# news & tips

A collection of helpful articles on teachers and teaching

# Calorie Science

January is usually a time when people begin diets and try to work off the extra cookies and snacks they ate over the holidays. Students are interested because either they are looking more closely at their own nutrition or their parents are on diets. Healthy eating is always a good focus and in January you have every news report and major advertising campaign supporting your efforts.

The labs I love in this diet crazed time have to do with an understanding of what a calorie is and how we determine how many calories that belly buster burger contains. That understanding lives in the science of thermochemistry.

Every bite of food we eat has energy stored inside the chemical bonds. A simple peanut can be the beginning of understanding this phenomenon. You have to start with some basic understandings.

First, water heats at a rate that can be useful in helping determining how many calories there are in a substance. It takes one calorie to raise the temperature of one gram of water one degree Celsius. So, in theory if you could burn a peanut and get all the heat from burning the peanut to go into a known quantity of water you could simply measure the temperature change of the water and with a little simple math; determine the calories the peanut gave off in the chemical transformation (burning).

There are lots of sites that walk you through using a simple tin can to construct a calorimeter and measure the calories in a peanut. The best one is from the Science and Health Education Partnership.

http://seplessons.ucsf.edu/node/349

How this method works is covered in this site.

http://www.dummies.com/how-to/content/how-nutritionists-measure-calories.html

You may want to brush up on some of the background on thermochemistry from the Purdue chemistry folks.

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch5/tempframe.html

Now, to take that in a different direction it is always good to give kids a chance to apply some science knowledge in learning how to read nutrition labels. The FDA has an entire set of pages devoted to just that idea.

http://www.fda.gov/Food/LabelingNutrition/ConsumerInformation/ucm078889.htm

To apply the science common in middle school the students have to understand a little bit about how our body uses nutrients like sodium or how it processes fats and perhaps the difference between saturated and unsaturated fats. There is an entire nutrition course in those labels but keep it understandable. Students will be anxious to bring in new labels and add them to the class collection. My students enjoyed trying to find the food with the lowest sodium, highest sodium, and greatest percentage of specific vitamin requirements. If one of the most important math concepts is percentages, then food labels provide an excellent way to interest students and help them learn how to calculate and use them.

We talk about total number of calories you need in a day with different activity levels. Then, we calculate what percentage of your daily calorie requirement that glass of orange juice provides. We can do the same with vitamin C or sodium. At the end of this week long experience with labels the students know more about healthy calorie intakes, how much sodium they should have, what foods to avoid, and of course percentages. This label reading work is as effective in secondary classes as it is in middle school.

For the lower grade levels there are some web sites that are a bit more understandable than the FDA site.

http://kidshealth.org/kid/stay_healthy/food/labels.html