Understanding energy expenditure for better sport goal achievement!
Whether you do sports to keep fit, to lose weight or to improve your performances, energy expenditure is often discussed, but do we know what it really means?
Let's go back to basics!
▶ The helpful tools:
- Connected body fat scale to assess your body composition
- Tips by Aptonia nutritionist
- Training watch to measure your calorie expenditure in real time
At any time of the day, the body uses energy to live.
Energy expenditure therefore varies throughout the day (physical activity, digestion, etc.), throughout life (child growth, pregnancy, etc.), and even at rest, it varies between individuals(3).
Indeed, energy expenditure depends on the body mass, the efficiency and the efficacy of movements, all of these making any comparison between individuals rather difficult (1).
It is estimated that daily energy expenditure results primarily from three major metabolisms:
- rest energy expenditure
- exercise energy expenditure
- digestive energy expenditure
Overall distribution of the daily energy expenditure
(McArdle & coll.(2) modified, 1996, p. 152)
Typically, energy expenditure measurements assess rest metabolism only.
Why? Simply because, unlike any expenditure due to exercise or digestion, rest energy expenditure barely varies.
Rest metabolism is divided into 3 sub-parts:
- basal metabolism (see below)
- wake metabolism: expenditures when the body is awake, but not active (e.g.,sitting position)
- sleep metabolism: expenditures of the body when you are asleep
Let's focus on the most essential: basal metabolism.
Specifically, basal metabolism is defined by the minimal quantity of energy needed to perform the vital body functions (DuBois definition, early 20th century).
It is therefore the basic minimum your body needs to survive.
Basal metabolism accounts for 45 to 10% of our daily expenditures(3) and is reduced by approximately 10% when we sleep (4). It is typically lower in women and decreases with age(2).
It is measured in a lying position, after at least 8 hours of sleep and 12 hours of fast(5). Now you understand why basal metabolism is only assessed following medical staff prescription…
However, it can be estimated using equations, some of them based on the age, weight, gender and height.
But please note that these equations only provide an indicative estimate and are difficult to generalize to the whole population(6).
Due to lack of reliable solutions, the World Health Organization and the Food and Agriculture Organization of the UNited Nations decided to keep using the 1985 Schofield equations that are adaptable to various age ranges(3) :
Basal metabolism (BM) estimating equation based on body weight (W).
|AGE/YEARS||BM : KCAL/DAY||AGE/YEARS||BM / KCAL/DAY|
|<3||59,512*W - 30,4||<3||58,317*W - 31,1|
|3-10||22,706*W + 504,3||3-10||20,315*W + 485,9|
|10-18||17,686*W + 658,2||10-18||13,384*W + 692,6|
|18-30||15,057*W + 692,2||18-30||14,818*W + 486,6|
|30-60||11,472*W + 873,1||30-60||8,126*W + 845,6|
|>60||11,711*W + 587,7||>60||9082*W + 658,5|
(Schofield (7) 1985, modifiied)
▶ Thanks to this table, you can get an estimation of the number of kilocalories (1 kcal = 1000 calories = 1 Cal) required by your body to ensure its basic functions over a day.
For example, if you are a 25 year-old woman who weighs 60kg, your basal metabolism will be:
14.818 * 60 + 486.6 = 1376 kcal/day
Let's have a look at the two following diagrams:
Weight distribution in % of the various organs weight in the total weight:
Distribution in % of the rest energy expenditure of various organs
We find that there is a significant difference between the weight of certain organs and the energy they use (8).
For example, the heart, kidneys, brains and liver alone use about 60% of the energy, while they only account for 5-6% of the total body weight(9).
On the other hand, the muscle mass and fat mass only use an average 21% of energy while they account for 51% of our total body weight!
▶ In brief: Whether you want to lose fat, gain muscle mass or reach a weight equilibrium, you need to act on about half of your body weight! Unfortunately, the muscles and fat only use very little energy at rest…
▶ The solution? Doing exercise and learning how to manage the energy intake-expenditure ratio by eating what you need to reach your goal:
- Weight/muscle mass gain: the energy intakes should be higher than the expenditures - but in a controlled manner to avoid boosting fat storage - and combined with appropriate exercise.
So: Energy expenditure < Food intake
- Fat/weight loss: the energy intake should be lower than the expenditures, also in a controlled manner to avoid losing muscle mass.
So: Energy expenditure > Food intake
- Weight maintenance or weight equilibrium: the energy intake should be equal to the expenditures
So: Energy expenditure = Food intake
Research and Development Engineer, Decathlon SportsLab
(1) SCHUTZ, Yves, WEINSIER, Roland L., et HUNTER, Gary R. Assessment of free‐living physical activity in humans: an overview of currently available and proposed new measures. Obesity Research, 2001, vol. 9, no 6, p. 368-379.
(2) MCARDLE, William D., KATCH, Frank I., et KATCH, Victor L. Exercise physiology: nutrition, energy, and human performance. Lippincott Williams & Wilkins, 1996.
(3) UNITED NATIONS UNIVERSITY et WORLD HEALTH ORGANIZATION.Human Energy Requirements: Report of a Joint FAO/WHO/UNU Expert Consultation: Rome, 17-24 October 2001. Food & Agriculture Org., 2004.
(4) PASSMORE, R. et DURNIN, J. V. G. A. Human energy expenditure. Physiol Rev, 1955, vol. 35, no 4, p. 801-840.
(5) MCNAB, Brian K. On the utility of uniformity in the definition of basal rate of metabolism. Physiological and Biochemical Zoology, 1997, vol. 70, no 6, p. 718-720.
(6) Indeed, for most of the formulas given, studies have shown low accuracy in certain ethnic groups and types of populations.
Source : HENRY, C. J. K. Basal metabolic rate studies in humans: measurement and development of new equations. Public health nutrition, 2005, vol. 8, no 7a, p. 1133-1152.
(7) SCHOFIELD, W. N., SCHOFIELD, Claire, et JAMES, William Philip Trehearne.Basal metabolic rate: review and prediction, together with an annotated bibliography of source material. J. Libbey, 1985.
(8) The various body organs each have a different energy consumption: heart and kidneys (440 kcal/kg/day), brain (240 kcal/kg/day) and liver (200 kcal/kg/day). By comparison, muscles at rest or tissues containing fat have a very low energy consumption, i.e.13kcal/kg/day for muscles 3 times less for fat (4.5 kcal/kg/day).
Source : ELIA, Marinos. Organ and tissue contribution to metabolic rate. Energy metabolism: tissue determinants and cellular corollaries, 1992, vol. 1992, p. 19-60.
(9) WANG, ZiMian, HESHKA, Stanley, ZHANG, Kuan, et al. Resting energy expenditure: systematic organization and critique of prediction methods.Obesity research, 2001, vol. 9, no 5, p. 331-336.