Lesson focus: Dietary health depends on long-term patterns, energy balanceWhether the energy you get from food matches the energy your body uses. and nutrient sufficiency, while single measurements such as BMIBody mass index: a number worked out from your mass and height to check if body mass is in a healthy range. have important limits.
Use dietary evidence to explain malnutritionBeing unhealthy because your diet has too little, too much or the wrong balance of nutrients., energy imbalance and risk without judging health from one food or body measurement.
Build on earlier learning
Food tests: interpreting evidenceFood tests identify selected nutrients in samples. This lesson considers the broader pattern, amount and long-term health context.
You will be successful when you can…
- Define malnutrition as nutrient or energy imbalance.
- Explain effects of selected deficiencies and excess energy intake.
- Use energy-balance reasoning.
- Evaluate BMI and dietary evidence cautiously.
Words that carry the science
- balanced diet
- A dietary pattern providing suitable amounts and variety for a person’s needs.
- malnutrition
- Poor nutrition caused by deficient, excessive or imbalanced intake.
- deficiency
- Insufficient intake or availability of a required nutrient.
- energy balance
- The relationship between energy intake and energy transferred by the body.
- BMI
- Mass in kilograms divided by height in metres squared, used as a population screening measure.
- risk factor
- A characteristic associated with an increased chance of an outcome, not a guaranteed cause.
Evaluate dietary patterns without oversimplifying health
01Malnutrition includes deficiency and excess
Persistent vitamin C deficiencyNot getting enough of a nutrient, which can make you ill. can cause scurvy, vitamin D deficiency increases rickets risk in children, and iron deficiency can cause anaemia. Protein-energy malnutritionBeing unhealthy because your diet has too little, too much or the wrong balance of nutrients. can impair growth and tissue maintenance.
Long-term excess energy intake can increase body-fat storage and raise risk of conditions including type 2 diabetes and cardiovascular disease. Risk is influenced by many interacting factors.
02Energy balance explains change over time
If average energy intake persistently exceeds energy transferred through basal processes, activity and growth, the surplus is stored, much of it as fat. If intake remains below requirements, stored tissue is used.
Short-term body-mass change also reflects water and digestive contents, so one day of intake does not determine long-term health.
03BMI is a limited screening tool
BMIBody mass index: a number worked out from your mass and height to check if body mass is in a healthy range. can help compare patterns across adult populations, but it does not directly measure body fat, fitness, diet or health. Muscle mass, age, growth, pregnancy and body composition affect interpretation.
For children and adolescents, age- and sex-specific growth references are required. Health advice should use multiple sources of evidence and qualified professional judgement, not classroom self-diagnosis.
Energy in, energy out
Food gives us energy, measured in kilojoules (kJ). If you take in more energy than you use, the extra is stored as fat and your mass goes up. If you take in less, your body uses its stores and your mass goes down.
Controls
Energy needs are illustrative; real needs depend on age, size and growth. About 32 000 kJ is stored in 1 kg of body fat. A healthy diet is about balance, not just energy.
Interpret an energy pattern
A person’s average intake exceeds their average energy transfer by 800 kJ each day for several months.
- Recognise a sustained positive energy balanceWhether the energy you get from food matches the energy your body uses..
- The body cannot simply discard all of the surplus chemical energy.
- Some surplus is stored in molecules and body tissue, including fat.
- Predict a tendency for body mass to increase, while acknowledging individual variation and measurement uncertainty.
How to make the reasoning visible: The pattern supports a likely trend, not an exact prediction for one person.
Separate evidence from overclaiming
Decide what each observation can support and what additional evidence would help.
| Evidence | Supported interpretation | Unsafe overclaim | Useful additional evidence |
|---|---|---|---|
| Low iron intake over months | Anaemia risk may increase | The person definitely has anaemia | Blood tests and clinical assessment |
| Energy intake exceeds transfer long term | Stored tissue may increase | One meal causes obesity | Repeated pattern and body-composition context |
| High adult BMI | Screening category indicates possible risk | The person is unhealthy | Medical, activity and body-composition evidence |
| Low vitamin D intake | Deficiency risk may increase | Rickets is certain | Sun exposure, blood level and clinical evidence |
Why is “healthy food” an incomplete scientific label?
Explain why BMI may misclassify a highly muscular adult.
Check your understanding
Answer from memory, then check against the suggested answer.
What is malnutrition?
Which deficiency can cause anaemia?
What two measurements are used for BMI?
A headline says one type of snack “causes diabetes”. Explain why this causal claim is too strong.
Explain why an intervention can reduce a risk factor without guaranteeing prevention.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A student claims that BMI and one day’s food record are enough to decide whether a teenager has a healthy diet.
Give one strength and two weaknesses of using BMI.
(3)Evaluate using one day’s food record, and suggest better evidence.
(3)Total for this question: 6 marks
Command word: For evaluateA command word: weigh up the good points and bad points, then give your overall judgement., acknowledge limited usefulness before explaining why the evidence cannot support a diagnosis.