-- I don't believe there's any magical mathematical equation between the speed of the food and the circumference of the waistline. After all, you can gain weight eating slow food as well as fast food. You can bulk up with haute cuisine as well as Big Macs. And you can, alas, trust me on this.

So I was inclined to scoff at the Conspiracy Theory of Obesity. This is the idea that McDonald's dunnit. That Burger King and Wendy's and their speed-eating cohorts are responsible for the Incredible Expanding American.

Right before Thanksgiving, some lawyers went to court in pursuit of this theory. They filed a class action against McDonald's on behalf of New York children with health problems. These plaintiffs ate at Ronald McDonald's more than at Mom's. One 13-year-old weighed 278 pounds, while a 15-year-old weighed in at 400.

I would have called the case frivolous, except my dictionary defines frivolous lawsuits as "of little or no weight." Nevertheless, the story was enough to make me want to cross lawyers off my dinner party list. Who wants to be sued for serving cheesecake?

Now I'm not so sure. I think the lawyers have made their point, if not their case.

Consider the toy in my hand. It comes with the Happy Meal at my neighborhood McDonald's. The yellow rattle has a safety warning on the plastic wrapper. But the nutritional information for this beginner meal -- 20 fat grams and 36 sugar grams -- is nowhere to be seen. It is stashed under the counter and printed in agate that's off the eye chart.

Then there is the Mighty Kids meal, sold with a collection of Disney "Treasure Planet" toys. This newer, bigger, presumably "happier" meal for little kids totals around 1,160 calories. The Burger King version, dubbed the "Big Kids Meal," is marketed with a question for the 4-and-over eater: "Do you want to be a Big Kid?" It cheerfully supplies answers: "You Should." Indeed eat this often enough and you will.

A few facts? On any given day, one-quarter of Americans eat at a fast-food restaurant. In any given month, 90 percent of American children between the ages of 3 and 9 eat at a McDonald's.

They're not forcing hamburgers down open gullets. But if people have their share of personal responsibility for what they eat, is it really frivolous to expect some responsibility on the part of corporations for what and how they market? If parents are supposed to protect their little kids' health, is it really okay for Big Food to market and advertise in and around and over the heads of parents?

In a motion to dismiss the case, the lawyers for McDonald's wrote, "Every responsible person understands what is in products such as hamburgers and fries." They sound more than vaguely like all those tobacco moguls who righteously announced that "everyone knows" smoking is dangerous while they sent Joe Camel out on a recruiting mission.

Of course, food and tobacco are not the same, though some of the same lawyers who fought big tobacco have turned their sights to a big fat target. As Dick Daynard, head of Northeastern University's Tobacco Products Liability Project, says, "Nobody needs to smoke cigarettes unless they're hooked, but everyone needs food. And there's no such thing as secondhand eating."

But a deep, dark secret of the fast-food industry is that it makes most of its money from the people targeted as, ahem, "heavy users." Like the tobacco companies, says Daynard, "food companies have very sophisticated motivational people on their payroll to figure out how to get kids to use their product."

That's fine if there aren't any health problems associated with the product. But if fast food is good for you, how come Mickey D's took out an ad in France telling parents that kids shouldn't eat les hamburgers more than once a week?

I don't like to talk about the obesity epidemic; fat isn't exactly contagious. But today 61 percent of adults and 14 percent of adolescents from 12 to 19 are overweight, an increase of 300 percent over three decades.

That's not just a Big Mac mistake. Blame it on a sedentary lifestyle. Blame it on portion (out of) control, from candy bars on steroids to the bagels that ate New York. Blame it on schools selling soda pop in the hallway. If we are what we do and what we eat, we're potatoes: couched and fried.

I don't think the best lawyers in town can prove that the fast-food industry fattened its customers. But they may prove it fooled its customers. Especially the young ones.

Mark my words and label your lunch. This is just the beginning of a big, fat food fight.