In Part 1 of this series, I reviewed what digestion is, why it is so important, and began a journey through the digestive system.

We started in the mouth, moved down the esophagus and into the stomach, and took a brief stop to talk about the #1 digestive complaint: reflux.

Today, we will continue the digestive journey from the stomach through the small intestine, large intestine, and beyond.

a pencil drawing of the word love — Photo by Europeana on Unsplash

Small Intestine

When partially digested food leaves the stomach, it enters the small intestine, where most digestion and absorption occur.

Remember, digestion includes many mechanical and chemical processes that break food down into tiny pieces so they can be absorbed. Absorption is the process of moving nutrients from the digestive system into the bloodstream to then be delivered throughout the body.

The small intestine has three sections: the duodenum, jejunum, and ileum (I still remember “DJI” as my memorization trick in college).

Duodenum

The gallbladder, liver, and pancreas all connect to the duodenum to supply additional components involved in chemical digestion.

Bile is produced in the liver, stored in the gallbladder, and released on demand to emulsify dietary fat. Emulsification is essentially breaking fat into smaller droplets for easier digestion.
- Without a gallbladder, bile drips continuously rather than being released in a concentrated burst, which may result in loose stools and bowel urgency after high-fat meals.
Pancreatic enzymes are released to digest carbohydrates (amylase), fats (lipase), and proteins (protease).
- When the pancreas doesn’t produce or deliver enough digestive enzymes to the small intestine, it’s known as Exocrine Pancreatic Insufficiency (EPI), which is managed with pancreatic enzyme replacement therapy (PERT) taken before each meal.

Jejunum

Most nutrients are absorbed in the jejunum section of the small intestine. Villi and microvilli (folds and folds-within-folds of this section) increase surface area to allow for maximum absorption.

Ileum

The longest section of the small intestine, the ileum is where vitamin B12 is absorbed with help from intrinsic factor. The ileum also contains immune tissue that responds to harmful substances before the remaining contents enter the large intestine.

Diseases of the Small Intestine

Small Intestinal Bacterial Overgrowth (SIBO)

We all have health-promoting bacteria in our large intestine (more on the microbiome next time). But when these bacteria overcolonize the small intestine, symptoms such as bloating, gas, diarrhea and/or constipation, abdominal pain, and nutrient deficiencies may occur. This condition is known as Small Intestinal Bacterial Overgrowth, or SIBO.

However, since many of these symptoms are “non-specific” (meaning they can arise due to many factors), SIBO isn’t diagnosed by symptoms alone. SIBO diagnosis is made based on the results of a hydrogen or methane breath test and is typically treated with antibiotics.

Preventing SIBO from returning requires awareness of dietary and supplement (including probiotics!) triggers.

Celiac Disease:

While gluten sensitivity is more common than we once thought (and has earned the term Non-Celiac Gluten Sensitivity), celiac disease is an autoimmune condition triggered by gluten, a protein found in wheat, barley, and rye.

Common celiac disease symptoms include bloating, diarrhea, and/or constipation after eating gluten. Long-term, unmanaged symptoms may include fatigue, anemia, bone loss, skin rashes, and weight loss.

Celiac disease is diagnosed by blood antibody testing and/or intestinal biopsy, and the only treatment is a lifelong gluten-free diet.

It’s important to keep in mind that having one autoimmune condition increases a person’s risk for others, including rheumatoid arthritis, type 1 diabetes, psoriasis, and more.

Food Intolerances

Food intolerances occur when the digestive system has difficulty digesting a food. This may be due to a missing or inadequate enzyme (ex: lactose intolerance) or poor absorption (like fructose or FODMAPs).

Food intolerances differ from food allergies and food sensitivities:

Food allergies are an immune system response to a food protein, resulting in reactions that can range from mild to severe or life-threatening (such as with peanut allergy). Even tiny exposures can trigger a reaction.
Food sensitivities are a less medically precise and less validated term for reactions that don’t clearly fit the intolerance or allergy category, such as foods that cause headaches, fatigue, or skin issues.

Common Food Intolerances

Lactose Intolerance: Inadequate lactase enzyme to break down lactose (dairy sugar).
Fructose Malabsorption: Incomplete absorption of fructose (fruit, honey, high-fructose corn syrup).
Polyol (Sugar Alcohol) Sensitivity: Sorbitol, mannitol, xylitol, and other “-ols” (found naturally in peaches, plums, apricots, cherries, apples, and pears, and in many “sugar-free” products).

Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols — aka FODMAPs — refer to a group of compounds that may be difficult to digest for some people. Lactose is a disaccharide, fructose is a monosaccharide, and polyols are, well, polyols.

If undigested food components make their way into the large intestine, gas, bloating, and/or diarrhea may occur. Much more on the large intestine and microbiome next week, but for now, here’s what you need to know about why those oh-so-undesirable symptoms occur:

Gas is produced as a byproduct of fermentation in the large intestine.
Bloating occurs when excess gas builds up and puts pressure on the intestinal walls.
Diarrhea occurs because unabsorbed components pull water into the large intestine by osmosis, while other fermentation byproducts speed up how quickly contents pass through (and out).

If this last section made you squirm, just wait until we really take on the large intestine, microbiome, and fiber next week.

Thanks for being here,

~Allison

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Thanks for being here,

Allison

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This information is meant to inform and inspire and is not personal health or medical advice. Please speak with your healthcare team about what is right for you.

Insight Into Health

The Ins & Outs of Digestive Health — Part 2