The goal of this chapter is to introduce the reader to the principles of energy requirement, basal metabolic rate, total energy expenditure, physical activity level and components of energy expenditure. It reviews the different methods of measuring energy expenditure such as direct calorimetry, indirect calorimetry, heart rate monitoring, doubly labeled water, and their physiological correlates. Since the estimation of energy requirement is one of the key steps in planning a dietary schedule for an obese or diabetic patient, this chapter also discusses how to arrive at estimates of energy requirements in an individual.
The human body requires energy for maintaining body temperature, metabolic activities, physical work, and growth. Recommendations for dietary energy intake from food must satisfy these requirements for the attainment and maintenance of optimal health, physiological function, and well-being (WHO, 2004).1 Energy intakes of individuals vary on a daily basis and it is possible for an individual to have a grossly inadequate food intake, lose weight, and become underweight or have high energy intakes leading to obesity. The methods used to assess energy intake are weighed or observed diet records, dietary recalls and food frequency questionnaires. Measurements of total energy expenditure (TEE) by doubly labelled water (DLW) has shown that reported energy intakes are underestimated2,3 and the underreporting varies from 10% to 45% depending on age, gender, and body composition of the individuals.4
Currently, it is recommended that the requirements of energy should be assessed in terms of energy expenditure rather than energy intake. The energy requirements can be specified in terms of measures of energy expenditure plus the additional energy needs for growth, pregnancy, and lactation. Body weight is an important indicator of whether the energy intake is adequate, inadequate, or excess, and this is reflected over time by changes in body weight. In order to achieve energy balance, the dietary energy intake (input) must be equal to TEE (output). An individual is assumed to be in a steady state, when energy balance is maintained over a prolonged period (WHO, 2004).1 While humans can adapt to small changes in energy intake through various physiological and behavioral responses related to energy expenditure, large changes (high or low) in energy intakes could cause biological and behavioral compromises, such as reduced growth velocity, loss of muscle mass, increased deposition of body fat, increased risk of disease, forced rest periods, and physical or social limitations in performing certain activities and tasks.
Components of Energy Expenditure
Total energy expenditure is composed of three main components: (1) basal energy expenditure, (2) thermic effect of food (TEF), and (3) energy expenditure of activity (activity thermogenesis). The components of energy expenditure are highly variable and the total effect of these variances determines the variability in daily energy expenditure between individuals. The main components of TEE are depicted in figure 1.
Basal Metabolic Rate
The BMR is the minimum amount of energy needed to carry on the basic functions of life. A person's BMR reflects the amount of energy used during a 24-hour period, at physical and mental rest in a thermo-neutral environment that prevents the activation of heat generating processes such as shivering. The BMR is measured under standard conditions of being awake in the supine position, 10–12 hours of fasting, 8 hours of physical rest, and being in a state of mental relaxation in an ambient environmental temperature. The BMR remains relatively constant on a daily basis. Depending on age and lifestyle, BMR represents 45–70% of daily TEE.
Due to the restrictive conditions of the BMR, it is often more practical to measure the resting metabolic rate (RMR). The RMR is measured under the same conditions as the BMR, but a 3–4 hour fasting period is adequate and is the energy expended by an individual for activities, necessary for normal body functions and homeostasis (respiration, circulation, synthesis of organic compounds, pumping of ions across the membranes, and maintenance of body temperature).
Since it is practically difficult to measure BMR, the RMR which is about 10–20% higher is used more often.5 There are many factors that affect the RMR. They are:
- Age: The RMR is highest during the first 2 years of life when there is rapid growth6 and a growing child stores 12–15% of the energy value of food as new tissue. The RMR decreases by 1–2%/kg of fat free mass (FFM), with every decade after early adulthood,7 may be related to age associated changes in lean body mass (LBM).8 Regular exercise can maintain a higher LBM and RMR
- Body composition: The main predictor of RMR is the FFM, which is the metabolically active tissue in the body. The FFM contributes to about 80% of the variations in RMR.9 Organs that have a high metabolic rates such as the liver, brain, heart, spleen, and kidneys account for about 60% of RMR10 and thus the differences in FFM between different ethnic groups could be due to the total mass of these organs,8 with the RMR being affected by small variation in the mass of these organs11
- Body size: Lean body mass is highly correlated with the total body size and thus, though obese children have a higher RMR than nonobese children, no differences in RMR are found when the RMR is adjusted for body composition, FFM, and fat mass12
- Climate: The RMR is 5–20% higher for people living in tropical climates than those living in temperate climates. Increased sweat gland activity caused by exercise in high temperature also increases the RMR
- Gender: The differences in body size and body composition are primarily the reason for the gender differences in metabolic rates, with women having 5–10% lower metabolic rates due to their increased fat mass13
- Hormonal status: Conditions such as hyperthyroidism and hypothyroidism can increase or decrease the metabolic rate. Menstrual cycle affects energy metabolism, with small increases in the metabolic rate during the luteal phase14 and all the various changes in pregnancy causes a gradual change in BMR.15 Gut hormones such as ghrelin and peptide YY are involved in appetite regulation and energy homeostatsis16
- Temperature: There is about 13% increase in RMR during fever for each degree higher than 37°C17
- Miscellaneous factors: Factors such as alcohol, nicotine, and caffeine can affect the metabolic rate. Alcohol consumption increases RMR by 9% in women,18 while nicotine increases RMR by 3–4% in men and 6% in women. The increase in RMR induced by caffeine intakes of 200–350 mg is about 7–11% in men and 8–15% in women.18
Thermic Effect of Food
The TEF also known as diet induced thermogenesis, specific dynamic action of food is the energy expenditure associated with the consumption, digestion, and absorption of food and accounts for about 10% of TEE. The size and the macronutrient content of a meal affect the TEF.
