Health, Diet, Protein and BMI
What is a balanced or healthy diet?
Like other animals, you have to get food by eating it. Food is a source of energy. A balanced diet contains the right amount of the different foods and the right amount of energy to keep you healthy. It also includes nutrients that do not provide energy: minerals and vitamins, water and fibre.
Why do you need to eat it?
Where is it stored?
Carbohydrates (made up of simple sugars like glucose)
to give you energy
stored in the liver as glycogen or converted to fats
Fat (made up of fatty acids and glycerol)
to give you energy
stored under the skin and around organs as adipose tissue
Proteins (made up of amino acids)
for growth and repair (you can use proteins for energy if you don't have enough fat or carbohydrate)
Iron (a mineral)
to make haemoglobin
Vitamin C (a vitamin)
to prevent scurvy
to prevent constupation
Water (your cells contain about 70% water)
to prevent dehydration, replacing water lost in tears, urine and faeces
Some people do not eat a balanced diet. They eat the wrong amount or types of food. A balanced diet is not the same for everyone. It may vary according to:
- how active you are
- medical reasons (eg diabetes, allergies)
- personal choice (eg vegetarian/vegan)
Calculating the EAR for protein
We can calculate how much protein we should eat each day. This is called the estimated average requirement or EAR.
EAR in g = 0.6 x body mass in kg
So a 60kg boy should eat 0.6 x 60 = 36g of protein daily.
Remember that the EAR is an average amount. However, there is really no such thing as 'the average person'. A person's protein needs may vary depending on age, pregnancy or lactation (making milk).
What happens if you do not eat enough protein?
You are growing fast, and need protein to grow and develop properly.
In some developing countries people do not get enough protein. This is linked to
- overpopulation - too many people to feed properly
- limited investment in agricultural techniques which result in less food being produced
- eating more second class proteins from plants than first class proteins from animals. First class proteins contain essential amino acids that cannot be made by the body.
If children do not eat enough protein they can suffer from a deficiency disease call kwashiorkor. They have very thin arms and legs and a swollen belly. Their bodies can't fight infection very well.
In developed countries some people choose to eat too little. They may have a low self-esteem or a poor self-image and think that by being thin they will look better. Being so undernourished can lead to heart problems and poor health.
You can work out whether you have a healthy weight by calculating your body mass index or BMI. This is your mass in kg divided by your height in metres, squared.
So if a girl weighs 50kg and is 1.60m tall, her BMI is 50 ÷ (1.60)² which is 50 ÷ 2.56 = 19.53 kg/m2.
A person with a BMI of
- under 18 kg/m2 is underweight
- 18 to 25 kg/m2 is normal
- 25 to 30 kg/m2 is overweight
- over 30 kg/m2 is obese
You have seen that there are health risks linked to being underweight. If you are very overweight there are also health risks. Obese people are most likely to suffer from
- heart disease
- breast cancer
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