Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into the blood stream. This process begins in your mouth. Chewing your food properly makes it easier for your digestive system to break down your food, which in turn puts less wear on your organs.
The digestive track is about 30 feet long. In a healthy human adult the digestive process can take between 24 and 72 hours. A healthy plant based meal will enter and exit the digestive system within a 24 hour period, while a meat based meal will take closer to 72 hours. That is an extra 48 hours of unnecessary, age accelerating work on the body. A meal with high amounts of fresh vegetables will always do better in the body than a meal without.
The stomach is a distensible organ and normally expands to hold about 1 fluid quart of food, but can hold as much as 2-3 fluid quarts. Eating a meal that is 1 fluid quart or less will do much in relieving the pressure on the digestive system. Also, eating meals with high volumes of fiber rich and nutrient dense foods (fruit & vegetables) will increase the sense of fullness faster, which helps to decrease the volume eaten.
It takes about 3 to 4 hours for a meal to past through the gastric phase (stomach). Here is where the food is broken down before it is released into the small intestine. In this part of the digestive process many are over working their organs by eating too frequently. It will take around 4 hours for the average meal to pass through the stomach and then we should allow for at least 1 hour of rest before the next meal. Eating in between meals or too late at night does not allow the stomach to finish the process and rest before next meal, but instead leaves in the stomach an acid reflux toxic soup. If you don't want to look tired or feel lethargic, then start by giving your digestive organs a well deserved rest.
God gave you one body so be gentle with it, because when you abuse it, you are abused and when you kill it, you are dead.