ALEXANDRIA, Va. (AP) -- First lady Michelle Obama framed her national campaign against childhood obesity in intensely personal terms Thursday, relating that her own daughters were starting to get off-track before the family's pediatrician gave her a wake-up call and warned her to watch it.

"In my eyes, I thought my children were perfect," the first lady said. "I didn't see the changes."

But the family's pediatrician, she said, kept a close eye on trends in African-American children and "warned that he was concerned that something was getting off-balance." The doctor "cautioned me that I had to take a look at my own children's BMI," or body mass index, the first lady said.

Mrs. Obama said parents often recognize that kids in general don't eat right and aren't exercising enough, but "we always think that only happens to someone else's kids, and I was in that position."

"Even though I wasn't exactly sure at that time what I was supposed to do with this information about my children's BMI, I knew that I had to do something," she said. "I had to lead our family to a different way."

The first lady said that over the next few months she made some small changes that got her daughters back on track. No more weekday TV. More attention to portion sizes. Low-fat milk. Water bottles in the lunch boxes. Grapes on the breakfast table. Apple slices at lunch. Colorful vegetables on the dinner table.

"It was really very minor stuff, but these small changes resulted in some really significant improvements, and I didn't know it would," Mrs. Obama said. "It was so significant that the next time we visited our pediatrician, he was amazed. He looked over the girls' charts and he said, 'What on earth are you doing?'"

Mrs. Obama said that's the message she hopes to share in her anti-obesity campaign, that "small changes can lead to big results."

The first lady made her remarks at a YMCA in Alexandria, Va., where she appeared with Surgeon General Regina Benjamin, Health and Human Services Secretary Kathleen Sebelius, and Dr. Judith Palfrey, president of the American Academy of Pediatrics.

Benjamin released a report that serves as an update to a 2001 surgeon general's report that was a call to action against obesity.

"Although we've made some strides since 2001," Benjamin said, "the number of Americans -- like me -- who are struggling with their weight and health conditions related to their weight, remains too high."

Almost one-third of kids are at least overweight; about 17 percent are obese.

The first lady is to formally launch her campaign against childhood obesity in a few weeks.

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