March 30, 2008

You Ask, I Answer: Basal Metabolic Rate/Daily Caloric Intake

How can one correctly find their BMR and the calories intake needed for the day?

I have messed up my BMR with my undereating and am in almost malnourished state.

I want to increase my BMR and lose some fat.

From what I understand, maintenance and weight loss is figuring out the equation between calories intake and daily activity.

I just want to know how to estimate a calorie range I should go for and amount of exercise I need to do daily.

I am small - medium frame woman, 130 pounds, and 5' 4", with almost no muscle tone.

-- Mandy (last name unknown)
Halifax, Canada

I’m confused.

You claim to have messed up your basal metabolic rate due to undereating to the point where you are in a “malnourished state”, yet are looking to lose fat?

In any case, to answer your question – yes, weight loss and maintenance comes down to figuring out the net result of calories in (food) minus calories out (metabolism).

Our basal metabolic rate -- the amount of calories we burn off simply by existing -- is ultimately determined by a variety of factors, among them age, genetics, physical activity, dietary paterns, body composition, and hormonal activity.

This last point is especially important. Thyroxin, produced by the thyroid gland, plays a crucial role in metabolism.

In hypothyroidism, very little thyroxin in produced, and BMR is significantly lowered.

If you are cutting calories appropriately and upping physical activity for several weeks and see absolutely no changes, pay a visit to an endocrinologist and have your thyroid gland checked.

Thyroid issues apart, many people appear to forget that some of these factors change with time, age being the most obvious.

This is one reason why, as people age, they find that weight “creeps up on them.”

The 2,500 calories once needed to maintain weight can be too many -- and cause weight gain -- ten years later.

This is where knowing TDEE (total daily energy expenditure) also comes in handy.

TDEE lets you know how many calories you approximately burn each day on top of what your body uses up as a result of standard bodily processes.

So how do you determine all these numbers?

First, calculate your BMR.

You can easily find that out by plugging some basic numbers into Discovery Health’s BMR Calculator.

If you want to get slightly more technical, you can also use the Mifflin-St Jeor formula, developed in 1990, which goes something like this:

Male BMR = 10* (weight in kg) + 6.25* (height in cm) - 5* (Age)+ 5
Female BMR = 10* (weight in kg)+ 6.25* (height in cm) - 5* (Age) -161

NOTE: To convert pounds to kilograms, divide by 2.2 To convert inches to centimeters, multiply times 2.54.

Prior to this, the Harris-Benedict formula (created in 1919) was used. While useful, Mifflin-St.Jeor results in more accurate numbers.

Ok, now: to calculate TDEE multiply your BMR by:

1.2 if you perform little to no physical activity
1.38 if you perform light physical activity a few times a week
1.55 if you perform moderate physical activity at least 3 times a week
1.725 if you perform intense physical activity on a daily basis

1.9 if you perform intense physical activity several times a day or have a very physically demanding job.

Whatever number you get is how many calories you need to maintain your desired body weight.

If you wish to lose -- or gain -- weight, simply subtract – or add – fifteen percent to that figure.

By consuming fifteen percent less calories and increasing your physical activity, you will certainly shed weight.

The fact that you mention having “no muscle tone” is significant, since increasing lean muscle mass is a sure-fire way to speed up metabolism.

This is why weight-bearing exercises are highly recommended -- they help with bone density and metabolism.

Alas, weight loss comes back to the tried and true advice of “eat less, move more.”

1 comment:

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