Energy expenditure and energy efficiency

Daily Energy Expenditure

The daily energy expenditure of an individual has 3 components:

  1. The energy required to maintain the body at rest: referred to as resting metabolic rate or RMR.
  2. The energy required for all activity: referred to as the thermic effect of activity or TEA
  3. The energy required by food consumption: referred to as the thermic effect caused by food consumption or TEF.
A pie chart of the 3 components of daily energy expenditure

RMR is the energy cost of maintaining all body systems including temperature regulation while the individual is at complete rest. Excluded from RMR is any biological work done by the body in regard to recent food intake or recovery from recent physical activity (27).

RMR differs between individuals due to range of factors but in particular the main factor is the fat free mass (FFM) of the body: that is the mass of the body including muscle, bone and organ tissue but excluding all fat (24). Thus, if an individual has a greater amount of muscle mass (an important constituent of FFM), they will have a higher RMR. Consequently, if an individual loses muscle mass as happens with the aging process, RMR decreases and that is one of the reasons people put on weight as they age if they do not reduce their energy intake.

This dependency of daily energy requirement on RMR has important consequences on bodyweight stabilisation. For example, if an athlete goes on an energy restricted diet to make a bodyweight, they may also lose muscle mass in the process (25) and this means their RMR goes down. As a result they will have to cut their energy intake more because RMR is a key component of daily energy needs.

In sedentary individuals, RMR accounts for 60-80% of total energy expenditure (1, 2). But when a person engages in strenuous exercise, there is a proportionate increase in TEA and proportionate (but not actual) decrease in RMR. Some athletes may expend as much as 2000 Kcal/d on their daily sport activities (3) and under these conditions TEA may expand to 50% of total energy expenditure, and RMR less than 50%. It is of interest to Weightlifters that the resynthesis of protein after training is energy expensive and results in an elevated RMR for extended periods of time post training (26).This may have a detrimental effect on bodyweight maintenance if the athlete does not sufficiently compensate with dietary intake following training.

In addition to fat free mass (FFM), RMR is influenced to a much lesser degree by environmental factors such as temperature or altitude, emotional factors such as anxiety or stress and other physical factors such as growth, menstruation and significant physical injury (5). Changes in RMR as a result of environment and emotion are collectively termed Adaptive Thermogenesis.

A small proportion (6-10%) of total daily energy expenditure is consumed by ingestion, digestion and metabolism of food. This is called the ‘thermic effect of food consumption’ (TEF). TEF varies considerably in accordance with a number of factors that include types of food consumed, composition of the diet and degree of obesity (10, 11). For example, the thermogenic effect of protein ranges between 20-30% compared to fat (3-5%) and glucose (5-10%) (12).

The concept of ‘energy efficiency’

Normally, if energy intake was less than energy expenditure on an ongoing basis, the consequence would be a gradual reduction in bodyweight. However, some researchers have described a phenomenon known as ‘energy efficiency’ (13). This is a situation where an individual’s bodyweight remains steady even though energy intake is significantly reduced (13). If energy efficiency exists, it may have two effects on the athlete. Firstly, if an athlete is attempting to reduce bodyweight, energy efficiency makes the task harder. Secondly, the energy efficiency may result in increased lethargy and this would be a logical but undesirable consequence of having an energy imbalance. None of these things are good news for Weightlifters!

Evidence for energy efficiency has arisen from investigations (14) into highly active female athletes who were able to maintain body mass over relatively long periods of time despite a deficient energy intake reported to be 35Kcal per Kg bodyweight per day or less. In the female athlete, such a substantial energy efficiency might arise as a survival mechanism by which bodyweight can be maintained at the expense of least-essential body functions such reproductive functionality. Studies (15, 16) indicate that female athletes with disturbances of normal menstrual rhythm had significantly lower RMR. However, energy efficiency has been also been found in male athletes. An investigation by Thomson (17) compared low-energy balance and adequate-energy balance male athletes. The activity of both groups was similar but the RMR in the low-energy balance group was significantly lower (~7%). Thomson (23) again investigated male athletes with a low-energy balance and probed for possible reasons. The findings of this study indicated that low-energy intake athletes may be better at saving energy at rest, for example less spontaneous physical activity (3).

The argument against the existence of energy efficiency arises from studies that found no such effect (7, 19, 20, 21). For example, Fogelholm (20) tested gymnasts and found that although their energy balance was lower than sedentary control subjects, there was no difference in RMR. But in all studies of energy efficiency, there is a possibility of test errors, that is accuracy in measuring energy intake and energy expenditure is difficult. Another confounding variable is the phase of menstrual cycle (22). Researchers need to test female athletes at the same stage of the menstrual cycle.

