Total energy expenditure in 9 month and 12 month ...

European Journal of Clinical Nutrition (1997) 51, 249±252 ß 1997 Stockton Press. All rights reserved 0954±3007/97 $12.00

Total energy expenditure in 9 month and 12 month infants PSW Davies1,2, JCK Wells2, A Hinds2, JME Day2 and A Laidlaw2 1 Queensland University of Technology, School of Human Movement Studies, Kelvin Grove Campus, Victoria Park Road, Locked Bag No 2, Red Hill, Queensland 4059, Australia and 2 Infant and Child Nutrition Group, Dunn Nutrition Unit, Downham's Lane, Milton Road, Cambridge CB4 1XJ

Objectives: To measure the total energy expenditure of 9 and 12 month old infants and compare with current recommendations for energy intake. Design: Cross-sectional study. Total energy expenditure assessed using the doubly labelled water technique over a 10 d period. Classical anthropometric measurements taken. Setting: Community based study in and around Cambridge, UK. Subjects: Twenty infants aged 9 months of age and 20 infants aged 12 months of age recruited via local hospital birth records. Main outcome measures: Total energy expenditure calculated via the doubly labelled water technique. Results: Measurements of total energy expenditure was successful in 34 cases. Mean total energy expenditure was 73.5 kcal=kg, 73.2 kcal=kg, 77.1 kcal=kg and 77.6 kcal=kg in the nine month old boys, nine month old girls, twelve month old boys and twelve month old girls respectively. These measurements are approximately 17% below current recommendations (FAO=WHO=UNU, 1985) at nine months of age and 22% below at one year of age. Conclusion: The data are consistent with ®ndings in younger infants and older children in that the measurements of total energy expenditure are about 20±25% below current recommendations. It is unlikely that contemporary infants are being underfed and thus more likely that changes in feeding practices and modi®cation of infant formula composition has led to the reduction in energy intake and energy expenditure in such infants. Sponsorship: NestleÂ Foundation. Descriptors: Infants; energy expenditure; doubly labelled water.

Introduction A number of studies have now been reported that have measured total energy expenditure, non-invasively, in what are usually termed free-living infants and young children (Prentice et al, 1988; Davies et al, 1989; Goran et al, 1993; Fontvieille et al, 1993; Davies et al, 1994). Despite the fact that these studies come from different laboratories in Europe and North America, the ®ndings are remarkably consistent, in that measured total energy expenditure is considerably below current recommendations for energy intake (Prentice et al, 1988; Davies, 1996) at least to about 5 y of age. These differences are still apparent when adjustments are made for the energy cost of growth in order to produce more equitable comparisons of expenditure and intake. Such data are of special interest to expert groups who determine and re®ne recommendations for energy intake in infants and children. For nearly 50 y both national and international expert committees have made recommendations on the energy requirements of infants to satisfy the components of energy expenditure, namely basal metabolic rate, thermogenesis, physical activity and growth. Such data are used to produce information and guidance to infant food manufacturers on the composition of arti®cial Correspondence: Dr PSW Davies, School of Human Movement Studies, Faculty of Health, Queensland University of Technology, Kelvin Grove Campus, Locked Bag No 2, Red Hill, Queensland 4059, Australia. Received 30 September 1996; revised 29 Novermber 1996; accepted 14 December 1996

formulas for infants that will be suitable as the sole source of nutrition. Secondly, knowledge of energy requirements in infancy are needed in order to derive the special needs of sick children and ®nally, recommendations are used for medical and political purposes to assess the needs of infants at risk of malnutrition. A recent paper concerning energy requirements in infancy (Butte, 1996) noted that there was a speci®c need for more information on total energy expenditure in the second six months of life. Not only would such data contribute to the existing knowledge but will offer an insight into the variability in total energy expenditure in infancy at a time when the growing child is undergoing many changes, especially in nutrition and mobility. This paper reports such data in a group of 40 infants aged 9 months and 12 months of age. Subjects and methods Twenty infants aged 9 months and twenty infants aged 12 months of age were recruited into the study from the Rosie Maternity Hospital, Cambridge, England. This hospital serves the city of Cambridge and the surrounding area including the city of Ely, and oversees approximately 4000 births per year. Data on all births were received monthly from the Child Health Administration Department of Addenbrooke's Hospital in Cambridge. Parents were approached ®rst by letter and then by telephone, approximately 10 weeks after the birth of the

