Do try this at home

How healthy is your food?

Why does this work?

Most of us love to eat crisps, but in today's world we have to think about the health consequences of eating junk food.

Have you ever read the nutritional information on the back of a crisp packet? Try having a look next time and check out the lines which tell you how much fat there is in your food and what the calorie content is. We all know that the more calories you eat, the more likely you are to put on weight if you're not burning it off. So how much fat are you eating in your favorite bag of crisps?

This experiment should help teachers or parents demonstrate how unhealthy certain types of crisp are, and can help you learn to think about what goes into your food and how it gives us energy. Hopefully, kids will be able to come up with some good ideas of their own so I have only included a few experiments you can try below.

Ingredients

• Crisps (a selection)
• Long tongs or tweezers
• Matches
• ADULT SUPERVISION!
• Brown paper bags
• A microscope
• Foods - marshmallows, peanuts, cereal (anything that will burn)
• Cork and pin
• Test tube
• Thermometer

Recipe

There are lots of ways you can investigate what goes in to your food. Try to think up your own ways to test this. You can also do some research and find out how the nutrional values printed on your crisp packets are determined.

What ways can you think of to test how much salt there is in your crisps? How about trying a taste test? Or looking at the crisps under and microscope? Record all your findings and at the end of the experiment, you can compare your results with what is printed on the packets.

What about fat content? Again, the microscope is a good way to investigate your crisps. But my favorite way is to crush up the crisps in a brown paper bag and look at the size of the greasy, fatty patch on the bag. Does it correlate with what the nutritional information on the packet says? Teachers - fat burns well, so why not take the class outside and (holding the crisp with tongs) set it on fire and look at the size of the flame. Before you start burning, can you guess what foods will give the biggest flame? What determines how well something burns?

How about calorie content? When we eat food, our body breaks it down and energy is released. We can test how much energy is released by burning the food and investigating how much energy is given off (older students only). First of all, think about what your hypothesis is. To do the experiment, you'll need to place the pin in the cork and sit on a heatproof surface. Weight your piece of food and attach it to the pin. With tongs, hold a test tube containing 20 ml water and a thermometer (don't let it touch the sides) above the food and set the food alight. Measure the change in temperature of the water. To increase the temperature of 1 g of water by 1 degree celcius requires 1 calorie of heat. Use this to work out the calorie content of your food.

When you've investigated your crisps and other foods, how about making a table of the fat, salt and overall calorie content of the different types you looked at? Does it match with your results? What food is the best for you? Are diet options always better when you look at overall calories?

 

 

The labels on your foods should tell you how much salt, fat and overall calories are found in the stuff you eat every day. We can also demonstrate what is in our foods using a few simple experiments.

Salt: Our mouths can taste 5 types of taste (sweet, bitter, savory, sour and salty), so we're a really good judge of how much salt is in a food just by tasting it. If you looked down the microscope, you should have been able to see salt crystals too. Of course, salt ca sometimes be hidden in a food instead of sprinkled on the top, so you might not realise you're eating it unless you think about it carefully or read the packet. A good school project is to investigate the salt content of lots of foods. Did you know that lots of ready meals contain so much salt that it could be harming your health? The UK recommened salt intake is 5g (if you're 7-14) or 6g if you're older than 14. Kids should be having less than 2g and babies less than 1g. Even one kids' meal at a burger restaurant can take you well over the recommended healthy levels! It's thought that most people eat more than twice the amount of salt that they should be. Its hard to cut back because of the hidden salt found in so many of our daily foods - white bread, tinned pasta shapes, burgers, canned soup etc.

Fat: The fat content of your food is really important if you want to be healthy. While the overall calories content is what determines how much energy you will get from food, eating low fat products can help you be healthy. Afterall, heart disease can be caused by eating a high fat diet. We can demonstrate how much fat is in food firstly by looking at it and thinking about what has gone into making it. Crisps used to always be made by frying potato in oil, but today you can get baked versions that are much healthier. But be warned - some diet foods can contain more calories than the original version even though they have less fat.

Calorie content: The amount of energy the body gets from a food depends on how much energy is released when the food is broken down. This energy is stored in the bonds holding the food together and we can release it in the lab through a combustion reaction. Ie. By burning the food. A calorie is defined as the amount of energy required to increase the temperature of 1g water by 1 degree celcius. If we burn food and measure how much it heats water, we can work out its calorie content. This is very similar to the method used to work out the nutritional information found on food packets.

We can use a simple formula to work out the calorie content of a food by measuring how much it can heat up a known volume of water:

Q = mcDT

where Q is the heat transferred to the water in calories
m is the mass of the water in grams
c is the specific heat of water which is 1 degree per calorie per gram (this is a constant for whatever type of material you are heating - in our case, water)
and DT is the temperature change in °C

So, if your water went up by 10 degrees, the calculation would look like this:

Q = 20 * 1 * 10 = 200 calories

Express your results as calories per 100g of the food (divide the calories you worked out above by the mass of your food and times by 100).

In your experiment, what other varibles would have altered the result? Think about where the heat goes...how could you improve the experiment?

This work is licenced under a Creative Commons Licence.