How your resting metabolic rate impacts your body composition


April 13, 2017

When assessing body composition goals, most people are looking to gain muscle or lose fat. More often than not, they want to do both at the same time. The starting point for either of these body composition goals involves estimating total calorie (kcal) intake needs.

Simply put, when your calorie intake (what you eat) is greater than your calorie expenditure (what you burn), you gain scale weight. The same is true for scale weight loss: calorie intake is less than calorie expenditure. Maintenance occurs when the two are equal.

However, even though lots of people discuss weight loss in terms of scale weight, it is much more appropriate to look at weight loss from a body composition perspective. Yes, you may wish to lose weight but more specifically you are trying to lose body fat while gaining/maintaining muscle.

Unfortunately, since most scales cannot differentiate between lean mass and fat mass, total calorie intake will not necessarily be best judged by looking at scale weight alone.

The total number of calories a person needs each day depends on a number of different factors including age, body weight, activity level, gender, diet, training program, body composition, and genetics. Before we can determine the energy (calorie) needs of an individual we must first look at these factors, which determine a person’s ability to use the calories ingested.

What is Basal Metabolic Rate?

Basal metabolic rate (BMR) is the energy requirement to maintain the body's basic functions such as respiration, blood circulation, and gastrointestinal and renal processing when the body is in a resting state.

BMR is the largest contributor to an individual’s total energy expenditure; accounting for approximately 65 to 70% of daily caloric burn. 1,2,3.

What is the difference between Basal Metabolic Rate and Resting Metabolic Rate?

Although often used interchangeably BMR & RMR (resting metabolic rate) are slightly different. BMR is measured after an overnight fast. More precisely, this means 12 to 14 hours laying down completely motionless flat on your back, without any food – not the most pleasant experiment.

RMR on the other hand does not require a fasting period, so due to its ease of use compared to BMR testing, it has become the more common approach for taking measurements.

Since you are more active during an RMR measurement compared to the completely motionless state required for a BMR measurement, RMR is higher than BMR on average by about 10 to 20%.

Factors influencing RMR

Body compostion

Your ratio of fat and lean body mass. Even at rest, a muscle cell is metabolically much more active than a fat cell. Variations in fat-free mass, explain approximately 70 to 80% of the difference in RMR among individuals. 4, 5, 6.


Younger people tend to have a higher metabolic rate than older people, largely because of their higher lean body mass and more active hormonal processes.


Poor nutritional strategies such as following generic ‘fad' diets. eating too little, eating nutrient deficient foods, or being malnourished lowers your metabolic rate.

Endocrine function

Insulin efficiency, cortisol secretion and other hormonal deviations such as hypo or hyperthyroidism can influence your metabolic rate.

Environmental factors

Temperature or altitude change can play a role in the metabolic rate of an individual. Increased heat, cold or altitude forces the body to work harder to regulate and maintain homeostasis, therefore increasing RMR.


A number of genes play a role in an individual’s metabolic rate. Here at FitnessGenes, we focus on guiding you in the right direction when it comes to training and nutrition strategies to help increase the largest components of total energy expenditure – increasing overall lean muscle mass and genetically optimizing nutritional and workout choices.

The secret to increasing your overall daily energy requirements

The more energy expended through physical activity, the higher the energy requirements to fuel the workout. In other words, the harder the workout, the more calories you burn.

Out of all the factors mentioned above, this is one that has the most variability among individuals. The number of calories you expend through physical activity increases with the frequency, intensity, and duration of the training program, not to mention the extra activities you do on a daily basis such as walking the dog, cleaning the house, etc. In general, approximately 20 to 30% of total daily energy expenditure is from physical activity.

* A rise in physical activity levels will result in this section having a greater influence on total energy expenditure.

Activities that are anaerobic in nature such as strength training and HIIT are proven to enhance lean muscle tissue growth and promote sustained increases in RMR/BMR, which is why they are the cornerstones of the FitnessGenes exercise recommendations.

