Digestion begins in the mouth — and most people skip that step entirely
Overeating, inadequate chewing and eating too quickly each impair the body's ability to extract nutrients from food — through separate but compounding mechanisms.
nutrition
Digestion is not a simple conveyor belt where food goes in one end and nutrients come out the other. It is a tightly coordinated sequence of mechanical and chemical events, each step preparing the substrate for the next. It begins in the mouth — not the stomach — and disruptions at the earliest stage propagate downstream through every subsequent process.
Chewing serves two purposes that are often underestimated. The mechanical one is obvious: breaking food into smaller particles increases the surface area available to digestive enzymes. A poorly chewed piece of meat or a swallowed chunk of leafy green presents a much smaller surface to pepsin, lipase and amylase than the same food ground to a fine consistency. The chemical purpose is less well known: saliva contains amylase, which begins the digestion of in the mouth before the food even reaches the stomach. Swallowing quickly bypasses this first enzymatic step entirely.
Increasing the number of chews per bite has been shown to increase the release of gut hormones that signal satiety — including GLP-1 and cholecystokinin — and to reduce self-reported hunger and total food intake at a meal. Slower eating is not merely aesthetic advice; it is physiological
The stomach can accommodate roughly one to two litres of food. When a large volume arrives quickly, gastric acid and digestive enzymes become diluted relative to the food mass — reducing the efficiency of breakdown by pepsin and the acid-dependent conversion of pepsinogen to its active form
Fat emulsification in the small intestine depends on bile and pancreatic lipase. These are released in proportion to the signals received from the duodenum as chyme arrives. Overeating floods the duodenum faster than these signals can mobilise adequate bile and enzyme response, leaving fat partially undigested and potentially feeding bacteria in the lower gut that should not have access to dietary fat
Eating too quickly impairs the cephalic phase of digestion — the anticipatory release of stomach acid, digestive enzymes and bile that begins before food even reaches the stomach, triggered by the sight, smell and taste of food. Distracted eating, particularly while looking at screens, blunts this phase significantly
Chronic overeating stimulates what researchers have described as 'amplified digestion' — an adaptation where Western high-fat, high-glycaemic diets chronically overstimulate biliary and pancreatic secretion, driving excessive nutrient absorption that contributes to insulin resistance and progressive metabolic dysfunction
The volume and speed at which food is consumed affects not just what is absorbed but where. Poorly digested food that reaches the large intestine intact feeds bacteria in ways that can produce gas, inflammation and altered gut motility. Some of these bacterial populations, when overfed with undigested or fat, produce metabolites — including ammonia, hydrogen sulphide and secondary bile acids — that damage the gut lining and contribute to systemic inflammation.
None of this requires an overhaul of what you eat. It requires attention to how you eat. Smaller bites. More chewing — most people chew 5 to 10 times before swallowing; 20 to 30 is closer to optimal for most foods. Eating without a screen. Stopping before fullness rather than at it. These are not wellness clichés — they are interventions at the mechanical level of a biochemical process that depends on mechanical preparation to work properly.