Physical Activity Thermogenesis
The most variable component of TEE is the energy expenditure for physical activity. It is of two types—(1) exercise and (2) non-exercise activity thermogenesis (NEAT). For individuals who do not take part in any sporting activity, the exercise related activity is zero, while it is about 10% for individuals who exercise regularly. The PAL is the ratio of the TEE to BMR (TEE/BMR).
Measurement of Energy Expenditure
There are many methods available to measure human energy expenditure. They include:
- Direct calorimetry
- Indirect calorimetry
- Heart rate monitoring
- Doubly labelled water
- Physiological correlates.
Direct calorimetry involves the measurement of an individual in a whole body calorimeter, which is equipped to measure the amount of heat produced by the individual inside the chamber. There are three principal types of direct calorimeter: (1) isothermal, (2) heat sink, and (3) convection systems. These approaches have on occasion been used in combination. This method of measuring energy expenditure is not representative of a free living condition as the physical activity is restricted.
Indirect calorimetry estimates heat production indirectly by measuring oxygen consumption (VO2), the CO2 production and the respiratory quotient (RQ), which is the ratio of the VCO2 to VO2. The RQ reflects substrate utilization and reflect the fuel mixture being metabolized.
The RMR is obtained from the oxygen consumption using the Wier's equation.19 A mouthpiece, mask, or a ventilated hood is generally used to collect the expired carbon dioxide.
The indirect calorimetry can be measured using total collection system (rigid total collection system, flexible total collection system), open-circuit indirect calorimeter system (ventilated open-circuit system, expiratory collection open circuit systems), and closed circuit system. Figure 2 depicts a volunteer undergoing indirect calorimeter using a ventilated hood.
Heart Rate Monitoring
The heart rate monitoring method is based on the linear relationship between heart rate and energy expenditure;20 however, the relationship needs to be calibrated for every individual as there are variations due to age, gender, body size, and nutritional status.21 The factors that could affect the energy expenditure to heart rate relationship are ambient temperature, hydration status, food intake, emotional state, and smoking. Heart rate monitors are portable, nonrestraining, and can be measured for several days. The heart rate monitoring method provides a reasonably accurate estimate of TEE on a group of individuals rather than on individuals, where it is likely to be subjected to errors.
Doubly Labelled Water
The measurement of TEE by the DLW technique provides a means of validating other methods and measures TEE in free living conditions. DLW is a mixture of stable isotope labelled waters (2H2O and H2 18O). TBW is measured by isotope dilution as part of the DLW procedure, therefore, an estimate of body composition can be made at the same time as TEE using the DLW technique.
Two stable isotopic forms of water (H218 O and 2H2O) are administered to the individual and their 18O and 2H2O disappearance rates from the body are measured for 7–21 days, which is equivalent for these isotopes. The sample used is urine, saliva, or blood. The method is based on the principle that carbon dioxide production can be estimated from the difference in the elimination rates of body hydrogen and oxygen. The water flux is reflected by the disappearance rate of 2H2O, while the water flux plus the VCO2 is reflected by H2 18O, due to the rapid equilibrium of body water and bicarbonate pools by carbonic anhydrase. VCO2 is calculated by the difference between the two disappearance rates, and then assuming a RQ, energy expenditure is calculated. In conditions of energy balance, the RQ is calculated from the composition of the diet using the food quotient (FQ). The accuracy of the DLW method is about 5% and the main advantage is that it is noninvasive, and can be measured in a free living state, while the disadvantages are the high costs of the isotope and the mass spectrometric equipment needed for the analysis.
