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7 Energy Requirements, Energy Intake, and Associated Weight Gain During Pregnancy Optimal maternal and fetal outcomes of pregnancy are contingent upon nutrient intakes sufficient to meet maternal and fetal requirements. Energy is the major nutrient determinant of gestational weight gain, although specific nutrient deficiencies may restrict that gain. Clinical and public health interventions designed to improve gestational weight gain may be directed at energy intake or expenditure (see Figures 2-2 and 2-3 in Chapter 2~. Effective dietary intervention, however, requires an understanding of the energy requirements of pregnancy and the relationship between energy intake and gestational weight gain. The subcommittee reviewed energy intakes in the context of gestational weight gain, the effectiveness of energy supplementation on weight gain, and net energy balance during pregnancy. Extra energy is required during pregnancy for the growth and main- tenance of the fetus, placenta, and maternal tissues. Basal metabolism increases because of the increased mass of metabolically active tissues; maternal cardiovascular, renal, and respiratory work; and tissue synthesis. Energy requirements are greatest between 10 and 30 weeks of gestation, when relatively large quantities of maternal fat normally are deposited. Substantial fetal demands (56 kcal/kg per day) are offset in the last quarter of pregnancy by the near cessation of maternal fat storage (Sparks et al., 1980~. Hytten (1980) estimated the energy cost of pregnancy to be 85,000 kcal, or 300 kcaVday, based on theoretical calculations that assumed a 3.4-kg infant, deposition of 0.9 kg (2.0 lb) of protein and 3.8 kg (8.4 lb) of fat, and an increase in basal metabolism ('Ibble 7-1~. No allowance was made for the increased energy cost of moving a heavier maternal body 137

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138 NUTRITIONAL STATUS AND WEIGHT GAIN TABLE 7-1 Theoretical Cumulative Energy Cost of Pregnancy and Its Componentsa Energy Cost, kcal/day (Mean Daily Increments of Protein and Fat, g/day) by Period of Gestation, wk Component () 10 1~20 2~30 30~0 Cumulative . Total, kcal (g) 5,186 (925) Protein deposition 3.6 (0.64) b Fat deposition 55.6 (5.85) Increase in basal 44.8 metabolism Total net energy 104.0 Additional energy 114.0 required from food (total net energy + 10%) 10.3 (1.84) 26.7 (4.76) 34.2 (6.1) 235.6 (24.80) 207.6 (21.85) 31.3 (3.3) 36,329 (3,825) 99.0 148.2 227.2 35,717 344.9 382.5 379.0 421.0 292.7 77,234 322.0 84,957 a From Hytten (1980), with permission from Blackwell Scientific Publications, Inc. b Heat of combustion defined as 5.6 kcal/g for protein and 9.5 kcal/g for fat. mass; it was assumed that this expenditure was compensated by a reduction in physical activity. The validity of these estimates has been challenged, as described later in this chapter. On the basis of theoretical calculations, recommended allowances for energy intake during pregnancy have been set at 200 to 300 kcaVday (FAO/WHO/UNU, 1985; NRC, 1989) above nonpregnant levels; however, few dietary studies of pregnant women corroborate increments of this magnitude. Hytten (1980) suggested that the increased needs of pregnancy could be met by reductions in physical activity. RELATIONSHIP BETWEEN ENERGY INTAKE AND GESTATIONAL WEIGHT GAIN Tables 7-2A and 7-2B list studies in which the relationship between energy intake and gestational weight gain was described. Longitudinal studies of well-nourished pregnant women indicated a slight, although not always statistically significant and not universal, increase in energy intake during pregnancy. One study showed that the energy consumption of Scottish women increased gradually through the second and third trimesters to the extent that energy consumption at parturition was approximately 150 kcal/day higher than intake before pregnancy (Durnin, 1987; Durnin et al., 1986~. In a study of well-nourished Dutch women, energy intake was unchanged throughout the first two trimesters and increased in the third trimester by approximately 47 kcaVday (van Raaij et al., 1986, 1987~. In an

