Think about your favorite foods. About how they taste and how they make you feel. A lot of the foods we crave -- and we use that word intentionally -- are so good because of three main ingredients: Salt, sugar and fat.

When mixed in just the right amounts, they're an almost irresistible combination. And the food industry knows it.

"Salt, Sugar, Fat" is also the title of Michael Moss's new book about how food companies keep us coming back for more. They've built a sophisticated system, from food engineers looking for the exact combination of flavors to inspire the deepest craving, to marketing departments that coach kids to beg parents for Lunchables and sugary snacks.

One of the tricks of the trade? Vanishing caloric density. "If you can fool people into a product that melts in their mouth, their brain is less apt to detect that there's a ton of calories in there."

But Moss says it's not quite as black and white as "healthy" or "unhealthy." Food companies may have goals to provide healthy food, but they're also sensitive to what shoppers are putting in their carts. And there's financial pressure. "Every time the companies cut back a bit, Wall Street is there, watching the sales, watching the profits, urging the companies to go back to salt, sugar, fat. And they do."

As for his own favorite tastes? Moss says he usually craves salty and fat-filled treats.