Subject: Physics    / General Physics
5: Daily Energy Balance
Invitation to Inquiry
Many kinds of foods are marketed to those who participate in various kinds of sports. The implication is that these foods have additional nutrients or higher quantities of nutrients need by the athlete. Go to a store and read the ingredient label on one of these products. Compare it to an equivalent product that is not marketed in such a manner. For example, you could compare a sports drink to a soft drink or orange juice. You could compare a “nutrient bar” to an equivalent candy bar or snack food. Look specifically at quantities of calories, fats, proteins, sodium, and potassium. How are they different? What other foods could you eat that would provide the same calories and nutrients?

The theoretical biological sciences of biochemistry, anatomy, cell biology, and physiology are brought together in the practical biological field of nutrition. The science of nutrition is the study of the processes involved in taking in, assimilating, and utilizing nutrients. The amount of food and drink consumed by a person from day to day is a person’s diet. There has been an increased interest in diet and personal nutrition as more information concerning these subjects becomes available through the popular press, scientific publications, health clubs, and schools. Not only are people “counting calories” and concerned with the grams of fat they consume, but they are becoming scientifically literate enough to ask significant questions to their physicians, teachers, food manufacturers, and government officials. With a minimal amount of nutrition information, it is possible to get a better handle on your own nutritional status.
In this exercise, you determine your daily basal metabolic rate, voluntary muscular activity, and specific dynamic action per day. These are used to estimate your total energy requirements per day in kilocalories (kcal). You then calculate your total daily kcal intake. By comparing these two figures, you can determine whether or not your present diet should result in your maintaining, losing, or gaining weight.
You will determine your:
1.    basal metabolic rate;
2.    voluntary muscular activity level;
3.    specific dynamic action;
4.    kilocalorie intake per day by adding your BMR, activity level, and SDA;
5.    total energy requirements and compare to your energy kcal intake per day; and
6.    energy balance.


Determining Your Basal Metabolic Rate
Your BMR (basal metabolic rate) is the rate at which kcals are used for maintenance activities and can be measured on a daily basis. This is also the total amount of energy per kilogram per hour expended after a 12-hour fast. Energy is measured in kilocalories, the amount of energy needed to raise the temperature of 1 kg of water 1?C. BMR can be estimated by using a short formula that is based on 1.0 kcal per kilogram of body weight per hour for men, or 0.9 kcal per kilogram of body weight for women. Even though this is a crude method, it does give some idea of the BMR.

Body weight ? BMR factor = Estimated BMR (kcal/kg/hour)
For example: If a male weighs 150 lbs, his mass in kilograms will be 68 kg. Therefore, the estimated BMR is
68 kg ? 1.0 kcal/kg/hr = 68 kcal/kg/hr
24 hours/day ? Estimated BMR/hour = Estimated energy expenditure/day
68 kcal/kg/hr ? 24 hours = 1632 kcal/kg/day
If a female weighs 120 lbs, her mass in kilograms will be 55 kg. Therefore, the estimated BMR is
55 kg ? 0.9 kcal/kg/hr = 49 kcal/kg/hr
24 hours/day ? Estimated BMR/hour = Estimated energy expenditure/day
49 kcal/kg/hr ? 24 hours = 1176 kcal/kg/day

These are estimated basal metabolic rates for these two people. Using this method, calculate your own BMR:
Body weight in kg ? BMR factor in kcal/kg/hr = Estimated energy expenditure in kcal/kg/hr
24 hours/day ? Your estimated energy expenditure/hour = kcal/day (your estimated energy expenditure/day or kcal/day used while at rest)

For a more accurate determination of your BMR, use standard tables from your text and calculate your skin surface area from your height and weight. A table of kilocalories per day per square meter of skin lists the kilocalories expended by a female or male by age group. This kilocalorie figure should be multiplied by your skin surface area to determine your BMR more accurately.

