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  • Karen Haralson

Fourth Phase of Digestion

Updated: Nov 9, 2023

Nurturing Your Gut Health for a Better You: Breakdown in the Intestinal Phase

Your digestive system is your body’s gateway to optimal health. When you digest well, your body can perform vital functions. Digestion is the breakdown of food, absorption of nutrients, and elimination of waste. Healthy digestion is essential for energy, tissue repair, and the growth of new cells.

Your digestive system uses chemical, biological, and mechanical processes and nervous impulses to break down and absorb food. Digestion can be broken down into four phases:

1. Cephalic (head) phase – the sensory organs (taste, smell, etc.) and mouth.

2. Esophageal phase – the esophagus.

3. Gastric phase – the stomach.

4. Intestinal phase – the small and large intestines.

This article describes the curvy intestinal highway or fourth phase of digestion. Food breakdown is finalized in the intestines, absorbed through the walls, and sent to the body via the bloodstream. The microbiome and gut-brain axis play a role in that process. What doesn’t get used is finally eliminated.

Understanding digestive function helps in healthy decision-making regarding food and lifestyle choices. You’ll also find practical tips here to help you naturally improve gut health.

The Marvelous Small Intestine: Your Nutrient Highway

The small intestine functions to finish processing fats, carbohydrates, and leftover protein into easily absorbed particles. The acidic food, with a pH of 2-3 from the stomach, is buffered to a pH of 6-7 with the aid of bicarb, bile, and pancreatic enzymes.

Bile, made by the liver and stored in the gallbladder, breaks fat into fatty acids. The pancreas secretes powerful enzymes that help convert carbohydrates into simple sugars. These enzymes help finish the breakdown of protein into amino acids.

These smaller food particles, called nutrients, are easily absorbed through a tightly packed cellular lining called villi. The villi are curvy, folded, and have small finger-like extensions. Because many nutrients must be absorbed, the curves, folds, and extensions create vastly more places for absorption. Most of the absorption happens in the small intestine.

Dr. Ron Waloff, MD, a gastroenterologist at Los Palos Gastroenterology Specialists, has performed thousands of colonoscopies over 41 years of practice and discusses how villi become affected during inflammation or infection. He notes that sometimes people wait too long to see him. "If you have an ongoing period of digestive symptoms, you need to come in. We need to be sure you're not having a problem that could continue to worsen."

Blunted villi can be an expression of disease, maybe celiac disease, or H. pylori infection … You would not be able to absorb the nutrients because you don’t have the surface area.” This, he states, can lead to becoming malnourished.

Unveiling the Colon’s Microbiome: Your Inner Ecosystem

The large intestine (colon) contains mostly leftover nutrients, indigestible products, water, and old cells from the digestive tract. Most of the water is reabsorbed, along with nutrients and electrolytes. The rest is eliminated as waste.

The first part of the colon is a section called the cecum, where most of the gut microbiome lives. Technically, the microbiome lives throughout the entirety of our digestive system. It’s made up of bacteria and other organisms (microbiota). The microbiota are essential for a nutrient breakdown process called fermentation. The microorganisms help to make vitamins and other simple compounds (metabolites). In doing so, they manage blood sugar regulation, weight management, cardiovascular health, colon cancer prevention, and many other body functions.

Microbiota lacking diversity are implicated in health problems such as obesity, diabetes, cognitive decline, and inflammatory diseases. While more is being learned about our gut ecosystem, we do know many factors that affect them. The environment, our emotional patterns, food, medications, smoking, and physical activity are a few of the influences on the microbiome. Thankfully, we have control over many of them based on our lifestyle and dietary habits.

Dr. Waloff expresses the need for the Western diet to include more fiber, which is generally lacking, for digestive health. He states, "Often its' just lifestyle changes, such as watching our diets and exercising. It's going to be the answer to a lot of questions about improving gut health. And getting enough sleep, he added. "The simplest things can make the most difference."

Gut-Brain Axis: An Information Super-Highway

Nerves in the digestive system are wired closely to the brain. The gut-brain axis is a term used to describe this two-way information super-highway. Different types of traffic travel to and from your brain on this network, which involves the vagus nerve. In other words, while your brain influences your digestion, your digestion also impacts your brain.

Communication in the gut-brain axis uses the following:

· microbiome,

· immune system cells – 70-80% of the immune system lives in our intestines

· neurotransmitters – 90% of serotonin is produced in the small intestine, and

· metabolites (including vitamins).

Although more research is needed, imbalances in this network could lead to various symptoms:

· emotional problems - depression, anxiety, stress,

· movement disorders - weakness, tremors, stiffness,

· immune sensitivities - headaches, rashes, hives, eczema,

· digestive symptoms - nausea, vomiting, diarrhea, constipation, gas, bloating, and

· and others - fatigue, memory loss, sleep disorders, palpitations.

Out with Waste: Elimination Explained

Stool, poop, feces, or bowel movements. They are all synonyms for what is eliminated when you’re finished digesting. And it’s an essential indicator of your digestive health. Bowel movements hold clues that highlight whether you need some tweaking to regain digestive balance. Questions you may want to ask yourself include:

· Do my stools float or sink?

· What is the color and odor?

· Do I have liquid, formed, or hard stools?

· What is my bowel movement frequency?

· Is there any undigested food in my poop?

