To understand the relationship among the amount of food energy (calories) consumed, weight, and metabolism and how making good decisions about diet and exercise can lay the groundwork for a healthy lifestyle.
Obesity, or being too heavy for your weight (Healthy People Library Project, 2006, The Science Inside: Obesity, American Association for the Advancement of Science, p. 1, Washington, DC.), is a major problem for children and adults in the United States. The number of children who are considered obese has increased almost four times since the early 1970s; 15% of children and 16% of teens were obese in the year 2000. In addition, today one in five children—of all ages, races, and gender—is overweight, or weighs more than is desirable, placing those children at higher risk for becoming obese. These statistics are particularly grim because there is considerable evidence indicating that overweight children tend to become overweight adults, with a greater likelihood of having overweight children themselves. (Carol Torgan, “Childhood Obesity on the Rise,” The NIH Word on Health, June 2002, National Institutes of Health, Bethesda, MD, http://www.nih.gov/news/WordonHealth/jun2002/childhoodobesity.htm.)
To address the problem of obesity, it is first important to know what weight is healthy for each individual. Physicians use a tool called the body mass index (BMI), which evaluates weight in terms of height. But this tool is not perfect. It does not distinguish between how much of a person’s weight comes from fat as opposed to muscle. Other approaches, such as using calipers to measure body fat in particular parts of the body, try to overcome this problem by focusing on where fat is located in the body. (Healthy People Library Project, 2006, The Science Inside: Obesity, American Association for the Advancement of Science, p. 6, Washington, DC.) Whichever measurement is used, the bottom line is that people should not have an excessive amount of fat on their bodies. For women, body fat should not exceed 25% of their total body. For men, the amount of fat should be about 17%. (Healthy People Library Project, 2006, The Science Inside: Obesity, American Association for the Advancement of Science, p. 5, Washington, DC.)
The way to prevent being overweight and obese is to strike a balance between how much food we eat, what kinds of food we eat, and how active we are. The energy in food is measured by a unit called a calorie. Although one calorie of fruit is the same as one calorie of chips, the chips have considerably more calories than the fruit. Your body’s numerous activities, including moving, growing, breathing, digesting food, and maintaining the body’s temperature, use up energy as measured by calories. The rate at which the body accomplishes this is called metabolism. The goal of healthy living is to eat as many calories as the body needs to accomplish its metabolic functions. The way to do this is by eating the right foods in the right amounts and maintaining a high level of physical activity through exercise. This lesson is designed to help students understand these ideas by learning more about their own bodies and what they need to stay healthy.
To learn about how nutrition instruction can fit into the K-12 science curriculum and what roles communities, schools, culture, and people play in addressing the problem of childhood obesity, view the Understanding Obesity and Childhood Nutrition video, produced by the American Association for the Advancement of Science. This video highlights one community’s actions to decrease childhood obesity. Visit the AAAS Obesity and Childhood Nutrition Town Hall page for more information from leading health and nutritional specialists.
In the Motivation part of the lesson, students discuss what obesity is and read about some of its consequences (pages 25-31 of The Science Inside: Obesity). Then they use the formula for finding BMI (on p. 5 of The Science Inside: Obesity). Make sure that students understand that although BMI is a rough measurement, it is a starting point for finding out if they are at an unhealthy weight. Then students are given a student sheet, which provides space for them to write out a daily diet and exercise plan. At this stage, students should begin thinking about these issues and what they can do to make positive changes in their lifestyle.
Before developing a daily diet and exercise plan, students should visit the Activity Calorie Burn Rate site from Discovery Health to calculate how many calories they are burning based on their current activity level. Then they can visit many other websites to learn more about diet, exercise, and how their bodies work. Students also can refer to the pages provided from The Science Inside: Obesity or find these resources online. This material provides background information on obesity, nutrition, and the health problems associated with obesity. As students become more familiar with the topic, they can fill in the student sheet. By the end of the lesson, students will have a new plan for healthy living based on their own research.
Ideas in this lesson are also related to concepts found in the following standards from the Mid-continent Research for Education and Learning:
- Health Standard 6. Understands essential concepts about nutrition and diet (6-8) #2
Begin the lesson by asking students what they think the term “obesity” means. Write down their ideas on a sheet of newsprint. As a class, arrive at a class definition of obesity, which is as follows:
- The condition of being too heavy for one’s height.
Next, refer students to the selections from The Science Inside: Obesity. Ask students to read pages 3-7, which explain what obesity is and how to measure it, and pages 25-31, which discuss the consequences of obesity. Encourage students to ask questions if they are having trouble understanding the main ideas. Then give students time in class to calculate their body mass index (BMI). The formula for doing so is given at the top of page 5.
Alternatively, students can use the Making Good Decisions about Diet and Exercise student esheet to go to When Being Overweight is a Health Problem. This site has an online BMI calculator that can give students their BMI by simply supplying the information requested. In general, a BMI over 30 means that an individual falls into the category of obesity. (A person with a BMI 25 or under is considered to be at his/her optimal weight.) Make sure students understand that the BMI is only a rough estimate and does not take into account the difference between how much of a person’s weight is from fat and how much is from muscle. Nonetheless, it does provide a baseline from which to begin thinking about weight, diet, and exercise.
Conclude this part of the lesson by handing out the Nutrition and Exercise and Plan for Healthy Living student sheets, which present information and a template for developing a plan for healthy living. Encourage students to begin thinking about their plan in preparation for the Development phase of the lesson.
