Using Nutrition to Teach Science
From the book, How to Teach Nutrition to Kids, by Connie Liakos Evers, MS, RD
When my daughter was a first grader, she approached me about project ideas for her school science fair. I naturally thought of all the possiblities that related to food and nutrition science. The idea that spiked her interest the most was to survey her classmates and analyze their eating habits. By the time we finished this project, she had gained skills in a variety of subject areas. She developed a simple questionnaire that her classmates used to record their diets for one day, analyzed and compared their daily diets with the Food Guide Pyramid and presented her data graphically, using her best art skills to design, color and display her work.
Because nutrition is a science, the prospects for science activities are limitless. This chapter presents learning ideas in three areas: food in the body, the study of plants as food and how kids can use the scientific method to conduct nutrition research.
FOOD IN THE BODY
Nutrition is the science of how the body uses food. Even young children can gain an appreciation of how food is broken down and used inside the body. The food we eat goes through five stages of processing: digestion, absorption, circulation, metabolism and excretion. Simple explanations with engaging experiments and activities will bring these concepts to life.
TASTE AND SMELL
Our experience with food starts with our noses and tongues. The sensation of taste is actually a combination of smelling the food and using the taste buds on our tongues. While it was once believed that we use different areas of our tongues to taste different sensations - salty, sweet, bitter or sour - scientists now believe that we actually can detect most types of taste with most of our taste buds. In other words, the concept of the "tongue map" is outdated.
Scientists have also discovered an additional taste sensation named umami (pronounced oo-mommy) which is thought to be the savory or meatlike taste found in the chemical glutamate. Examples of umami taste includes meat, the seasoning MSG and aged cheeses.
At snack or mealtime, instruct children to take a bite of one food and describe how it tastes. Next, have them hold their noses and take a bite of the same food. Ask them to describe the taste of the food and how it changed. Discuss how the sense of smell plays a part in detecting the flavor of foods. That is why the sense of taste is diminished when we are suffering from colds.
Digestion is the process of breaking food down into millions of tiny pieces. Beginning in the mouth and ending in the toilet, food covers a route about 25 feet long, all inside the body! After the mouth, food travels to the stomach by way of a tube known as the esophagus. Most of the "action" of digestion occurs in the small intestine, a coiled-up organ that completes digestion and transfers nutrients through its walls to the blood stream. This so-called "small" intestine would stretch more than 20 feet if it were uncoiled! In the large intestine (larger around, but much shorter in length than the small intestine), water is added to waste products, making a paste that can be excreted.
While food is broken down somewhat by chewing and grinding, most digestion takes place by body chemicals. Chemicals known as enzymes break down food in the mouth, stomach and small intestine. Other chemicals include acid in the stomach and bile (which helps break down fat) released into the intestine by the gall bladder.
Trace children's bodies onto larger sheets of paper. Students will be concentrating on how they look on the inside. Ask the children to draw and label the parts of the digestive system on their life-sized silhouettes.
A digestive tract is more than 20 feet long in a child four feet tall? How could that be? Using a tape measure and string, have the children measure 25 feet of string. Using their life-sized body silhouette, ask them to "fit" the digestive tract into the one they just drew, affixing it with glue if they wish.
Even as we are enjoying the taste of food in our mouths, digestion is beginning. As the teeth grind and crush the food, an enzyme in the saliva begins breaking down carbohydrates into sugar. To demonstrate this concept, pass out small pieces of saltine crackers. Read the label, pointing out that saltines are made from flour and have little or no sugar. Ask children to hold the cracker on their tongues without chewing or swallowing. What do they taste? After a few minutes, ask children whether the taste of the cracker has changed. Elicit possible explanations for this happening. Explain that the sweet taste means a chemical called an enzyme in their saliva has digested the starch to sugar.
Who was the first scientist to understand that body chemicals, not just mechanical actions, are responsible for digestion? In 1822 an ambitious army doctor named Dr. William Beaumont was able to conduct digestion experiments on a living man! When fur trader Alexis St. Martin was shot in the stomach, he survived despite slim odds. But a small hole into his stomach never successfully healed, allowing Dr. Beaumont to conduct a multitude of digestive experiments and withdraw stomach acid for study. This fascinating story is told in Dr. Beaumont and the Man with the Hole in His Stomach, by Sam and Beryl Epstein (Coward, McCann & Geoghegan, 1978). Read this book to the children or encourage intermediate students (third through fifth grade) to read and report on it.