· How does sleep or stress affect my digestion?

· What foods or drinks help me go, give me diarrhea, or constipate me?

While a bowel movement pattern isn’t standard for everyone, Dr. Waloff says, “A normal bowel movement would be a formed stool that’s not too hard and doesn’t cause a lot of discomfort. There should be no pain or bleeding. It should be produced comfortably.”

Top Tips for Boosting Your Gut Health Naturally

In learning about gut health, you can see how poor breakdown of food, an unhealthy diet, nutrient malabsorption, microbiome dysbiosis, and nervous system dysregulation can impact your health. Without the nutrients and metabolites needed for movement, thinking, breathing, circulation, filtering waste, wound healing, digestion, and more, the body has trouble functioning properly. Over time, poor function leads to poor health.

Like your car, your body wants to use good fuel for optimum performance. Here are practical tips for enhancing your gut health in everyday life.

1. Stay hydrated. Your digestive system requires water to support the gut bacteria and help with nutrient, electrolyte, and vitamin absorption. Water is a crucial element to prevent constipation. Depending on your health, climate, and activity level, you may need more or less water.

Here is a water drinking schedule to consider:

· When you wake up in the morning. Give it a splash of lemon juice to add fiber and boost your stomach acid.

· Thirty minutes before or after meals.

· Two hours before going to bed to prevent those late-night bathroom trips.

2. Increase fiber. Fiber is essential to colon health. Fiber adds bulk and keeps food moving, giving you a full and satiated feeling. It also stabilizes blood sugar and assists in removing harmful bacteria and excess cholesterol. Increase fiber slowly over time to allow your body to adjust.

Healthy sources of high-fiber foods include:

· Kale

· Sweet potatoes

· Brown rice and quinoa

· Broccoli and brussels sprouts

· Barley, oatmeal, artichokes, avocado

· Raspberries, blueberries, apples, pears

· Kidney beans, chickpeas, split peas, lentils

· Chia, flax, pumpkin, sunflower seeds, and pistachios

3. Add fermented foods. Ferments also feed your microbiome. As with fiber, start with a small amount and work your way to more over time. In a 2021 Stanford study, a diet high in fermented foods increased the diversity of bacteria and decreased inflammation. This is important to prevent obesity, diabetes, and other chronic diseases.

Ferments include:

· Sourdough bread, yogurt

· Fermented coconut water, kefir, kombucha

· Sauerkraut, kimchi, miso, pickled vegetables

4. Eat a rainbow. Eating diverse colored foods provides your intestines with polyphenols, among other benefits. These foods, with the help of our friendly microbes, increase your absorption of metabolites. They play a role in cancer prevention and help balance the microbiome with helpful bacteria. Polyphenols have antioxidant properties, which means they can reduce free radical damage resulting from normal body functions, aging, and environmental exposure.

· Raw cacao

· Green tea, coffee

· Spinach, artichokes

· Hazelnuts, chestnuts, pecans

· Italian herbs, cloves, curcumin, chilis

· Blueberries, plums, cherries, pomegranate

5. Move that body. Physical activity improves peristalsis and keeps food moving through the digestive tract. It helps create a diverse microbiome, improves blood sugar regulation, and increases overall energy. Other benefits include strengthening the immune system, balancing mood, reducing stress, and weight management. Before starting an exercise routine, check with your doctor to see what is best for you.

Exercises for gut health include:

· Taking a brisk walk or cycling after eating a meal on the lighter side. Exercising after a heavy meal may cause digestive symptoms such as indigestion or diarrhea.

· Yoga or Qigong. Yoga poses help digestion by toning the vagus nerve. They include seated twists, forward bends, cat-cows, and corpse poses. Qigong techniques for digestion include deep abdominal breathing, meditation, and mindful movements. These exercises help relax the nervous system while strengthening abdominal (core) muscles.

· Strengthening core muscles. Exercises such as planks, reverse sit-ups, and boat pose decrease gas, bloating, and constipation. Take caution in preventing back injuries by performing core exercises with the correct form. A personal trainer can help you find the right core exercises for your body.

Achieving Optimal Health through Digestion

The impact digestion has on your overall health cannot be overstated. You can support your digestion and overall health within each phase, starting with the cephalic, esophageal, and gastric phases. This article discusses the intestinal phase of digestion, noting:

· Small intestine juices mix with bile and pancreatic enzymes to digest fats, carbohydrates, and proteins,

· Nutrients are absorbed by villi in the small intestine and are transported into the bloodstream,

· The large intestine holds the diverse microbiome, which helps to create vitamins and metabolites,

· Key players along the gut-brain axis and symptoms of imbalance and

· Bowel movements hold clues about how we’re digesting.

Tips to improve digestion include drinking water with a suggested schedule and eating fiber to help stabilize blood sugar. You can also feed your microbiome with ferments and limit aging by increasing your antioxidants. Movement, whether walking, yoga, or core exercises, is also a great way to improve digestion.

By learning about healthy digestive function, nutrition, and lifestyle choices, you can control your body's functions and optimize your health.


Robin Fillner is an Oncology Nurse and Health Writer. Using her Functional Nutrition Certification and healthcare expertise, her passion is writing about healthy food and lifestyle choices through the functional lens. When not on an ocean wave or a forest trail, find her at or


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