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ENERGY AND ASSOCLi4TED HEIGHT GAIN 165 FACTORS INFLUENCING ENERGY BALANCE DURING PREGNANCY Weight gain during pregnancy is a direct consequence of energy bal- ance, that is, the difference between energy intake and energy expenditure. The basic components of energy expenditure basal metabolism, thermo- genesis, and physical activi~are discussed below in relation to pregnancy. Basal Metabolism Longitudinal measurements of basal metabolic rate (BMR) or resting metabolic rate (RMR) have been made to ascertain the degree to which metabolism is increased during pregnancy (%ble 7-4~. Basal metabolism is measured in the morning after awakening, whereas resting metabolism may be measured at any time during the day after resting for at least 30 minutes. Resting metabolism tends to be about 10% higher than basal metabolism. Both are related to the amount of lean body mass. Since lean and fat tissues are increased in obese women, their basal requirements are higher than those of women of normal weight. Although all reports indicate a net increase in basal or resting metabo- lism, the magnitude of change differed considerably between populations (Banerjee et al., 1971; Blackburn and Calloway, 1976a; Durnin et al., 1986; Forsum et al., 1985; Illingworth et al., 1987; Lawrence et al., 1986; Nagy and King,.1983; Thongprasert and Valyasevi, 1986; 1hazon et al., 1986; van Raaij et al., 1986~. The reported increase in RMR by the third trimester ranged from 5% in unsupplemented Gambian women to 39% in well- nourished women in the United States. The increase was generally greater in pregnant women from developed countries (27%) than it was in those from developing countries (15%~. Compared with the nonpregnant state, the total increment in resting metabolism for the entire pregnancy ranged from a reduction of 10,700 kcal in unsupplemented Gambian women to an increase of 46,500 kcal in well-nourished Swedish women. The increase in total resting metabolism in women from developing countries was lower than the theoretical value (36,000 kcal), in part as a consequence of their smaller size, but possibly also the result of metabolic adaptations. Thermogenesis The thermic effect of feeding refers to the increase in energy expen- diture above basal metabolism following the ingestion of food. It is due mainly to the energy costs of digestion, absorption, transport, and storage and averages approximately 10% of the energy intake. A reduction in the thermic effect of feeding during pregnancy could minimally conserve energy.

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ENERGY AND ASSOCIATED WEIGHT GAIN 167 The thermic effect of feeding was measured in seven primigrav~d women at 12 to 15, 25 to 28, and 34 to 36 weeks of gestation and after the cessation of lactation (Illingworth et al., 1987~. The metabolic response to a 533 it 41-kcal (standard deviation) liquid test meal was significantly reduced by 28% (5 kcal) in the second trimester compared with postpartum values. The response was reduced by 15% in the third trimester, but the reduction failed to reach statistical significance. In a contrasting report, the thermic response to a 750-kcal meal was not different among six women in early pregnancy (10 to 20 weeks of gestation), four women in late pregnancy (30 to 40 weeks of gestation), and six nonpregnant subjects studied cross-sectionally (Nagy and King, 1984~. Physical Activity Assuming that increased energy costs of pregnancy were compensated by a reduction in physical activity, Hytten (1980), in his theoretical estimates of energy requirements, did not include an allowance for the energy cost associated with movement of a heavier body mass. Studies of activity patterns of North American pregnant women do not indicate reduced activity (Blackburn and Calloway, 1974, 1976b). Women from industrialized societies tend to have sedentary life-styles but they do not become even less active during pregnancy; reductions in recreational activities during pregnancy are slight. Subtle changes in physical activity, i.e., less walking and more sitting, by pregnant Scottish and Dutch women were noted in two reports (Durnin et al., 1986; van Raaij et al., 1986~. Women in developing countries are generally more active and may have more latitude in adjusting their level of physical activity during pregnancy. For example, pregnant women in The Gambia conserved energy by reducing the amount of heavy farm work and housework they performed (Roberts et al., 1982~. In New Guinea, they decreased the intensity and duration of arduous tasks (Durnin, 1980~. Thai and Philippine women increased their sitting time and decreased the heavy agricultural and household tasks they performed during gestation (Thongprasert and Valyasevi, 1986; 1hazon et al., 1986~. Despite these adjustments, food scarcity combined with hard work during the rainy season in The Gambia was detrimental to fetal growth (Prentice et al., 19874. The rates of weight gain in Ethiopian pregnant women who engaged in hard work were lower, and the birth weights of their children were compromised, compared with women with lighter work demands (safari et al., 1980~. Lower energy intake and lower weights during early pregnancy in the Ethiopian women may have been contributory factors. The energy cost of physical activities has been measured at progressive stages of pregnancy (Durnin et al., 1986; Emerson et al., 1972; King et al.,

