Writing in yesterday's Times, Tara Parker-Pope reported on studies done in California and Italy about how rats reacted when given a high-fat drink:

"The body immediately began to release natural marijuanalike chemicals in the gut that kept them craving more. ... The compounds serve a variety of functions, including regulation of mood and stress response, appetite, and movement of food through the intestines. Notably, they were released only when the rats tasted fat, not the sugar or protein."

One key point is that when the body's chemistry is thus activated, we are driven to act in ways we wouldn't freely choose — in this case, to eat past when we've taken on sufficient fuel.

This truth is very important to recognize, for several reasons. For people who tut-tut toward fat people for being morally weak, it's important to know that for some people, there's more at work than just moral fiber.

And for everyone, it's important to know because food manufacturers know, and they use the knowledge to design food products that are more likely to trigger these responses, because it translates into higher sales. The other key point, the one that moral-fiber proponents would want to emphasize, is in Parker-Pope's last paragraph, a quote from Dr. David Kessler, former FDA commissioner and author of "The End of Overeating."

“But just because your brain is being hijacked, that doesn’t mean you don’t have a responsibility to protect yourself.”

Precisely. Overeating, and obesity, arise from a number of causes, which is partly why they're so hard to define and defeat. But as we learn more about how the food-products industry seeks to manipulate us, we become more responsible for defending ourselves. They can produce all the tarted-up crap they want, and they can shove as much advertising and promotion down our throats as they're willing to pay for, but so far at least, they can't shove the food itself down our throats.