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.

Every year, the average American eats as much as 33 pounds of cheese. That's up to 60,000 calories and 3,100 grams of saturated fat. So why do we eat so much cheese? Mainly it's because the government is in cahoots with the processed food industry. And instead of responding in earnest to the health crisis, they've spent the past 30 years getting people to eat more. This is the story of how we ended up doing just that.

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.

Take a cup of coffee, keep adding sugar until you reach the point that you like it the most, and then when you add more sugar, you actually like it less. Well, the food industry knows that, and they spend huge amounts of effort finding the perfect spot, not just for sugar, but for fat and salt, as well.

As a culture, we've become upset by the tobacco companies advertising to children, but we sit idly by while the food companies do the very same thing. And we could make a claim that the toll taken on the public health by a poor diet rivals that taken by tobacco.

What I found, over four years of research and reporting, was a conscious effort — taking place in labs and marketing meetings and grocery-store aisles — to get people hooked on foods that are convenient and inexpensive.

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.