Jason is a body builder. despite being more fit, he weighs more than his brother ryan, who is the same height. which is a possible reason?

One possible reason is because Jason has more muscle mass (from the body building). A pound of muscle takes up less volume than one pound of fat. This would contribute to Jason weighing more than Ryan, despite being more fit. 

Because muscle weighs more than fat. So we have to assume Jason has more muscle in proportion to fat than brother Ryan even though they weigh the same.

If he tries to grape you then get a grape and grape him back