Skin surface area ? Kilocalories per day per square meter of skin = BMR

Your skin surface area ? Kilocalories per day per square meter of your skin = kcal/day

Estimating Your Energy Output per Day
Energy output per day is an estimate of your voluntary muscular activity per day. For a person who engages in only sedentary activities such as desk work, the estimated energy output is approximately 50% of his or her already determined BMR. For example, if the male in the previous example were a typist, his voluntary muscular activity level for the day would be:
0.50 ? 1632 kcal/day = 816 kcal/day
For a person who engages in light activities such as standing, talking, and minor amounts of walking, the estimated energy output is approximately 60% of his or her already determined BMR. For example, if the female in the previous example were a teacher, her voluntary muscular activity level for the day would be:
0.60 ? 1176 kcal/day = 706 kcal/day
For a person who engages in moderate activities that exceed those described as light, the estimated energy output is approximately 70% of his or her already determined BMR. For example, if the male described were a nurse, his voluntary muscular activity level for the day would be:
0.70 ? 1632 kcal/day = 800 kcal/day
Those participating in heavy activities are estimated to use an equivalent of their BMR per day. For a person engaged in heavy lifting and moving or a daily workout of an hour or more:
1.00 ? 1632 kcal/day = 1,632 kcal/day
Estimate your voluntary muscular energy expenditure per day:
Percent of BMR based on activity level ? BMR = kcal/day
(your voluntary muscular energy expenditure)
Estimating Your Specific Dynamic Action (SDA)
The specific dynamic action (SDA) is the amount of energy needed to metabolize food for the day. This is approximately 10% of a person’s total daily basal expenditure and total daily voluntary muscular activity. For example, the male nurse had a voluntary muscular activity level for the day of 800 kcal, and his daily expenditure was 1,632 kcal. Therefore, his SDA for the day would be anestimated 243 kcal.    (Your basal energy expenditure + Your voluntary daily physical activity) ? 0.10 = kcal/day (your SDA) Add together your BMR and your voluntary muscular energy expenditure.    BMR + voluntary muscular activity = kcal/day Total Daily Energy Requirements Your total daily energy requirements are the sum of your BMR + voluntary muscular activity + SDA = kcal/day
Determining Your Daily Caloric Intake
Before you can draw any conclusions about your daily energy balance, you must determine your total energy intake. This can be estimated by recording your total consumption of nutrients and determining their kcal values. Fill in Table 5.1 beginning with the first meal of your day and ending with the last snack you consume. The estimate of your kcal intake can be determined by using the tables found in many supermarkets, bookstores, and libraries. Such tables are usually referred to as pocket calorie counters.

Compare your total daily energy requirement with your actual kilocalorie intake per day:

Total daily energy requirement – Actual kilocalorie intake = Gain/maintenance/loss

If these two figures are the same, you are meeting your energy requirements and maintaining your weight. If your total daily caloric intake is greater than your caloric requirement, you are exceeding your energy requirements and, therefore, gaining weight. The opposite is true if you are not meeting your caloric requirement. Therefore, you are losing weight.

Table 5.1 Total Energy Intake Food Food Serving Size Energy kcal Breakfast




Total = ________________

Determining Your Daily Energy Balance
Name ___________________________________________ Lab section____________________
Your instructor may collect these end-of-exercise questions. If so, please fill in your name and lab section.
End-of-Exercise Questions
1. What is basal metabolic rate?

2.    Do basal metabolic rates differ between males and females? On what evidence can you base your answer?

3. What factors are involved in accurately determining your BMR?

4. What is specific dynamic action?

5.    If your total kilocalorie intake per day is higher than your total kilocalorie requirements, what happens to your weight?

6. What can you do to bring about an energy balance?

7.    Other than kilocalories, what information is important in determining whether or not you are consuming a healthy diet?

8. What resources are available to help you develop a balanced diet?

Part 2 – BMI
A: Define BMI-You must define BMI and not just as a general definition indicating its relationship to height and weight. Please also do not forget to define the actual term BMI!

B: Calculate BMI- Do no use an online calculator – show your actual math calculations. Please include all stages of the math calculations associated with determining your BMI.

C: Tie it all together. Consider the diet plan that you created in Table 5.1 for the determining total energy input. Based on your own BMI and how you fall according to the standard tables (underweight, normal, overweight, obese), evaluate your dietary plan. Build on the caloric intake you’ve already listed to include an exercise plan, being as specific as possible. The goal of this section is to develop a plan that incorporated all of the components of a sound fitness program (flexibility, endurance, strength training, body fat, and cardiovascular) as well as discuss specific exercises that you planned on doing.

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