Measuring Calories in Food
Grade level(s):Grade 4, Grade 5, Grade 6, Grade 7, Grade 8, Grade 9
Topic:Nutrition and Food chemistry
-Understand the concept of calories and how they can be measured
-Be able to give examples of high calorie and low calorie foods
-Understand how calories relate to body weight and obesity
Calorie, energy, high calorie food, low calorie food, physical activity, weight gain, nutrition label, carbohydrates, protein, fat, calorimeter.
What you need:
- Pre-weighed food items containing 200 calories: broccoli, celery, carrots, peanut butter, butter and Hershey kisses (see weblink)
- To make a home made calorimeter: coffee can, small metal can, 1 ml pipette, cork, paper clip,
- graduated cylinder, water bottle, thermometer (in °C), lighter, safety glasses, forceps, weigh boats, scales, gloves, lab coat,
- food item for calorimeter activity (peanuts, pop corn, Cheetos, Dorritos all work well)
- hand-outs: procedure, lab report, pictures of calorimeters, formula for calculations.
Part 1: Concept of calories = whole class discussion
Part 2: Calorimeter = Students will work in groups of 6 students and each student will have one task:
- Weighing the food
- Reading the temperature of the water
- Recording the data
- Assembling the calorimeter system
- Filling the water
- The introduction will take place in the classroom.
- Building the calorimeter will occur in the classroom.
- The experiment will takeplace in the courtyard (burning of food items) unless you have a fume hood in your classroom.
- 45 minutes to introduce the topic and show example foods.
- 60 minutes to assemble calorimeter, use calorimeter and record data.
- 30 minutes to complete and discuss the lab report.
The lesson introduces the concept of calories and provides examples of high calorie and low calorie foods. Students learn a number of ways to determine how many calories a food item has and discuss how calories influence body weight. Students learn how to measure calories by constructing and using a calorimeter.
- using balance to weight food.
- measuring volume of liquids.
- reading thermometer and measuring temperature change.
- Knowledge of basic mathematical calculations (multiplication, division and subtraction).
Students will be able to:
- define what a calorie is.
- explain why the body needs calories and what happens to excess calories
- give examples of low calorie and high calorie food items
- read nutrition labels
- build a calorimeter using supplies from home
- use a calorimeter to determine calorie content of a food item
A calorie is a unit of energy. We tend to associate calories with food, but they apply to anything containing energy.
A calorie is the amount of energy, or heat, it takes to raise the temperature of 1 gram of water 1 degree Celsius (1.8 degrees Fahrenheit).
Humans need energy to survive -- to breathe, move, pump blood, think -- and they get this energy from food.
The number of calories in a food is a measure of how much potential energy that food has.
See weblink "What does 200 calories look like" to see examples of high and low calorie foods.
We will be using a homemade calorimeter in this lesson. A particular food item will be ignited, the homemade calorimeter will trap the heat of the burning food, and the water above will absorb the heat, and cause the temperature (T) of the water to increase. By measuring the change in temperature (ΔT) of a known volume of water, students will be able to calculate the amount of energy in the food tested because the heat gained by the water will equal the heat lost by the food item.
- purchase food items including those to be burnt in calorimeter.
- weigh out 200 calories of each food item (See weblink: How does 200 calories look like)
- drill holes in coffee can and small can to make calorimeter assembly easier. Assemble calorimeter according to diagram below.
(kit with pre-assembled calorimeters is now available at SEP).
- make hand-outs
Lesson Implementation / Outline
Have students brainstorm what a calorie is and what they know about it so far.
I. What is a calorie? A calorie is a unit of energy. Often used to describe how much energy your body gets from eating or drinking a certain food or drink.
Record responses and keywords on the board and together come up with a definition for calorie.
Assess students' misconceptions about calories by asking whether calories are bad or good for a person.
II. Are Calories Bad for You? Calories aren't bad for you. Your body needs calories for energy. But eating too many calories - and not burning enough of them off through physical activity - leads to weight gain.
Activity 1: calorie content of example food
Whole class discussion:
- Ask students to give examples of high versus low calorie foods
- Show students the pre-weighed amount of each food item that equals 200 calories
For this activity it is fun to have students guess for each food item how much makes 200 calories first. Put amount of food on plate until students agree that it makes 200 calories and then present them with the pre-weighed amount. This will be a shocker for some!
- Show students how to determine the calorie content of various food items by reading the nutritional label.
You can find out how many calories are in a food by looking at the nutrition label. (The label also will describe the components of the food - how many grams of carbohydrate, protein, and fat it contains. Here's how many calories are in 1 gram of each:
• carbohydrate - 4 calories
• protein - 4 calories
• fat - 9 calories
That means if you know how many grams of each one are in a food, you can calculate the total calories. You would multiply the number of grams by the number of calories in a gram of that food component. For example, if a serving of potato chips (about 20 chips) has 10 grams of fat, 90 calories are from fat. That's 10 grams X 9 calories per gram.
