It turns out our bodies didn't get the marketing distinction memo. Here's the lead paragraph from Time magazine: (link)
If you think you're cutting calories by eating diet or low-calorie versions of your favorite foods, think again. A new study by Canadian scientists published in the journal Obesity suggests that our bodies can't be fooled that easily.It turns out that rats fed diet food tended to overeat. They understood that low calorie foods meant they needed to get more calories.
Thanks to evolution, our bodies are excellent at storing food and fat. For most of the history of humans, our ancestors didn't know when the next meal was gonna be. Thus, they were able to store fat really well. Skip a few thousand years, to a time when your next meal is not only scheduled, it might just be an all-you-can-eat buffet, and it's not a quick leap to an obese country. We eat at lunch, but our bodies still don't know we'll eat again at dinner. When we eat at dinner, it still doesn't trust that breakfast (or a late night snack) is on the way.
But there is a way. The first step is to realize your body is on a diet whether you eat so-called diet foods or regular foods. Your body doesn't get the distinction. It gets calories. Eat them, and then burn them, and your body will adjust.
So eat food. And then get out and walk it off. That's the best diet.