STAMFORD - A Stamford High School student has grabbed the attention of first lady Michelle Obama after losing 70 pounds and sending a letter to the White House. Sophomore Samantha Pesiri, 15, says she weighed nearly 200 pounds, and had received warnings from doctors that she could face diabetes and other medical problems if she failed to make serious lifestyle changes. Pesiri then sent before-and-after photos of herself to Obama, who has spearheaded a nationwide campaign against childhood obesity. She received a handwritten letter from the first lady, congratulating her on the accomplishment. Pesiri says she now wants to help other young people with similar weight issues.