The most slowly digested nutrient is fat. That is why a greasy meal can leave a person feeling stuffed for hours! One reason is that fat travels through the digestive system in big droplets or globules. When fat encounters the dark liquid bile in the small intestine, it is broken down into small droplets. Bile acts as an emulsifier, a substance that can break fats into small globules that will mix with water.
Using water, liquid vegetable oil and a raw egg yolk, students can observe how bile breaks down fat during digestion. An egg yolk contains the emulsifier lecithin. (Lecithin is often added to salad dressings and other processed foods because it breaks up the fat particles, resulting in a smooth product.) In a clear glass, mix 1 cup of water and 2 tablespoons of oil. What happens? Try stirring the mixture vigorously. Does the fat break down? Next, add the egg yolk to the mixture and stir. What happens to the fat droplets? This reaction is similar to how bile breaks down fat in the small intestine. (Incidentally, egg yolks do not work as emulsifiers in the body since they are changed by both cooking and stomach acid before they reach the small intestine.)
After food is digested into small particles, it must somehow move from the digestive tract to the rest of the body. That movement into the bloodstream is called absorption and happens mainly in the small intestine.
The small intestine is made up of millions of fingerlike projections called villi. The villi are covered with a hairlike brush that traps the nutrients. The nutrients are then passed through the villi into tiny blood vessels called capillaries, which eventually empty into the body's major blood vessels.
To explain the concept of absorption visually, use a sample of carpet to illustrate the surface of the small intestine. Each yarn fiber sticking out of the carpet is like a villus, ready to absorb nutrients and pass them into the bloodstream.
Books for young readers that explore digestion include What Happens to a Hamburger, by Paul Showers (HarperCollins Juvenile Books, 2001) and Burp! The Most Interesting Book You'll Ever Read About Eating, by Diane Swanson (Kids Can Press, 2001).
How do nutrients find their way up to our noses and down to our toes? Every cell of the body requires a continuous supply of energy from nutrients and oxygen from the air we breathe. Oxygen and nutrients are transported to cells by arteries, while veins carry carbon dioxide and waste products out of the cells. This network of blood vessels, including the small, weblike, connecting vessels known as capillaries, make up the circulatory system. The circulatory system relies on a very important pump, the heart, to continually move blood through the body.
Once nutrients finally make their way to the billions of tiny cells that make up the body, they are used to supply the building blocks for energy, healing, maintenance and growth. Each cell of the body is like a tiny factory, taking the raw materials of nutrition and producing energy or growth and replacement parts. At any given moment, the cells of an active child are busy supplying energy to run at recess, creating new cells to make bones and muscles bigger, sending sugar to the working brain, and producing skin cells to heal a scraped knee.
Fortunately, the body does all these things without conscious effort. The only thing a healthy child really needs to think about is eating a diet that supplies the necessary raw materials.
What is hunger? It is the body's message to the brain that more nutrients are needed for growth, maintenance, repair and energy. By the time hunger sets in, the body's energy stores are running low and the ability to focus on tasks becomes difficult. To illustrate this point, ask children to respond to their hunger in other ways than eating: by reading, doing math problems, taking a walk, etc. (If possible, delay their lunch period by 30 minutes in order to carry out this experiment.)
Ask the children how they felt doing other activities when they were hungry. Were they able to concentrate? How were their energy levels? Their moods? Discuss the role that nutrition plays in learning. Point out that kids who skip meals, especially breakfast, often don't learn as well as kids who eat regular meals.
Ask students if they know what the word "breakfast" meals (break the fast). Explain that a fast is a period of time without food. Elicit how many hours their bodies normally "fast" from suppertime to breakfast.
On a display board, write the sentence, "Breakfast is the most important meal of the day." Ask children to write or tell whether this statement is true and why or why not. Encourage them to write about their own experiences with breakfast, including where and what they usually eat.