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168 NUTRITIONAL STATUS AND WEIGHT GAIN 1987; Seitchik 1967; Torun et al., 1982~. The energy cost of non-weight- bearing activities, such as cycling, was not increased during pregnancy. In absolute terms, the energy expended in sedentary activities such as sitting and standing was 15 to 30% higher in pregnant women, but was not different if standardized by body weight. The energy expenditure of weight-bearing activities such as walking was increased in proportion to gestational weight gain; however, the energy expenditure of treadmill walking expressed per unit of body mass did not differ between pregnant and nonpregnant women. Because of their higher weight for height, obese women expend more energy during physical activity than do lighter women. In contrast to these findings, results of the Dutch, Thai, and Gambian studies suggested greater energy efficiency for weight-bearing activities during pregnancy. When expressed per kilogram of body weight, the energy cost of walking on a treadmill at a fixed speed was reduced by approximately 5% in late pregnancy compared with prepregnancy or early pregnancy values (Thongprasert and Valyasevi, 1986; van Raaij et al., 1986~. No increase in the energy cost of 40 activities was found in pregnant Gambian women, despite substantial weight gain (Lawrence et al., 1985, 1986~. Rates of energy expenditure, normalized by body weight, were reported to be less than those of nonpregnant Gambian women, suggesting higher levels of work efficiency. However, walking (nonstandardized and at a set pace on a treadmill) displayed the expected increase in energy expenditure in Gambian women. Various investigators have reported that pregnant women reduce the pace and intensity of certain activities (Banerjee et al., 1971; Blackburn and Calloway, 1974; van Raaij et al., 1986~. Pregnant women may expend less energy per unit of time performing a task, but they take longer to complete the task. Although activity patterns and work intensity can be adjusted to con- serve energy in pregnant woman, the energy expenditure of weight-bearing activities increases in most populations in proportion to weight gain. The impact of physical activity on the energy requirements of pregnancy depends on the proportion of time spent in such activities. Total Daily Energy Expenditure The total energy requirements of pregnancy have been estimated to be 2,115, 2,275, and 2,356 kcal/day for the three successive trimesters. The mean ratio of total expenditure to basal energy expenditure was 1.5 (Blackburn and Calloway, 1976b). The doubly labeled water technique has been applied to three pregnant women in Britain to estimate their total daily energy expenditures (Prentice et al., 1985~. Total energy expenditures of 1,912, 2,490, and 3,009 kcal/day were equivalent to 1.40, 1.39, and 1.77

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ENERGY AND ASSOCIATED WEIGHT GAIN 169 times the basal expenditure, respectively, emphasizing the considerable in- dividual variation in physical activity. The total energy expenditure of rural Gambian women has been estimated from time-motion studies (Lawrence and Whitehead, 1988~. Total daily energy expenditure declined from 2,400 kcal/day in early pregnancy to 2,200 kcaVday at term. When adjusted for stage of pregnancy or lactation, total daily energy expenditure averaged 2,300 kcal/day, or 1.68 times the basal expenditure in the dry season, and 2,700 kcaVday, or 1.97 times the basal expenditure in the wet season. Energy Balance During Pregnancy The mean total energy cost of pregnancy computed from data derived from five diverse populations (Table 7-5) was approximately 55,000 kcal for all groups except the Gambian women (Durnin, 1987~. Small differences between the Scottish, Dutch, Thai, and Philippine women may be due primarily to variable amounts of fat deposition, which ranged between 1.3 and 2.3 kg (2.9 to 5.1 lb). Although the ranges of weight gains (8.5 to 11.7 kg, or 18.7 to 25.7 lb) and fat gains (1.3 to 2.3 kg) were wide, variability diminished when these rates of fat gain were expressed as a percentage of initial weight (2.9 to 4.0% of initial weight). Total weight gain was from 17 to 20% of initial weight. The Gambian women had exceptionally low weight gain (7.3 kg, or 16 lb), fat storage (0.6 kg, or 1.3 lb), and cumulative increase in basal energy expenditure (1,900 kcal). Chronically undernourished Gambian women apparently adapted to their pregnancy by decreased basal metabolism and activity and mobilization of adipose tissue; energy supplementation partially reversed these changes by increasing the BMR and fat deposition. In all countries, the estimation of the energy cost of pregnancy was subject to error, specifically in the estimation of maternal body fat and nonpregnant baseline values of BMR, but their estimates were all substantially lower than the theoretical estimates of Hytten (1980~. Increases in energy intake recorded for these populations did not approach the estimated energy costs of pregnancy, except for the Thai women. Apparent energy deficits may be explained by an underestimation of energy intake or by undetected compensatory reductions in physical activity. With the exception of the Gambian study, the investigators were confident of their food intake records. There was some question in the Thai study as to whether the energy intakes recorded at 10 weeks of gestation underestimated prepregnanc`,r intakes and resulted in inflated estimates of increased intake during pregnancy. Underreporting of food intake in the Gambian study was strongly suspected. The investigators fully recognized the limitations of the techniques used to derive energy balance values. The methods used to measure energy intake and energy expenditure during pregnancy were not sufficiently accurate to discriminate to levels of 150

