Dinner is over and you are sitting on the couch watching TV. You may be resting but your body has just kicked into high gear to deal with the avalanche of food you’ve ingested. All 29 feet of your digestive tract will be working to breakdown, process, absorb, and utilize the chicken, broccoli, potatoes, and every other bite of food you’ve just eaten.
Most of the nutrients you eat – proteins, fats, and carbohydrates – are bound in large molecules that can’t be absorbed into your body. The major job of your digestive tract is to convert food into absorbable units you can use. Think about the GI tract as a long tunnel going through your body from the mouth to the anus. Food in the GI tract is technically not inside your body. It is in transit and will pass from one end out the other, without being absorbed, unless certain events occur.
It all begins in the mouth. Chewing and wetting are the first mechanical steps that process food. Your teeth grind and crush dinner while the quart and half of saliva you produce each day wets it. Swallowing is the last voluntary step you take in the digestive process. From here down your body takes over and the rest of the process occurs without your input.
Your esophagus is essentially a 10-inch long tube connecting your mouth and stomach. Its tissues are delicate. If you swallow something hot, like chilies, or don’t chew thoroughly you’ll have hic-ups. If the acidic contents of your stomach backsplash onto the esophagus you’ll have heartburn. This is more likely to happen if you overeat, drink too much, or end a meal with coffee or chocolate. The lowest ringed muscles of the esophagus relax and allow stomach acid to back up and burn the delicate tissue of your food tube.
Waves of muscular contractions in the esophagus propel food into the stomach which acts as a reservoir, blender and funnel into the small intestine. The stomach churns dinner into a smoothie and stomach acid begins to breakdown food and kills off mold, bacteria, or viruses you ate along with your meal. It will take 1 to 4 hours for your stomach to empty. If eaten alone carbs leave the stomach quickly, but in a typical mixed meal emptying takes longer. High fat meals leave the stomach slower often causing bloating, heartburn and an uncomfortable feeling of fullness.
The heavy work of digesting food happens in the small intestine – 22 feet of coiled tubing lying just below your stomach. The ringed muscles at the bottom of the stomach regulate a steady flow of liquefied food into the small intestine. During emotional stress these lower stomach muscles often tighten leading to indigestion – the reason many of us lose our appetite when we’re upset.
The small intestine is the assembly line of digestion, broken into the 3 sections, upper, middle and lower. In the upper section, the duodenum, digestive enzymes break down large molecules into smaller fragments that can be absorbed by the body. Carbs become simple sugars, proteins are broken into amino acids, and fats become fatty acids. In the middle and lower sections, the jejunum and ileum, absorption takes place.
Over 95% of the food you eat is absorbed, an incredibly efficient processing system. Absorption is so efficient because the inner surface of the small intestine is covered with millions of tiny fingerlike projections called microvilli. These increase the absorptive surface of the small intestine to an area larger than a tennis court.
The large intestine, also called the colon, is the last 5 feet of your digestive tunnel. It’s your body’s recycling and garbage plant. Water and sodium are recycled to prevent dehydration. The water is absorbed back into the body leaving semi-solid stools – the body’s garbage. Colonies of friendly bacteria that live in your colon will break down fiber in your waste to be used as food to keep them healthy. They also make vitamins K and B12. These friendly squatters keep you healthy and prevent harmful bacteria from taking up residence in your colon.
In the past we’ve considered the appendix a simple evolutionary leftover attached to the colon. An intriguing theory suggests that the appendix is actually a warehouse for healthy bacteria that can be emptied back into the colon after an illness to repopulate your beneficial bacteria.
The total digestive process – from chewing to garbage disposal — will take 12 to 36 hours. You may be resting on the couch but for the next 8 hours your digestive process will be in high gear, followed by the absorption of needed nutrients, recycling of precious water, synthesis of vitamins, and disposal of garbage. Time for a nap!