The Foods We Eat: Complex Carbs

FIELD: Life Science DURATION: 45 min.
OBJECTIVE: Students will identify the relative amounts of carbohydrates in different foods and food groups.
METHOD: Students hypothesize and test the starch content of different foods using iodine.
KEY VOCABULARY: Carbohydrates, Starch, Iodine. GROUP SIZE: Any


Carbohydrates are molecules present in many foods, especially vegetables. Sugars, starch, and cellulose are common examples. Every carbohydrate molecule has a certain number of carbon molecules (Carbo-) attached to a certain number of water (-Hydrate) molecules. When these numbers are relatively large we say that the total carbohydrate is 'complex'.

Complex Carbohydrates are crucially important in our diet because they provide the main source of our bodies' energy production. It's important to consume enough carbohydrates or the body won't be able to function efficiently.

In this experiment you will test different foods for one of the primary complex carbohydrates: starch. Since starch stains blue with iodine, we can use it as an indicator for the presence or absence of starch in foods.

MATERIALS (per group):

2 clear cups
cornstarch - 2 tsp.
tap water - 1/4 cup
iodine - 100ml
Small food samples from a variety of food groups: bread, apple, potato, milk, tofu, etc.


1. Fill the two cups 1/4 full of water.
2. Stir 1/2 tsp. of cornstarch into one cup. The other cup will serve as an experimental control.
3. Add 2 drops of iodine to each cup and observe what happens.
4. When iodine touches starch it turns blue.
5. Give each student or group a set of food samples. Have them make hypotheses about the amount of starch in each and order the foods from least to most.
6. Place 2-3 drops of iodine on each sample and observe the blueness. The deeper the blue, the more starch in the food.
7. Reorder the food according to starch content.
8. Reorder the food into the basic food groups: protein, milk, grains, fruits, and vegetables. Draw conclusions about which food groups have the most carbohydrates.


1. Using a color chart showing shades of blue (this could be created with a computer and color printer) create a numbering scale from lightest blue to darkest. Match each food's iodine color to a number in the scale and label each sample. Average all students' values for each food. Create a display with a line labeled from 0 to the value of deepest blue. Place a label for each food on the line at its appropriate value.
2. Create a display chart of the food groups with each food ordered by starch content. Think of other foods in each food group and include in display.

Created April 24, 1997 by Danica Nuccitelli.
Maintained by
Last updated April 24, 1997.