U.S. childhood obesity rates have increased over the past 14 years, according to a study published on Monday, casting doubt on a recent analysis by government health researchers that found a sharp drop in preschool obesity rates over the past decade.

The good news, announced in February by researchers at the U.S. Centers for Disease Control and Prevention (CDC), received widespread media coverage and prompted first lady Michelle Obama to say she was “thrilled at the progress we’ve made over the last few years in obesity rates among our youngest Americans.