22  •  Nutrition and Digestion 873

At rest and at play: optimizing human physiological functioning

Food provides the raw materials for growth and the fuel to make it happen. 874

22.1

Why do organisms need food? 874

22.2

What’s on the menu? Animals have a variety of diets. 875

22.3

Calories count: organisms need sufficient energy. 876

Nutrients are grouped into six categories. 878

22.4

Water is an essential nutrient. 878

22.5

Proteins in food are broken down to build proteins in the body. 879

22.6

Carbohydrates and lipids provide bodies with energy and more. 881

22.7

Vitamins and minerals are necessary for good health. 885

We extract energy and nutrients from food. 888

22.8

We convert food into nutrients in four steps. 888

22.9

Ingestion is the first step in the breakdown of food. 889

22.10

Digestion dismantles food into usable parts. 890

22.11

Absorption moves nutrients from your gut to your cells. 892

22.12

Elimination removes unusable materials from your body. 894

22.13

Animals have some alternative means for processing their food. 896

What we eat profoundly affects our health. 898

22.14

What constitutes a healthy diet? 898

22.15 This is how we do it: Does human judgment depend on blood sugar? 900

22.16

Obesity can result from too much of a good thing. 902

22.17

Weight-loss diets are a losing proposition. 904

22.18

Diabetes is caused by the body’s inability to regulate blood sugar effectively. 906

22.19

Food and infection: spicy foods may act as natural antibiotics. 908

StreetBIO: KNOWLEDGE YOU CAN USE

“An Apple a Day Keeps the Doctor Away.” Silly rhyme? Sound, data-backed advice? Or something in between? 910