).  Have you ever seen a child run after an ice cream truck?  After a certain time, our motivation to obtain a food that we perceive as rewarding increases, and so does our consumption of it.  Rats accustomed to eating human junk food will endure foot shocks and extreme temperatures to obtain it, even when much healthier unprocessed rodent chow is freely available (5, 6).

Here's the fundamental concept that I think explains a lot of obesity in industrialized nations.  We live in a more or less Darwinian economic framework (capitalism).  Food manufacturers are in constant competition, and any food that sells poorly will rapidly disappear from stores.  How do you get people to buy your product?  You produce something that causes them to come back and buy it again.  In other words, the goal of processed food manufacturers is to create a product that maximally reinforces purchase and consumption behaviors-- food reward!  If the product is not extremely rewarding, it won't sell because it's competing against other products that are extremely rewarding. Only the most rewarding products survive.

It doesn't matter whether or not you like the Little Debbie cake once it's in your mouth.  It doesn't matter how you feel afterward.  The only thing that matters is whether or not you'll buy another one tomorrow.  That's food reward. 

*I say flavor, but technically I mostly mean smell.  The tongue can detect five tastes, while the nose can detect thousands of smells.  Both flavor and smell are important for reward.


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montmorency said...

@Stephan May 30, 2011 10:21 PM

You make a good case for there being such a phenomenon as leptin resistance.

I don't think that you have (in this post, anyway) identified the cause of leptin resistance (although possibly your number 5) hints at it.

I am guessing however from some of your other posts, that you think it is because of the modern diet, especially "highly palatable" items.

However, what exactly would it be about the diet / these items that causes it? What do you think would be the biological mechanism (in reasonably simple terms)?

Also, I am not clear whether you think that leptin-resistance is a cause of obesity, or a consequence of obesity (or perhaps a consequence of overweight which then leads to obesity as in a vicious circle).

Thank you.

Steve said...

I think 'itsthewoo' has a point and something to teach the OP. By chance I started researching leptin on a bodybuilding forum and came across a woman who seemed to suffer the exact same type of problems as 'isthewoo' to a tee. She struggled with her weight and was fanatic about working out. Her problem was she was hypoglycemic along with some other ailment and it triggered such hunger signals she couldn't even sleep. Even with every prescription sleeping drug, she can't get more than 3 hours of sleep because her intense hunger. And of course flippant fools tell her to have some discipline, but this isn't the type of site where 'fatties' just complain about not losing weight. It's a hardcore forum of very dedicated, disciplined people and judging by her posts, she has more discipline than 99% of all the members there, including me. I linked her to this site because I'm pretty sure 'itsthewoo' might be able to help her. Others also mentioned leptin but she said she hasn't had it checked.

Anyway, great blog. Hopefully itsthewoo will spark some new ideas about the causes of obesity outside just food reward systems.

Leroy Pfeister said...

I've spent most of my adult life in Japan and Korea, where the traditional food culture hasn't been completely lost. When talking about the longevity and leanness of the Japanese, people harp on about low-fat and seafood, but here in Japan, the concept of "usuaji" or "thin flavour"is synonymous with healthy eating.

Usuaji is definitely not the same as "bland" though. In fact, the more expensive the restaurant is, typically the "thinner" the seasoning gets. Instead of strongly sweet or salty or meaty, you're supposed to appreciate instead the flavours of the ingredients themselves, be it the seasonal vegetables, plain rice, miso soup and sashimi of a traditional home-cooked meal or the crab brains, squid tentacles, trout seamen, boiled clams, seared bonnito, salmon roe, duck eggs, wild mountain yam, and natto rolls I had for dinner at a nice restaurant a few nights ago (plenty of nutrient-dense foods there)cheap football jerseys

Deanna Kate said...

I've noticed that cold leftover food is less rewarding than the same food was hot the night before. This post helped me to understand why. In your * comment, you make a distinction between flavor and smell and note the fact that smell is important to reward and is more varied. Hot food features a smell that wafts through the air to the nose. Cold food does not. By that mechanism, hot food is much more tempting. Food ads take advantage of this fact by picturing hot food with steam coming off of it.

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