Q: Most people know what they should and shouldn't be eating. Why do so many of us choose the wrong foods so much of the time?

A: Wow, there are a lot of things going on here. I'll limit myself to naming just a few:

1. Everyone's confused about what to eat

Every month a new study, telling us that last month's study turns out to be wrong. Red wine, bad. Red wine, good. Chocolate, a fattening killer. Chocolate, food of the gods. Tomatoes, protect against cancer. Tomatoes, lead to arthritis. Yikes!

Here's the thing: the science on what constitutes a healthy diet is extremely clear and consistent. What's not clear or consistent is the industry and media spin. Think about it: if people started eating healthy food en masse, the economy would lurch like you've never seen it before. Processed foods, animal products – they're a multi-billion dollar a year industry. That's a lot of marketing and PR muscle to keep us eating badly.

2. Processed food is literally addictive

Literally, as in biophysically. The best book on this subject is The Pleasure Trap, by Goldhamer and Lisle. The purpose of most processed food is to concentrate the pleasure-producing chemicals (fats and sugars, principally) and strip out the nutrients. So we're overpleasured and undernourished. Just like the rats pushing the cocaine buttons in the lab experiments, we go for foods that are clearly bad for us in the long run.

Remember our evolutionary strategy – get as many calories as we can with as little energy expenditure as possible. It worked when we were hunter-gatherers. It no longer works when we have easy access to supermarkets and convenience stores.

3. Nobody wants to be told what to do

We have a strange attitude toward food – we worship and hate it at the same time. Most people talk about their diets like they're on some religious quest – the language is all about guilt and cheating and self-worth.

As Atkins fades into oblivion, the new trend in eating seems to be "who wants to live to 100 eating sticks and dirt?" Pleasure is in, and worrying about the consequences is out.

People eat healthy when it feels better to eat healthy than any other way. The trick is to give yourself experiences of healthy food that taste good, feel good, and are as convenient as the other stuff. Once you finish going through withdrawal (again, literally), you'll gravitate toward the foods that make you feel good.