Posted on 13 March, 2017

What is Basal Metabolic Rate and How do I Work it Out?

By Jacob Andreae in Health, Nutrition, Fitness What is Basal Metabolic Rate and How do I Work it Out?

[Image source: bodybuilding.com]

The human body requires a huge amount of energy just to function. Breathing, blinking and beating your heart requires a significant amount of energy. Just staying alive takes a lot of work. The energy your body requires to simply function is called your basal metabolic rate, and it’s different for everyone.

How to Work out BMR (Metric)

My basal metabolic rate (BMR) is 1,663. This means that I will burn 1,663 calories (6,961 kilojoules) each day if I engage in no activity for the entire day. To work out your BMR, follow this formula. 

This is called the Mifflin St. Jeor Equation:

Women: BMR = (10 x weight in kg) + (6.25 x height in cm) — (5 x age in years) — 161

Men: BMR = (10 x weight in kg) + (6.25 x height in cm) — (5 x age in years) + 5

To convert this value from calories to kilojoules, multiply your answer by 4.184.

Keep in mind, the body is a sophisticated organism. While this formula takes into account weight, height, age and some seemingly random numbers, it is not exact. It does do a pretty good job though and is a good place to start if you want to measure your energy expenditure in and out.

Knowing your BMR is important because it gives you a clear idea of what foods you should be eating and how much if your goal is to lose weight, maintain your weight, or put weight on. It is also very valuable for athletes, especially in relation to endurance sports.

Knowing how to calculate your BMR and the factors that influence it help you with better understanding its limitations, as well as how to interpret it. Stress, illness and changes in physical activity influence BMR. A formula is all well and good but the most accurate way to measure BMR is in a lab. You are required to fast for 12 hours and get a full nights sleep, before a specialist measures your breathing and heart rate using sophisticated instruments.

An Explanation of the Emphasis on Weight, Height, Age & Gender

Weight and Height
The bigger you are and the more mass you carry, the harder your body has to work to function. When you lose weight, your BMR will decrease. This is why you often hear people say they can’t eat as much when they lose weight. Not changing how much you eat to meet your reduced daily needs can also be a reason why people put weight back on.

Age
As you get older, you naturally lose muscle mass — about 10% every decade after the age of 30. The good news is, you can reduce this by engaging in regular strength training. Less muscle means a lower BMR. This is what is meant when you hear people say that increasing your muscle mass increases your metabolism.

Gender
The male body is typically different to the female body. Males have higher levels of muscle mass, bone density and lower levels of fat. These differences are accounted for in calculating BMR but as we know, while these differences are typical, they are not always the case.

Basal metabolic rate is the minimum amount of energy required to keep you alive. There are several ways to work out your basal metabolic rate. For accessibility, simplicity and accuracy, the formula I recommend is the Mifflin St. Jeor Equation.

Using the Mifflin St. Jeor equation above, what is your BMR?

About Jacob Andreae

About Jacob Andreae

I write and speak about Fitness, Nutrition and Mindset. 

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What is Basal Metabolic Rate and How do I Work it Out?A quick start guide to losing weight and staying on track. Learn the strategies I use to eat and move for optimal health. Includes worksheets to enhance your motivation, commitment and discipline, along with a sample eating plan and exercise program.