Nutrition and balanced dietIB MYP Sciences: Revision notes
Section 1
Nutrient groups and their roles
Food contains seven nutrient groups.
- Carbohydrates: the main source of energy (e.g. rice, bread, potatoes)
- Proteins: growth and repair of tissues (e.g. meat, fish, beans, eggs)
- Fats (lipids): a concentrated energy store, insulation and protection of organs (e.g. oils, butter); they release the most energy per gram
- Vitamins: needed in small amounts for health, e.g. vitamin C for healthy skin and gums, vitamin D to absorb calcium
- Minerals: e.g. calcium for bones and teeth, iron for haemoglobin in red blood cells
- Water: a solvent, transports substances in the blood and is needed for chemical reactions
- Fibre: adds bulk to food so the gut muscles can move it along; it is not digested
Section 2
Food tests
Each nutrient can be identified with a test.
- Starch: add iodine solution. Positive: orange-brown turns blue-black.
- Reducing sugar: add Benedict's solution and heat in a hot water bath. Positive: blue turns green, then yellow, orange and finally brick-red.
- Protein: add biuret reagent (sodium hydroxide, then copper sulfate). Positive: blue turns purple.
- Fat: shake the food with ethanol, then pour into water. Positive: a cloudy white emulsion.
Name the reagent, the condition (heating for Benedict's) and the colour change for a positive result.
Section 3
A balanced diet
A balanced diet contains all seven nutrient groups in the right amounts for a person's age, sex, size and activity. A growing teenager needs more protein and calcium; an athlete needs more carbohydrate for energy. Eating more energy than you use is stored as fat, and eating too little energy leads to weight loss.
Section 4
Deficiency diseases
A deficiency disease is caused by a lack of a nutrient.
- Scurvy: lack of vitamin C; bleeding gums and slow healing of wounds. Cured by eating fresh fruit.
- Anaemia: lack of iron, so less haemoglobin is made and less oxygen is carried; the person feels tired and pale.
- Rickets: lack of vitamin D (or calcium); soft, weak bones that bend.
- Not enough protein or energy overall leads to malnutrition.
Section 5
Problems of eating too much
Eating too much can also harm health.
- Too much energy-rich food (especially fat and sugar) leads to obesity, which raises the risk of heart disease and type 2 diabetes.
- Too much sugar causes tooth decay.
- Too much saturated fat can lead to heart disease.
Balance means getting enough of every nutrient without eating too much overall.
Fibre is not a source of energy because humans cannot digest it. It is still needed in the diet.
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Nutrition and balanced diet
- A school canteen in Dubai is redesigning its lunch menu so that students get a range of nutrient groups. Menu items include a chicken and rice bowl, buttered toast, an orange and a bean salad.Explain why fibre is an important part of a balanced diet.2 marks
- A student in Auckland is given an unknown food sample, mixed with water, and carries out three tests. With iodine solution the sample turns blue-black. After heating with Benedict's solution it stays blue. With biuret reagent it stays blue.Describe how the student could test the sample for protein, and the result that would show protein is present.2 marks
- On long sea voyages in the 18th century, many sailors developed bleeding gums, extreme tiredness and wounds that would not heal. Their diet was mostly dried biscuits and salted meat. When ships began to carry limes, the sailors recovered and the symptoms disappeared.Identify the deficiency disease the sailors had and explain why eating limes cured it.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).