Professional athletes have coaches. I am not sure what their coaches tell them.
Anyone that eats and moves afterward will not digest their food well. They will also be lacking in nourishment because they are not breaking down their food completely.
Complications can also range from heartburn to bloated stomach which creates the big bulge that makes them look fat. If these people would take time, even 20 minutes of sitting they can relieve the bloating stomach. I often give this advise when I treat weight loss for my patients.