What does it mean when digestion isn't working, and where does the cascade actually break down?

What does the digestive cascade actually look like?

Digestion happens in sequence, with each organ doing specific work:

• Mouth. Chewing breaks down food mechanically; saliva begins carbohydrate digestion via amylase
• Stomach. Hydrochloric acid denatures protein, activates pepsin (a protein-digesting enzyme), kills ingested bacteria, and signals downstream digestive processes. Adequate acid is foundational
• Pancreas. Produces enzymes (amylase, lipase, proteases) that break down carbohydrates, fats, and proteins in the small intestine
• Liver and gallbladder. Bile (produced by the liver, stored and concentrated by the gallbladder) emulsifies fats, allowing absorption. Bile also has antimicrobial effects in the small intestine
• Small intestine. The primary site of nutrient absorption. The intestinal lining is the barrier between gut contents and systemic circulation
• Large intestine. Bacterial fermentation of fiber, water reabsorption, formation and elimination of stool

When any step is off, the downstream effects compound. Low acid means undigested protein reaches the small intestine, fermenting and contributing to bloating. Insufficient bile means fat malabsorption. Slow motility means bacteria have more time to overgrow.

What is low stomach acid, and why is it so often missed?

Low stomach acid (hypochlorhydria) is more common than excess acid in modern adults, particularly with age, chronic stress, and PPI (proton pump inhibitor) use. The symptoms are surprisingly broad:

• Feeling full quickly after small meals
• Bloating after meals, especially after protein
• Reflux (paradoxically, low acid often causes reflux because the lower esophageal sphincter doesn't close properly)
• Undigested food visible in stool
• Fingernail ridges
• Hair thinning
• Iron deficiency, B12 deficiency, magnesium issues despite adequate intake (because mineral absorption requires acid)

Low stomach acid is one of the most underdiagnosed gut issues. It's not part of standard testing, and it's often masked by reflux symptoms that look like excess acid but actually reflect inadequate digestion.

What's the issue with long-term PPI use?

Long-term proton pump inhibitor use (omeprazole, esomeprazole, pantoprazole, and similar) is associated with several problems:

• Nutrient deficiencies. B12, magnesium, calcium, iron
• Bone density loss. Increased fracture risk over years
• Kidney disease. Both acute and chronic
• Increased infection risk. C. difficile and pneumonia
• Possibly increased dementia risk (the evidence is mixed but concerning)
• Rebound acid hypersecretion when discontinued, which is part of why PPIs are hard to stop

PPIs have appropriate uses (active GERD, peptic ulcer disease, Barrett's esophagus, prevention of NSAID-induced ulcers) but are often continued for years without reassessment. Many patients on long-term PPIs can be tapered off with appropriate support: often the original reason for starting them no longer applies, or the symptoms can be managed with addressing low acid rather than further suppressing it.

How does pancreatic enzyme function affect digestion?

Pancreatic enzymes break down fats, proteins, and carbohydrates in the small intestine. Insufficient enzyme production (exocrine pancreatic insufficiency) presents as:

• Fat malabsorption with oily, floating stools
• Weight loss despite adequate intake
• Fat-soluble vitamin deficiency (A, D, E, K)
• Bloating after fatty meals

Less severe forms produce subtle bloating and incomplete digestion without the dramatic symptoms. Stool elastase testing (a stool test that measures pancreatic enzyme output) assesses pancreatic function. Many patients with chronic bloating after meals benefit from enzyme supplementation, particularly with fattier meals.

What about bile flow and gallbladder function?

Bile flow and gallbladder function affect fat digestion. Sluggish bile flow (often after gallbladder removal, but also possible with intact gallbladders) causes:

• Nausea after fatty meals
• Fat malabsorption
• Deficiency of fat-soluble vitamins (A, D, E, K)
• Pale or floating stools

Bile acid sequestrants and digestive support can help post-cholecystectomy (post-gallbladder-removal) patients who develop these symptoms. The standard advice that "you don't need a gallbladder" understates how often gallbladder removal produces lasting digestive issues that can be addressed.

What is increased intestinal permeability ("leaky gut")?

Increased intestinal permeability is the clinical term replacing the older popular term "leaky gut." The intestinal lining is normally a tight barrier; in this condition, the connections between cells (called tight junctions) become more permeable than they should be, allowing partially digested food and bacterial components to cross into circulation.

This triggers immune activation, food sensitivities, systemic inflammation, and contributes to autoimmune conditions. Causes include chronic inflammation, dysbiosis (imbalanced gut bacteria), certain medications (NSAIDs, antibiotics, steroids), food sensitivities, alcohol, chronic stress, and some infections.

Markers include zonulin (the protein that regulates tight junctions) and lipopolysaccharides (LPS, fragments of bacterial cell walls in circulation). The phenomenon is now recognized in mainstream literature as relevant to autoimmune conditions, food sensitivities, systemic inflammation, and metabolic dysfunction; the older dismissal of "leaky gut" as fringe has largely shifted.

What do motility disorders look like?

Motility disorders affect digestion and gut microbiome stability:

• Slow motility predisposes to SIBO and constipation
• Fast motility causes diarrhea and malabsorption

Drivers of motility issues include:

• Thyroid dysfunction (hypothyroidism slows motility; hyperthyroidism speeds it up)
• Vagus nerve function (the migrating motor complex that clears the small intestine between meals depends on vagal signaling)
• Magnesium status
• Certain medications (opioids slow, PPIs alter, some antidepressants can do either)
• Chronic stress
• Gut infections that have damaged the intestinal nerves

Motility problems often improve when the underlying cause is identified.

What does a useful digestive dysfunction workup include?

A comprehensive workup typically involves:

• Comprehensive stool analysis. Assesses digestive function markers, microbiome composition, inflammatory markers, pathogens
• Pancreatic elastase if pancreatic insufficiency is suspected
• Zonulin and LPS for permeability assessment
• H. pylori testing
• Organic acids panel for bacterial and fungal markers
• Depending on history: motility studies, gallbladder function tests, SIBO breath testing

The pattern across multiple markers, combined with symptom timeline and dietary triggers, points toward where in the cascade dysfunction is happening.

The deeper picture

Digestive dysfunction is rarely a single problem; it's usually a cascade where dysfunction at one stage creates dysfunction at the next. Identifying where the cascade started and addressing it systematically tends to resolve issues that symptomatic management has failed to fix. Extend approaches digestive complaints with this kind of comprehensive evaluation.