Total energy expenditure in 9 and 12 month infants PSW Davies et al

250

child, and the nature of the study was explained to them. Written informed consent was obtained from participating parents before the measurements were made over a one week period. The study was granted ethical approval by Cambridge Area Health Authority and by the Medical Research Council's Dunn Nutrition Unit, Cambridge. TEE was measured by the doubly labelled water method, which was described in detail elsewhere (Davies et al, 1989). Brie¯y, carbon dioxide production is estimated from the difference between the turnover rates of two tracer isotopes, 2H and 18O, in the body water pool. The 2H tracer is lost from the body as water, whereas the 18O tracer is lost both as water and as carbon dioxide. The difference between the elimination rates of the two isotopes is therefore an estimate of the carbon dioxide production rate. Carbon dioxide production can be used to predict oxygen consumption if an assumed respiratory quotient (RQ) based on the food quotient is used (Black et al, 1986), and hence, with Weir's equation, energy expenditure. The appropriate RQ varies depending on the age of the infants, ranging from 0.87 in infants aged less than 4 months to 0.855 in children aged 4±12 months. This latter ®gure is based upon approximately two hundred measured food quotients. The technique has been successfully validated in studies of infants (Roberts et al, 1986). In this study the isotopes were administered orally either as water or added to approximately 10 mL infant formula. Dose and formula or dose alone was taken to the infants' homes in a small infant feeding bottle, sealed in a polythene bag. Dosings were carried out as close as possible to the expected time of a feed. Most infants drank the dose easily and quickly. It was not imperative that the entire solution was consumed, so long as the exact amount consumed could be calculated by weighing the dose, bottle and bag prior to, and after the dosings to 0.01 g. Consequently, little effort was made to ensure complete dose consumption once the child has consumed the vast majority of the dose. Preweighed tissues were available to mop up any loss etc. that occasionally occurred while the infant was taking the dose. Whenever some dose loss occurred, dose loss was assumed to be 50% of the difference between tissues weighed prior to, and after dosing. The dose was calculated according to the body weight of the infant and was intended to give 0.28 g H2 18O=kg body weight and 0.10 g 2H2O=kg body weight. A 1.5 ml sample of the dosing mixture was retained for mass spectrometer analysis. Urine samples were obtained from the infants before dosing and daily for the following 7 d by using an established method in which cotton wool balls are left inside the baby's diaper and, after they urinate, the urine sample is obtained by inserting the cotton wool into a

syringe (Roberts and Lucas, 1985). The parents were asked to check the diaper frequently for urination, and the time of voiding was taken as the midpoint between the last two times of checking. Urine samples and dosing mixtures were analysed by using an AQUA-SIRA (VG Isogas, Middlewich, UK) dual mass spectrometer system for simultaneous analysis of 18 O-16O and 2H-1H isotope ratios in water. Each sample was analysed nine times by using consecutive 5 L injections to overcome memory effects in the mass spectrometer. Samples were also analyses in duplicate in order ®rst of ascending and then of descending isotopic enrichment. Tracer dilution spaces were calculated by using the back extrapolation method (Davies and Wells, 1994). The fractionalisation factors were those used in the original experiments with the doubly labelled water technique (Lifson et al, 1955), and the proportion of water subject to fractionalisation was taken to be 0.15 (Vasquez-Velasquez, 1988). Precision of the estimate of carbon dioxide production rate was calculated as described by Cole and Coward, 1992. To assess the body composition of the infants, the 18O dilution space was divided by 1.01 to derive total body water. Fat-free mass was calculated from body water by using the assumption that the fat-free mass was 79.2% water at 9 months of age and 78.9% at 12 months of age (Fomon et al, 1982). Fat mass was calculated as body weight minus fat-free mass. Results Measurement of total energy expenditure was successful in 34 cases. Data were lost due to either poor parental compliance in collecting urine samples or the infant vomiting or regurgitating within 2 h of the dose being given. Four measurements of energy expenditure were then unsuccessful at 9 months of age and two at 12 months of age. Characteristics of the infants in whom measurements were successful are shown in Table 1. Data relating to the 18O and 2H dilution spaces, the elimination rates of the two isotopes (ko and kd) and the percentage error of the estimates of carbon dioxide production rate are in Table 2. The results for total energy expenditure in kcal=day and kcal=kg body weight per day are shown for both age groups and by sex in Table 3. There were no signi®cant differences in mean energy expenditure between sexes at either 9 months or 12 months of age. The coef®cient of variation of total energy expenditure (sexes combined) when expressed in kcal=d and kcal=kg per day was 20.8% and 18.6% respectively at 9 months of age; 16.7% and 18.0% respectively at 12 months of age.

Table 1 Some physical characteristics of male and female infants at 9 months and 12 months of age. Percentage body fat was calculated via the dilution space

18

O

Age 9 months Male (n 7)

Weight (kg) Length (m) Tricep skinfold (mm) Subscapular skinfold (mm) % Body fat

12 months Female (n 9)

Male (n 10)

Female (n 8)

Mean

s.d.

Mean

s.d.

Mean

s.d.

Mean

s.d.

