Another reason is , if you have a weak cardiac sphincter (esophageal sphincter) at the top of your stomach - which I do - it can allow stomach acid to splash up into your esophagus and cause heartburn, and eventually acid reflux disease.
Keeping your upper body slightly elevated will prevent that.
Digestion considerably slows since your body perceives laying down as "sleepy time". Since you're not digested, you're not burning off those calories from the food, & therefore gaining weight.
The digestive tract uses gravity to help push down food, so when you are laying down it makes it harder on your body to digest your food properly.
it's always good to wait at least an hour to lay down after you eat because that's the average time it takes to digest
Bad for digestion, taking a walk after eating is best.
Because your food doesnt fully digest right.