Interpreting a Diet and Energy Balance Case
A 14-year-old student reports feeling tired during afternoon lessons and has been skipping breakfast. A typical school-day intake is: no breakfast; a packet of crisps and a sugary drink at break; a white-bread sandwich with cheese at lunch; and a large evening meal of rice, chicken, and vegetables. She drinks little water and walks 20 minutes to school each day. Her height and mass are within the healthy range for her age. She asks whether she should take a vitamin supplement or a protein powder to 'get more energy'.
1. Using the idea of energy balance and nutrient groups, explain why her tiredness is more likely to be a meal-timing and food-choice issue than a need for supplements.
Read the worked answer
Her body mass is stable and within the healthy range, so total energy intake is roughly matching output - she is not starving. The problem is distribution and quality of intake.
Skipping breakfast means a long overnight fast is extended into the school morning. Blood glucose falls, and the brain relies heavily on glucose, so concentration and energy dip in the afternoon. The crisps and sugary drink give a rapid rise in blood glucose followed by a fall, producing a 'sugar crash' rather than sustained energy.
Nutrient groups:
- Carbohydrates are the main energy source; wholegrain or slow-release sources (oats, wholemeal bread) give steadier glucose than white bread and sugary drinks.
- Protein (cheese, chicken) supports growth and repair but is not a quick energy source.
- Vitamins and minerals are needed in small amounts; a supplement does not supply energy.
Protein powder would add protein she already obtains from cheese, chicken, and other foods; extra protein is not used as the body's preferred fuel and excess is stored or excreted.
A better plan: eat breakfast, choose slow-release carbohydrate and some protein at each meal, and drink water regularly.
2. Explain the role of water in her diet and why her low water intake may contribute to feeling tired.
Read the worked answer
Water is needed for:
- Transport: blood plasma is mostly water, carrying glucose, oxygen, and waste products around the body.
- Temperature regulation: sweating and evaporation cool the body during exercise such as her 20-minute walk.
- Chemical reactions: digestion and many metabolic reactions occur in solution.
- Removing waste: the kidneys use water to excrete urea.
Even mild dehydration reduces blood volume, so the heart must work harder and delivery of glucose and oxygen to muscles and brain is less efficient. This can cause headaches, poor concentration, and a sense of tiredness. Her sugary drink at break supplies some fluid but also a lot of sugar, which does not replace the need for plain water.
Judgement: increasing water intake during the day is a low-risk, sensible change that supports the other dietary improvements. It is not a substitute for eating breakfast, but it is part of the same picture.
3. A friend says 'she should just take an iron supplement because teenagers need iron'. Evaluate this advice.
Read the worked answer
Iron is needed to make haemoglobin, which carries oxygen in red blood cells, and teenagers do have increased iron needs during growth. However, assuming a supplement is needed without evidence is poor practice.
Points to consider:
- Her diet includes chicken, which supplies iron; the actual iron content of her diet would need to be assessed before concluding she is deficient.
- Tiredness has many causes - poor sleep, skipped meals, low water intake, stress, or illness. Attributing it to iron deficiency without investigation is guesswork.
- Taking supplements unnecessarily can be harmful; excess iron is not simply excreted and can cause digestive problems.
- A doctor would consider symptoms, diet, and possibly a blood test before recommending supplements.
Conclusion: the advice is well-meant but not justified. The first steps should be dietary improvements - breakfast, slower-release carbohydrates, and adequate water - and a medical check if tiredness persists. Supplements should follow evidence, not assumption.