In a key--but commonly overlooked--aspect of obesity, weight gain can be caused by the slightest increases in consumption, if it continues day in and day out.

The fast-food industry has moved into the grocery store, so you no longer have to go to a fast-food chain to find problematic foods.

As I spoke with scientists about the way fat behaves, I couldn't resist drawing an analogy to the realm of narcotics. If sugar is the methamphetamine of processed food ingredients, with its high-speed, blunt assault on our brains, then fat is the opiate, a smooth operator whose effects are less obvious but no less powerful.

Health messages are simply overwhelmed, in volume and in effectiveness, by junk-food ads that often deploy celebrities or cartoon characters to great effect. We may know that eating fruits and vegetables is good for us, but the preponderance of the signals we get - and especially the signals children get - push us in the direction of junk food.

Some of the largest companies are now using brain scans to study how we react neurologically to certain foods, especially to sugar. They've discovered that the brain lights up for sugar the same way it does for cocaine...

Science is starting to show that our brains are less able to detect calories in liquids. So, people in the know, including food industry executives, when they run into health trouble, the first thing they do is cut calories out of all the liquids that they drink as a way of maintaining their weight.

In a key--but commonly overlooked--aspect of obesity, weight gain can be caused by the slightest increases in consumption, if it continues day in and day out.