When you get into a discussion of weight loss, the word metabolism is bound to come up.
You hear, "That person has such high metabolism, they can eat whatever they want to.
" Sometimes it is, "My metabolism dropped when I was in my thirties and I immediately gained 20 pounds".
But what is metabolism and why does it affect our ability to lose weight so much? Metabolism is the process that determines what parts of the food we ingest are used and how.
There are 2 basic processes that combine for our metabolism.
Catabolism is the process of breaking down foods into energy.
Anabolism is the process our body uses to build new molecules.
Anabolism needs the energy that catabolism produces to build these new molecules.
Both processes depend upon our diet and activity level to do their jobs efficiently.
Basal metabolic rate (BMR) is the amount of energy expended just for the functioning of the vital organs.
In other words, the energy needed to sustain life when you are inactive, as in when you are sleeping.
Your BMR decreases as you get older and as you lose lean muscle mass.
So if you have become less active as you've aged, then the second statement above is probably accurate.
But can you do something about it? Certainly! You can increase your BMR by increasing your muscle mass.
Illness, previously consumed food and beverages, environmental temperature, and stress levels can all affect one's BMR as well, so we need to adjust for these as well.
BMR can be calculated based on body height, weight, and age.
You can figure it by taking your weight in kilograms and multiplying it by 9.
99, then add your height (in centimeters) multiplied by 6.
25, then subtract your age multiplied by 4.
92, and, finally add 5 for males or subtract 161 for females.
If you prefer a formula, here is a simplified version of it: Males: [(Weight in kg x 9.
99) + (height in cm x 6.
25) - (age x 4.
92)] + 5 = kcal burned per day Females: [(Weight in kg x 9.
99) + (height in cm x 6.
25) - (age x 4.
92)] -161 = kcal burned per day Using this formula, a 50 year old woman weighing 125 lb (46.
6kg) at 63 in (160 cm) would have a BMR of 1060 kcal/day.
In other words, if she slept for 24 hours, her body would still burn 1060 calories! This formula is based on body weight, which does not take into account the difference in metabolic activity between lean body mass and body fat.
A more accurate formula is the Katch-McArdle formula based on lean body mass.
Here it is, simplified: 370 + (21.
6 x LBM) = kcal burned per day In this formula, LBM is the Lean Body Mass in kg.
So, according to this formula, if the woman in the example above has a body fat percentage of 30%, her BMR would be 1075 kcal per day.
Now, remember that you can increase your BMR by increasing your body mass.
How do you do that? Strength training! Studies published in 1992 [1] and 1997 [2] indicate that the level of aerobic fitness of an individual does not have any correlation with the level of resting metabolism.
That does not mean that aerobic exercise is not important! It is very important for the health of your cardiovascular system, so don't stop aerobics, running, biking, or whatever you do to keep your heart healthy.
Instead, add weight exercises to your routine.
Build muscle mass that will successfully burn more calories.
So if your metabolism "drops" it is because there is a natural tendency to decrease as we get older.
It will also drop if we become couch potatoes.
How can this drop be avoided? We need to eat the right foods so that the right nutrients can be sent to the right places.
We also need to strengthen our muscles so we use the fuel more efficiently.
We can't do anything about our body aging so we should take care of it as best we can.
Again, the stronger your muscles are, the higher your BMR.
Thus a strong, healthy body that gets plenty of exercise burns fat even when it is sleeping! So next time you think you have no power over your metabolism, remember that your metabolism depends wholly upon you! You do have the ability to control it! Eat the right foods, get the exercise you need, and let your body do what comes naturally.
1 CE Broeder, KA Burrhus, LS Svanevik and JH Wilmore (1992).
"American Journal of Clinical Nutrition".
The effects of aerobic fitness on resting metabolic rate.
2 D.
A.
Smith, J.
Dollman, R.
T.
Withers, M.
Brinkman, J.
P.
Keeves, and D.
G.
Clark (1997).
"Journal of Applied Physiology".
Relationship between maximum aerobic power and resting metabolic rate in young adult women.
