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Kilocalorie, commonly referred to as simply "calorie," denotes the energy value of food, or the amount of heat energy that the food yields as it passes through the body. It finds expression as the quantity of heat required to raise the temperature of 1000 grams of water by one degree Celsius. Understanding the quantum of calories an individual burns in a normal day allows to increase or decrease food intake and yet maintain optimal body weight.
It is easy to ascertain the approximate quantity of calorie burned on a normal day. The exact figure for an individual is however harder to obtain.
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Physical activities remaining constant, men tend to burn more calories than women do, young people tend to burn more calories than old men do, and people with a big body frame, more weight or greater muscle mass tend to burn more calories than people with small body frame, less weight, or lesser muscle mass do.
As a rule of thumb, the greater the physical activity, the greater the calories burnt. For instance, a 30 year old man of average height and weight will burn 68 calories per hour watching television and 88 calories per hour reading a book. A woman of the same age, height, and weight will burn about 59 calories per hour watching television and 77 calories per hour reading. A basketball game will drain one player weighing 130 lbs of 472 calories, and the same game will drain another player weighing 190 lbs of 690 calories.
A person staying in bed all day and doing nothing however still burn some calories. This minimum amount of calories that a person burns is his or her Basal Metabolic Rate (BMR). An average man of 30 years with a normal height and weight burns about 61 calories during an hour of sleep in a reclined position. A woman of similar age, height and weight burn about 53 calories during an hour of sleep.
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The Mifflin Equation and "Activity Factor"
If you want a specific answer to "how many calories do I burn in a normal day," apply the Mifflin equation to calculate the Basal Metabolic Rate (BMR).
The Mifflin equation for men is: (10 x weight in kgs) + (6.25 x height in cms) - (5 x age in years) + 5.
The Mifflin equation for women is : (10 x weight in kgs) + (6.25 x height in cms) - (5 x age in years) – 161.
These equations requre their weight in Kgs and height in centimeters. One inch equals 2.54 cerntimeters, and one lb equals 0.45359237 kg.
Next, multiply the BMR obtained from the Mifflin equation by an "Activity Factor" derived from the Harris Benedict equation, to obtain the calories burned.
The "Activity Factor" is an index based on one's lifestyle, and is listed in the Harris Benedict equation. An "Activity Factor" of 1.2 denotes a "Sedentary Lifestyle" with a desk job and little or no exercise. An "Activity Factor" of 1.375 denotes a "Lightly Active Lifestyle" with light exercises, an "Activity Factor" of 1.55 denotes a "Moderately Active Lifestyle," an "Activity Factor" of 1.725 denotes a "Very Active Lifestyle" accompanied by hard exercise or sports, and an "Activity Factor" of 1.9 denotes an "Extremely Active Lifestyle" centered on exercise, sports or a physical job.
To illustrate, consider the case of a thirty year old female 167.6 cm tall and 54.5 kg heavy, with a desk job.
- BMR = (10 x 54.5) + (6.25 x 167.6) + (5 x 3) – 161 = 1446.5 calories (k.cals)
- Activity factor = 1.2
- Calories Burned in a normal day = 1446.5 x 1.2 = 1735.8 calories (k.cal) per day
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The method indicated to determine the calories burnt during a normal day only gives a rough indication and is based on a general level of activity. The actual amount will vary for each individual depending on one’s body composition, and a measure of the percentages of muscle and fat composing your body.
The information contained in this article should not be constructed as medical advice.
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- American Journal of Clinical Nutrition: http://www.ajcn.org/cgi/content/abstract/51/2/241
- American Dietetic Association: http://www.eatright.org
Image Credit: freedigitalphotos.net/Grant Cochrane