So I'm not and never was a really big guy, buy at one point in my life (around the age of 29 during my residency) I was actually technically overweight. I was 10 pounds over a healthy weight, and 22 over my ideal weight. A combination of eating and sleeping poorly, not working out, and some other factors led to my problem.
A common misconception some people have is that they fool themselves into not working out saying "I'm too tired to work out". Studies have shown that the rest that a healthy person gets is so much better than an unhealthy person that is far outweighs any time during the day spent working out.
Anyway I dropped 20 of the 22 pounds and hover around there right now. I like to keep in shape for myself, my family, and hopefully as an inspiration to my patients showing them that it is possible even for busy people to stay in shape.