Activity Recall and Time and Motion Studies
Habitual activity and information on NEAT can be obtained using questionnaires, interviews, and time and motion studies. Although the errors in the data are highly possible due to inaccurate recall and improper data recording, the approaches can be used to assess trends in certain activities such as occupational activities.
Measuring Activity Related Energy Expenditure
Uniaxial monitors are portable devices which measure the degree and intensity of movements in a vertical plane. These monitors have found to be acceptable for estimates of activity related energy expenditure in groups, but have limitations in individuals. A triaxial monitor employs three uniaxial monitors to measure multidirectional movement and has shown to correlate well with energy expenditure from DLW technique.22
Estimating Energy Requirements for Indian Adults
The FAO/WHO/UNU expert consultation in 1985 (FAO/WHO/UNU, 1985)23 used the BMR factors (factorial method) for estimating the energy requirements and this method was adopted by the Indian Council of Medical Research (ICMR) expert group in 1989 to arrive at energy requirements estimates for Indian man and woman.
This method is based on the time allotted to activities that are performed habitually and the energy cost of those activities and it combines two or more factors such as the sum of energy spent while sleeping, resting, or in household or leisure activities. The time allotted to each activity and its energy cost is used to calculate the energy spent. The TEE is measured as product of predicted BMR and PAL. Equations to predict BMR using body weight of an individual are available.23 Since the BMR of Indians is about 5% lower24 than the BMR reported in developed countries, the ICMR developed a set of equations for computing BMR of Indian adults.25 Table 1 provides the list of equations for predicting BMR, proposed by FAO/WHO/UNU and those for Indians.26
Physical Activity Level
The PAL is a major determinant of TEE and can be measured or estimated from the TEE and BMR.
The PAL values for Indian reference adult man and woman for different categories of work are 1.53 for sedentary work, 1.8 for moderate work, and 2.3 for heavy work.26 The PAL of an individual can also be obtained from the different physical activity ratio (PAR) values of activities performed in a day.
The PAR is the ratio of energy cost of an individual activity per minute to the cost of the BMR per minute
The metabolic equivalent of task (MET), is a physiological measure of expressing the energy cost of physical activities and is defined as the ratio of metabolic rate (and, therefore, the rate of energy consumption) during a specific physical activity to a reference metabolic rate, set by convention to 3.5 mL of oxygen/min/kg.27 The MET values of activities range from 0.9 (sleeping) to 18 (running at 17.5 km/h). The Compendium of Physical Activities, published in 1993, 2000, and updated in 201127-29 is used mainly in epidemiologic studies to standardize the assignment of MET intensities in physical activity questionnaires and has been used widely to assign intensity units to physical activity questionnaires. MET is a measure of intensity and rate, and thus “MET-minute” can be used to quantify the total amount of physical activity in a way comparable across different persons and types of activities.
Example of calculating Physical Activity Level of an individual spending (Box 1)
A detailed list with PAR values for various activities has been provided in Appendix 5. The energy requirements of Indians at different ages are summarized in table 2.
In order to promote weight loss, regardless of the type of diet, it is important to reduce the energy intake to achieve weight loss and once weight loss is achieved, the lower energy intake has to be sustained to prevent weight gain. Calorie restriction of 500–600 kcal/day results in weight loss of 0.5 kg/week and 10% weight loss in 6 months.30 The amount of energy required for each overweight/obese patient varies and should be planned individually with the help of a dietician.
- Joint FAO/WHO/UNU. Human Energy Requirements. Report of a Joint FAO/WHO/UNU Expert Consultation, Rome, 17-24 Oct 2001. Rome, FAO/WHO/UNU 2004.
- Schoeller DA. How accurate is self-reported dietary energy intake? Nutr Rev. 1990;48(10):373-9.
- Goldberg GR, Black AE, Jebb SA, Cole TJ, Murgatroyd PR, Coward WA, et al. Critical evaluation of energy intake data using fundamental principles of energy physiology: 1. Derivation of cut-off limits to identify under-recording. Eur J Clin Nutr. 1991;45(12):569-81.
- Johnson RK, Soultanakis RP, Matthews DE. Literacy and body fatness are associated with underreporting of energy intake in US low-income women using the multiple-pass 24-hour recall: a doubly labeled water study. J Am Diet Assoc. 1998;98(10):1136-40.
- Institute of Medicine of the National Academies, Food and Nutrition Board. Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein and amino acids. The National Academies Press; Washington DC: 2005.
- Butte NF, Hopkinson JM, Wong WW, Smith EO, Ellis KJ. Body composition during the first 2 years of life: an updated reference. Pediatr Res. 2000;47(5):578-85.
