Ideas to Stimulate the Non-Major
Biology Student

Understanding Human Energy Requirements
A Laboratory Exercise

Roberta B. Williams

Department of Biological Sciences
University of Nevada, Las Vegas
4505 Maryland Parkway
Las Vegas, NV 89154

Roberta Williams is an instructor and the undergraduate laboratory Coordinator for the Department of Biological Sciences at the University of Nevada, Las 'Vegas. She recieved a B.S. from chestnut Hill College in Philadelphia (chemistry) and a M.S. from the University of Nevada, Las Vegas (botany). Williams teaches Human Biology, a science course for non-majors, and is involved with teaching post-baccalaureate science classes to primary and secondary teachers. Her research interests are involved with developing new laboratory experiences for all grade levels. Roberta hosted the 1985 ABLE meeting and is currently Labstracts editor.

© 1988 University of Nevada
[ABLE's Copyright Policy]

Reprinted from: Williams, R. B.  1988.  Ideas to stimulate the non-majors biology student. Understanding human energy requirements - A laboratory exercise. Pages 207-231, in Tested studies for laboratory teaching, Volume 9.  Note: This workshop consisted of three separate subtitles and presentations.  (R. W. Peifer, Editor). Proceedings of the 9th Workshop/Conference of the Association for Biology Laboratory Education (ABLE), 396 pages. Although the laboratory exercises in ABLE proceedings volumes have been tested and due consideration has been given to safety, individuals performing these exercises must assume all responsibilities for risk. The Association for Biology Laboratory Education (ABLE) disclaims any liability with regards to safety in connection with the use of the exercises in its proceedings volumes.

Contents

• Objectives
• Introduction
• Total Energy Needs
• Procedures: Activity Diary, Measuring Basal Metabolic Rate, Measuring Physical Activity, Estimating Specific Dynamic Action, Measuring Energy Intake, Making Measurements (Skinfold Test), Calculating Percent Body Fat
• Summary
• References

Objectives

1. Understanding energy metabolism, the process by which the body stores or releases energy from nutrients consumed.
2. Determine your own energy input balances with your energy output. Weight gain or loss depends on the difference between these two factors. A difference of 3500 calories can mean a pound more or less of body weight.
3. Determine your own percent body fat and understanding the relationship between body fat and body weight.

Introduction

The American public is becoming increasingly more conscious of their individual responsibility for wellness and the role of nutrition and exercise in maintaining good health. The news media bombards us daily with tidbits on the latest research concerning nutrition and exercise and their correlation with cancer and heart disease. We are aware that obesity is American's number one malnutrition problem and that solving this problem is one of the least understood areas in the science of nutrition. We hear that anorexia nervosa and bulimia are increasing at an alarming rate as some of our brightest young females become more and more obsessed with weight. But how many of us know what our own ''ideal weight'' should be?

Teaching a course in Human Biology to college non-science majors has made me realize how little students really know about their own energy metabolism. They seem to be aware of nutritional requirements, but what happens after they eat is a mystery. To solve this mystery, I designed a laboratory exercise that deals with daily caloric intake, energy metabolism and body composition. This exercise enables the individual student to evaluate his cal- intake and caloric expenditure for an average day and examine why he or she may be gaining or losing weight. The exercise then enables the student to determine his or her percent body fat and calculate what their "ideal weight" should be. Each semester the majority of my 200 students rate this particular laboratory experience as their favorite and the one from which they learn the most.

Body fat plays important roles in maintaining health. It serves as an insulator from heat, cold and mechanical shock and as an energy supply to be used when glycogen reserves are exhausted. Without a protective layer of fat, the body is fragile and unable to withstand environmental stresses. Some body fat is essential, but excess body fat serves no useful function in a society where food is abundant and easily obtained and the hazards of being obese are numerous.

Fat normally makes up about 18% of an adult males's body and about 22% of an adult female's body. The rest of the body composition is muscle, bone, other connective tissues and water. The relative amounts of muscle and bone vary widely from person to person. An athlete or person doing heavy physical work, whose skeleton has become dense through constant stress on the bones, may have a slender figure with no excess fat tissue and still be heavier than another person of the same height, sex, age and body shape. An ideal weight for a person cannot be stated on the basis of height alone. The "ideal weight" tables published by insurance companies are merely averages for the U. S. population and have little scientific validity. At best, they can serve as arbitrary measures for too little or too much body weight. A person more than 10% over the weight on the tables is overweight; a person 20% over is obese. Similarly, a person 10% below the weight on the tables is underweight.

