Each year, food companies use an amount of salt that is every bit as staggering as it sounds: 5 billion pounds.

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.

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.

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.

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.

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.

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.