- Gallagher D, Albu J, He Q, Heshka S, Boxt L, Krasnow N, et al. Small organs with a high metabolic rate explain lower resting energy expenditure in African American than in white adults. Am J Clin Nutr. 2006;83(5):1062-7.
- Bosy-Westphal A, Reinecke U, Schlörke T, Illner K, Kutzner D, Heller M, et al. Effect of organ and tissue masses on resting energy expenditure in underweight, normal weight and obese adults. Int J Obes Relat Metab Disord. 2004;28(1):72-9.
- Gallagher D, Belmonte D, Deurenberg P, Wang Z, Krasnow N, Pi-Sunyer FX, et al. Organ-tissue mass measurement allows modeling of REE and metabolically active tissue mass. Am J Physiol. 1998; 275(2 Pt 1):E249-58.
- Javed F, He Q, Davidson LE, Thornton JC, Albu J, Boxt L, et al. Brain and high metabolic rate organ mass: contributions to resting energy expenditure beyond fat-free mass. Am J Clin Nutr. 2010;91(4):907-12.
- Byrne NM, Weinsier RL, Hunter GR, Desmond R, Patterson MA, Darnell BE, et al. Influence of distribution of lean body mass on resting metabolic rate after weight loss and weight regain: comparison of responses in white and black women. Am J Clin Nutr. 2003;77(6):1368-73.
- Poehlman ET. Regulation of energy expenditure in aging humans. J Am Geriatr Soc. 1993;41(5):552-9.
- Ferraro R, Lillioja S, Fontvieille AM, Rising R, Bogardus C, Ravussin E. Lower sedentary metabolic rate in women compared with men. J Clin Invest. 1992;90(3):780-4.
- Butte NF, Wong WW, Treuth MS, Ellis KJ, O’Brian Smith E. Energy requirements during pregnancy based on total energy expenditure and energy deposition. Am J Clin Nutr. 2004;79(6):1078-87.
- Larson-Meyer DE, Ravussin E, Heilbronn L, DeJonge L. Ghrelin and peptide YY in postpartum lactating and nonlactating women. Am J Clin Nutr. 2010;91(2):366-72.
- Hardy JD, DuBois EF. Regulation of heat loss from the human body. Proc Natl Acad Sci U S A. 1937;23(12):624-31.
- Compher C, Frankenfield D, Keim N, Roth-Yousey L, Evidence Analysis Working Group. Best practice methods to apply to measurement of resting metabolic rate in adults: a systematic review. J Am Diet Assoc. 2006;106(6):881-903.
- Weir JB. New methods for calculating metabolic rate with special reference to protein metabolism.1949. Nutrition. 1990;6(3):213-21.
- Levine JA. Measurement of energy expenditure. Public Health Nutr. 2005;8(7A):1123-32.
- Research Methods in Nutritional Anthropology. Edited by Gretel H Pelto, Pertti J Petto. United Nations University Press; Ellen Messer. 1989.
- Plasqui G, Westerterp KR. Physical activity assessment with accelerometers: an evaluation against doubly labelled water. Obesity (Silver Spring). 2007;15(10):2371-9.
- Joint FAO/WHO/UNU: Energy and Protein requirements. Report of Joint FAO/WHO/UNU Expert Consultants, WHO Tech Rep Series 724, 1985.
- Shetty PS, Soares MJ, Sheela ML. Basal metabolic rates of South Indian males. Report of FAO, Rome, 1986.
- Indian Council of Medical Research: Nutrient Requirements and recommended dietary allowances for Indians. A report of the expert group of the Indian Council of Medical Research, ICMR, New Delhi, 1989.
- Indian Council of Medical Research: Nutrient requirements and recommended dietary allowances for Indians. A report of the expert group of the Indian Council of Medical Research, ICMR, New Delhi, 2010.
- Ainsworth BE, Haskell WL, Herrmann SD, Meckes N, Bassett Jr DR, Tudor-Locke C, et al. 2011 Compendium of Physical Activities: a second update of codes and MET values. Med Sci Sports Exerc. 2011;43(8):1575-81.
- Ainsworth BE, Haskell WL, Leon AS, Jacobs DR Jr, Montoye HJ, Sallis JF, et al. Compendium of physical activities: classification of energy costs of human physical activities. Med Sci Sports Exerc. 1993;25(1):71-80.
- Ainsworth BE, Haskell WL, Whitt MC, Irwin ML, Swartz AM, Strath SJ, et al. Compendium of physical activities: an update of activity codes and MET intensities. Med Sci Sports Exerc. 2000;32(9 Suppl): S498-504.
- Klein S. Medical management of obesity. Surg Clin North Am. 2001;81:1025-38.