How to Calculate your Basal Metabolic Rate

As previously discussed earlier within this section of our webiste, an individual's Basal Metabolic Rate (BMR) is the minimum number of calories required to sustain their life in a state of rest. In other words, an individual's Basal Metabolic Rate is the amount of energy (measured in calories) required by their body to perform all of its bodily functions while remaining asleep in bed all day.

The first step for any individual who has a fitness goal to lose or gain weight is to determine the total number of calories that their body burns per day. More specifically, an individual’s BMR value is the total number of calories their body requires for all normal bodily functions (excluding all activity factors).

Such bodily functions include keeping the heart beating, inhaling and exhaling air, digesting food, making new blood cells, maintaining body temperature and every other metabolic process that occurs within the body. An individual's BMR can account for burning as much as 70% of the total calories expended. While the BMR of an individual is the total number of calories that an individual burns while at rest over a 24-hour period, the total daily energy expenditure (TDEE) value takes into account their BMR value plus all of their physical activities as well.

An individual's TDEE level can be considered their personal maintenance level. By knowing the number of calories your body burns on a typical day, you can then design a weight loss program that is centered around your specific TDEE value. According to research conducted by exercise physiologists William McArdle and Frank Katch, the average maintenance level for women in the United States is 2,000-2,100 calories per day, and the average for men is 2,700-2,900 per day. Please note that these figures are only averages and can vary greatly. For example, there are triathletes that require a diet consisting of 6,000 or more calories per day just to maintain their current weight level.

There are several methods an individual can use to determine their TDEE value. These methods typically include factors such as age, sex, height, weight, lean body mass and activity level. The most accurate methods include taking into account an individual’s lean body mass. This article will discuss two of the most accurate methods that an individual can use to determine their specific TDEE value.

The first method discussed will be the Harris-Benedict formula, which is based on total body weight. In addition, the Harris-Benedict formula utilizes factors such as height, weight, age and sex to determine an individual's BMR. Once an individual's BMR level has been determined, it will then be necessary to calculate their specific TDEE value. This will be accomplished by multiplying their BMR value by their specific activity multiplier. It should be noted that the Harris-Benedict formula does not include an individual’s lean body mass. Because of this, the Harris-Benedict approach will be very accurate for all but the extremely muscular (will underestimate caloric needs) and the extremely overweight (will overestimate caloric needs).

The second method is the Katch-McArdle formula, based on an individual’s lean body mass. This approach can be taken by individuals that have had their body composition tested and know their lean body mass. This approach is more accurate than the Harris-Benedict approach since the Harris-Benedict approach is based on total body weight.

The Harris-Benedict Formula (BMR based on total body weight)

The Harris-Benedict formula utilizes separate equations for men and women. This is due to the fact that men generally have a higher level of lean body mass (LBM) than women, and this phenomenon is accounted for in the men's equation. Since the Katch-McArdle formula accounts for LBM, a single equation applies to both men and women.

• Women BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years)

• Men BMR = 66 + (6.23 x weight in pounds) + (12.7 x height in inches) - (6.8 x age in year)

• Women BMR = 655 + (9.6 x weight in kilos) + (1.8 x height in cm) - (4.7 x age in years)

• Men BMR = 66 + (13.7 x weight in kilos) + (5 x height in cm) - (6.8 x age in years)

Note: 1 inch = 2.54 cm., 1 kilogram = 2.2 lbs.

BMR Example

Subject: Female, 30 years of age, 5' 6" tall (167.6 cm), 120 pounds (54.5 kilos)

BMR Formula (Standard English)

Women BMR = 655 + (4.35 x weight in pounds) + (4.7 x height in inches) - (4.7 x age in years)

Calculated BMR: 655 + 522 + 310 - 141 = 1,346 calories/day

BMR Formula (Metric)

Women BMR = 655 + (9.6 x weight in kilos) + (1.8 x height in cm) - (4.7 x age in years)

Calculated BMR: 655 + 523 + 302 - 141 = 1,339 calories/day

NOTE: Although the standard English and Metric calculations yield a slightly different result, it is not statistically significant.

Calculate Your TDEE value

Now that you have calculated your BMR using the Harris-Benedict approach, it is time to calculate your TDEE value. To do this, simply multiply your BMR value by your activity multiplier from the chart below:

Activity Multiplier

• Sedentary = BMR X 1.2 (little or no exercise, desk job)

• Lightly Active = BMR X 1.375 (light exercise/sports 1-3 days/wk)

• Moderately Active = BMR X 1.55 (moderate exercise/sports 3-5 days/wk)

• Very Active = BMR X 1.725 (hard exercise/sports 6-7 days/wk)

• Extremely Active = BMR X 1.9 (hard daily exercise/sports & physical job or 2X day training, etc.)

Our female subject's BMR (Metric) is 1,339 calories/day. Activity level is moderately active (work out 3-4 times per week), so her activity factor is 1.55.

