Every bite of food begins a carefully coordinated journey through the digestive system. Digestion changes large food molecules into smaller nutrients that cells can absorb and use. This process matters because nutrients provide energy, build body tissues, support the immune system, and help organs work properly.
Food science connects biology and chemistry by showing how carbohydrates, proteins, fats, vitamins, minerals, and water affect health.
The journey starts in the mouth, where chewing and saliva begin mechanical and chemical digestion. Food then moves through the esophagus to the stomach, where acid and enzymes break it down further into a liquid mixture called chyme. In the small intestine, enzymes and bile complete most digestion, and nutrients pass into the blood through tiny villi.
The large intestine absorbs water, forms waste, and supports helpful bacteria that can affect digestion and overall health.
Key Facts
- Digestion includes mechanical breakdown, such as chewing, and chemical breakdown by enzymes.
- Salivary amylase begins carbohydrate digestion in the mouth by breaking starch into smaller sugars.
- The stomach uses hydrochloric acid and pepsin to help break proteins into shorter chains.
- Bile emulsifies fats, which means it breaks large fat droplets into smaller droplets for easier digestion.
- Most nutrient absorption occurs in the small intestine through villi and microvilli.
- Energy from food is often measured in Calories, where 1 Calorie = 1000 calories = 1 kilocalorie.
Vocabulary
- Digestion
- Digestion is the process of breaking food into smaller molecules that the body can absorb and use.
- Enzyme
- An enzyme is a protein that speeds up a specific chemical reaction in the body.
- Peristalsis
- Peristalsis is the wave-like muscle movement that pushes food through the digestive tract.
- Villi
- Villi are tiny finger-like structures in the small intestine that increase surface area for nutrient absorption.
- Chyme
- Chyme is the partially digested liquid mixture of food and stomach juices that moves from the stomach to the small intestine.
Common Mistakes to Avoid
- Thinking digestion happens only in the stomach is wrong because digestion begins in the mouth and continues mainly in the small intestine.
- Confusing digestion with absorption is wrong because digestion breaks food apart, while absorption moves nutrients into the blood or lymph.
- Assuming all foods release energy at the same rate is wrong because fiber, fat, protein, and food structure affect how quickly nutrients are digested and absorbed.
- Ignoring water and fiber is wrong because they do not provide much energy, but they are essential for healthy movement through the digestive system and waste formation.
Practice Questions
- 1 A snack contains 20 g of carbohydrates, 6 g of protein, and 8 g of fat. Using 4 Calories per gram for carbohydrates, 4 Calories per gram for protein, and 9 Calories per gram for fat, how many Calories are in the snack?
- 2 The small intestine is about 6 meters long. If food moves through it at an average speed of 0.02 meters per minute, about how many minutes does it take to travel through the small intestine?
- 3 Explain why the small intestine has many villi instead of having a smooth inner surface. Connect your answer to absorption and surface area.