How can being overweight affect your sporting peformance?

Obesity taxes every aspect of one's physiology. The added weight places demands on circulatory-respiratory systems in terms of oxygen requirement, additional tissues require blood flow, O2, nutrients, waste removal (toll on the kidneys and lymphatic system)...extra weight also is hard on bones, which are often not supported by enough muscle to carry the weight...risk of injury increases dramatically. Working out must commence gradually for an obese person in order to avoid serious injury, exhaustion or heart attack.

This is answer number 1: I have moved it because I believe the Answerer mis-read the question:

if you are obsessed with your body, then you would want to work out. so they would be better at it.