The final stop for food is the excretion of waste products. Even the most nutritious food has parts that cannot be digested and used, such as fiber. After food leaves the small intestine, it enters the large intestine where water is added to form a paste that can be easily excreted. Other nutrient waste products are filtered through the kidneys and excreted through the urine (breakdown products of protein metabolism and salt, among others).
PLANTS AS FOOD
Studying and growing edible plants is a wonderful way to reinforce nutrition and introduce children to scientific concepts and processes. Observation, prediction and data collection are skills gained by applying science to gardening. A "growing" classroom or home can be as simple as a few seeds planted in a milk carton or as elaborate as a greenhouse or large outdoor garden plot.
Young botanists should be encouraged to keep a journal when studying and growing edible plants.
A miracle really, life as we know it starts in the leaves of a plant. Using energy from the sun, carbon dioxide and water, chlorophyll - containing cells in green plants manufacture carbohydrate. Plants comprise the first link of the food chain, providing food energy for other living organisms, including people!
To observe the effects of photosynthesis, start with a green potted plant. Instruct children to observe, draw and record how the plant looks. Place it in a dark closet. Continue to water regularly, but do not expose to light. Every two days, bring the plant out briefly to allow children to observe and record the changes. How does the plant change? Ask children to draw a conclusion about the effect light has on plants. Explain that photosynthesis cannot occur, thus the plant can make no food, when light is removed.
Even when dormant for a period of years, seeds will sprout when given the right conditions of warmth and moisture. This process is called germination.
To watch germination in action, place dry beans in a clear glass jar containing a moistened sponge. The sponge will keep the seeds moist and hold them against the side of the jar where they are visible. Ask children to carefully record or draw the germination process in their plant journals, including any predictions they make about the process or how long it will take (and later, notes on whether their predictions came true and why or why not).
Ask if anyone's seed sprouted "upside down" or "sideways." (The answer should be NO.) Elicit from the children how seeds know to sprout "right side up." (ANSWER: Seeds respond to gravity by sprouting root down, stem and leaves up. This concept is known as phototropism.)
To grow edible sprouts, you will need small jars or clear plastic cups (Baby food jars work great), clean 3-inch squares of nylon stocking, rubber bands, and 1 teaspoon of rinsed lentils or dry beans. Place the seeds in the jar and fill it with water. Fasten the nylon square over the top with the rubber band. Let them soak overnight.
The next day, drain off the water by turning the jar upside down until all the water shakes off. Rinse the seeds with cool water and drain again. Place the jar on its side in a dark place. Rinse the seeds twice a day and drain off water. For green sprouts, place them in a sunny window for one day. Eat and enjoy on salads, in sandwiches or stir-fried with other vegetables.
Potting soil or planting mix, empty milk cartons, and a sunny window (or grow light) will suffice for young gardeners just starting out.
Radishes are a great vegetable for the beginning gardener. Many varieties germinate in 4 to 7 days and are ready to eat in 25-28 days. First, fill cleaned half-pint milk cartons with potting soil. Read the seed packet instructions to find out the planting depth (usually 1/4 inch). Ask the children to think of ways they can accurately measure the soil to arrive at the correct planting depth. (A ruler or marked stick will work.) Next, have children place four or five seeds in the soil (apart from each other), cover lightly and gently water. (To maximize drainage, poke a small hole in the bottom of the carton and place on a lid or in a tray.)
Encourage children to describe the planting process in their journals. Ask children to predict when their seeds will germinate and how the seedlings will look when they first sprout. Every day children can check on their plants and record any observations or changes. Keep plants moist, but avoid overwatering.
Once the seedlings sprout, encourage students to make daily or weekly measurements and/or predictions about the growth and record them in their plant journals. Results can be presented in a variety of ways - through drawings, tables or graphs, for instance.
The radishes should be thinned to two plants per carton. They are ready to pick and eat when the roots become round and begin to pop up out of the soil. After harvesting, weigh the radishes and record that in the plant journals. Wash, slice and taste the radishes.
A great springtime gardening activity is to "start a salad." Children can then take their seedlings home and plant them in small garden patches or in large pots placed on their decks or patios.
