What it shows
Packaged foods list energy, fat, sugar, protein and salt on the label. Comparing foods fairly means using the per 100 g column and not the per pack figure, which depends on pack size.
The science
Energy on a label is given in kilocalories or kilojoules, and carbohydrates, fat and protein supply it. Each gram of fat gives about 9 kcal, and each gram of carbohydrate or protein gives about 4 kcal. A per 100 g column lets you compare two packs on equal terms.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three empty biscuit packets or photos of labels
- A calculator
- Chart paper and coloured pens
- A ruler
- A notebook
- An adult to help find the labels
Safety
For this project: Use empty packets or photos only, and do not open and share food in class unless the school permits. This is a label-reading exercise, not diet advice.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Choose three similar products, such as three kinds of biscuit.
Find the nutrition information table on each pack and copy the per 100 g values.
Make a table with energy, fat, sugar, protein and salt for each product.
Check the energy by multiplying grams of fat by 9 and carbohydrate and protein by 4, then adding.
Compare your answer with the printed energy and note the small differences.
Look at the ingredient list and note which ingredient is first, since the list is in order of weight.
Draw grouped bar graphs for sugar and fat per 100 g.
Write two sentences on which pack has the lowest sugar and highest protein, and note that this is not advice.
What you should see
A comparison chart showing how three similar snacks differ per 100 g, and a check that the printed energy matches the calculation within a few percent.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Why compare per 100 g?
It puts every product on the same footing.
2How many kcal does a gram of fat give?
About 9 kcal.
3What does the ingredient order tell us?
Ingredients are listed from the largest amount to the smallest.
4What does FSSAI on a pack mean?
It is the food safety authority’s licence number printed by the maker.
Take it further
Compare a homemade snack with a packet snack by calculating its energy from ingredients.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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