It is suggested that from a health and aesthetic standpoint, adult males should have 16% or less body fat, and adult females should have 23% or less body fat. At no time should the percent body fat of an adult male drop below 5% or that of an adult female below 10%. Severe medical problems can occur with too little body fat as well as with too much body fat. Marginal obesity occurs when the body fat of an adult male increases to over 20% or that of an adult female increases to over 30%. The percent body fat of an individual can change with exercise or diet. You can remain at the same weight while changing your percent body fat. Well conditioned athletes, such as marathon runners and swimmers, usually have about 10-12% body fat, while football players and weight lifters may have as high as 19-20% body fat. Life style can play an important role in an individual's physical makeup (Golding, 1982).

Total Energy Needs

• Energy to support basal metabolism: basal metabolism, basal metabolic rate (BMR), factors that influence BMR
• Energy for muscular activity
• Energy to digest and metabolize food

Energy to Support Basal Metabolism

Basal Metabolism

Basal metabolism is the minimum amount of energy the body needs at rest in the fasting state. Certain processes necessary for the maintenance of life proceed without conscious awareness. The beating of the heart, the inhaling of oxygen and the exhaling of carbon dioxide, the metabolic activities of each cell, the maintenance of body temperature, and the sending of nerve impulses from the brain to direct these automatic activities are some of the basal metabolic processes that maintain life. Their minimum energy needs must be met before any calories can be used for physical activity or for the digestion of food.

Basal Metabolic Rate (BMR)

The basal metabolic rate (BMR) is the rate at which calories are spent for these maintenance activities. The BMR varies from person to person and may change for one individual with a change in circumstance, physical condition or age. The BMR is lowest when a person is lying down in a room with a comfortable temperature and is not digesting any food. At this time, the least amount of oxygen is needed and the least amount of heat is being generated by the activities of the cells. During sleep, the person is more relaxed, but there is more muscular activity, so BMR tends to be slightly higher.

Factors that Influence BMR

The BMR is influenced by a number of factors. In general, the younger the person is, the higher the BMR. This is due to the increased activity of cells undergoing division. After growth stops, the BMR decreases about two percent per decade throughout life (Food and Nutrition Board, 1974). Body surface area, but not weight, influences BMR. Two people with different shapes who weigh the same will have different BMR. A short, stout person will generally have a slower BMR than a tall, thin person even if they weigh the same. The tall thin person has a greater skin surface from which heat is lost by radiation and so must have a faster metabolism to generate the lost heat. Another factor that influences BMR is gender. Males generally have a faster metabolism rate than females due to the greater percentage of muscle tissue in the male body. Muscle tissue is always active while fat tissue is comparatively inactive. Conditions such as fever, malnutrition and hormonal secretions can temporarily alter BMR. However, the latest research shows that physical training and conditioning does not seem to influence BMR after exercise has ceased (personal communication, Golding).

Energy for Muscular Activity

The second component of energy metabolism is physical activity voluntarily undertaken and achieved by the use of skeletal muscles. This amounts to an average of about 30% of the total caloric expenditure, while BMR accounts for 60%. Unlike basal metabolism which cannot be changed at will, physical activity can be increased or decreased by an individual. Contraction of muscles uses a large number of calories, and in a moving body the heart must beat faster, this also accounts for additional caloric usage. A heavier person uses More calories performing the same task in the same time as a lighter person, because it takes extra effort to move the additional body weight. The longer an activity lasts, the more calories are used; therefore, measurement of physical activity is expressed as calories per weight per unit time.

Energy to Digest and Metabolize Food

The final component of energy expenditure has to do with processing food. When food is taken into the body, many cells become active. Muscles move the food through the intestinal tract by speeding up their rhythmic contractions, while the cells that Manufacture and secrete digestive juice begin to do their jobs. All these cells need extra energy to participate in digestion, absorption and metabolism of food. In addition, the presence of food stimulates general metabolism. All of this is referred to as Specific Dynamic Action of food (SDA) and represents about 10% of the total calories expended by a person per day.

