Digestive System Journey

Pick a food and follow it through the entire digestive system. Watch nutrients get absorbed at each organ, see the enzymes at work, and discover how long the full journey takes.

Choose a Food

Digestive System

MouthStomachSmallIntestineLarge IntestineRectum

Click any organ or stage button to jump to that stage.

1

Mouth

Transit time: 30 sec

Teeth grind food into smaller pieces. Amylase in saliva begins breaking down starch into simple sugars. The tongue shapes food into a bolus for swallowing.

Active Enzymes

Salivary amylaseLingual lipase

Did you know? Your mouth produces about 1 to 1.5 liters of saliva every day.

Cumulative Time

30 sec

Calories Absorbed

5.0 / 104.7 kcal

Absorption Efficiency

4.8%

Nutrient Absorption Tracker — Apple

Carbohydrates1.3 / 25.0 g absorbed
Absorbed 5%Remaining 95%
Protein0.0 / 0.5 g absorbed
Absorbed 0%Remaining 100%
Fat0.0 / 0.3 g absorbed
Absorbed 0%Remaining 100%
Fiber0.0 / 4.0 g absorbed
Absorbed 0%Remaining 100%
Water2.6 / 130.0 mL absorbed
Absorbed 2%Remaining 98%
How to read this chart: Each bar shows what fraction of each nutrient has been absorbed so far. The darker color is absorbed; the lighter color is still in transit. Fiber (purple) is mostly indigestible and passes through.

Reference Guide

The Six Digestion Stages

Mouth (30 sec) Mechanical breakdown by teeth. Salivary amylase starts starch digestion.
Esophagus (10 sec) Peristaltic waves move the food bolus to the stomach. No digestion occurs.
Stomach (4 min) Gastric acid (pH 2) and pepsin break down proteins. Fat digestion begins.
Small Intestine (4.5 min) Main absorption site. Villi and microvilli absorb most nutrients into the blood.
Large Intestine (24 hr) Water and electrolytes are reclaimed. Gut bacteria ferment fiber.
Elimination Indigestible materials exit as feces. Total transit time is roughly 24-72 hours.

Nutrient Absorption

Different nutrients are absorbed at different rates and locations. The small intestine handles most of the work.

Carbohydrates 90%+ absorbed in small intestine
Protein 90%+ absorbed in small intestine
Fat 95%+ absorbed, needs bile salts
Water Absorbed across all segments
Fiber Mostly indigestible, feeds gut bacteria

Caloric density: carbohydrates and protein provide 4 kcal per gram; fat provides 9 kcal per gram, making it the most energy-dense macronutrient.

Digestive Enzymes

Enzymes are biological catalysts that break large food molecules into smaller ones the body can absorb. Each enzyme works best at a specific pH.

Salivary amylase

Breaks starch into maltose. Active at neutral pH (6-7) in the mouth.

Pepsin

Cleaves proteins into peptides. Activated by stomach acid (pH 1.5-3.5).

Lipase

Breaks fats (triglycerides) into fatty acids and glycerol. Active in stomach and small intestine.

Trypsin

Produced by the pancreas. Breaks proteins into amino acids in the small intestine.

Bile salts

Not enzymes but emulsify fat globules, increasing surface area for lipase.

Key Facts About Digestion

  • The small intestine is about 6 meters long. Its folded inner lining has a surface area roughly equal to a tennis court.
  • The stomach produces about 2 liters of gastric acid each day and replaces its protective lining every 3-4 days.
  • Peristalsis is so effective that you can swallow food while upside down. Gravity is not required.
  • The large intestine hosts over 500 bacterial species collectively weighing about 1 kg. These bacteria produce vitamins B and K.
  • Total transit time (mouth to elimination) ranges from 24 to 72 hours, mainly depending on how long food spends in the large intestine.