There's no experimentally proven waiting time after eating. But the expert recommendations are close together: the DGE sports nutrition working group gives 2 to 3 hours for the last meal, the position paper 1 to 4 hours, and the consumer advice centres' coach handout 3 to 4 hours. The workout clock converts these windows to your training time.
3 to 4 hours before: the right meal
With a gap of three to four hours, a full meal is fine: a carbohydrate source like rice, pasta, potatoes or bread, plus a portion of protein and vegetables, but not much fat. Gastric emptying shows why the gap matters: even a small, low-fat test meal of 255 kilocalories is still 30 to 60 per cent in the stomach after two hours, and has almost fully moved on after four. Fat, protein and fibre slow things down even more. If you don't get round to cooking during the day, you can drink your meal instead; just add a carbohydrate source.
1 to 2 hours before: a small portion
If you only have one to two hours, the meal shrinks to a small, carb-focused portion with little fat: yoghurt with banana and oats, a bread roll with jam and a bit of turkey breast, rice pudding with strawberries, a pretzel with milk. In their guidance for coaches, the German consumer advice centres name an hour and a half before the start as the time for the last small portion. Protein is fine in moderation: skyr or low-fat quark is light on fat and leaves the stomach quickly, a cheese omelette doesn't.
30 to 60 minutes before: just something small
In the last hour, all that fits is a handful of fast carbs without fat: a banana, four dates, three rice cakes with honey, a slice of toast with jam. The old advice not to eat sugar in the last hour because your blood sugar will crash during exercise is considered disproven: in almost all studies, performance stayed the same or improved. Some people still feel a dip, though. If you're sensitive, eat 2 to 3 hours before or take your carbs during your warm-up.
How long after eating should you exercise?
After a big meal, 2 to 3 hours is a good guide, after a snack 30 to 60 minutes, and a walk is fine straight away. Only the mechanism is proven here, not the exact minute: a full stomach and drinks with lots of sugar or fizz make a stitch more likely, and how quickly your stomach empties depends on the calories, fat and protein in the meal. Swimming is no different from any other sport: the American Red Cross considers the warning about drowning after eating a myth; swimming within an hour of eating doesn't raise the risk.