[Home] [BMR] [Foods] [Hydration] [Muscle] [Vitamins] [Supplements] [Body Weight] [Nutriquest] [Links]

Basal Metabolic Rate (BMR)

Basal Metabolic Rate is the mimimal caloric requirement needed to sustain life in a resting individual. This is the amount of energy your body would burn if you slept all day (24 hours). Let's look at some factors that affect BMR:

Age: In youth, the BMR is higher; age brings less lean body mass and slows the BMR.

Height: Tall, thin people have higher BMR's.

Growth: Children and pregnant women have higher BMR's.

Body Composition: The more lean tissue, the higher the BMR. The more fat tissue, the lower the BMR.

Fever: Fevers can raise the BMR.

Stress: Stress hormones can raise the BMR.

Environmental Temperature: Both the heat and cold raise the BMR.

Fasting/Starvation: Fasting/starvation hormones lower the BMR.

Malnutrition: Malnutrition lowers the BMR.

Thyroxin: The thyroid hormone thyroxin is a key BMR regulator; the more thyroxin produced, the higher the BMR.

Let's now talk about ways to measure BMR:

1. General Calculation: BMR = your body weight in lbs x 10 kcal/lb

Ex. Joe weighs 150 lbs

BMR = 150 x 10 kcal/lb = 1,500 kcals

2. The Harris-Benedict Equation:

Males: 66 + (13.7 x W) + (5 x H) - (6.8 x A)

Females: 655 + (9.6 x W) + (1.7 x H) - (4.7 x A)

where W = actual weight in kg (weight in lb/2.2 lb/ kg)

H = height in cm (height in inches x 2.54 cm/in)

A = age in years

Ex. Joe weighs 150 lbs, stands 5'6", and is 21 years old

150 lbs/2.2 lb/kg = 68 kg

5'6" = 66 inches x 2.54 cm = 168 cm

BMR = 66 + (13.7 x 68) + (5 x 168) - (6.8 x 21)

BMR = 66 + 932 + 840 - 143 = 1695 kcals per day

****Just to note, these values are approximations. We can see that we came up with 1,500 and 1,695 kcals per day with two different approaches to figuring out BMR. I would stick to the Harris-Benedict Equation if I were you. I believe it is more accurate!****

Link to BMR on the Web: Actually calculates your BMR for you. Definitely check this out!!!!!!

Energy Expenditure

These two charts show approximate energy expenditure during performance at various physical activities.
The reason that I added these to this section is so we can figure out how much energy someone burns in a 24 hour period. The best way to calculate this would be to do a 24 hour activity recall, where you have an individual write down everything (I mean everything that they performed in one day). You need to write down how many hours you spent walking, standing, running, exercising, biking, sleeping, etc. Once you come up with these values, we can then approximate what your total energy expenditure is for that particular day. This is a rather tedious process, but it is the most accurate way to predict how much energy you are expending in various activities throughout the day.

For example, we'll use Joe again. Let's say that he spent 10 hours sitting, 3 hours walking, 1 hour standing, 3 hours studying, 1 hour of running at 7.5 mph, and 6 hours of sleeping. This is Joe's activity record for that day. Now we can use these charts to calculate approximately how much energy Joe burned this day.

From these charts we see that:

1.1 kcals per minute were burned during sleep:

1.1 x 360 minutes (6 hours) = 396 kcals

1.7 kcals per minute were burned when he studied:

1.7 x 180 minutes (3 hours) = 306 kcals

5.2 kcals per minute were burned walking at 3.5 mph

5.2 x 180 minutes (3 hours) = 936 kcals

14.1 kcals per minute were burned running at 7.5 mph

14.1 x 60 minutes (1 hour) = 846 kcals

2.5 kcals per minute were burned standing

2.5 x 60 minutes (1 hour) = 150 kcals

1.5 kcals per minute were burned sitting

1.5 x 600 minutes (10 hours) = 900 kcals

We can now add all of these values to approximate Joe's total energy expenditure for that 24 hour period.

396 + 306 + 936 + 846 + 150 + 900 = 3,534 kcals

We can now say that Joe expended 3,534 kcals during this day. This would mean that Joe needs to consume this much in his diet to maintain his body weight. If he wanted to gain weight, he would have to eat more. If he wanted to lose weight, he would have to expend more energy with exercise and partially cut his food intake, but nothing drastic. Body weight issues will be discussed in another topic (Click on Body weight issues above to get to that link).

***Just to note, when doing a 24 hour activity record you do not need to add BMR to your total energy expenditure. BMR is already taken into account with the values that are given in the chart.***

If the 24 hour activity record is too tedious for you, then you can just estimate the amount of time you spend exercising each day and add this number to your BMR. This is not as accurate, but could be another way to estimate your caloric needs. So let's say that Joe runs for 1 hour at 7.5 mph and sleeps for 7 hours. He has used only 8 hours of the day, but this is probably the activities that will cost the most energy.

