The Harris-Benedict Equation

How does the Harris-Benedict equation relate to bulking up?

In 1918, two biochemists named J. Arthur Harris and Francis G. Benedict published a paper entitled, “A Biometric Study of Human Basal Metabolism“. It is archived on the web here.

Basal metabolic rate measures the number of calories burned daily as your body attends to its autonomic functions

In this paper, Harris and Benedict developed a formula that you can use to estimate your basal metabolic rate (BMR). BMR is a measure of the number of calories your body burns each day as it attends to its autonomic functions including circulation and breathing. It does not include the energy used to digest food. Basically, your BMR is the number of calories you would burn each day if you were in a coma and not digesting food.

As you begin to design a bulking diet, the major question you need to answer is how much food you should consume. Each day, in addition to your basal metabolic rate, you burn calories to fuel the process of digestion and to complete your daily activities including weight lifting.

As a skinny guy, you can't gain muscle mass unless you gain body weight

The US government sponsors research that determines the calories used during various sports and activities. So we can estimate, with a fair degree of reliability, how many calories we burn as we lift weights and go about our daily lives. Here is a partial list of activities and their associated caloric costs.

As for digestion, scientists estimate that 10% of our total caloric maintenance level is used during digestion.

That leaves us with the basal metabolic rate. Unfortunately, it is difficult to estimate your BMR with any degree of reliability. Absent a whole-body calorimeter and a few days during which your BMR is measured, you can’t get an accurate number to use when you design your bulking diet.

This is where the Harris-Benedict equation comes in.

In their paper, Harris and Benedict show how to estimate the basal metabolic rate by plugging your height and weight into a simple equation. After calculating your estimated BMR, you multiply it by a factor that varies based on the amount of exercise or activity you engage in. This factor varies from a low of 1.2 to a high of 1.9 times your BMR, depending on how much exercise you get.

In this way, you can estimate how many daily calories you need to maintain your weight. When it comes time to bulk up, simply eat more calories than the Harris-Benedict formula calls for, and you should be good to go.

How do I apply the Harris-Benedict formula to my own personal circumstance?

By way of example, let’s assume you are a 155 pound man who stands 5 foot 10 inches in height at 25 years of age (70kg and 1.8m).

Here is the Harris-Benedict formula for calculating BMR:

(6.23 x weight in pounds) – (6.8 x age in years) + (12.7 x height in inches) = BMR

Plug in the numbers like this:

(6.23 x 155) – (6.8 x 25) + (12.7 x 70) = 965 – 170 + 889 = 1648 calories per day

Then, determine the amount of exercise you engage in. A typical skinny guy trying to bulk up on a 3-day per week bulking program would fall into the “moderate exercise” category.

Multiply your BMR by the factor of 1.55 from the chart below:

1648 x 1.55 = 2610 calories per day

Amount of exercise Daily Caloric Requirement
Sedentary BMR x 1.2
Very Light Exercise BMR x 1.375
Moderate Exercise BMR x 1.55
Heavy Exercise Daily BMR x 1.725
Extremely Heavy Exercise BMR x 1.9

 

So, according to the Harris-Benedict equation, our 25-year old, 5 foot 10 inch, 155-pounder needs 2610 calories every day simply to maintain his body weight while lifting weights three days a week.

To gain a pound per week, our lifter needs an extra 3500 calories per week (or 500 per day) above his maintenance level. Therefore, he needs:

2610 + 500 = 3110 calories per day

This is the estimated number of daily calories that our example subject should consume each day while on a lifting program; theoretically, he will gain a pound per week while consuming his 3110 calories per day and using a thrice-weekly weight lifting program consisting of heavy, compound lifts.

Once you estimate the number of calories you need while bulking up, try to shoot for that amount as you design your bulking diet. Coupled with accurate record keeping, this estimate will give you the information you need to adjust your diet up or down until you are consistently gaining a pound of body weight every week.

What does the Harris-Benedict formula mean for me?

How reliable is the Harris-Benedict formula? Obviously, no BMR equation can be one size fits all. Your maintenance level of calories will be different than that estimated by the Harris-Benedict formula if you are overweight, or if you are severely underweight. Additionally, if you are exceptionally short or tall for your weight, the formula will return incorrect results. Finally, if you are a woman, the constants in the formula are different (because of increased body fat).1

Lift weights while you are on a bulking diet

That is why it is so important to keep accurate records of your diet and exercise. Only with detailed data about your personal circumstance will you be able to achieve optimal results.

Equations like the one detailed in this article can give you a starting point for your bulking strategy, but ultimately it comes down to diligent record keeping and timely adjustments to your plan. Success or failure rests on your willingness to take the steps necessary to reach your goal.

1) For women, the Harris-Benedict forumla is: 655 + (4.35 x weight in pounds) + (4.7 x height in inches) – (4.7 x age in years)

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