Food labels and other guides often use “serving size” to describe a recommended single portion of a food. Serving sizes are different for various kinds of food (liquid vs. solid, or cooked vs. raw). In general, adolescents tend to overestimate portion sizes. The “Nutrition Facts” labels on most foods provide important information about serving sizes and the number of servings contained within a single package. For example, even though most soft drink consumers drink an entire 12- or 16-ounce container at one time, most soft drink labels identify the contents as two or more servings.

Students need easy guidelines to help them estimate appropriate serving sizes of different kinds of foods. Some rules of thumb include the following.

Palm of hand or deck of cards = one serving of meat, fish or poultry.
Size of closed fist or a tennis ball = one serving (one cup) of rice, pasta, fruit or raw vegetables.
Cupped hand = one serving (one cup) of dry cereal.
Two fingers or a domino = one serving (one ounce) of cheese.
Tip of thumb = one serving (teaspoon) of butter or margarine.

Consumption of large food portions, combined with sedentary lifestyles, is linked to overweight and obesity in adolescents and adults.

Serving sizes on food labels are designed to make it easier to compare the calorie and nutritional content of similar products and to identify nutrients present in a food. At a minimum, food labels contain information about serving sizes; calories; calories from fat (dietitians generally recommend that no more than 30% of calories come from fat over the course of the day); percent daily values of major nutrients; total fat; saturated and trans fat (these unhealthy fats are listed under total fat—saturated fat and trans fat raise cholesterol and increase a person's risk for developing heart disease); unsaturated fats (liquid at room temperature, these are the healthy fats); cholesterol; sodium; total carbohydrates (which includes dietary fibers, sugars, and other carbohydrates); protein; vitamins A and C; calcium and iron.

Carbohydrates are the most abundant source of calories in most people’s diets. Carbohydrates are either simple (called sugars) or complex (called starches). Cereals, rice, potatoes, breads, pastas, fruits, and vegetables all contain high amounts of carbohydrates. Not all sugar in food is added. Lactose, or milk sugar, is a natural ingredient in milk. Fruit also has high amounts of naturally occurring sugar.

When reading a food label, it is important to pay attention to the number of servings contained within a package and the amount of saturated fat. Saturated fat contributes to heart disease—the number one killer of adults in the US. Most saturated fats are solid at room temperature. The words, "hydrogenated," "partially hydrogenated," or "shortening,” also are used to describe saturated fats.  With true “low-fat” foods, fewer than 30%  of the total calories come from fat.

The amount of energy stored in food usually is measured in calories. One calorie is defined as the amount of energy needed to raise the temperature of one gram of pure water (equivalent to one milliliter of water) one degree Celsius. The calories shown on most food labels actually are kilocalories (=1,000 calories). The word “Calorie,” when written with an upper case “C,” also denotes kilocalories.

When a carbon-containing molecule is burned (combustion), it consumes oxygen, produces carbon dioxide and water, and liberates energy (which can be felt as heat).

Since this activity involves an open flame, teachers may prefer to conduct it as a demonstration for the class. If students are performing the investigation in groups, the following safety guidelines from the Council of State Science Supervisors should be followed.

1. Demonstrate the procedure before allowing students to replicate the activity. Look for possible hazards in the classroom. Alert students to potential dangers.

2. Constant surveillance and supervision of student activities are essential.

3. Smoke, carbon monoxide, and heat detectors are recommended in every laboratory. Units should be placed in the laboratory and related areas (storerooms, preparation rooms, closets, and offices).

4. A positive student attitude toward safety is imperative. Students should not fear doing experiments, using reagents, or equipment, but should respect them for potential hazards. Students should read lab materials in advance, noting all cautions (written and oral).

5. Teachers must set good safety examples when conducting demonstrations and experiments. They should model good lab safety techniques, such as wearing aprons and goggles.