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170 NUTRITIONAL STATUS AND WEIGHT GAIN TABLE 7-5 Energy Requirements of Pregnancy as Estimated by the Five-Country Studya Energy Cost and Additional Intake During Pregnancy, kcal, by Country FactorScotlandHollandThe GambiaThailandPhilippines Energy cost Fetus8,1108,2307,1407,1406,900 Placenta730740560600600 Maternal tissues2,8902,9502,4802,4802,410 Maternal fat25,23014,3006,60015,40014,300 Basal metabolism30,10034,5001,90024,00019,000 Total energy67,06060,72018,68049,62043,210 cost Additional energy21,0005,200NRb56,9000 intake Discrepancy in - 46,060 - 55,520 NR - 7,280 - 43,210 energy balance a Adapted from Durnin (1986~. b NR = Not reported. to 200 kcaVday-the expected net increment. Although the absolute COSt of pregnancy is uncertain for such diverse populations, strong scientific evidence suggests that the energy cost of pregnancy is less than previous theoretical estimations. SUMMARY Effective public health intervention aimed at improving gestational weight gain, and thus birth weight, requires an understanding of energy requirements during pregnancy. The total energy cost of pregnancy is now believed to be approximately 55,000 kcal. Prenatal energy supplementation may increase birth weight through greater rates of gestational weight gain. The impact of energy supplemen- tation appears to be influenced by the nutritional vulnerability of pregnant women and the extent to which the supplement diminishes the deficit between usual energy intakes and requirements. Gestational weight gain is a function of energy intake, although this re- lationship can be modified by the extent to which basal metabolism changes, by increased work efficiency, by compensatory reductions in physical activity, and by the composition of accumulated maternal and fetal tissue. Within the limitations of these physiologic and metabolic adaptations, gestational weight gain may be affected by changes in energy intake.

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ENERGY AND ASSOCIATED WEIGHT GAIN CLINICAL APPLICATIONS . 171 Extra dietary energy is ordinarily required to meet the increased growth needs during pregnancy. Women who remain physically active at weight-bear~ng activities during pregnancy are likely to have energy requirements higher than those of sedentary women. Because of their larger body mass, obese women require energy intakes higher than those of normal-weight women. Gestational weight gain Is a function of energy intake, although the strength of the relationship Is confounded by intenen~ng factors. Prenatal energy supplementation may increase birth weight through greater rates of gestational weight gain; however, the effectiveness Is con- ditional upon the nutritional vulnerability of the pregnant woman. Energy supplementation is most likely to improve the gestational weight gain of women whose usual diet Is low In calories (e.g., below about 1,900 kcal/day). REFERENCES Abraham, R., M. Campbell-Brown, A.P. Haines, W.R.S. North, V. Hainsworth, and I.R. McFadyen. 1985. Diet during pregnancy in an Asian community in Britain energy, protein, zinc, copper, fibre and calcium. Hum. Nutr.: Appl. Nutr. 39A:23-35. Adair, L S., and E. Pollitt. 1983. Seasonal variation in pre- and postpartum maternal body measurements and infant birth weights. Am. J. Phys. Anthropol. 62:325-331. Adair, L.S., E. Pollitt, and W.H. Mueller. 1983. Maternal anthropometric changes during pregnancy and lactation in a rural Taiwanese population. Hum. Biol. 55:771-787. Adair, L S., E. Pollitt, and W.H. Mueller. 1984. The Bacon Chow study eliect of nutritional supplementation on maternal weight and skinfold thicknesses during pregnancy and lactation. Br. J. Nutr. 51:357-369. Adams, S.O., G.D. Barr, and R.L. Huenemann. 1978. Effect of nutritional supplementation in pregnancy. I. Outcome of pregnancy. J. Am. Diet. Assoc. 72:144-147. Ancri, G., E.H. Morse, and R.P. Clarke. 1977. Comparison of the nutritional status of pregnant adolescents with adult pregnant women. III. Maternal protein and calorie intake and weight gain in relation to size of infant at birth. Am. J. Clin. Nutr. 30:568-572. Anderson, A S., and M.E.J. Lean. 1986. Dietary intake in pregnancy. A comparison between 49 Cambridgeshire women and current recommended intake. Hum. Nutr.: Appl. Nutr. 40A 40-48. Banerjee, B., K.S. Khew, and N. Saha. 1971. A comparative study of energy expenditure in some common daily activities of non-pregnant Chinese, Malay and Indian women. J. Obstet. Gynaecol. Br. Commonw. 78:113-116. Beat, V.A. 1971. Nutritional studies during pregnancy. II. Dietary intake, maternal weight gain, and infant size. J. Am. Diet. Assoc. 58:321-326. Bhatnagar, S., N.S. Dharamshaktu, K.R. Sundaram, and V. Seth. 1983. Effect of food supplementation in the last trimester of pregnancy and early post-natal period on maternal weight and infant growth. Indian J. Med. Res. 77:366-37Z Blackburn, M.W., and D.H. Calloway. 1974. Energy expenditure of pregnant adolescents. J. Am. Diet. Assoc. 65:24-30. Blackburn, M.W., and D.H. Calloway. 1976a. Basal metabolic rate and work energy expenditure of mature, pregnant women. J. Am. Diet. Assoc. 69.24-28.

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