You may be surprised to learn that digestion actually begins before you even take your first bite of food. This is called the cephalic phase of digestion and is kicked off by the mere sight or smell (or even thought or taste) of food as your body prepares to eat.
Once you’ve taken your first bite, the saliva in our mouth both moistens and helps digest food, for example amylase for carbohydrates and starches. As nutrition scientist Ashley Jordan Ferira, Ph.D., RDN explains, “Along with chewing, your mouth is where digestion, or the breakdown of food into smaller bits, begins. In fact, your mouth (aka oral cavity) features its own unique set of microbes known as the oral microbiome.”
From our mouth, the food, beverages, and supplements we consume journey down the pharynx and esophagus to the stomach where they are broken down further. This continued digestion happens through unique acidic compounds, as well as protein- and fat-digesting enzymes, in the stomach. “Muscular contractions in the stomach also contribute to the digestive process,” adds Ferira. From chewing our food to stomach digestion, this movement of food takes about two hours.
Your meal, or “bolus of digested food known as chyme,” Ferira explains, will then move into the small intestine via the pyloric sphincter where digestive enzymes, many of which are secreted by the pancreas, and bile from the gallbladder break it into even smaller pieces before they are absorbed from the gut into the bloodstream to be utilized by the entire body.
“These smaller constituents being transported and utilized throughout our body are peptides that make up proteins, sugars that make up carbs, fatty acids that comprise fat, plus vitamins, minerals, and even phytonutrients,” shares Ferira. “A unique array of probiotic species reside in the small intestine, also interacting with our dietary inputs,” Ferira adds.
You can expect food to travel through the muscle-lined small intestine for one to five hours depending on what you’ve eaten (more on that later.) Immediately following the small intestine is the large intestine (aka colon) where the gut musculature gradually moves along any remaining digested and undigested compounds.
The large intestine section of the gut is where another unique habitat of gut flora microbiota reside. “Of course, this assumes our dietary and supplement inputs are nourishing gut microbial abundance and diversity daily,” adds Ferira.
Another important act is achieved in the colon: bulk. While significant amounts of water are absorbed from the gut into the bloodstream in the small intestine, “the final water absorption activity occurs in the colon, to functionally solidify the remaining indigestible components of our diet, creating stool,” Ferira explains.
The colon is also where certain the bacteria work to ferment key remaining nutritional components (e.g., prebiotic fibers) to glean any additional nutrients and “produce unique nutritional byproducts like short-chain fatty acids that confer health benefits,” says Ferira. In fact fiber consumption will directly impact how long food stays in the large intestine, and fiber assists in bulking up the stool that will then exit your body (via the rectum and finally, anus) at the end of the digestive tract.