03/12/2015
What is a Calorie?
Why do we eat? • The human body burns food as fuel, just like a car does, to provide energy (power to go!) • Energy is measured in joules (J). Food Energy is more commonly measured in calories. • One calorie is the amount of energy required to raise the temperature of one gram of water one degree Celsius. • Food energy is often given in kilocalories or Calories ** notice the capital C. 1 kilocalorie is equal to 4.18kJ
1
03/12/2015
Energy provided by food • Each component of food provides a predictable amount of energy. However, our bodies use each component differently and at different rates.
Component of food
Energy Provided (kJ/g)
Energy provided (kcal/g)
Carbohydrates
17
4
Proteins
17
4
Fats
38
9
Alcohol
29
7
Vitamins and minerals
0
0
How is it all used? • Half of our daily food intake is used to maintain the body at a constant temperature. • The basal metabolic rate (BMR) is the energy required to maintain the body at rest (awake, but not doing anything) • The BMR for an adult male ranges from 16001800 kcal/day. • The BMR for an adult female ranges from 12001500 kcal/day.
2
03/12/2015
BMR Factors • Body composition: Lean tissue is metabolically more active than fat tissue (more reactions are going on in lean tissue than fatty tissue) • Age: BMR drops about 2% per decade after the age of 20 years • Gender: Female BMR is usually 10% lower than male BMR due to a higher percentage of body fat at similar body weight • Energy intake: As the body consumes less energy, it performs more efficiently.
Metabolism • Metabolism is the sum of all the chemical reactions that occur within the body cells. • A chemical in your thyroid gland is responsible for the rate at which your body converts food energy into other forms of energy. As the chemical increases, your metabolism increases. • Part of the energy from metabolism is converted into heat energy to warm the body
3
03/12/2015
Low vs High Metabolism • A person with a low metabolism uses food energy very efficiently. Little food energy is converted into heat, and therefore less energy escapes the body. Instead, the food energy is converted into fat – for storage. • A person with a high metabolism converts a large portion of their food energy into heat. More energy escapes the body, and less is available for storage (fat), so the person remains relatively thin.
It’s all about balance • The energy in food that is consumed should equal the energy output. • The energy output is used for growth, exercise, and normal metabolic reactions. • When an imbalance occurs, the body either stores the excess energy, or uses what is has in storage.
4
03/12/2015
Daily Energy Requirements Description
Newborn
Energy Requirement (kJ per day) 2000
Energy Requirement (kcal per day) 480
Child (2-3 years)
6000
1440
Teenage girl
9500
2270
Teenage boy
12000
2870
Office worker
11000
2630
Manual worker
15000
3590
Activity and Energy • For a person to maintain body weight, the intake of food energy must equal the BMR plus the energy used for activity (remember BMR is for awake, but doing nothing) • When resting, the body may need 20% fewer calories per day than when doing hard physical work (including exercise). • The rate at which stored energy is used during activity depends on the intensity of the activity and on body size.
5
03/12/2015
Sample Problem (math) • How much energy does a 75-kg person require to sleep all day? The energy factor for sleeping is 4.1 kJ/kg/h. The total energy required can be calculated by multiplying the energy factor by the body mass, in kilograms, by the amount of time spent on an activity.
Solution • Given: – Energy factor = 4.1 kJ/kg/h – Body mass = 75 kg – Time = 24h – Energy required = energy factor x body mass x time
» =4.1kj/kg/h x 75kg x 24h » =7380 kJ
6
03/12/2015
Remember the dangers of too much body fat… • The presence of excess body fat has been linked to cardiovascular disease, diabetes, high blood pressure, cancer, arthritis, gall bladder disease, certain reproductive disorders, and psychosocial difficulties. • Body fat can be estimated using tools such as BMI – but remember its restrictions!
BALANCING ACT • Weight loss requires a negative energy balance. • A negative energy balance may be achieved by eating less or exercising more, or by a combination of the two • Weight gain requires a positive energy balance. • A positive energy balance may be achieved by consuming more energy than is required. • 1 kg of fat has the energy value of 32 200 kJ or 7700 kcal.
7
03/12/2015
Calculating BMR p 398 • Female: BMR = [655 + (9.6 X mass in kg) + (1.8 X height in cm) – (4.7 X age in years)] X4.18 • Male BMR =[66 + (13.7 X mass in kg) + (5.0 X height in cm) – (6.8 X age in years)] X 4.18
Type of Activity
Energy Factor (kJ/kg/h)
Sleeping
4.1
Sitting
5.2
Writing
6.0
Standing
6.3
Singing
7.1
Keyboarding, card playing
9.0
Washing the car, cooking
10.5
Playing Piano
11.2
Walking (3.2 km/h)
11.6
Bowling
13.6
Cycling (13 km/h)
15.8
Walking (4.8 km/h)
16.2
Walking (6.4 km/h)
20.6
Badminton
21.5
Cycling (15.3 km/h)
25.8
Hiking, fast dancing
27.0
Tennis, downhill skiing
36.2
Climbing stairs, running (8.8 km/h)
37.5
Cycling (20.9 km/h)
40.5
Cross-country skiing
42.0
Swimming crawl (45.7m/min)
49.1
Handball
49.5
Running (12.9 km/h)
62.0
Competitive cross-country skiing
73.6
8
03/12/2015
Activity • Using your food journal, calculate the average amount of Calories you consumed daily. • Using the activity table, estimate your daily activities and their energy requirements – don’t forget to convert the energy to the same units (kJ or kcal) • Are you balanced? Imbalanced? Are you surprised?
Are you physically active?
9
03/12/2015
Internet Activity •
Find Canada’s Physical Activity Guide to Healthy Active Living and its accompanying handbook on the Nelson Web site (www.science.nelson.com). Study the handbook and answer the following questions – List the benefits of regular physical exercise – List the health risks of inactivity – What is a reasonable goal for daily physical activity? Do you meet this goal? – If you exercised for 40 minutes, felt warm, and noticed that your breathing rate increased, what types of activities would likely result in these effects? – Design a 20-point matching question that categorizes activities as Endurance, Strength, or Flexibility. – How much energy would you have to expend each day to meet the Canadian definition of “physically active”? Are you physically active? – Set goals for incorporating more physical activity into your daily life. Read the case histories and the activity suggestions for ideas. – Take the Physical Activity Readiness Questionnaire (PAR-Q), found in the handbook. How did you rate?
10
