Nutrients, food energy and dietary fibre
Compare the sources and functions of the named macronutrients, vitamins, minerals, water, food energy and non-starch polysaccharide.
Exam scope and assessment notes
This original StudyForA lesson maps Cambridge IGCSE Food & Nutrition 0648 topic 2 for examinations in 2026–2029. These are not Cambridge questions, mark schemes or official grades. The practical examination is a real, centre-administered cooking test with a planning session and assessed preparation, time management, results and quality. These screen-based lessons can teach the theory and help rehearse planning and evaluation, but they cannot provide a kitchen, verify safe food handling or practical skill, replace teacher-supervised cooking, award the practical mark, or guarantee an exam grade. Follow your centre’s instructions, local food-safety rules, medical advice and emergency procedures. Any meal examples are for syllabus practice, not individual dietary or medical advice.
Before you begin
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Before you start: What is a food source?
What you will learn
- Compare the broad roles of protein, carbohydrate and fat
- Match the named vitamins and minerals to sources and functions
- Explain food energy and the role of water
- Describe sources and functions of dietary fibre
Macronutrients, energy and water
Protein supports growth, repair and maintenance. High-biological-value sources such as eggs, dairy, fish and meat provide all essential amino acids in suitable proportions; low-biological-value proteins from foods such as cereals, pulses and nuts have less of one or more. Combining different plant sources can improve the amino-acid pattern. Carbohydrates include monosaccharides (for example glucose in fruit), disaccharides (sucrose and lactose) and polysaccharides (starch in cereals and potatoes); they are important energy sources. Fats in oils, butter, nuts, seeds, dairy and meat provide concentrated energy, insulation, protection and help with absorption of fat-soluble vitamins.
Food energy from carbohydrate, fat and protein supports metabolism, movement and maintaining body temperature; carbohydrate and fat are principal sources, while protein also has essential growth and repair functions. Water supports transport, chemical reactions and temperature regulation and comes from drinks and foods. Non-starch polysaccharide (NSP), or dietary fibre, is found in plant cell walls in vegetables, fruit, pulses, nuts and wholegrain cereals. It adds bulk and helps food move through the digestive tract. A textbook source list describes typical contributions, not a personal prescription.
Vitamins, minerals and non-starch polysaccharide
Vitamins have different sources and jobs. Vitamin A is found as retinol in animal foods such as eggs and dairy, and as carotene in dark-green or orange vegetables; it supports vision and epithelial tissues. Vitamin C comes from citrus fruit, berries, peppers and green vegetables; it supports collagen formation and helps iron absorption. Vitamin D occurs in oily fish, egg yolk and fortified foods and supports calcium use and healthy bones. Vitamin E is found in vegetable oils, seeds and nuts and protects cell components. Vitamin K occurs in leafy green vegetables and is needed for normal blood clotting. B-group sources include wholegrain cereals, meat, dairy, eggs, legumes and fortified foods: thiamin, riboflavin and nicotinic acid take part in energy-releasing reactions; cobalamin supports red blood cell formation and normal nerve function. Sources vary with food and processing.
Minerals also have specific sources and functions. Calcium in dairy foods, fish eaten with bones and some leafy vegetables supports bones and teeth and muscle action. Iron in meat, liver, pulses and leafy vegetables is needed for haemoglobin. Phosphorus in dairy, fish, meat and cereals contributes to bones and energy-transfer compounds. Potassium in potatoes, fruit and vegetables supports fluid balance and nerve and muscle function; sodium and chloride are supplied mainly by salt and support fluid balance, while chloride also contributes to stomach acid. Fluoride in fluoridated water, tea and some fish helps protect tooth enamel. Iodide in seafood and iodised salt is needed to make thyroid hormones. Exam answers should link a named nutrient to both a plausible source and function; requirements and health advice depend on the person.
Sources for this lesson
Pause and explain
Which pairing is accurate?
Worked example
A packed meal contains rice, egg, leafy vegetables and water. Give one likely source of protein, one source of carbohydrate, and one reason the vegetables and water contribute to the meal.
Show the worked solution
- Egg is a protein source; rice is a carbohydrate source.
- Vegetables can supply vitamins, minerals and NSP.
- Water contributes fluid; the meal still cannot be judged without portions and the person’s needs.
Answer Egg supplies protein and rice mainly supplies carbohydrate. Leafy vegetables can contribute micronutrients and dietary fibre, and water contributes fluid. Whether the whole meal meets someone’s needs depends on amounts, the rest of the diet and individual circumstances.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
A learner says that an egg is “only protein”. Improve the statement with two other nutritional points and explain why a food may not fit one category.
Give me a hint
Foods can provide more than one nutrient and may also contain water or micronutrients.
Compare my reasoning
- Keep protein as one important contribution.
- Name another plausible contribution without claiming it is the only one.
- Explain that food composition is mixed and depends on quantity.
An egg is a useful protein source, but it also contains fat and provides some vitamins and minerals. Foods contain mixtures of nutrients, so a sensible answer names a main contribution without claiming exclusivity; the amount supplied depends on portion size.
Look for these in your work
- Identifies protein accurately
- Adds other plausible nutrients
- Avoids an exclusive category
A meal provides little fruit, vegetables or wholegrain food. Explain one possible fibre concern and one limitation of that conclusion.
Give me a hint
Connect plant cell-wall material to bowel movement, then qualify what a single meal shows.
Compare my reasoning
- Identify non-starch polysaccharide as dietary fibre from plant foods.
- Explain its role in supporting bowel movement.
- State that a meal alone does not show total daily intake or individual health.
The meal may provide little NSP, which supports bowel movement. This observation applies only to the meal described; foods eaten during the rest of the day and a person’s circumstances are unknown, so it cannot establish a deficiency or diagnose a problem.
Look for these in your work
- Names NSP/dietary fibre
- Explains a function
- Qualifies the evidence
A food label lists iron and vitamin C. Explain one reason a meal planner might consider them together while avoiding a medical claim.
Give me a hint
Recall a relationship between vitamin C and iron absorption.
Compare my reasoning
- State that vitamin C can help absorption of non-haem iron.
- Connect that relationship to meal planning and food sources.
- Avoid claiming the meal treats anaemia or guarantees an individual outcome.
Vitamin C can help the absorption of non-haem iron, so a planner may consider including suitable vitamin-C-containing foods alongside plant iron sources. A label alone does not show how much is absorbed or diagnose or treat an individual health condition.
Look for these in your work
- States the nutrient relationship
- Applies it to a food choice
- Avoids an unsupported treatment claim
Common mistakes
- Claiming every vitamin has the same function
- Confusing NSP with an energy-yielding nutrient
- Treating one meal as proof that a person meets all nutrient needs
What can you explain now?
Which pairing is accurate?
Compare with the explanation
Iron is used in haemoglobin; dietary fibre supports bowel movement
Use the syllabus concept, connect it to the stated evidence or needs, and explain any limit on your conclusion.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Choose one named vitamin, one mineral and NSP; how do their functions differ?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.