Materials to start a salad include an empty paperboard egg carton, potting soil and a variety of "salad" seeds. If possible, take the children on a field trip to a garden center or nursery to choose seeds for this project. Examples of salad greens include spinach, arugula, watercress and lettuce varieties such as romaine, oakleaf, butternut and redleaf. Fill egg carton compartments with potting soil and plant seeds according to package directions. When they have reached a height of 2 inches, send them home with a note to parents, encouraging them to transplant the plants outside or into a larger container. For easy transplanting, cut apart the compartments of the carton, poke a hole in the bottom of each compartment, and place it in the soil, carton and all.
Encourage children to monitor the progress of their "salad" and record it in their plant journals.
Just like all living things, plants have a lifecycle. Growing lettuce can make a fascinating study of the lifecycle of a plant.
As a class project, plant and grow lettuce in a large container in the day care. Observe and record the progress of the plants and taste the lettuce when it reaches maturity. Allow at least one of the plants to "go to seed," a process where the lettuce will produce long shoots with flowers. Eventually the flowers will form small seed pods. (This process, from start to finish, takes a few months.) Start all over again by harvesting and planting the seeds - a perpetual experiment!
Ask children why plants "go to seed" and why harvesting seems to prolong the process. Discuss the ways other fruits and vegetables produce seeds. Ask the children to bring in examples from home (e.g., avocado pit, cantaloupe seeds) and experiment with planting.
PARTS OF PLANTS WE EAT
The vegetables we commonly eat comprise a wide variety of "plant parts." There are six general classifications for edible plant parts including roots, stems, leaves, fruits, flowers and seeds. The activities below allow young botanists to classify, observe and eat various parts of plants.
Explain that vegetables can be classified by the part of the plant from which they come. The six general categories are roots, stems, leaves, fruits, flowers and seeds. (NOTE: The classification of vegetables as the "fruit" part of the plant can be tricky. Explain that a "fruit" refers to the edible part that grows from a flower and contains seeds on the inside. The "fruits" that lack significant sweetness are generally classified as vegetables.) Brainstorm examples of vegetables in each category.
Roots: carrot, beets, radish (potatoes are technically tubers while onions are actually bulbs)
Stems: celery, asparagus
Leaves: lettuce, spinach, cabbage
Fruits: tomato, cucumber, eggplant, squash, pepper
Flowers: broccoli, cauliflower, artichoke
Seeds: corn, pea, green bean
Take a field trip to a grocery market, farmers' market or produce farm. Encourage children to take note of the variety of produce they see. Upon return to the day care, make a list of the observed vegetables and name the part of the plant each comprises.
Bring a variety of vegetables into the day care for observation and tasting. Include less common varieties, including diakon radishes, broccoli-cauliflower hybrid, Brussels sprouts, bok choy and kale. Provide hand-held microscopes that children can use to examine the vegetables.
Make "plant-part-art" for a snack. You will need: large flat crackers, peanut butter or low-fat cream cheese, broccoli florets, celery sticks, lettuce leaves torn into small pieces and shredded carrots. Students will first lightly spread crackers with either cream cheese or peanut butter. Next, they will create a plant or garden design using shredded carrots for roots, celery sticks for stems, lettuce for leaves and broccoli for flowers. This is an amazingly novel (and effective) way to get students to eat vegetables!
USING SCIENCE TO ANSWER FOOD & NUTRITION QUESTIONS
Children can practice using the scientific method and also learn answers to food and nutrition questions at home. The scientific method involves formulating a question, developing a hypothesis, coming up with a method of experiment to test the hypothesis, evaluating the results and forming a conclusion. The hypothetical examples below illustrate how children can apply this method to food and nutrition research. Children should also be encouraged to take the results of their experiment and use them to make recommendations for change.
GARBAGE AS SCIENTIFIC EVIDENCE
Children can monitor garbage to answer questions about what children eat or throw away at lunch time. The example below outlines one possibility for an experiment. Working in groups, children can come up with other ways of monitoring diets and influencing cafeteria choices by studying plate-waste.
Question: Which fruit do most children eat more of: fresh grapes or canned pears?
Hypothesis: Children will eat more fresh grapes than they will canned pears.