Ask students to have their student sheet available. Then tell them that before they can complete the sheet, they need to learn more about their bodies, diet, and exercise.
Have students use the student esheet to add to their knowledge. The directions are on the esheet. At the end of Part I of the sheet are the following questions, which students can answer on the Nutrition and Exercise student sheet. Once students have had a chance to do Part 1, bring them back together as a class to discuss the questions:
- What is a calorie? Why are calories important? (A calorie is the basic unit of energy in food. Your body needs calories to grow, think, move, breathe, and carry out its necessary functions.)
- When does the body work most efficiently? (The body works most efficiently when there is a balance between how many calories we put into our bodies and how many we use up. Weight becomes an issue when more calories are going in than the body needs to function.)
- What fats should be in our diet? What fats should not be? (Monosaturated and polysaturated fats are found in olives, olive oil, most nuts, avocados, fish, and most liquid vegetable oils. Saturated fats and trans fatty acids are not good for us. Saturated fats are found in whole milk and other dairy products, red meat, chocolate, and coconuts. Trans fatty acids are made by people and are the worst kinds of foods. They include partially hydrogenated vegetable oil, vegetable shortening, and most margarines. Foods such as French fries and burgers often are fried in these substances.)
- What is the cholesterol found in our bodies? (Cholesterol is a soft, waxy substance found throughout the body. There are two types of cholesterol—good and bad. Bad cholesterol, or LDL, comes from the liver to the rest of the body. If there is too much, it can stick inside arteries, preventing blood from flowing freely. The result can be heart attacks or strokes. Good cholesterol, or HDL, flows back in the blood from the rest of the body to the liver, where it helps blood vessels and the liver clean up and eliminate excess cholesterol.)
- What is metabolism? (Metabolism refers to the chemical processes involved in maintaining the body; it includes such functions as digestion, waste elimination, breathing, circulation, and temperature regulation. The faster the metabolism, the more efficient the body is in processing calories. Unfortunately, metabolism tends to slow down as people get older. The way to keep its rate up is through muscle building and exercise.)
Next, students will calculate how many calories they burn each day by using the Activity Calorie Burn Rate. Directions are provided on the student esheet.
Students are now ready to work on Part III of the esheet. The websites listed provide information about appropriate servings of fruits and vegetables (Eat a Variety of Fruits and Vegetables Every Day), how to select healthful meals (BAM! Food and Nutrition), and how to get started on an exercise program (BAM! Physical Activity). Directions on how to navigate each site are provided on the esheet.
Now have students consider these questions, which they can answer on their student sheet:
- Based on your age and sex, how many servings of fruits and vegetables do you need each day? What counts as a fruit or vegetable?
- Did you learn about some new fruits and vegetables to try? If so, what are they?
- Did you find any recipes to try?
- After playing the BAM! Dining Decisions game, what are your thoughts about planning meals? Have your ideas changed as a result of playing the game?
- Did you learn anything new after answering the questions in “I Heard a Hurdle Race?” If so, how will you change your exercise habits?
- Did you learn anything else after exploring these two sites? Write down any thoughts you have.
Answers will vary. Encourage students to explain their responses.
After working online, students will be ready to work on the Plan for Healthy Living student sheet. Remind students to use what they have learned to make realistic changes in their diet and exercise habits. Encourage students to consider these issues in making their plans:
- Fats in their diet: Do they eat too much fat? Do they eat the right kind of fat? What changes would benefit their health? Unsaturated fats such as olives, olive oil, and avocados help maintain a good balance of cholesterol in the bloodstream.
- Refined sugars: Do they eat too many candy bars, drink too much soda, or use too much table sugar? What changes should be made?
- Complex carbohydrates: Are foods like beans, whole grain bread and cereal, and starchy vegetables in their diet? Remind students that these foods provide necessary vitamins, minerals, and fiber. Because these foods take longer for the liver to break down, they keep people feeling full longer.
Have students redo the Activity Calorie Burn Rate. Ask students if they have noticed any changes in their activity level. If so, how has it changed?
As students complete each sheet, go over them, looking for how well students are grasping new ideas. You could also encourage a class discussion to find out what they have learned. Ask questions such as:
- What factors should you consider when planning a meal? (Picking healthful foods, including fruits and vegetables, and making sure the portion sizes are reasonable are some factors you should consider.)
- If a person ate a hamburger, how long would it take to work it off? (It would take approximately 30 minutes of exercise at the gym.)
- If you have been filling your plate with food, have you been eating too much, too little, or the right amount? (Too much. In fact, most people probably eat close to twice as much food as they need.)
- Describe a meal you would have for dinner. Why do you think it is healthful? (Answers will vary.)
- Describe an exercise plan that you think is appropriate. (Answers will vary.)
If appropriate, encourage students to implement their diet and exercise plans. You could check in with students periodically to discuss any changes they notice in how they feel. To help students “stay with the program,” have them involve their parents or caregivers. To inform parents/caregivers about the project, consider using the Plan for Healthy Living letter.
The Science NetLinks lesson, MyPlate Food Guide, provides a good introduction to the food pyramid and the importance of eating healthy foods and exercising regularly.
The Food and Fitness section on the KidsHealth website, has useful information about diet, nutrition, exercise, and new research on these topics.