Nutritionists commonly refer to Basal Metabolic Rate (BMR) when they try to explain to a client how to lose or gain weight. But rarely do they explain what it actually means and why it plays a key role in weight management.

Energy balance to achieve stable weight

As you may know, to achieve a stable weight, it is vital to balance out the energy you consume in form of food and the energy you need for all your daily activities or your total energy expenditure. The total energy you will need during a day consist of energy needed for growth and tissue repair, physical activity, energy needed for digestion and metabolism of foods and the basal metabolic rate.

An adult with rather low activity levels uses roughly 60% energy for BMR, 10% for digestion and metabolism of foods and roughly 30% for physical activity. The energy needed for tissue repair and growth is negligible in adults but contributes significantly to the total energy expenditure of children.

You may have realised that the BMR is the largest contribution to total energy expenditure. BMR is understood as the energy expenditure. BMR is understood as the energy your body needs without doing any mental or physical work. This is why there are qute strict rules applied when the BMR of a person is measured.

Measuring BMR

People who would wish to get their BMR measured would need to be at total rest, lying and awake, ideally just woken up, they should have not eaten or drunk for about 10 hours and the temperature of the room where the measurement is taken should be within the range of body temperature. All these considerations must be taken to avoid the use of additional energy of the body.

But how will energy expenditure be measured? Several methods have been developed and one of the oldest and still most  commonly used methods the amount of oxygen expelled by a person within a certain time. This is based on observations which showed exhaling 1 litre of oxygen averages 20kJ (4.78kcal).

Measuring BMR is quite time consuming and a lot of specialist equipment is needed and mathematical methods were developed based on BMR measurements of thousands of people. To measure BMR, there are various factors taken into consideration and are commonly observed within the research. So for example the BMR is influenced by gender, lean body tissue (or how much muscle you have in relation to fat), age, genes and ethnicity. This means for instance, men usually need more energy than women of the same age and weight for BMR or people of the same gender, weight and age who are well-trained usually have higher energy needs than those who are less well-trained of the same gender, weight, age and so on.  

Calculating BMR

The most commonly used equations to calculate BMR is called Schofield equations. Here an extract of these 12 equations.

BMR equation per day for males aged 18-30 years:

(0.063 x current weight in kg +2.896) = BMR in MJ x1000 = BMR in kJ: 4.184 kJ = BMR in kcal

Example calculation

 [(0.063 x 80kg +2.896) = 7.936MJ x 1000 = 7936 kJ : 4.184 kJ = 1896.75kcal per day]

BMR equation per day for males aged 30-60 years:

(0.048 x current weight in kg +3.653) = BMR in MJ x1000 = BMR in kJ: 4.184 kJ = BMR in kcal

BMR equation per day for females aged 18-30 years:

(0.062 x current weight in kg + 2.036) = BMR in MJ x1000 = BMR in kJ: 4.184 kJ = BMR in kcal

BMR equation per day for females aged 30-60 years:

(0.034 x current weight in kg + 3.538) = BMR in MJ x1000 = BMR in kJ: 4.184 kJ = BMR in kcal

Although the Schofield equations are used frequently they have their limitations, so they are for example not as reliable for people with unusually high or low Body Mass Indexes (people who are severely under or overweight), for people of ethnic minorities, very old people and very young children are also people who are ill or under permanent medications as both has been shown to influence BMR.

Why all that fuss about BMR?

The basal metabolic rate is the largest contributor to your overall energy needs and will also determine how much energy you will be using during every activity in a day. It might be compared with the efficacy of petrol used in your car. (If your car needs 2 litre per 100 kilometres on a flat street that will consequently influence how much it will consequently influence how much it will need going up a hill). The only health possible way to influence your BMR towards higher energy needs is to exercise regularly as this will influence your lean body tissue and should increase your overall BMR.     
If you would like to read more about these topics a good introductory book is:

“Introduction to Nutrition and Metabolism” from David A. Bender 4th edition (2008)

Other materials which were used for this article are:

Binnert,C., Schneiter, P. and L. Tappy (2003) energy expenditure, physical activity and body weight control, Proceedings of the Nutrition Society, 62, 663 – 666

Black, A.E., Henry, C.J.K., Prentice, A.M. and P.S. Shetty (1996) Energy requirements of adults: an update on basal metabolic rates (BMRs) and physical activity levels (PALs), European Journal of clinical Nutrition, 50, Suppl. 1, 11-23

Calderon, L., Chang, L.C., Davies, R., Martinez, E., Tam, C.F., Tsai, S. and Yeh, I. (1996) A comparison of dietary  artherogenicities, energy balance and physical activity levels of male and female college students, Nutrition Research, 16, 1861-1880.

Camblor, M., Cuerda, C. Breton, I., Garcia-Peris, P., Ruiz, A and C. Velasco (2007) How accurate are predictive formulas calculating energy expenditure in adolescent patients with anorexia nervosa?, Clinical Nutrition, 26, 100-106.

Durnin, J.V.G.A. and R. Passmore (1967) Energy, Work and Leisure, London: Heinemann Educational Books Ltd

Garrow, J.S., James, W.P.T. and A. Ralph (2000) Human Nutrition and Dietetics, 10th edition, London: Churchill Livingstone

Geissler, C. and H. Powers (2005) Human Nutrition, 11th edition, London: Elsevier Limited

Gibson, R.S. (2005) Principles of nutritional assessment, 2nd edition, New York: Oxford University Press

Groff, J.L., Gropper, S.S. and S. M. Hunt (1995) Advanced Nutrition and Metabolism, USA: West Publishing

Lanningham-Foster, L., Levine, J.A and L.J, Nysse (2003) Labor saved, Calories lost: The energetic impact of domestic labour saving devices, Obesity Research, 11, 1178-1181.

Henry, C.J.K. (2005) Basal metabolic rate studies in humans: measurement and development of new equations, Public Health Nutrition, 8(7A), 1133–1152

Levine, J.A. (2005) Measurement of energy expenditure, Public Health Nutrition, 8, 1123-1132

Schofield (1985) Energy and Protein Requirements, A report of a joint FAO/WHO/UNU Expert Consultation, Report No. 724, WHO: Geneva

Mann J. and S. Truswell (2002) Essentials of Human Nutrition, 2nd edition, Oxford: Oxford University Press