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.