Understanding General Digestive Function

Digestion is one of the most taken-for-granted processes in the human body. We eat, we absorb, we eliminate — and only when something goes wrong do we start paying attention. Yet digestion is not a simple conveyor belt. It is a highly coordinated, multi-stage physiological process that links food to every system in the body.

Digestion is where nutrition becomes biology.

Every nutrient that supports energy, immunity, hormones, brain function, repair, and resilience must first pass through the digestive system. If digestion is inefficient, dysregulated, or under strain, even the best diet cannot do its job properly.

To understand digestive health, it helps to walk through the process from beginning to end — not as isolated organs, but as an integrated system shaped by nerves, hormones, microbes, and metabolism.

Digestion Begins in the Nervous System

One of the most misunderstood aspects of digestion is where it starts.

Digestion does not begin in the stomach. It begins in the brain.

The sight, smell, anticipation, and even thought of food activate the parasympathetic nervous system, often referred to as the “rest and digest” state. This neural activation triggers saliva production, stomach acid release, digestive enzyme secretion, bile flow, and coordinated gut movement.

This phase, known as the cephalic phase of digestion, sets the tone for everything that follows.

When this signalling is impaired — through chronic stress, rushed eating, distraction, or eating on the move — digestive secretions are reduced before food even enters the mouth. This creates a cascade of inefficiency further down the system.

In other words, digestion cannot function optimally in a body that perceives threat, urgency, or distraction.

The Mouth and Mechanical Breakdown

Chewing is not optional decoration. It is a critical mechanical and chemical step.

Thorough chewing increases surface area for enzymes to act on food, mixes food with saliva, and initiates carbohydrate digestion through salivary amylase. It also sends feedback signals to the stomach and intestines, preparing them for incoming food.

When chewing is rushed or incomplete, the stomach and intestines are asked to compensate for work that should have been done earlier. Over time, this contributes to bloating, discomfort, and digestive fatigue.

The Stomach: Acid, Enzymes, and Control

The stomach is not simply a holding tank. It is a chemical processing chamber.

Hydrochloric acid in the stomach performs several essential functions. It denatures proteins, activates digestive enzymes such as pepsin, helps sterilise incoming food, and signals the lower digestive tract to prepare for nutrient absorption.

Contrary to popular belief, low stomach acid is far more common than excess acid.

Stress, ageing, nutrient deficiencies, chronic dieting, and acid-suppressing medications all reduce acid production. When stomach acid is insufficient, protein digestion suffers, minerals such as iron and zinc are poorly absorbed, and partially digested food enters the small intestine.

This places strain on the rest of the digestive system and increases the likelihood of bloating, reflux-like symptoms, and microbial imbalance.

The Small Intestine: Digestion and Absorption

The small intestine is where the majority of digestion and nutrient absorption takes place.

Here, bile from the liver emulsifies fats, allowing them to be broken down and absorbed. Pancreatic enzymes digest carbohydrates, proteins, and fats into their absorbable components. Hormones released from the intestinal lining coordinate gut movement and signal satiety to the brain.

The lining of the small intestine is only one cell thick, maximising absorption efficiency while maintaining a selective barrier.

This barrier function is critical.

The intestine must allow nutrients through while preventing pathogens, toxins, and large undigested particles from entering circulation. When this balance is disrupted, immune activation increases and systemic symptoms may appear.

The Role of the Liver and Bile

The liver is deeply integrated into digestion.

Bile produced by the liver is essential for fat digestion and absorption of fat-soluble vitamins. Bile also carries waste products, including metabolised hormones and toxins, into the gut for elimination.

Efficient bile flow supports digestion, microbial balance, and detoxification. Impaired bile flow contributes to bloating, fat malabsorption, nutrient deficiencies, and altered bowel habits.

Fibre plays an important role here by binding bile and supporting its removal. Without adequate fibre, bile can be reabsorbed, increasing metabolic and hormonal load.

The Large Intestine and Microbial Fermentation

By the time food reaches the large intestine, most digestible nutrients have been absorbed. What remains is fibre, resistant starch, water, electrolytes, and microbial biomass.

The large intestine is home to trillions of microbes that ferment these remaining compounds. This fermentation produces short-chain fatty acids that nourish the gut lining, regulate inflammation, influence metabolism, and communicate with the brain.

This process is beneficial, but it must be well regulated.

When fermentation occurs too early, too aggressively, or in a sensitised gut, discomfort, bloating, and altered bowel habits can occur. These symptoms are often a reflection of upstream digestive inefficiency rather than a problem with fibre itself.

Gut Motility and Rhythm

Digestion depends on movement.

Coordinated muscular contractions move food through the digestive tract at an appropriate pace. Between meals, the gut performs cleansing waves that clear residual material and bacteria.

These rhythms are disrupted by constant grazing, irregular eating patterns, chronic stress, and poor sleep. When motility slows or becomes erratic, stagnation, bloating, and discomfort become more likely.

Regularity matters more than speed.

The Gut as an Immune and Sensory Organ

The gut is one of the body’s largest immune organs and one of its most sensitive sensory systems.

Immune cells in the gut continuously assess what passes through, maintaining tolerance to harmless substances while responding to genuine threats. Nerve endings in the gut relay information about stretch, pressure, and movement to the brain.

When the gut environment becomes inflamed or stressed, these systems become more reactive. Sensations that would normally remain unconscious are amplified. This contributes to discomfort, urgency, and heightened awareness of digestion.

Why Digestive Symptoms Are So Common

Modern life places digestion under constant strain.

Chronic stress suppresses digestive signalling. Ultra-processed foods challenge enzymatic capacity. Irregular meal timing disrupts rhythm. Low fibre intake starves beneficial microbes. Poor sleep impairs repair.

Digestive symptoms are not signs of failure. They are signals that the system is being asked to operate under conditions it was not designed for.

 

Diet and Lifestyle Factors That Commonly Disrupt Digestive Function

• Rushed, distracted eating.
• Chronic psychological stress.
• Constant snacking without digestive rest.
• Low protein intake.
• Low fibre diversity
• Excess ultra-processed foods
• Poor sleep and irregular routines
• Sedentary behaviour

These factors rarely act alone. Their effects accumulate gradually.