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

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.

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.

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.

They may have salt, sugar, and fat on their side, but we, ultimately, have the power to make choices. After all, we decide what to buy. We decide how much to eat.