10.21 0.744 10.1 6.9 28.0

0.79 0.026 3.1 1.3 5.5

8.61 0.723 8.8 5.8 30.4

0.85 0.014 2.7 1.8 8.0

10.89 0.783 9.7 6.7 24.7

1.33 0.038 2.3 1.4 5.0

9.37 0.753 8.1 6.3 25.0

0.82 0.032 1.7 2.3 9.8


4 kcal=kg body weight and 5 kcal=kg body weight per day or about 40±50 kcals, in absolute terms, per day at each of the ages. Thus the addition of these ®gures to measures of total energy expenditure will produce estimates of energy intake for direct comparison with recommendations for energy requirements. Such estimates in the infants studied here produce values for energy intake which are approximately 17% below current recommendations (FAO=WHO=UNU, 1985) at 9 months of age and 22% below at one year of age. These ®ndings are consistent with data for younger infants (Prentice et al, 1988; Davies et al, 1989) and older children (Davies, 1996), certainly up to about 5 y of age. In the older children it has been suggested that such reductions in total energy expenditure may be a consequence of a reduced level of physical activity (Davies, 1996; Goran et al, 1993) but, as the energy cost of activity is much less in infants than in children, this would not fully explain the reduction in total energy expenditure reported here in 9 and 12 month old infants. Also, it is very unlikely that contemporary infants are being underfed and thus more likely that changes in feeding practices and modi®cation of infant formula composition has led to the reduction in energy intake of such infants. When infants are offered a calori®cally more dense formula they do not reduce the volume of formula they ingest, and conversely, infants offered a relatively diffuse formula do not seem able or willing to increase the volume consumed (Fomon, 1974; Fomon, 1967). The energy density of human breast milk is now thought to be in the order of 58 kcal=100 ml (Lucas, 1990) as opposed to earlier estimates of about 70±75 kcal=kg (Fomon, 1974; DHSS, 1977). Consequently, infant formula manufacturers have altered their product accordingly, leading to a reduced calori®c intake in formula fed infants. It is likely that previous estimations of energy requirements were overestimations as they were based primarily on formula fed infants using older formula designs, and breast fed infants in which an inappropriate calori®c density for human milk was applied. The coef®cient of variation of total energy expenditure in both sexes and at both ages is quite high, being about 19%. This is similar to previously reported values for younger infants (Davies et al, 1989), and presumably re¯ects the variations in level of maturity and hence variations in level of physical activity. It has long been accepted that, due to the fact that observed energy intakes may not represent desirable intakes, measurements of total energy expenditure would be preferred as the basis for determining energy requirements. Nevertheless, as stated recently (Butte, 1996), the existing database of measurements of total energy expen-

Table 2 Data relating to the 18O and 2H dilution spaces and their ratio, rate constants ko and kd, the isotopic enrichment relative to standard mean ocean water (SMOW) at time zero in delta units (%) and the percentage error of CO2 production using the doubly labelled water technique

18

O dilution space (ml) H dilutionn space (ml) O : 2H ratio Isotopic disappearance rate constant for 18O (ko) Isotopic disappearance rate constant for 2H (kd) Error (%) CO2 production 2 H enrichment at time zero (%) 18 O enrichment at time zero (%) 2

18

Mean

s.d.

5704 5901 1.035 0.2382

829 927 0.003 0.0359

0.1918

0.0318

6.5 763.1 195.6

3.9 174.7 43.7

Discussion The infants recruited into this study had a mean body weight and length slightly above the 50th centile for UK reference data (Freeman et al, 1995), and mean body weight was also very similar to the mean weight of the infants used to derive current international recommendations for energy requirements (FAO=WHO=UNU, 1985). Measurement of percentage body fatness via 18O dilution space produced mean values for these infants which are greater than values reported both for reference infants (Fomon et al, 1982) and more contemporary data (Davies, 1992). As reported previously (Butte, 1996), there are few data to which to compare our measurements of total energy expenditure. However at 9 months of age, absolute energy expenditure (kcal=d) (sexes combined) found in this study of 679 kcal=d is lower than the mean value of 750 kcal=d that has been previously measured (Butte, 1996), however it should be noted that these values are within one standard deviation of each other. There are no previously reported measurements of total energy expenditure at one year of age for comparative purposes. However, extrapolation of data (Butte, 1996) indicates that in absolute terms total energy expenditure in boys is approximately 840 kcal=d at 1 y and 820 kcal=d in girls at the same age. While the ®gures reported here of 877 kcal for boys compares extremely well, the value of 723 kcal=d we have found in girls is considerably below the extrapolated estimation. These measures of total energy expenditure will differ from energy intake by a factor which is equivalent to the energy cost of growth. The energy cost of growth consists of two parts, ®rstly the energy cost of producing and laying down new tissue which is actually included in the measurement of total energy expenditure, and secondly the energy deposited in the new tissue which is not a part of total energy expenditure. By the age of 9 months and 12 months the energy cost of growth is very smallÐamounting to Table 3 age

Mean and standard deviation of total energy expenditure in kcal=d and kcal=kg=d for the male and female infants at 9 months and 12 months of Age 9 months Male (n 7)

Total energy expenditure (kcal=d) Total energy expenditure (kcal=kg=d)

12 months Female (n 9)

Male (n 10)

Female (n 8)

Mean

s.d.

Mean

s.d.

Mean

s.d.

Mean

s.d.

751 73.5

160 13.2

623 73.2

100 14.8

833 77.1

104 13.5

729 77.6

143 15.2

251


252

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