Why are water and dietary fibre essential even though they give no energy, and what happens when we go short of them?
Describe the functions and sources of water and dietary fibre, and explain the effects of having too little of each
A simple, focused answer on water and dietary fibre for N(A)-Level Nutrition and Food Science: why both are essential, their functions and sources, and the effects of dehydration and a low-fibre diet such as constipation.
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What this dot point is asking
SEAB wants you to describe what water and dietary fibre do in the body, name their sources, and explain what goes wrong when a person has too little of each. Neither gives any energy, but both are essential: water keeps almost every body process running, and fibre keeps the digestive system healthy. The marks come from clear functions, the signs of dehydration (too little water) and constipation (too little fibre), and sensible ways to get more of each.
The answer
Why water is essential
Water makes up about two-thirds of the body. We lose it all the time through sweat, breath and urine, so it must be replaced by drinking and from food.
Functions of water
Water has several vital jobs:
- It forms most of the blood and body fluids, which transport nutrients to cells and carry waste away.
- It controls body temperature, because sweating and its evaporation cool the body down.
- It helps remove waste from the body in urine.
- It keeps the lining of the gut, the eyes and the joints moist and working smoothly.
Sources of water and the effects of too little
Water comes from drinks (plain water, milk, soup and other beverages) and from foods with a high water content such as fruit, vegetables and soup. Too little water causes dehydration, with signs such as thirst, dark yellow urine, headache, tiredness and poor concentration. In Singapore's hot, humid climate people sweat more and so need to drink more.
Why dietary fibre is essential
Dietary fibre is the part of plant foods that the body cannot digest for energy. Instead of being absorbed, it passes through the gut and does its work there.
Functions of fibre and the effects of too little
Fibre's main jobs are to:
- Add bulk to the food in the gut and hold water, making the stools soft and easy to pass.
- Keep the bowels moving regularly, which prevents constipation.
- Help you feel full after a meal, which supports a healthy weight.
Fibre comes from wholegrains (wholemeal bread, brown rice, oats), vegetables and fruit (especially with skins), and beans and lentils. Too little fibre causes constipation and, over time, raises the risk of bowel problems.
Examples in context
Example 1. Staying hydrated in the heat. A student playing sport on a humid Singapore afternoon sweats heavily to cool down and so loses a lot of water. Drinking plain water before, during and after activity replaces that loss and prevents the headache and tiredness of dehydration, showing why water needs are higher in a hot climate.
Example 2. A higher-fibre breakfast swap. Changing a breakfast of white toast with kaya to wholemeal toast with a banana, plus a bowl of oats adds fibre from the wholegrain bread, the oats and the fruit. The extra fibre keeps the bowels moving and helps the student feel full until lunch, a simple way to lift the fibre in a daily meal.
Try this
Q1. State three functions of water in the body. [3 marks]
- Cue. Any three of: forms blood and body fluids, transports nutrients and waste, controls body temperature, removes waste in urine, keeps linings and joints moist.
Q2. Explain how dietary fibre helps prevent constipation. [2 marks]
- Cue. Fibre adds bulk and holds water, softening the stools so they pass easily and keeping the bowels moving.
Q3. Suggest two changes to a diet to add more fibre. [2 marks]
- Cue. Any two of: choose wholemeal bread or brown rice, eat more vegetables and fruit, add beans, lentils or oats.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marks(a) State three functions of water in the body. (b) Explain two signs that a person is not drinking enough water. (c) Suggest why people in Singapore may need to drink more water than people in cooler countries. (Section B style)Show worked answer →
(a) Any three of: water makes up most of the blood and body fluids; it helps transport nutrients and waste; it controls body temperature through sweating; it helps remove waste in urine; and it keeps the lining of the gut and the joints moist.
(b) Any two of: feeling thirsty; dark yellow urine and passing less urine; headache, tiredness or poor concentration; and dry mouth or skin. (These are signs of dehydration.)
(c) Singapore is hot and humid, so people sweat more to cool down and lose more water, which must be replaced by drinking more.
What markers reward: three genuine, separate functions of water, two real signs of dehydration, and linking the hot, humid climate to higher water loss through sweating.
Original4 marksA person eats mostly white rice, meat and few vegetables, and often has constipation. (a) Name the nutrient most likely lacking. (b) Explain how this nutrient helps the digestive system. (c) Suggest two changes to the diet to add more of it. (Section B style)Show worked answer →
(a) Dietary fibre.
(b) Dietary fibre adds bulk to the food in the gut and holds water, making the stools soft and bulky so they pass through easily. This keeps the bowels moving and prevents constipation.
(c) Any two of: switch white rice or bread for wholemeal or brown versions; eat more vegetables and fruit (with skins where suitable); and add beans, lentils or wholegrain cereals such as oats.
What markers reward: correctly naming dietary fibre, explaining that it adds bulk and holds water to keep the bowels moving, and two realistic higher-fibre swaps.
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