6. Rough play or mischief should not be permitted in science classrooms or labs.

7. Closed-toe shoes are required for labs involving liquids, or heated or heavy items that may injure the feet.

8. Confine long hair and loose clothing. Laboratory aprons should be worn.

9. Proper eye protection devices must be worn by all persons engaged in supervising or observing science activities involving potential hazards to the eye.

10. Give consideration to the National Science Teachers Association's recommendation to limit science classes to 24 students or less for safety.

The complete Food and Fitness Activities Guide for Teachers may be downloaded as a PDF file from the Teacher Resources menu on BioEd Online: http://www.bioedonline.org/resources/nsbri.cfm

One calorie is defined as the amount of energy needed to raise the temperature of one gram of pure water (equivalent to one milliliter of water) by one degree Celsius. Students can approximate the calories in each of the foods tested by multiplying the temperature change in each case by 50. This measure, of course, is just an estimate. Calorie content actually is measured in a calorimeter in which all conditions are carefully controlled.

Carbohydrates, fats and proteins are the main energy sources in foods. Sugars, starches (such as those in breads, pasta and potatoes) and fiber (as in bran and many vegetables) are the primary forms of carbohydrates. Foods rich in fats include animal and vegetable oils, lard, butter and cream. Proteins, the building blocks of muscles and molecules within cells, are present in meats, as well as in plant materials, such as nuts and beans. In this activity, the oat cereal consists almost entirely of carbohydrates (sugar and oat flour). The pecan contains both proteins and oil. The oil content contributes to the higher calorie content of the nut on a per-gram basis. At the same time, nuts are a denser food than the baked cereal, which also contributes to their higher calorie content.

The calories reported on most food labels represent one kilocalorie, or 1,000 calories, and often are written with an uppercase “C.”

Carbohydrates and proteins supply four Calories (kilocalories) per gram. Fats and oils provide about nine Calories per gram.

The complete Food and Fitness Activities Guide for Teachers may be downloaded as a PDF file from the Teacher Resources menu on BioEd Online: http://www.bioedonline.org/resources/nsbri.cfm

Activity Four: Serving Sizes, of the instructional unit, Food and Fitness, helps students learn how to estimate portions and use serving size information provided on Nutrition Facts labels.

Science concepts covered in this activity include the following.

• Objects have observable properties that can be measured.

• Serving sizes on food labels can help guide food choices.

The complete Food and Fitness Activities Guide for Teachers may be downloaded as a PDF file from the Teacher Resources menu on BioEd Online: http://www.bioedonline.org/resources/nsbri.cfm

Viewing  this presentation fulfills part of the requirements for completing the Virtual Workshop on Energy, Food and Nutrition (“Food and Fitness”), offered for professional development contact hours on BioEd Online.

Funding for development of the Food and Fitness unit and accompanying online professional development was provided by the National Space Biomedical Research Institute (NSBRI), a consortium of leading biomedical research centers funded by the National Aeronautics and Space Administration (NASA). Visit the following sites for more information about these organizations.

Center for Educational Outreach, Baylor College of Medicine: http://www.ccit.bcm.tmc.edu/ceo/
National Space Biomedical Research Institute: www.nsbri.org
National Aeronautics and Space Administration: http://www.nasa.gov

Food labels and other guides often use “serving size” to describe a recommended single portion of a food. Serving sizes are different for various kinds of foods (meats, fruits and vegetables, etc.), liquid and solid foods, and cooked versus raw foods. In many case, the amount specified as a serving size for a particular food is smaller than the amount typically eaten.

To help students learn to estimate appropriate serving sizes, challenge groups of students to predict appropriate servings sizes of a vegetable, snack food, cereal and liquid, and to record their predictions. Next, have students actually measure out the quantities that they predicted. You may need to explain that food portions in the US typically are measured in “cups.” Show students examples of measuring cups for liquid and solid foods.

As an extension to this activity, have students investigate the metric equivalents of cups for liquids (liters) and solids (grams).

The complete Food and Fitness Activities Guide for Teachers may be downloaded as a PDF file from the Teacher Resources menu on BioEd Online: http://www.bioedonline.org/resources/nsbri.cfm