Your metabolic rate
works a lot like the engine of an automobile except that, unlike a car, your
engine must work 24/7 to keep you alive. Some people have a Hemi® under the hood,
while others are more like hybrids. Athletes have a keen interest in their
metabolic rate or resting energy expenditure because it can help them determine
their energy needs and help them lose, maintain or even gain weight.
The nutrition world
is full of advice for how to increase your metabolic rate – they tell you to
exercise, lift weights, eat hot peppers, drink tea and even develop a nervous
twitch. However, new research shows that your body’s metabolism is largely
determined by factors that you cannot change—like the size of your liver,
spleen, heart, lungs and brain—and that the many suggested ways to increase
metabolic rate have little, if any, effect.
Below are some key
points about the metabolic rate concept and the truth behind what really
increases or decreases it from a research presentation given at a body
composition meeting held by the Sports, Cardiovascular and Wellness
Nutritionists (SCAN) at the American Dietetic Association’s Annual Conference
in
What is your
metabolic rate? Your metabolic rate is measured as either the basal metabolic
rate (BMR) or resting metabolic rate (RMR). The BMR is usually measured in the
morning after an overnight fast and lying down for 30 minutes whereas the RMR is
often measured in the afternoon, several hours after eating. It generally
provides a result that is 10-20% higher than the BMR. Both are values that
describe how much energy your body needs to sustain itself.
The RMR, or BMR,
represents about two-thirds of your total daily energy needs. Muscle movement
(exercise, fidgeting, walking and daily activities) represents about 23 percent
of the total energy expenditure in the average American, while the thermic effect of food (the energy used to turn food into usable
energy and waste) represents another 10 percent. Only very active individuals
can match or surpass their RMR with calories expended from their physical
activities.
Do thinner people
have higher metabolic rates? Nope. In fact, the opposite is true. One
effective way to increase your metabolic rate is to actually gain weight.
That’s because both fat and muscle require energy to sustain themselves.
And, for every pound you gain, one-quarter of it is generally lean tissue.
The same thing
applies for when you lose weight – for every pound lost, one-quarter of it is
lean tissue. That’s why when you lose weight, for every pound lost, your body requires about 10 fewer calories. Lose 10
pounds and you now need to cut 100 calories from your diet (or burn an additional
100 calories through exercise) to maintain your weight. This is part of the
reason why weight maintenance is so much more challenging than actually losing
weight.
Doesn’t aerobic
exercise or resistance training accelerate your metabolic rate? If this were true,
fit individuals would have higher metabolic rates than an unfit person of the
same size and sex. Research shows this isn’t the case. Even highly trained
athletes often have RMR equal to their sedentary counterparts. While exercise
is great for total energy expenditure, is good for your heart and
cardiovascular system and has many other health benefits, increasing the
metabolic rate is not one of the major benefits of exercise.
Does
adding muscle mass increase your metabolic rate? Compared to fat
tissue, muscle mass is more metabolically active. But in comparison to organs,
your muscles are like a hybrid car while your organs are gas-guzzling V8s.
Muscles burn about 13 calories per kilogram of bodyweight per day
(kcal/kg/day), fat burns 4.5 kcal/kg/day, but organs burn 200 to 400
kcal/kg/day. In the end, your organs represent 60-70% of your metabolic rate
and muscles represent 16-22%.
So the most muscle
mass that you can realistically add in a year (4-5 pounds of muscle) would add
just 28-50 kcals to your metabolic rate per day.
Should I have my
metabolic rate measured? If you are trying to lose weight, it’s probably not a
bad idea to get your metabolic rate measured. In fact, many health clubs now
offer on-site testing. At the very least, it will probably tell you that your
weight woes are not due to a low metabolism. You can also estimate your BMR
fairly accurately using the formula below:
Estimating your
Metabolic Rate
To estimate your metabolic rate, follow these steps:
For example, Matt
(31) is a 6'2" triathlete who weighs 198 pounds.
Matt's height: 74 inches x .0254 = 1.88 meters
Matt's weight: 198 pounds/ 2.2 = 90 kilograms
Matt's estimated BMR = 294 - (3.8 x 31 years) + 456.6 x 1.88 meters) +
(10.12 x 90 kilograms) = 1,943 kcals/day
In fact, Matt had
his BMR tested and it was measured at 2000 kcals/day,
very close to his calculated BMR.
Estimating your
Total Caloric Expenditure
To estimate total caloric expenditure, you need to
factor in the energy expenditure of your daily activity and exercise.
BMR x 1.5 = Weight
maintenance for people who do little exercise
BMR x 1.7 = Weight maintenance for moderately active people (up to
1 hour per day of activity)
BMR x 1.9-2.5 = Weight maintenance for athletes
Matt, the triathlete, is very active, exercising for over two hours
most days so his estimated total daily caloric expenditure is estimated as
follows.
Matt's Total Caloric
Expenditure Estimation =
1943 kcals/day x 1.9-2.5 = 3692 to 4858
kcal/day
But Matt is also
trying to lose weight. If Matt bases his caloric intake on an activity factor
of 1.7 to 1.9:
1943 kcals/day x 1.7-1.9 = 3303 to 3692 kcal/day
Applying this, he
should be able to lose about one pound per week. The effects of this caloric intake
would need to be monitored and adjusted according to his rate of weight loss
per week.
For people with
lower levels of activity, adjusting daily caloric intake below the estimated
daily caloric expenditure should bring about weight loss. For example, for
people who do little exercise:
BMR x 1.0 = Weight
Loss of about 1 pound per week
BMR x 1.3 = Weight loss of about 1/2 pound per week
Again, the effects
of this caloric intake should be monitored and adjusted according to the rate
of weight loss per week. See this month's Ask the Nutritionist to help determine
if or when you should seek individualized professional nutritional guidance.