Aug. 28. 2015
Written By:
McKel (Hill) Kooienga
McKel Kooienga, MS, RDN, LDN

McKel Kooienga, MS, RDN, LDN

Dietitian, Founder and CEO

Dietitian Nutritionist McKel shares a basic guide to the digestion process.

There’s a lot of information about digestion issues and how to improve digestion here on Nutrition Stripped, but what exactly is happening in digestion?

In a perfect world, we would eat our food and it would digest well with little to no side effects like bloating, diarrhea, constipation, or cramps. Our bodies would be able to pull out all the nutrients from the food and utilize it as intended. But unfortunately, it’s not a perfect world and our digestive systems go through so much “wear and tear” over the years that it affects how efficient our digestive system operates and how our bodies absorb key nutrients from our delicious and healthy food.

Several factors have an impact on our digestion including but not limited to: hormonal shifts, stress in our life, activity, genetics, food intolerances, vitamin and mineral status, metabolism, thyroid health, chronic diseases, illness, medication use, supplement use, sleep, environmental toxins, everyday exposure to elements, antibiotic use as infants, and of course what we put in our bodies as food. To understand ways to improve digestion, it is helpful to first understand the basics of the digestion process.

What Is The Digestive Process? 

Digestion is the act of consuming, breaking down, processing, and utilizing food for energy. There are two ways food is digested: one way is by mechanical digestion when food is chewed and physically broken up into tiny little pieces; the second way is by chemical digestion where food is broken down into even smaller molecules with the help of digestive enzymes.

Enzymes actually start at the first site of digestion — the mouth — with saliva. Saliva contains an enzyme called amylase which helps start the chemical process of breaking down the food while our teeth start the mechanical. This is why chewing food well is VITAL for good digestion. Eating quickly means larger food particles enter the stomach and more digestive enzymes and energy are required to break the food down.

Next, food goes through the esophagus then reaches the stomach where chemical digestion continues as gastric juices start to break down food. Gastric juice is mostly made up of pepsin and hydrochloric acid (HCL). Our bodies must have enough acid to help break down food and proteins in our digestive system. Those who suffer from low HCL level can actually experience higher incidences of GERD or reflux issues.

Our bodies can secret about two liters of HCL a day, but has enough mucus lining the stomach to protect the organ from acid damage. While chemical digestion is occurring due to acid breaking down the food, mechanical digestion is still happening in the stomach through a process called peristalsis. Peristalsis is a process that makes the muscles in the stomach wall contract and releases to mix up the food and enzymes. Here’s a video of how it works.

After food has been chemically and mechanically broken down, which can vary in time depending on how much food you eat and the variety but around one or two hours, it goes into the small intestine. The small intestine again breaks down the food but also absorbs many vital nutrients with little finger-like projections called villi and microvilli. Villi and microvilli provide enough surface area for our bodies to absorb molecules from food that are transported into our blood vessels of the intestinal wall.

The small intestine is about 22 feet long and 1 inch in diameter, so the surface area of the small intestine is about the size of a 2700 square foot tennis court. This is possible because the small intestine not only has folds, but on those folds are villi, and on those little villi are microvilli. There are layers on layers on layers all to help you absorb food.

Our liver and pancreas also support the digestion process, too. The liver produces bile, which is carried into the small intestine by a bile duct and used to aid chemical digestion. The pancreas secretes pancreatic juices and enzymes that aid in digestion as well. Lastly, after the food has been broken down and passed through the small intestine, the large intestine absorbs all remaining nutrients but mostly any remaining water. This is how stool is formed that then passes out of our bodies via the rectum.

How Macronutrients are Digested

  1. Carbohydrates: require amylase enzymes — broken down into simple sugars, glucose molecules
  2. Fats: require lipase enzymes — broken down into monoglycerides and fatty acids that involve emulsification, micelles, and chylomicrons
  3. Proteins: require pepsin enzymes — broken down into amino acids

Basically, the route of digestion is: mouth → esophagus → stomach → small intestine (pancreas and gallbladder are involved here as well) → large intestine → colon

How Do You Optimize Digestion?

There’s a saying I always teach and also practice myself as much as possible: “chew your liquids and swallow your solids”. This means chew your food thoroughly enough that it’s a puree texture, and then swallow and swish around liquids in your mouth so you’re not just guzzling smoothies, juices, or even water without activating the first part of digestion in the mouth from your saliva.

You could eat the healthiest diet, have everything in your health “aligned”, yet if your digestive system is under stress and isn’t functioning properly, you won’t be able to utilize your healthy diet and get the most out of what you just ate.

Do You Need to Take Digestive Enzymes?

Digestive enzymes in the form of a supplement can be quite helpful for those who need a digestive boost. For example, many can’t digest beans and legumes very well and there are many supplements on the market that help break down the polysaccharides in legumes that can be difficult to giest. There are also some foods that contain natural digestive enzymes that are more “powerful” than most other whole foods like pineapple and papaya. You don’t need to take digestive enzymes to optimize digestion, but in some cases, they can help alleviate gas and bloating. Always check with your doctor before taking a new supplement as it might interact with other medications or not be right for your body.

Now that we’ve covered the basics of how the digestive process works and how to begin your digestion by properly chewing, keep reading through the NS archives to continue to improve your digestion.

Additional Resources to Improve Digestion: