Nutrition in Obesity & Diabetes Rebecca Kuriyan Raj, Anura V Kurpad
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Energy RequirementsCHPATER 1

Abstract

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.
 
Introduction
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
2Currently, 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.

Key Terms

  • Energy requirement: Energy requirement is the amount of food energy needed to balance energy expenditure in order to maintain body size, body composition, and a level of necessary and desirable physical activity consistent with long-term good health. This includes the energy needed for the optimal growth and development of children, for the deposition of tissues during pregnancy, and for the secretion of milk during lactation consistent with the good health of mother and child.
  • Basal metabolic rate (BMR): The minimal rate of energy expenditure compatible with life. It is measured in the supine position under standard conditions of rest, fasting, immobility, thermoneutrality, and mental relaxation. Depending on its use, the rate is usually expressed per minute, per hour or per 24 hours.
  • Total energy expenditure: The energy spent, on average, in a 24-hour period by an individual or a group of individuals. By definition, it reflects the average amount of energy spent in a typical day, but it is not the exact amount of energy spent each and every day.
  • Physical activity level (PAL): Total energy expenditure for 24 hours expressed as a multiple of BMR, and calculated as TEE/BMR for 24 hours. In adult men and non-pregnant, non-lactating women, BMR times PAL is equal to TEE or the daily energy requirement.
  • Joule: It is a unit of energy, defined as the energy required to move 1 kg of mass by 1 m by a force of 1 Newton acting on it.
  • Kilocalorie (kcal): Kilocalorie is a commonly used unit of energy, defined as the heat required to raise the temperature of 1 kg of water by 1°C from 14.5°C to 15.5°C.
    • 1 kcal = 4.184 KJ (Kilo Joule)
    • 1 KJ = 0.239 kcal
    • 1,000 kcal = 4,184 KJ = 4.184 MJ
    • 1 MJ = 239 kcal
3
 
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).
zoom view
Figure 1: Main components of total energy expenditure.TEF, thermic effect of food; BMR, basal metabolic rate.
Since it is practically difficult to measure BMR, the RMR 4which 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, 5and 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
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
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.
Carbohydrate
=
1.0
Fat
=
0.71
Protein
=
0.84
Mixed meal
=
0.85
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.
6
zoom view
Figure 2: A volunteer undergoing indirect calorimeter using a ventilated hood.
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 7estimate 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.
 
Physiological Correlates
 
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.
8
TABLE 1   Prediction equations for BMR (kcal/day)26
Category
Age (years)
FAO/WHO/UNU 1985
ICMR expert group 2010
Males
18–30
15.1 × Bwt + 692.2
14.5 × Bwt + 645
30–60
11.5 × Bwt + 873
10.9 × Bwt + 833
>60
11.7 × Bwt + 587.7
12.6 × Bwt + 463
Females
18–30
14.8 × Bwt + 486.6
14.0 × Bwt + 471
30–60
8.1 × Bwt + 845.6
8.3 × Bwt + 788
>60
9.1 × Bwt + 658.5
10.0 × Bwt + 565
BMR, basal metabolic rate; FAO, Food and Agricultural Association; UNU, United Nations University; ICMR, Indian Council of Medical Research; Bwt, body weight in kg.
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.
zoom view
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
zoom view
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 9a 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.

Box 1 :  Example of calculating Physical Activity Level of an individual spending

8 hours of sleep (PAR = 1; 8 × 1 = 8 PAR -hours)
9 hours at work (PAR = 1.7; 9 × 1.7 = 15.3 PAR -hours)
4 hours of domestic work (PAR = 2; 4 × 2 = 8 PAR hours)
3 hours of leisure = (PAR = 1.4; 3 × 1.4 = 4.2 PAR hours)
Total PAR hours = 35.5 hours
zoom view
PAR, physical activity ratio; PAL, physical activity level
TABLE 2   Energy requirements of Indians at different ages26
Age group
Category
Body weight (kg)
Requirement (kcal/day)
Requirement (kcal/kg/day)
Men
Sedentary
60
2,320
39
Moderate
60
2,730
46
Heavy
60
3,490
58
Women
Sedentary
55
1.900
35
Moderate
55
2.230
41
Heavy
55
2.850
52
Pregnant
55 + GWG
+350
Lactating
55 + WG
+600
+520
10
Infants
0–6 months
5.4
500
92
6–12 months
8.4
670
80
Children
1–3 years
12.9
1,060
82
4–6 years
18.1
1,350
75
7–9 years
25.1
1,690
67
Boys
10–12 years
34.3
2,190
64
Girls
10-12 years
35.0
2,010
57
Boys
13–15 years
47.6
2,750
58
Girls
13–15 years
46.6
2,330
50
Boys
16–17 years
55.4
3,020
55
Girls
16–17 years
52.1
2,440
47
GWG, gestational weight gain; WG, gestational weight gain remaining after delivery.
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.
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