Nobody saw this coming:

Federal health authorities on Tuesday reported a stunning 43 percent drop in the obesity rate among 2- to 5-year-old children over the past decade, the first broad decline in an epidemic that often leads to lifelong struggles with weight and higher risks for cancer, heart disease and stroke.

The drop emerged from a major federal health survey that experts say is the gold standard for evidence on what Americans weigh. The trend came as a welcome surprise to researchers. New evidence has shown that obesity takes hold young: Children who are overweight or obese between age 3 and 5 are five times as likely to be overweight or obese as adults.

That is spectacular news. They’re not sure why it’s happening, though:

Experts point to several possible explanations for the fall, but say a full understanding remains elusive. Children now consume fewer calories from sugary beverages than they did in 1999. More women are breast-feeding, which can lead to a healthier range of weight gain for young children. Federal researchers have also chronicled a drop in overall calories for children in the past decade, down by 7 percent for boys and 4 percent for girls, but health experts said those declines were too small to make much difference.

Another explanation is that some combination of state, local and federal policies aimed at reducing obesity is starting to have an effect. Michelle Obama has led a push to change young children’s eating and exercise habits and 10,000 child care centers across the country have signed on. Many scientists doubt that anti-obesity programs actually work, but proponents of the programs say a broad set of policies applied systematically over a period of time can affect behavior.

This is wonderful. Just tonight, driving away from the sports park, one of my little ones asked for the thirty-fifth time if he and his sister could have some cookies when we got home. Yes, I said, you can. He had been asking all afternoon, and had gotten on my last nerve. I explained to them both that it must seem like Mom and Dad are being mean to them by not letting them snack between meals, and by restricting the amount of sugar they eat, but it’s our responsibility to raise them to be healthy. I told them that their father was a really fat kid because people in our family drew the short straw on genetics, because Dad was a junk food fiend as a kid, and because Dad would rather have weasels gnaw his toes than exercise. I struggle today with bad habits that set in when I was your age, I told them. Mom and Dad are helping y’all avoid these problems when you’re older.

I arrived at home, checked the NYT website, and saw this. Something is working. There are going to be a lot more kids who don’t end up like me in middle age. Hallelujah for that. To the extent Mrs. Obama’s work has contributed to this cultural shift, I am grateful for her advocacy.

Now, let us commence our usual obesity-and-culture argument in the comments thread…