Procedures

Activity Diary

The week before the lab is scheduled, students are told to keep a written diary of their physical activities for three consecutive days. Every minute of the day should be accounted for (1440 minutes in all). Figure 1 is an example of tie activity diary forms I provide my students. In addition to their activity diary, the student are told to keep a written food diary for the same three days. The food diary should list all the food and beverages consumed throughout the three day period. Students are reminded not to forget to include snacks and alcoholic beverages. I use three days activities and food consumption and take an average to represent a typical day. I have found it you ask a student to keep the diaries for only one day, they will pick a very atypical day. Both of these diaries are brought to lab and used to calculate the individual's energy expenditure and caloric intake.

Figure 1. An abbreviated sample of student's activity diary

Measuring basal metabolic rate

There are numerous ways to measure BMR some of which entail twelve hours of fasting and elaborate instrumentation. From these methods, Boothy (1936) has developed calculations and charts to give a mathematical estimate for BMR. I have adapted these for use in this laboratory exercise.

Scales and height-measuring devices are set up in the laboratory,and each student determines his or her own height and weight. The calculations required assume the individual is fully clothed and wearing shoes with a one-inch heel. Figure 2 is used to determine body surface area. A straight line drawn from height to weight on Figure 2 intersects the middle column to indicate the corresponding surface area in square meters. Table 1 is used next to determine a BMR constant for the subject's sex and age. The surface area determined in Figure 2 is multiplied by this factor to determine calories per hour. This number in turn is multiplied by 24 hours to obtain the student's BMR in calories per day.

For example, take a 17 year old male who weighs 170 lbs. (77.3 kg) and is 6 feet tall. His body surface area from Figure 2 would be 1.99217 square meters. From Table 2, he would have a basal metabolism rate constant of 41.5 calories per square meter per hour. This, multiplied by 1.99 square meters, equals 82.6 calories per hour and, by 24 hours, equals a BMR of 1982 calories per day. Numbers are rounded off because this method is not accurate enough to make decimals meaningful.

Figure 2. Nomogram to estimate body surface area from height and weight. A straight line is drawn from the subject's heights (Scale 1) to the subject's weight (Scale 3). The point at which the line intersects Scale 2 will give the subject's body surface area in meters squared. Adapted from Boothby, W. M., J. Berkson and H. L. Dunn, Studies of the Energy of Normal Individuals: A Standard for Basal Metabolism with a Nomogram for Clinical Application, American Journal of Physiology, 116, (1936); 468-484 with permission of the publisher.

Measuring physical activity

The term physical activity is used in this exercise to mean that energy expended during non-sleeping periods by skeletal muscles. The amount of energy expended will depend on the size of the body, the type of activity and the length of the activity. Table 2 lists the total energy expended (cal/kg) for various activities. Each activity in the diary prepared by the student the previous week should be grouped into one of the categories listed. Multiply the minutes spent in that activity by the appropriate factor and by the body weight in kilograms. Obtain a grand total for the three days and divide that by three to get an average caloric expenditure per day.

If the 17 year old's activities for the three days included:
1440 minutes of sleeping (no activity)
1440 minutes of sitting (very light)
360 minutes of walking (light)
360 minutes of standing (very light)
90 minutes of weight lifting (heavy)
450 minutes of driving (very light)
180 minutes of jogging (moderate)

he would have expended an average of 1044 calories/day calculated in the following manner:
1440 min. no activity X 0.0 cal/kg X 77.3 kg = 0 cals
2250 min. very light X 0.01 cal/kg X 77.3 kg =1739 cals
360 min. light X 0.02 cal/kg X 77.3 kg = 557 cals
180 min. moderate X 0.025 cal/kg X 77.3 kg = 348 cals
90 min. heavy X 0.07 cal/kg X 77.3 kg =487 cals
Total expenditure for three days = 3131 cals
Average daily expenditure = 1044 cals/day

Table 2. Examples of daily energy expenditures.

