Food provides the raw materials for growth and the fuel to make it happen.

• 22.1 Why do organisms need food?
• 22.2 What’s on the menu? Animals have a variety of diets.
• 22.3 Calories count: organisms need sufficient energy.

Nutrients are grouped into six categories.

• 22.4 Water is an essential nutrient.
• 22.5 Proteins in food are broken down to build proteins in the body.
• 22.6 Carbohydrates and lipids provide bodies with energy and more.
• 22.7 Vitamins and minerals are necessary for good health.

We extract energy and nutrients from food.

• 22.8 We convert food into nutrients in four steps.
• 22.9 Ingestion is the first step in the breakdown of food.
• 22.10 Digestion dismantles food into usable parts.
• 22.11 Absorption moves nutrients from your gut to your cells.
• 22.12 Elimination removes unusable materials from your body.
• 22.13 Animals have some alternative means for processing their food.

What we eat profoundly affects our health.

• 22.14 What constitutes a healthy diet?
• 22.15 This is how we do it: Does human judgment depend on blood sugar?
• 22.16 Obesity can result from too much of a good thing.
• 22.17 Weight-loss diets are a losing proposition.
• 22.18 Diabetes is caused by the body’s inability to regulate blood sugar effectively.
• 22.19 Food and infection: spicy foods may act as natural antibiotics.