Aerobic physical activity such as steady state running or cycling may improve endurance capabilities but have little effect on the basal or resting metabolic rate. The increase in resting metabolic rate from an aerobic activity is rather short lived and usually decreases during the cool down period of an aerobic session.

If you are looking for an exercise and nutrition program that can help increase your overall energy expenditure and optimizes your lean muscle building potential, then I recommend having a look at our genetically tailored workout programs.

Calculating RMR

Many different predictive equations can be used to estimate BMR or RMR calorie needs, with the most common being the Harris-Benedict equation, the Cunningham, and the Schofield equations, all of which take into account the sex, body weight, height and age of the individual.

Once RMR has been predicted this figure is then multiplied by the equations associated activity factor ranging from 1.2 (sedentary) to 1.9 (heavy physical activity) to predict total energy requirements. 1.

Alternatively, one of the best ways to accurately calculate your total daily caloric needs is to record your dietary intake for a week, during a period when you will maintain a stable body weight.

Your energy requirement is then assumed to equal the average number of calories consumed for each day. One of the downfalls of this approach, however, is that most people do not always accurately monitor their food intake, so using a fitness tracking app or simple food diary can be very helpful. Monitoring your calorie intake, and weight gain/weight loss can help you get a much better view of your energy requirements.

At FitnessGenes we take into account a host of genetic and lifestyle factors to give you an intelligent approximation of calorie requirements. We consider your current activity level and/or genetic training program intensity, fitness experience, sex, body weight, height and age to help gauge an approximate maintenance calorie intake. Our Nutrition Calculator can then be manually adjusted based on changes in body composition.

We then use your genetic results to determine the ratio of macronutrients required to help you achieve your body composition goals in a sustainable manner.

Take home points on RMR

1) Track the amount of food and drink you are consuming to become more mindful of your current calorie intake and whether it is altering your body aesthetically.

2) Increasing your energy expenditure with exercise will not only increase the number of calories burned during the exercise, but will also increase lean muscle mass and therefore RMR.

3) If you find yourself stalling with fat loss in particular, consider taking a look at all the variables in your life that could be contributing to a lower RMR score. Being stressed at work, not getting enough sleep, eating a nutrient-deficient diet, and not partaking in enough physically demanding activity could be the reason for this weight loss plateau.


  1. Haff, G.G. and Triplett, N.T. eds., 2015. Essentials of Strength Training and Conditioning 4th Edition. Human kinetics.
  1. Jequier, E. and Schutz, Y., 1983. Long-term measurements of energy expenditure in humans using a respiration chamber. The American journal of clinical nutrition, 38(6), pp.989-998
  1. Ravussin, E., Burnand, B., Schutz, Y. and Jequier, E., 1982. Twenty-four-hour energy expenditure and resting metabolic rate in obese, moderately obese, and control subjects. The American Journal of Clinical Nutrition, 35(3), pp.566-573.
  1. Zello, G.A., 2006. Dietary Reference Intakes for the macronutrients and energy: considerations for physical activity. Applied Physiology, Nutrition, and Metabolism, 31(1), pp.74-79.
  1. Nelson, K.M., Weinsier, R.L., Long, C.L. and Schutz, Y., 1992. Prediction of resting energy expenditure from fat-free mass and fat mass. The American journal of clinical nutrition, 56(5), pp.848-856.
  1. Ravussin, E., Lillioja, S., Anderson, T.E., Christin, L. and Bogardus, C., 1986. Determinants of 24-hour energy expenditure in man. Methods and results using a respiratory chamber. Journal of Clinical Investigation, 78(6), p.1568.
  1. A. DeFronzo, "Pathogenesis of type 2 diabetes: metabolic and molecular implications for identifying diabetes genes," Diabetes Reviews, vol. 5, no. 3, pp. 177–269, 1997.

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