Water and the Balanced Diet

Challenges to clear

• Work through all four cases correctly.
• Answer the roughage case correctly — a diet can be rich and still be wrong.

The task

A balanced diet is not the same for everyone. Think about each case.

What this lesson covers

• A construction labourer and an office clerk are the same age, height and weight. Should they eat the same amount? Best choice: No — the labourer needs considerably more energy-giving food — Heavy physical work greatly increases energy expenditure, so carbohydrate and fat intake must rise to match.
• A growing ten-year-old and a healthy sixty-year-old eat the same weight of food. Which nutrient should differ most in proportion? Best choice: Protein — the child needs proportionally more for growth — Growth means building new tissue, and only protein can do that. Children need more protein per kilogram of body weight than adults.
• On a hot day someone has been sweating heavily and feels thirsty, tired and headachy. What is happening? Best choice: They are dehydrated — water and salts lost in sweat need replacing — Sweat is water plus salts. Losing enough of both reduces blood volume and disturbs the body's balance, causing exactly these symptoms.
• Someone eats plenty of protein and energy but almost no fruit or vegetables, and becomes constipated. What is missing? Best choice: Roughage — indigestible fibre that gives the gut bulk to move — Fibre is not absorbed at all, and that is the point: it adds bulk and stimulates peristalsis.

Hint

A balanced diet supplies all nutrients in the right proportion FOR THAT PERSON — their age, sex, activity and condition all change what balance means.