1.1 kcals per minute burned sleeping

1.1 kcals x 420 minutes (7 hours) = 462 kcals

14.1 kcals per minute burned running at 7.5 mph

14.1 kcals x 60 minutes (1 hour) = 846 kcals

Rough Approximation of Energy Expenditure for this particular day would be:

462 + 846 + 1,695 kcals = 3,003 kcals

***Remember, this is a rough approximation. The values in the chart already take BMR into account, but if you didn't want to record all of your activities in one day, this could be another way to guesstimate your energy expenditure. This is what Joe should consume as a minimum caloric intake. His energy expenditure would be higher since we have not accounted for all the time he spends walking, sitting, standing, studying, etc. This is not a technically correct way to measure energy expenditure, but it could give a ballpark figure of what you might be looking for.***

Body Composition

% Body Weight from Specific Tissues

Male Female

Muscle 45% 36%

Bone 15% 12%

Total Fat
Essential Fat (women need more)
Storage Fat
15%
3%
12%
27%
12% (mainly for reproduction)
15%

Other Tissues 25% 25%

Total 100% 100%

Things that can affect these ratios:

1. Fitness Level and Exercise --usually leads to more lean body mass, which would increase BMR and Energy Expenditure

2. Genetics --your body size and composition may be predetermined by your genes

3. Age --the younger you are, the more lean body mass

4. Diet --less fat leads to less body fat

5. Gender --males, on the average, usually have less body fat

The Two Compartment Model

1. Body Fat Mass --approximately 10% is water

2. Body Fat Free Mass --approximately 70% water

--includes lean body mass and essential fat

***It is probably better to talk about body composition in terms of body fat mass and lean body mass (muscle)***

There are various ways to obtain a measure of your body composition, but most of these tests are inaccurate. They include:

1. Underwater Weighing --Gold Standard for measuring body composition

need very expensive equipment to perform these measurements
not easily accessible and can be very expensive
the subject is submerged in a tank of water and is asked to expel all the air out of their lungs; they are seated on a scale in the tank that records their weight under water; based on Archimede's Principle that the volume of an object can be determined by measuring its loss of weight in water

Factors affecting Buoyancy

Air in the lungs --this is why the subject is asked to expel as much air from their lungs as possible; can be frightening for some people so this might not be the test of choice; the more air in the lungs, the lighter the subject will weigh; ways to get around this would be to measure residual volume, but this can be difficult when in the water
G.I. Gas --once again, more air will make the subject weigh less
Hydration Status --muscle holds more water in the body than fat, so if the person was muscular and dehydrated, they would have a lower body weight; this could impact on the measurement

***The error of underwater weighing is about 2-2.5%. As previously stated, underwater weighing is the Gold Standard for determining body composition.
However, the equipment is very large and the technique is expensive so it may be difficult to obtain this type of measurement.***

2. Skinfold Measurements

measures the subcutaneous fat folds around the triceps, waist, thigh, back, and other areas of the body
there are assumptions that we are making when we take skinfold measurements:

Subcutaneous fat is supposed to be even dispersed throughout the body, even though you are taking the measurement in only one area
Skin may be droopy, as in older individuals so this could affect the % of body fat present
You are estimating total body fat by measuring only a few parts of the body

the accuracy of the test depends upon:

The technician; must make sure that you are using the same landmarks everytime
There are various calipers out there; make sure you are consistent using the same pair
There are various equations that you plug your values into; this adds to the error of skinfold measurements

***The error of the skinfold test is usually around 3-3.5%, but it could be as high as 5% depending on the various factors that were previously mentioned.***

3. Bioelectrical Impedence

this is a very simple, non-invasive technique
uses electrical conductivity to estimate fat-free mass; muscle holds the majority of water in the body so the more muscle the better the conduction
since you are also measuring the amount of water in the body, this test can be dependent upon hydration status; if you are dehydrated, you will probably come up with a higher % of body fat
the error of the bioelectrical impedence is also around the same as the skinfold test

4. Infrared Interactance

uses fiberoptic probe to measure the subcutaneous fat and muscle (usually done at the biceps)
validity is questionable: technique is relatively new

5. MRI/CT Scan

allows visualization of specific body areas, but is an extremely expensive technique with costly machinery
has not been proven to be any better than underwater weighing
shows deep fat with the correlation to the bone; shows great images

Body Fat Ranges for Individuals:

Males Females

Exceptionally Lean 6-10% 10-15% (Lower you go, more chance of amenorrhea)

Very Lean 11-14% 16-19%

Lean 15-18% 20-25%

Moderate 19-24% 26-29%

Overfat 25%+ 30%+

***One must individualize the body fat range for themself. Body fats can be dependent upon which sport, body type, and health issues that each and every person must deal with. These are just a range and there is no exact body fat % for anyone, or any particular athlete. This is very important to remember. A too low body fat may actually hinder performance, just as a too high body fat can do the same. Find what is best for you and work from there. Never compare yourself to others, for we each have our own body type and genetics.***

***Just to note, all three of these topics are going to vary with each individual. BMR is going to vary with age, body composition, and exercise. Energy expenditure is also going to vary on a daily basis. It is good to measure a training day and a rest day to see the differences. You want to check and make sure that you are in energy balance every day, if possible. Body composition is going to vary by the type of diet one eats, exercise activity, and genetics. The thing to remember is to individualize your data to you, don't compare it to anyone else. Just stick to what you have to do to perform your best.***

	Male	Female
Muscle	45%	36%
Bone	15%	12%
Total Fat Essential Fat (women need more) Storage Fat	15% 3% 12%	27% 12% (mainly for reproduction) 15%
Other Tissues	25%	25%
Total	100%	100%

	Males	Females
Exceptionally Lean	6-10%	10-15% (Lower you go, more chance of amenorrhea)
Very Lean	11-14%	16-19%
Lean	15-18%	20-25%
Moderate	19-24%	26-29%
Overfat	25%+	30%+