Some people watch their calories if they are trying to lose weight. Most kids don't need to do this, but all kids can benefit from eating a healthy, balanced diet that includes the right number of calories - not too many, not too few.
But how do you know how many calories you need?
Kids come in all sizes and each person's body burns energy (calories) at different rates, so there isn't one perfect number of calories that a kid should eat. But there is a recommended range for most school-age kids: 1,600 to 2,500 per day.
Most kids don't have to worry about not getting enough calories because the body - and feelings of hunger - help regulate how many calories a person eats. But kids with certain medical problems may need to make sure they eat enough calories. Kids with cystic fibrosis, for instance, have to eat high-calorie foods because their bodies have trouble absorbing the nutrients and energy from food.
Kids who are overweight might have to make sure they don't eat too many calories. (Only your doctor can say if you are overweight, so check with him or her if you're concerned. And never go on a diet without talking to your doctor!)
What happens to excess Calories?
If you eat more calories than your body needs, the leftover calories are converted to fat. Too much fat can lead to health problems. Often, kids who are overweight can start by avoiding high-calorie foods, such as sugary sodas, candy, and fast food, and by eating a healthy, balanced diet. Exercising and playing are really important, too, because activity burns calories.
How Does the Body Use Calories ?
Some people mistakenly believe they have to burn off all the calories they eat or they will gain weight. This isn't true. Your body needs some calories just to operate - to keep your heart beating and your lungs breathing. As a kid, your body also needs calories from a variety of foods to grow and develop. And you burn off some calories without even thinking about it - by walking your dog or making your bed.
But it is a great idea to play and be active for at least 1 hour and up to several hours a day. That means time spent playing sports, just running around outside, or riding your bike. It all adds up. Being active every day keeps your body strong and can help you maintain a healthy weight.
Watching TV and playing video games doesn't burn many calories at all, which is why you should try to limit those activities to 1 to 2 hours per day. A person burns only about 1 calorie per minute while watching TV, about the same as sleeping!
Activity 2: Calculate the amount of energy in a food itme using a calorimeter
- Students are provided with the lab report containing building instructions for the calorimeter, tables to record data and a formula to make calculation. Explain how calorimeter works and demonstrate how to assemble and use it.
- This activity is conducted in groups of 6 students; each is responsible of a specific task. The tasks assigned are the following:
a)Weighing the food items
b) Reading the temperature of the water
c) Recording the data
d) Assembling the calorimeter system
e) Filling the water into the calorimeter
- Choose a food item.
- Obtain a weigh boat and determine its weight. Record your data.
- Obtain a food item and using the same weigh-boat, determine the weight of the food (wi). Record your data.
- Using the graduated cylinder, measure out 100 ml of distilled water from the water bottle and pour it into the small metal can.
- Measure the initial temperature of the water (Ti). Record your data in table 1. Make sure to leave the thermometer in the water for a while before reading the temperature.
- Position the small can inside the large can and slide the glass rode through the holes of both cans.
- Unfold the paper clip and insert it into the cork.
- Gently wrap the paper clip attached to the cork around the food. It is better to have the food at a slight angle. If the food breaks, use another one; however, you will have to reweigh the new food item.
- Place the cork with the food on a nonflammable surface (outside of under fumehood). Put on your safety glasses and call the teacher. The teacher will help you light the food. It may take a while for the food to catch on fire.
- As soon as the food catches fire, immediately place the coffee can around the burning food.
- Allow the food to burn until it goes out. If possible try to keep an eye on it and if it goes out quickly (less than a minute), relight the food.
- Once the food has finished burning, carefully stir the water with the thermometer and then measure the temperature again (Tf). Caution! The cans and water will be warm! You may have to leave the thermometer in the water for a while in order to get the highest reading. Record your data.
- After the burnt food has cooled, transfer it to the original weigh-boat (use the forceps if necessary) and weigh the remnants (wf). Record your data.
- Calculate the amount of calories in the food item using the equation provided (students are shown how to calculate caloric content using a formula based on the data collected).
After the activity, the whole class discusses and compares the values obtained by each group and talks about possible sources of discrepancies between students.
Students learning is assesed based on their answers to questions during the discussion and based on their laboratory reports.
Wrap up by asking students to list something they learned in this lesson and make sure that each of the key points is discussed.
Extensions and Reflections
These activities are tied to other content areas such as: math, chemistry and health.
- Make sure to set up an area to use the calorimeter ahead of time.
- Get adult volunteer to help burn the food.
- Try burning the food item prior to the lesson (some items do not burn well in this system).
Weblinks and References
|Student instructions and lab report.doc||213.5 KB|