Michelle Obama’s child-obesity challenge

First lady Michelle Obama will formally announce her childhood obesity initiative Tuesday at the White House, an effort to reverse an epidemic in which almost one-third of American children are either overweight or obese.

But in making the fight against childhood obesity her signature cause, Obama has chosen to tackle a seemingly intractable problem that has thwarted experts for the past two decades.

Health professionals are optimistic that Obama’s personal appeal and the power of the White House may provide the necessary impetus to change the situation regarding child nutrition in this country, but they say she faces formidable barriers.