When we think about gut health, our minds often jump to the colon and probiotics. However, gut health encompasses the entire digestive tract, which begins at the mouth and ends at the rectum, with each part playing a vital role. The stomach, for instance, is mainly responsible for the mechanical grinding of food, breaking it down into a puree-like consistency. We can easily examine the stomach with an EGD. The colon, on the other hand, reabsorbs water and remaining nutrients and helps form and eliminate waste, and we can visualize it through a colonoscopy. The small bowel, though, is often overlooked due to its length and the difficulty in visualizing it. Yet, it’s where over 90% of nutrient absorption happens, making it absolutely essential for our survival. While we can live without a stomach or a colon in certain situations, the small bowel is irreplaceable.
Beyond its crucial digestive role, the small bowel also significantly influences many other aspects of our well-being. Key functions of the small bowel include:
1. Nutrient Absorption – The Body’s Nutrient Superhighway
The small bowel is the primary site for digestion and absorption of nutrients, responsible for handling over 90% of nutrient uptake. Its inner lining is covered with villi and microvilli, tiny finger-like projections that dramatically increase surface area—creating a “brush border” that maximizes contact with digested food.
- Macronutrients: Carbohydrates, proteins, and fats are broken down by enzymes and absorbed here.
- Micronutrients:
- Fat-soluble vitamins (A, D, E, K) are absorbed along with dietary fat in the jejunum and ileum.
- Water-soluble vitamins (like B-complex and C) are absorbed throughout, with vitamin B12 specifically absorbed in the terminal ileum, requiring intrinsic factor produced by the stomach.
- Minerals like iron (in the duodenum), calcium, magnesium, and zinc are absorbed selectively based on the body’s needs.
- Water and electrolytes: Also absorbed in significant quantities to maintain hydration and homeostasis.
When the small intestine is inflamed, damaged (e.g. celiac disease), or bypassed (e.g. surgery), nutrient deficiencies and malabsorption syndromes can result.
2. Immune Function – The Gut’s Immune Defense Headquarters
A remarkable 70% of the body’s immune cells reside in the gut-associated lymphoid tissue (GALT) of the small bowel, making it the largest immune organ in the body.
- Peyer’s patches in the ileum act like immune surveillance stations, constantly sampling intestinal contents for pathogens.
- T-cells, B-cells, plasma cells, and natural killer (NK) cells populate the intestinal mucosa and submucosa.
- Secretory IgA (sIgA) antibodies are released into the gut lumen to neutralize toxins and pathogens without triggering inflammation.
- The gut microbiota communicates directly with immune cells, helping train the immune system to distinguish between harmful invaders and harmless antigens (like food and commensal bacteria).
This immune environment not only defends against infections and prevents cancer cell formation, but also plays a critical role in modulating autoimmune conditions and allergic responses.
3. Hormonal Powerhouse
- GLP-1: The Natural Metabolic Regulator
The small bowel contains specialized L-cells that naturally produce GLP-1 (glucagon-like peptide-1), a powerful gut hormone that regulates blood sugar, suppresses appetite, and slows gastric emptying. GLP-1 is the key acting peptide behind blockbuster weight-loss and diabetes medications like Ozempic and Wegovy. But long before pharmaceuticals, our bodies were making it naturally—right in the small intestine. When GLP-1 production is optimized, it can help prevent or reverse many chronic conditions tied to metabolic syndrome, including type 2 diabetes, obesity, fatty liver disease, PCOS, and even cardiovascular disease. - Serotonin: The Gut-Mind Connection
Nearly 90% of the body’s serotonin—often called the “happy hormone”—is produced by enteroendocrine cells in the small bowel. This gut-derived serotonin plays a critical role not just in mood regulation, but also in sleep, gut motility, and overall emotional well-being. When serotonin levels are balanced through a healthy gut, we can reduce the risk of depression, anxiety, and other mental health challenges. In this way, nurturing the small bowel supports both mental and emotional health from the inside out.
The small bowel isn’t just essential for digestion — it’s a central command center for whole-body health. It plays a key role in preventing and managing a wide range of chronic conditions, including:
1. Metabolic syndrome — through natural GLP-1 production, such as type 2 diabetes, obesity, cardiovascular disease, and polycystic ovary syndrome (PCOS)
2. Cancer — through immune surveillance and inflammation control
3. Infections — by housing 70% of the body’s immune cells
4. Mood disorders — including anxiety and depression, via gut-derived serotonin and the gut-brain axis
5. Allergies and autoimmune diseases — such as lupus, rheumatoid arthritis, and inflammatory bowel disease (IBD), through immune regulation and tolerance training
Fermented foods, in particular, provide vital nourishment that strengthens the small bowel — enhancing its ability to absorb nutrients, regulate immunity, and support healing at the root level.
(To be continued…)