Digestion Stopwatch
Real-time tracking: automatic update every minute based on meal time.
3 physiological stages: stomach (pH 1.5–3.5), small intestine (pH 6.0–7.4) and large intestine (pH 5.5–7.0).
Macronutrient adjustment: liquids speed up transit (×0.5), fats slow it down (×1.5).
Day selector: works for meals eaten today or yesterday.
# The Physiology of Human Digestion
The human digestive system is one of the most sophisticated biological mechanisms in existence. From the moment we ingest food, a cascade of chemical, mechanical and neurological processes begins to extract the nutrients needed to sustain life. Understanding how long each stage takes not only satisfies scientific curiosity, but helps make better decisions about nutrition, exercise and rest.The stomach acts as a high-acidity chemical reactor (pH between 1.5 and 3.5). Hydrochloric acid denatures proteins and activates enzymes like pepsin. Fats spend the most time here, as the body must emulsify them before allowing passage to the small intestine. A high-fat meal can retain chyme in the stomach for up to 4 hours.Factors That Speed Up Digestion
Liquids pass almost directly to the intestine (30–120 min). Simple carbohydrates empty in 1–2 hours. Walking 15–20 minutes after a meal can reduce gastric emptying time by up to 15%. Stress, on the contrary, can halt transit by diverting blood away from digestive organs.# The Three Stages of Digestive Transit
- Stomach (2–5 hours): acid breakdown with pepsin and gastric lipase. The extremely acidic pH eliminates bacteria and breaks down protein structures.
- Small Intestine (3–5 hours): massive nutrient absorption. Intestinal villi multiply the contact surface to the equivalent of a tennis court. About 90% of nutrients are absorbed here.
- Large Intestine (10–60 hours): water and electrolyte reabsorption, fermentation by the microbiota and feces formation. Time in this stage varies enormously based on fiber consumed and each person's microbiome.