We all know that food provides our bodies with the energy we need every day. But do you know how this energy is measured, how much we each need, and how the energy from food is distributed within the body?
The energy that we get from food is measured in kilocalories or calories. Sound familiar? A calorie is used to measure the amount of heat released when food undergoes total combustion. We can measure that heat using a tool called a calorimeter. Because of this technology, we know that one gram of carbohydrate and one gram of protein both release four (4) calories of heat. Fat, on the other hand, releases nine (9) calories.
Right away you’ll notice that the energy content of fat is more than twice that of carbohydrates and protein. When we eat these fuels, our bodies release the contained energy by a process called oxidation. During oxidation, about 60% of the energy is released as heat and used to maintain our body temperature, while about 40% is used to produce energy for the body.
So how many calories do we each need in a day, and where do those calories go once they are in our bodies? To start, the recommended dietary energy intake for a 70 kg (or 154 lb.) adult male is about 2900 calories and for a 50 kg (or 110 lb.) adult woman, about 2100 calories.
The total energy required by an individual is the sum of three distribution “channels”:
Basal Metabolic Rate or BMR
The BMR is simply the total calories the body needs to carry out normal functions such as respiration, blood flow, and muscle maintenance.
Specific Dynamic Action or SDA
SDA is the way that the body actually uses increased energy during digestion. Our body temperature can actually increase to as much as 30% above normal after a meal.
Physical activity provides the greatest variation in energy expenditure. A sedentary individual may require about 30–50% more calories than his or her BMR, while an active individual may require 100% or more above the BMR.
Between these three channels, your calorie distribution will look like this: 60% of total calories consumed will keep our body functioning (BMR), 30% go to physical activities, and 10% go to the SDA.
Be sure to keep in this in mind if you’re thinking about trying to lose weight. If you know what your body needs, you can still provide it with energy and essential nutrients while manipulating physical activity and diet to ensure that you do not consume more calories than your body needs to function properly.