Sometimes public wellness campaigns win, and institutions change - even institutions as ingrained in American life as the Golden Arches.

On Thursday, McDonald's Corp. announced the introduction of the Adult Happy Meal, a boxed salad, water and pedometer that may make grown-up Americans lean if not actually happy.

The move is clearly a concession to the obesity lawsuits and nutritional criticism that health advocates have leveled at the fast-food giant, and is so clean and pure an offering - virtually immune to nutritional nitpicking - that who can argue its merit?

And so we don't, even as we wonder if anyone will actually order the meal or why those who do would go to McDonald's in the first place.

But as we applaud this light addition to a fat-heavy repertoire, we wonder - in a twisted echo of those obesity lawsuits - just where does McDonald's responsibility end and ours begin? Americans may have succeeded in changing McDonald's, but will a choice-restricted boxed lunch succeed in changing Americans?

For at least the last decade, overweight Americans have believed their salvation lay in stamping out temptation rather than developing sound, if difficult and disciplined, eating habits.

Thus came to life such oxymorons as fat-free sour cream and carb-free bread. Americans wanted to have their cake and eat for two.

Companies obliged. Americans grew fatter. It seemed one of life's not-so-little ironies. Rounds of blame resulted. Genetics was the bad guy. Trans fat. Chinese food. French fries.

In the end, most Americans were able to avoid the whole issue of making sound nutritional choices, balancing daily food intake, eating well but eating less.

Now McDonald's has offered a new concession in the responsibility war. The Adult Happy Meal may prove to be helpful. It may prove to be enabling.

For now, we welcome it - and love that pedometer - even as we know that one skinny meal does not a leaner nation make. As much as we wish it weren't true, life's menu will always offer hard choices.