You hear, "That person has such high metabolism, they can eat whatever they want to.
" Sometimes it is, "My metabolism dropped when I was in my thirties and I immediately gained 20 pounds".
But what is metabolism and why does it affect our ability to lose weight so much? Metabolism is the process that determines what parts of the food we ingest are used and how.
There are 2 basic processes that combine for our metabolism.
Catabolism is the process of breaking down foods into energy.
Anabolism is the process our body uses to build new molecules.
Anabolism needs the energy that catabolism produces to build these new molecules.
Both processes depend upon our diet and activity level to do their jobs efficiently.
Basal metabolic rate (BMR) is the amount of energy expended just for the functioning of the vital organs.
In other words, the energy needed to sustain life when you are inactive, as in when you are sleeping.
Your BMR decreases as you get older and as you lose lean muscle mass.
So if you have become less active as you've aged, then the second statement above is probably accurate.
But can you do something about it? Certainly! You can increase your BMR by increasing your muscle mass.
Illness, previously consumed food and beverages, environmental temperature, and stress levels can all affect one's BMR as well, so we need to adjust for these as well.
BMR can be calculated based on body height, weight, and age.
You can figure it by taking your weight in kilograms and multiplying it by 9.
99, then add your height (in centimeters) multiplied by 6.
25, then subtract your age multiplied by 4.
92, and, finally add 5 for males or subtract 161 for females.
If you prefer a formula, here is a simplified version of it: Males: [(Weight in kg x 9.
99) + (height in cm x 6.
25) - (age x 4.
92)] + 5 = kcal burned per day Females: [(Weight in kg x 9.
99) + (height in cm x 6.
25) - (age x 4.
92)] -161 = kcal burned per day Using this formula, a 50 year old woman weighing 125 lb (46.
6kg) at 63 in (160 cm) would have a BMR of 1060 kcal/day.
In other words, if she slept for 24 hours, her body would still burn 1060 calories! This formula is based on body weight, which does not take into account the difference in metabolic activity between lean body mass and body fat.
A more accurate formula is the Katch-McArdle formula based on lean body mass.
Here it is, simplified: 370 + (21.
6 x LBM) = kcal burned per day In this formula, LBM is the Lean Body Mass in kg.
So, according to this formula, if the woman in the example above has a body fat percentage of 30%, her BMR would be 1075 kcal per day.
Now, remember that you can increase your BMR by increasing your body mass.
How do you do that? Strength training! Studies published in 1992 [1] and 1997 [2] indicate that the level of aerobic fitness of an individual does not have any correlation with the level of resting metabolism.
That does not mean that aerobic exercise is not important! It is very important for the health of your cardiovascular system, so don't stop aerobics, running, biking, or whatever you do to keep your heart healthy.
Instead, add weight exercises to your routine.
Build muscle mass that will successfully burn more calories.
So if your metabolism "drops" it is because there is a natural tendency to decrease as we get older.
It will also drop if we become couch potatoes.
How can this drop be avoided? We need to eat the right foods so that the right nutrients can be sent to the right places.
We also need to strengthen our muscles so we use the fuel more efficiently.
We can't do anything about our body aging so we should take care of it as best we can.
Again, the stronger your muscles are, the higher your BMR.
Thus a strong, healthy body that gets plenty of exercise burns fat even when it is sleeping! So next time you think you have no power over your metabolism, remember that your metabolism depends wholly upon you! You do have the ability to control it! Eat the right foods, get the exercise you need, and let your body do what comes naturally.
1 CE Broeder, KA Burrhus, LS Svanevik and JH Wilmore (1992).
"American Journal of Clinical Nutrition".
The effects of aerobic fitness on resting metabolic rate.
2 D.
A.
Smith, J.
Dollman, R.
T.
Withers, M.
Brinkman, J.
P.
Keeves, and D.
G.
Clark (1997).
"Journal of Applied Physiology".
Relationship between maximum aerobic power and resting metabolic rate in young adult women.
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