Survival – Calories

Survival is all about playing the calorie game. Calories are a unit of measurement devised by Nicolas Clemant for the measurement of energy. A calorie is the energy required  to raise the temperature of 1 gram of water 1 degrees Celsius.

1 cal = 1gm water raised by 1 degree centigrade

The calorie has been replaced as a scientific unit of measurement by the joule, however it is now used to measure energy content of food.

In its simplest form we need calories (i.e. energy) in order to live or accomplish tasks at hand, as most of us will already know. As our level activity increases so does our calorie consumption. The need to understand how this works is important for any survival situation, not only for planning purposes, but also simply to live.

To calculate how many calories we are using you use this formula:

Basal Metabolic Rate + Thermic Effect + Activity = Calories Expended

Basal Metabolic Rate

The BMR is the amount of calories the body expends simply to function. Even doing nothing your body is using up calories. To calculate exactly how many calories are being burned we can use these formulas:

Male BMR = 66 + (6.3 x weight in lb) + (12.9 x height in inches) – (6.8 x age in years)
Female BMR = 655 + (4.3 x weight in lb) + (4.7x height in inches) – (4.7 x age in years)

If Person A is a male, weighs 175 lb, is 6 feet tall, and 27 years old
BMR    = 66 + (6.3 x 175) + (12.9 x 72) – (6.8 x 27)
            = 66 + (1102.5) + (928.8) – (183.6)
            = 66 + 1847.7
            = 1913.7

This means that Person A needs to consume 1914 (rounded) calories per day minimum. To put that in perspective Person A would need to eat just less then four BigMacs per day to meet his minimum requirement, although I don't recommend it.

I used the Imperial system of measurement becomes in terms of a persons weight, and height it is more common. The metric measurements are as follows:

Male BMR = 66 + (13.7 x weight in kg) + (5 x height in cm) - (6.8 x age in years)                                     
Female BMR = 655 + (9.6 x weight in kg) + (1.8 x height in cm) - (4.7 x age in years)

Thermic Effect

Ironically enough the body must expend energy to make energy. The amount of energy needed to digest and metabolize energy is known as the thermic effect. To calculate how much energy is used up is rather simple, it works out to about 10%:

Thermic Effect = Calories consumed x 0.1

Person A decides to actually eat those four BigMacs (I am only using these as an example, because we all know what they are). The burgers come in at 540 calories a piece for a total of 2160. Because of digestion and the energy expended to metabolize the meal we lose 216 of those calories.

Activity Related Metabolism

Every time you get off the couch and do something, your body will use up more calories. This we probably all understand. Many people nowadays are trying to get rid of their extra calories their body has stored up in their body for self image purposes. In a backpacking or survival situation we need to conserve all the calories we can.

I will delve more into activity related metabolism in another post. However, for the sake of demonstrations:

Person A is hiking through the woods for six hours with a 10lb pack on. Based on previously attained data we know that a 175lb person carrying an additional 10lb will expend 623 calories an hour. During this hike Person A expended 3738 calories.

Adding it all Together

We now know all this information required to figure out exactly how many calories were expended.

BMR = 1914
Thermic = 216
Activity = 3738

Total Cal Expended = 5868 calories
Total Cal Consumed = 2160 calories

We are now running a calorie deficit of 3708. To put this in perspective one pound of body fat will supply you with approximately 3500 calories, therefore we have used up just over one pound of our bodies stored energy in addition to the 2160 calories eaten. If you start multiplying this by a multi day hike (which will probably include longer hiking days, and heavier packs), you can see how easy it is to run into a great deal of trouble in a short time. This is one reason why most survival manuals will instruct you to stay where you are. By not doing any activity and not eating, we can see that our BMR used up LESS calories then actually eating and going somewhere. Food for thought.