Why does my identical twin look different?

We are 14 years old and are identical twins not furturnal. We looked the same until we turned 9 years old. After that he grew really taller and i grew fatter. right now he is 6'0 tall and weighs only 120 pounds. he has the body of a bean pole. he has not fat or muscle in his body he is just skin and bones and our doctor said he is underweight and should gain weight and i am 5'6 and around 280 to 300 pounds. my body shape is round i am fat and jiggly. my doctor says i am morbidly obese and should lose weight. fitness wise he has better cardio fitness he is in track and his 40 time is 5.6 sec and i am on the football team and my 40 was 10.8 sec. but i am way stronger than him and when we fight i always win i normally just sit on him. i can bench 180 pounds and he can bench only 80 pounds. his eating habits are eating healthy foods and eats small. i eat really fatty foods and alot of it, but when we arent doing after school sports i am active like playing football outside with friends and he normally just stays inside and plays video games?