Estimating specific dynamic action

To estimate the students SDA, add the calories calculated for BMR and those calculated for average daily physical activity and multiply by 10%. For the 17 year old example, this would be: 11982 cal (BMR) + 1044 cal/day (activity X 0.1 = 303 cal/day (SDA).

Total Energy Requirement For Average 24 Hour Period. Add all three figures, BMR, physical activities and SDA to obtain the number of calories needed in one day. The average 70 kilogram adult male requires about 2700 cal/day, while the average 55 kilogram adult female needs only 2000 cal/day. Our 17 year old example is younger and somewhat more active than the average person, and therefore, has a higher energy requirement (3329 cal/day).

Measuring energy intake

Using the data compiled during the week on the subject's food intake, have each student calculate the number of calories consumed from commercial calorie guides. I have found nutrition text books contain excellent appendices that include very complete calorie guides. For my class I have made numerous copies of the calorie guide from Hamilton and Whitney (1985). Measuring the amount of calories consumed is more accurate than measuring the number of calories expended. If the figures are within 10% of each other, the subject is most likely maintaining his or her weight. In order to maintain proper energy balance within the body, the calories expended must be replaced by an equal number of calories from food. If this does not occur, the subject will lose weight. If the number of calories consumed exceeds the number of calories expended, the subject will gain weight. An overage of 500 calories per day for one week can result in gaining a pound (3500 calories equal one pound of body fat). By the same token, expending 500 more calories than are consumed each day for a week can result in the loss of one pound. Estimation of Percent Body Fat.

When individuals gain fat, much of the adipose tissue is added to subcutaneous accumulations that are found in various parts of the body. This subcutaneous fat can be pinched up by the thumb and forefinger. As an individual gets fatter, these skinfolds get larger. Calipers have been designed to measure skinfolds in several parts of the body. Any single measurement does not give an accurate picture. At least three measurements, tricep, illium and abdomen must be taken on women and four measurements, chest, abdomen, illium and axilla are necessary for men. All these measurements can be done in the laboratory, provided the females are wearing two piece outfits. The more measurements that are done, the more accurate the results will be, however, these minimal measurements give a fairly reliable estimate.

Making measurements (skinfold test)

A direct measure of the amount of body fat can be obtained by means of the skinfold test. In this lab one student measures three or four skinfolds on another student using inexpensive calipers(Fat-O-Meters). The fat attached to the skin is roughly proportional to total body fat, and the measurements can be easily converted to percent body fat.

All measurements are taken on the right side of the person being measured. The fold of skin should be firmly grasped between the left thumb and the other four fingers and then lifted. Pinch and lift the fold several times to make certain that no musculature is grasped. Hold the skinfold firmly and place the contact side of the calipers below the thumb and fingers. Do not let go of the fold. Take the reading to the nearest half millimeter. Release the grip on the caliper and release the fold. To make sure that the reading is accurate, repeat the measurement two or three times. Unless each measurement is consistent (within 1-2 mm) reliability will be poor.

The tricep skinfold is measured on the back of the upper right arm, half-way between the elbow and the tip of the shoulder, while the arm is hanging loosely at the subject's side. Grasp the skinfold parallel to the long axis of the arm, and lift it away from the arm to make sure no muscle tissue is caught in the fold. The illium skinfold (hip) is measured with a diagonal fold, just above the crest of the hip bone, on an imaginary line that would divide the body into front and back halves.

The abdominal skinfold is measured vertically one inch to the right of the navel.

The chest measurement is taken diagonally, mid-way between the nipple and the armpit.

The axillary (side) measurement is taken vertically at the level of the nipple on an imaginary line that would divide the body into front and back halves.

When students do skinfold measurements on one another, lack of experience can produce errors. The most common errors occur when the mid-point is incorrectly marked or measured, when the caliper is too deep (muscle involved) or too shallow (only skin grasped), and when the arm being measured is not hanging loosely at the subject's side.

Calculating percent body fat

The percent body fat can be determined from these measurements using charts that accompany the calipers or by the use of two equations. The equations were developed by Jackson and Pollock (1978) and are widely used in physical fitness evaluation programs. For males the four measurements are sunned and percent fat is calculated (Golding, 1982) as follows:
% fat = 0.27784 (X₁) - 0.00053 (X₁)² + 0.12437 (X₂) - 3.28791
where X₁ = sum of four folds
X₂ = age of subject.

