A main factor is comfort, as swimming immediately after a large meal may cause temporary digestive discomfort, says Michael Richardson, MD, a family medicine physician at Mass General Brigham in Boston, who specializes in sports medicine. “It’s not unusual for someone to feel nauseous, sluggish, or develop a stomach cramp if they jump into heavy activity right after eating,” Dr. Richardson says. Depending on where you’re swimming or exercising, immediately after a large meal, it may create an unsafe situation if it affects your performance. “If the meal makes you cramp or feel heavy or sluggish, it can make swimming harder,” Richardson says. While many people can swim shortly after eating without any issues, others may benefit from a brief delay for these reasons.