Experiment: Empty lunch trays will be checked on two different days, including one day when fresh grapes are on the menu and one day when canned pears are on the menu. Children will stay by the area where lunch plates are cleaned and record whether the fruit was eaten, partly eaten, or not eaten. If a large group of children are used in the study, the number can be limited to the first 10 children to clear their plates.
Results: On the day fresh grapes were served, 6 out of 10 children ate the entire serving, 3 ate part of their grapes and 1 child did not eat any grapes. On the day canned pears were served, 4 out of the 10 children ate the entire serving, 5 ate part of the serving, and 1 did not eat any pears.
Conclusions/Recommendations: Hypothesis confirmed. Children prefer fresh grapes to canned pears. They ate more and wasted less on the day that fresh grapes were offered. Lunch menus should offer fresh grapes more often than canned pears. Better yet, children should get a choice of two or more fruits every day in order to eliminate waste and improve nutrition.
NOTE: Depending on the level of the children, the results can be manipulated mathematically, using graphs to plot raw results, or converting to percentages and presenting the data in a table or graph.
FINDING OUT ABOUT OTHER PEOPLE'S DIETS
Is it nosy to ask people what they eat? Maybe, but the government does it all the time when they conduct surveys of Americans' eating habits. Conducting nutrition surveys is a fun and informative way to learn about and compare the diets of different groups of people. Surveys can be descriptive, telling about the diet of a certain group of people (e.g. 8-year-old soccer players). Or a survey can be comparative, contrasting the difference in eating habits between two groups of people (e.g., soccer players versus piano players). The example below is a comparative study.
Question: Who eats or drinks more low-fat dairy products: girls or boys?
Hypothesis: Boys consume more low-fat dairy products than girls do.
Experiment: Design a simple checklist that includes the following foods: 1 cup low-fat milk (fat-free or 1%), 1 cup low-fat/fat-free yogurt, 1/2 cup frozen yogurt, 1/2 cup ice milk, 1 ounce low-fat cheese and 1/2 cup cottage cheese. Ask children to check off each serving of low-fat dairy products that they eat or drink for two days. Remind them to pay attention to the serving size, making one check mark for each amount listed. (For example, if they eat 3 ounces of cheese at one sitting, that's three check marks.) Do not tell them you are comparing boys to girls - they may make a contest out of it, which will bias the results. Instead, explain that they should eat and drink just as they normally do. Collect the surveys after two days.
Results: Fifteen girls and ten boys completed the survey. For the two days, the fifteen girls consumed 60 servings of low-fat dairy foods. The boys consumed 50 servings of low fat dairy foods. Using averages, the girls ate an average of 4 servings each in the two-day period (60 servings divided by 15 girls). The boys ate an average of 5 servings each in the two-day period (50 divided by 10).
Conclusion: Hypothesis confirmed. Boys ate an average of 2.5 servings of low-fat dairy products each day while girls ate an average of 2 servings of low-fat dairy products each day.
Once their minds are set in motion, children will enjoy using science to answer other food and nutrition questions. Encourage children to work cooperatively when planning and conducting their research. Perhaps the best gratification is that their projects can help initiate change in nutrition practices or policies.
Below is a brief list of other possibilities for nutrition research.
A study reported in the Journal of the American Dietetic Association showed that children ate more at lunch when they had active play time before lunch. Test this hypothesis in your home, comparing two days; one in which active play was directly before lunch and one where active play was scheduled after lunch.
Set up taste tests with children for new nutrition foods offered by food manufacturers.
Nutrients that are commonly in short supply in the diets of pre-adolescents include iron, calcium, vitamin E and folate. Analyze and identify foods in your home that are good sources of these nutrients and create a poster to display the information. A useful online resource for nutrient analysis is the food composition database from the USDA. You can access it online at www.nal.usda.gov/fnic/foodcomp/Data/SR16/sr16.html.
Design a study to test whether breakfast cereals with toys in the packages contain more sugar than cereals without toys.
To receive a certificate of training hours you must complete a quiz based on the material above. You are required to get all questions correct. If you do not get 100% on the quiz the first time, you may take it over again. The results of the quiz will be emailed to Mid Michigan Child Care Food Program. When we receive the results of your quiz, a certificate of training completed will pop up that you can print. A copy of the certificate will also be emailed to you.