TDEE: 1.55 X 1,339 = 2,075 calories/day (the average number of calories she burns/day)

Katch-McArdle Formula (BMR based on lean body weight)

BMR (Men and Women) = 370 + (21.6 X lean mass in kg)

Katch-McArdle Example:

Subject: Female, weighs 120 lbs. (54.5 kilos), body fat percentage is 20% (24 lbs. fat, 96 lbs. lean), lean body mass is 96 lbs. (43.6 kilos)

Calculated BMR: 370 + (21.6 X 43.6) = 1,312 calories/day

Now that you have calculated your BMR using the Katch-McArdle approach, it is time can calculate your TDEE value. To determine your TDEE from your BMR, simply multiply your BMR by your appropriate activity multiplier.

Our Female Subject's BMR is 1,312 calories/day, activity level is moderately active (work out 3-4 times per week), so her activity factor is 1.55.

TDEE: 1.55 X 1312 = 2,033 calories/day

As is evident from the previous example, the difference in the TDEE values derived from both formulas is statistically insignificant (2,075 calories vs. 2,033 calories). This is due to the fact that the female used in the example was of average body size and composition. The primary benefit realized from factoring lean body mass into the equation is an increased level of accuracy when the individual's body composition is skewed towards either end of the spectrum (very muscular or very obese).

Adjust Your Caloric Intake According to your Personal Fitness Goal

Once an individual has calculated their specific TDEE value, the next step is to adjust their daily caloric intake to facilitate the achievement of their weight loss goal. The mathematics associated with caloric balance are quite simple. For an individual to maintain their current weight level, they should match the number of calories consumed to the number of calories they burn. To lose weight, an individual will need to consume fewer calories than their body burns in a typical day (or leave their daily caloric intake constant while increasing their physical activity level). To gain weight, an individual will need to increase their caloric intake to a level that is greater than the number of calories they burn on a daily basis.

Negative Calorie Balance is Essential to Losing Body Fat

Caloric intake vs. caloric expenditure is the bottom line when it comes to effective weight loss. For example, if an individual is consuming more calories per day than they are burning per day, they will simply not lose any excess body weight, no matter what type of foods or food combinations they consume.

While it is true that certain foods are more readily stored as fat than others, it is important to remember that even healthy food will be stored as fat if the total number of calories consumed is greater that the TDEE value. Simply put, the human body must obey the laws of thermodynamics and energy balance. The human body must be at a caloric deficit to burn fat.

Once the human body is at a caloric deficit, the body will be forced to utilize stored body fat to make up for the energy deficit. Each pound of body weight consists of 3,500 calories. If an individual creates a 3,500-calorie deficit over a 7-day period through food consumption, physical exercise or a combination of both (recommended approach), they will lose one pound of body weight. Likewise, if that same individual creates a 7,000-calorie deficit over a 7-day period, they will lose two pounds of body weight.

Daily Calorie Deficit Guidelines

It's universally accepted that severely decreasing an individual’s caloric intake can lower their basal metabolic rate, decrease their thyroid output, and cause the loss of lean muscle mass. The most medically-approved guideline for decreasing an individual’s caloric intake is to reduce their calories by at least 500 per day, but no more than 1,000 per day below their TDEE value. As a lower ceiling for the minimum number of calories an individual should consume on a daily basis, the American College of Sports Medicine (ACSM) recommends that caloric intake levels never drop below 1,200 calories per day for women or 1,800 per day for men.

Another approved approach would be for an individual to reduce their caloric intake to a level that is 15% to 20% below their personal TDEE value. Although in some instances a larger caloric intake reduction may be necessary, the best approach is to maintain a safe caloric intake deficit and implement a physical fitness routine at the same time. The following examples depict how an individual could safely determine the number of calories they could eliminate from their daily caloric intake.

Example #1

• Female subject weighs 120 pounds

• TDEE is 2,033 calories/day

• Daily caloric deficit to support losing 1 pound of weight per week is 500 calories

Her optimal daily caloric intake to obtain her weight loss goal (losing 1 pound per week) is = 2,033 - 500 = 1,533 calories/day

Example #2

• Our subject's daily caloric deficit required to promote weight loss based on a 20% reduction of her TDEE is: (.20 X 2,033 = 406 calories/day)

Her optimal daily caloric intake to support her weight loss goal is = 2,033 - 406 = 1,627 calories/day

Determine Ideal Body Weight

Now that you have determined the total number of calories that your body burns in a given day, it is time to determine your ideal body weight. There are several methods that can be used to determine your optimum weight. Each of the techniques used for determining your optimum weight are thoroughly discussed within this section of our website.

Once you have determined your ideal weight, you will be able to define your personal health, fitness and weight loss goals. Once complete, it will be time to define the specific approach that you are going to take to achieve your personal fitness goals. For example, your personal fitness goal may be to lose 20 pounds in 12 weeks.

To begin, you will want to first, define a fitness routine and a dietary approach that will facilitate the achievement of your personal weight loss and fitness goals. Thereafter, as you embark on your path towards the obtainment of your personal fitness goals, you will want to monitor your progress to ensure that you are on schedule to achieve your fitness goal within your defined timeline.

We have specifically included articles that are designed to provide you with all of the information needed for you to put together a thorough health and fitness routine. The articles are designed to facilitate your specific fitness goals in not only a timely manner, but with a safe and medically approved approach.