Small Steps to Health

Breakdown of Calorie Expenditure in our Bodies

June 11th, 2008 by asithi · 4 Comments

Tagged Weight, calories, fat storage, metabolism

There are many factors that affect how our bodies convert the food we into energy.  Most people, including myself, have no problem with eating enough food to supply our bodies with the energy we need to function (though it is questionable whether we are supplying our bodies with premium or regular fuel).  This post is a discussion of the other side of the energy equation: other than fat storage for excess calories, how are the calories distributed inside our bodies?

Basal Metabolic Rate (BMR  60-75% of daily calories  used)
The basal metabolic rate is a measurement of energy used for the maintenance of our body functions.  This is the amount of calories our bodies burn in order for us to stay alive.  It is a very individualize rate since it depends on your body size, your body composition (fat and muscle ratio), nutritional state, thyroid function, and sympathetic nervous system activity.  In general, the bigger we are and the more muscle mass we have, the more calories are needed to run the machine.

The BMR rate accounts for 60-75% of the our daily calorie expenditure.  The calories require for our basic body functions decrease with weight loss.  So if we do not eat less as we weigh less, then we will eventually hit the dreaded diet plateau.  In general, for each pound we weigh, the daily caloric requirement is 10 calories.  For example, for a 150 pound woman, the daily caloric requirement is 1,500 calories.  But this is a very general estimate since it could be plus or minus 200 calories depending on your body, your age,  and your activity level.  The variation is even higher for people with more muscle mass than the average woman.

Exercise (15-30% of daily calories used)
This is the only area in our bodies’ energy expenditure within our control.  It is crucial for weight loss and absolutely indispensable to maintenance.

When we look the National Weight Control Registry (NWCR), all the participants that have loss over 20 pounds, use exercise for both during the weight loss period and the maintenance phase.  The participants expend an average of 2,800 calories each week through exercise (3,500 calories is equal to one pound).

Exercise does not have to be a formal routine, something as simple as gardening counts or housework.

Not only does exercise burns off excess fat, the way it rearranges your body fat might be just as important.  Strength training will increase our muscle mass, hence increasing our BMR rate.  So we will burn more calories just sitting in front of a computer monitor.

I feel that I need to mention this caveat: Exercise is not an excuse to eat more food! Though you burn more calories with exercise and diet than just diet alone, eating a candy bar will require you to workout for at least 30-40 minutes.  What is worth 30-40 minutes of your time?  Getting rid of your existing love handles or being able to eat that candy bar, but maintain your current love jelly?

Thermic burn of food (5-10% of daily calories used)
It requires energy to make energy.  There is a series of chemical reactions happening inside our cells when we eat.  Our body has to breakdown the fat, protein, and carbohydrate into adenosine triphosphate (ATP) and heat in the mitochondria before our bodies can use the energy.  So each time we eat, there is a small metabolic boost.  If you spaced your eating intervals evenly, the thermic effect of food accounts for 5-10% of our daily energy expenditure.  The top strategy for the participants of the NWCR is eating five times a day.

When we are trying to run our machine on a calorie deficit (dieting), we need both the thermic boost and the blood sugar stability that interval eating provides.

Facultative thermogensis (5-10% of daily calories used)
Your metabolic rate also response to the temperature.  When we are cold, our bodies burn more calories to produce more heat to prevent us from freezing to death.  This is the reason why we seem to eat more in the winter.  This process account for 5-10% of our daily energy expenditure.

When we are stress, our bodies respond with fight or flight, hence requiring us to burn more calories in case we have to power the body through either activity.  Notice how we seem to get the munchies when we are stressed?  This is part of the facultative thermogensis.  The problem is that with our current society, we do not have the same physical outlet for stress that our ancestors once did.  Though it might sound like a good idea to have prolonged stress in order to get this extra 5-10% metabolic boost, it is damaging to our bodies to be expose to prolong stress.  Google it and you will see what I mean.  Exercise is an appropriate outlet for our bodies to get rid of stress.

Big changes come from small gradual steps towards a healthier lifestyle.  Start slowly.  Give your mind and body time to accept and establish new habits, including making healthier eating choices and exercise.  It takes years for you to become a coach potato, so it will take some time to rediscover the energy you had as a child.  You know that you have positive behavioral results when you want to go outside to play again.

Until next time and thanks for stopping by.

PS.  I know these rates do not add up to 100%, but since our personal rates vary within those percentages, these numbers are a good estimation.

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