Furthermore, the quantity of exercise of individuals is also another variable to be considered. Redman (18) tested the difference between individuals losing weight under two protocols (a) caloric restriction with structured exercise and (b) caloric restriction with no exercise and found that there was no energy efficiency in the exercise group despite losing the same amount of weight. However Redman (18) concluded that physical activity may protect individuals against energy efficiency that is that without exercise RMR might decrease under caloric restriction (increased lethargy) but when individuals exercise such lethargy may not occur.

References

01Ravussin et al, 1986, in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 101.
02Ravussin and Bogardus, 1989 and 2000, in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 101.
03Manore, M.M. & Thompson J.L.  (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 96-115.
04Elia M., 1992, in Donahoo et al, 2004, Variability in energy expenditure  and its components, Current Opinion in Clinic Nutrition and Metabolic Care, 2004, 7:599-605
05Manore et al, 2009, in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 101
07Beidelman et al, 1995; in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 101.
08Rontoyannis et al,1989; in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 101.
09Chad and Quigley, 1991, in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 103
10Stock, 1999, in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 101.
11Westerterp et al, 1999, in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 101.
12Flatt JP, 1992,  in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 103
13Mulligan, K., & Butterfield, G. E. (1990). Discrepancies between energy intake and expenditure in physically active women. British Journal of Nutrition, 64(01), 23-36.
14Drinkwater, B. L., Nilson, K., Chesnut III, C. H., Bremner, W. J., Shainholtz, S., & Southworth, M. B. (1984). Bone mineral content of amenorrheic and eumenorrheic athletes. New England Journal of Medicine, 311(5), 277-281.
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16Lebenstedt, M.A., Platte, P.E., & Pirke, K. M. (1999). Reduced resting metabolic rate in athletes with menstrual disorders. Medicine and science in sports and exercise, 31(9), 1250-1256.
17Thompson et al, 1993; in M.M. Manore and J.L. Thompson (2010). Energy requirements of the athlete: assessment and evidence of energy efficiency. In Clinical Sports Nutrition 4th Ed. Edited by L. Burke and V. Deakin. McGraw-Hill, Sydney. pp 101.
18Redman LM, Heilbronn LK, Martin CK, De Jonge L, Williamson DA, Delany JP, Ravussin E. Metabolic and behavioral compensations in response to caloric restriction: implications for the maintenance of weight loss. PloS one. 2009 Feb 9;4(2):e4377.
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20Fogelholm CM, Kukkonen-Harjula TK, Taipale SA, Sievänen HT, Oja P, Vuori IM. Resting metabolic rate and energy intake in female gymnasts, figure-skaters and soccer players. International journal of sports medicine. 1995 Nov;16(08):551-6.
21Schulz LO, Alger S, Harper I, Wilmore JH, Ravussin E. Energy expenditure of elite female runners measured by respiratory chamber and doubly labeled water. Journal of Applied Physiology. 1992 Jan 1;72(1):23-8.
22Bisdee JT, James WP, Shaw MA. Changes in energy expenditure during the menstrual cycle. British Journal of Nutrition. 1989 Mar 1;61(02):187-99.
23Thompson JL, Manore MM, Skinner JS, Ravussin ER, Spraul MA. (1995). Daily energy expenditure in male endurance athletes with differing energy intakes. Medicine and science in sports and exercise. 1995 Mar; 27(3):347-54.
24Stiegler P, Cunliffe A. (2006). The role of diet and exercise for the maintenance of fat-free mass and resting metabolic rate during weight loss. Sports medicine. 36(3):239-62.
25Geliebter, A., Maher, M. M., Gerace, L., Gutin, B., Heymsfield, S. B., & Hashim, S. A. (1997). Effects of strength or aerobic training on body composition, resting metabolic rate, and peak oxygen consumption in obese dieting subjects. The American journal of clinical nutrition, 66(3), 557-563.
26Dolezal, B. A., Potteiger, J. A., Jacobsen, D. J., & Benedict, S. H. (1998). Muscle damage and resting metabolic rate after acute resistance exercise with an eccentric overload (Doctoral dissertation, University of Kansas, Health, Sport, and Exercise Sciences).
27Weststrate, J. A. (1993). Resting metabolic rate and diet-induced thermogenesis: a methodological reappraisal. The American journal of clinical nutrition, 58(5), 592-601.