"I thought I was doing what I was supposed to do, and I hadn't noticed any changes in my kids," she said. But she accepted the doctor's admonition as a "wake-up call" and began to make changes.
The point is that small changes made a difference.
"The point is that small changes made a difference," she said. "It wasn't a whole-scale upheaval of our lives to see the outcomes."
Obesity is linked to risk factors associated with cardiovascular disease, such as high blood pressure, high cholesterol and Type 2 diabetes.
In some ways, the family's life is like many others', she said. Her husband reads to the children at night and tucks them into bed.
The first lady described life in the White House as "like living in a big hotel with a whole bunch of fun people that you can work with. But then when -- when the doors close, it's -- it's like home."
She acknowledged, in response to a question, that sometimes her husband gets mad.
"Oh, yes. Yes, he's human. You know, if you prick him, he'll bleed."
She added, "I think it's wonderful to have strong female voices out there, but I don't know her."
The first lady was effusive about her husband's former rival for the top spot on the Democratic ticket, Hillary Clinton.
Asked what she expects on Valentine's Day, Obama told King, "Oh, I expect the moon, the stars and the sun, honey."
And what does her husband get?
"A nice card."