A "target" or"ideal" weight can be calculated using the percent fat figures. Target weight is defined as the lean body weight (LBW) plus a desirable percentage of fat. If a 20 year old male student is 210 pounds and has 23% fat, he may wish to know what he should weigh with 16% fat. To calculate this he would multiply 23% times 210 to determine that he is carrying 48.3 pounds of fat. Subtracting his fat weight from his total weight will give his LBW of 161.7 pounds. At 16% fat, this LBW equals 84% of the student's total weight. To determine what his weight should be with 16% fat, divide the LBW by 84% (161.7/.84 a 192.5). A target weight of 192.5 pounds is thereby obtained.

Summary

What makes this laboratory experience successful? I think it is the fact that although we are all aware of calories, none of us really sit down and evaluate what those calories really mean. Prepared foods give the caloric value on box tops and popular magazines frequently publish calorie expenditure guides. What this means on a day-by-day basis is rarely given more than a passing thought. In this exercise, the students get a chance to see what their actual energy balance is. Even if they only make this calculation once in their life time, it is something they will remember.

We are what we eat, and many researchers are now finding that patterns for both obesity and underweight may be set very early in our life time. Overweight or obesity is seen in more than 10% of school-age children in the United States, in about 15% of people under 30, and in 25 to 30% of adults. Among older people, a third of the men and half of the women are obese. Certain subgroups of the population have a markedly higher incidence of obesity than others: the lower socioeconomic classes, blacks, Mexican Americans, Native Americans and Eskimos (Hamilton, 1985). Statistics show that some people become fat in childhood and others later on. Research has shown that early onset obesity is especially resistant to treatment. According to the fat-cell theory, early overfeeding is is thought to stimulate fat cells to increase abnormally in number. The number of fat cells then become fixed in adulthood. Thereafter, a gain in weight can take place only through an increase in tie size of fat cells. The larger the number of fat cells in his body, the more hungry the person will be. Thus, people with abnormally large numbers of fat cells will tend to be abnormally hungry and to overeat.

The causes of underweight are as diverse as those of overeating. Psychological factors may contribute in some cases and metabolic ones in others. Clearly, heredity is involved. Early underfeeding may limit the fat-cell number, just as overfeeding my increase it. Habits learned early in childhood, especially food aversions, may perpetuate the problem. The demand for calories to support high levels of physical activity and growth often contributes; an extremely active boy during his adolescent growth spurt may need more than 4000 calories a day to maintain his weight. Such a boy may be too busy to take the time to eat that much. The concepts studied with this laboratory exercise help to make students aware of their body composition. I think this exercise is not only valuable for college students; rather, secondary science and health students can also gain much knowledge that can influence their future lives. A local elementary health and physical education teacher uses parts of this exercise with his students and claims he has had great success.

Literature Cited

Boothby, W. M., J. Berkson, and H.L. Dunn. 1936. Studies of the energy of normal individuals: A standard for basal metabolism, with a nomogram for clinical application, American Journal of Physiology, 116:468-484.

Boothby, W. M. 1956. In handbook of biological data (W. S. Spector, editor). Saunder's Publishing Co., Philadelphia, 259 pages.

Food and nutrition board, committee on recommended allowances. 1974. Recommended dietary allowances (8th ed). National Academy of Science, Washington, D. C.

Golding, Lawrence, C.R. Myers, and W.E. Sinning. 1982. The Y's way to physical fitness. National Board of YMCA, Chicago, IL.

Hamilton, E. M. N and E.N. Whitney. 1979. Nutrition: Concepts and controversies. West Publishing Co., St. Paul, MN.

Hamilton, E. M., N, E. N. Whitney, and F. S. Sizer. 1985. Nutrition: Concepts and controversies, (third edition). West Publishing Co., St. Paul, MN.

Jackson, A. S. and M.L. Pollock. 1978. Generalized equations for predicting body density of man. British Journal of Nutrition, 40:497.

All contents copyright © 1999. Association for Biology Laboratory Education. All rights reserved.