Evidence Considered to Determine the Estimated Energy Requirement

Basal Metabolism. Basal metabolism increases during pregnancy due to the metabolic contribution of the uterus and fetus and increased work of the heart and lungs. The increase in basal metabolism is one of the major components of the increased energy requirements during pregnancy (Hytten, 1991a). Variation in energy expenditure between individuals is largely due to differences in FFM, which in pregnancy is comprised of low energy-requiring expanded blood volume, high energy-requiring fetal and uterine tissues, and moderate energy-requiring skeletal muscle mass (Hytten, 1991a). In late pregnancy, approximately one-half the increment in energy expenditure can be attributed to the fetus (Hytten, 1991a). The fetus uses about 8 ml O2/kg body weight/min or 56 kcal/kg body weight/d; for a 3-kg fetus, this would be equivalent to 168 kcal/d (Sparks et al., 1980). FM, a low energy-requiring tissue, contributes to the variation in energy expenditure, but to a much lesser extent than FFM, which has been found to be the strongest predictor of BEE (Butte et al., 1999).

The basal metabolism of pregnant women has been estimated longitudinally in a number of studies using a Douglas bag, ventilated hood, or whole-body respiration calorimeter (Durnin et al., 1987; Forsum et al.,

DIETARY REFERENCE INTAKES

TABLE 5-22 Estimated Energy Requirements (EER) for Men and Women 30 Years of Agea

PAL*

Sedentary Low active Active Very active

Sedentary Low active Active Very active

Sedentary Low active Active Very active

Sedentary Low active Active Very active

Sedentary Low active Active Very active

Sedentary Low active Active Very active

Sedentary Low active Active Very active

Sedentary Low active Active Very active

Sedentary Low active Active Very active

ENERGY 187

EER, Men (kcal/d)

EER, Women (kcal/d) d

BMI of

BMI of

BMI of

BMI of

18.5 kg/m2

24.99 kg/m2

18.5 kg/m2

24.99 kg/m2

1,777

1,994

1,563

1,691

1,931

2,172

1,733

1,877

2,128

2,399

1,946

2,108

2,450

2,771

2,201

2,386

1,848

2,080

1,625

1,762

2,010

2,268

1,803

1,956

2,216

2,506

2,025

2,198

2,554

2,898

2,291

2,489

1,919

2,168

1,688

1,834

2,089

2,365

1,873

2,036

2,305

2,616

2,104

2,290

2,661

3,028

2,382

2,593

1,993

2,257

1,752

1,907

2,171

2,464

1,944

2,118

2,397

2,728

2,185

2,383

2,769

3,160

2,474

2,699

2,068

2,349

1,816

1,981

2,254

2,566

2,016

2,202

2,490

2,842

2,267

2,477

2,880

3,296

2,567

2,807

2,144

2,442

1,881

2,057

2,339

2,670

2,090

2,286

2,586

2,959

2,350

2,573

2,993

3,434

2,662

2,916

2,222

2,538

1,948

2,134

2,425

2,776

2,164

2,372

2,683

3,078

2,434

2,670

3,108

3,576

2,758

3,028

2,301

2,636

2,015

2,211

2,513

2,884

2,239

2,459

2,782

3,200

2,519

2,769

3,225

3,720

2,855

3,140

2,382

2,735

2,082

2,290

2,602

2,995

2,315

2,548

2,883

3,325

2,605

2,869

3,344

3,867

2,954

3,255

continued

188

DIETARY REFERENCE INTAKES

TABLE 5-22

Continued

Height (m [in])

pala

Weight for BMI of 18.5 kg/m2 (kg [lb])

Weight for BMI of 24.99 kg/m2 (kg [lb])

1.90 (75)

Sedentary Low active Active Very active

66.8 (147)

90.2 (198)

1.95 (77)

Sedentary Low active Active Very active

70.3 (155)

95.0 (209)

a For each year below 30, add 7 kcal/d for women and 10 kcal/d for men. For each year above 30, subtract 7 kcal/d for women and 10 kcal/d for men. b PAL = physical activity level.

c EER for men calculated as: EER = 662 - (9.53 X age [y]) + PA X (15.91 X weight [kg] + 539.6 X height [m]), where PA is the physical activity coefficient of 1.00 for sedentary a For each year below 30, add 7 kcal/d for women and 10 kcal/d for men. For each year above 30, subtract 7 kcal/d for women and 10 kcal/d for men. b PAL = physical activity level.

c EER for men calculated as: EER = 662 - (9.53 X age [y]) + PA X (15.91 X weight [kg] + 539.6 X height [m]), where PA is the physical activity coefficient of 1.00 for sedentary

1988; Goldberg et al., 1993; van Raaij et al., 1990). Cumulative changes in BEE throughout pregnancy ranged from 29,636 to 50,300 kcal or 106 to 180 kcal/d (Table 5-23). Marked variation in the basal metabolic response to pregnancy was seen in 12 British women measured before and throughout pregnancy (Goldberg et al., 1993; Prentice et al., 1989). By 36 weeks of gestation, the increment in absolute BEE ranged from 8.6 to 35.4 percent, or -9.2 to 18.6 percent/kg FFM. Energy-sparing or energy-profligate responses to pregnancy were dependent on prepregnancy body fatness. In 12 Dutch women, the late-pregnancy increment in absolute TEE varied from 9.5 to 26 percent (de Groot et al., 1994). Mean increments in BEE over prepregnancy values were 48, 96, and 263 kcal/d, or 4, 7, and 19 percent in the first, second, and third trimesters in healthy women with positive pregnancy outcomes (Prentice et al., 1996b). The cumulative increase in BEE was positively correlated with weight gain and body fatness.

Prediction equations for the BEE of pregnant women have not been published. Nonpregnant prediction equations based on weight are not accurate during pregnancy since metabolic rate increases disproportionately to the increase in total body weight. Prentice and colleagues (1996b) suggested that BEE could be predicted from weight using the Schofield equations, plus an additional 48, 96, and 263 kcal/d during the first, second, and third trimesters.

ENERGY 189

EER, Men (kcal/d)

EER, Women (kcal/d) d

BMI of

BMI of

BMI of

BMI of

18.5 kg/m2

24.99 kg/m2

18.5 kg/m2

24.99 kg/m2

2,464

2,837

2,151

2,371

2,694

3,107

2,392

2,637

2,986

3,452

2,692

2,971

3,466

4,018

3,053

3,371

2,548

2,940

2,221

2,452

2,786

3,222

2,470

2,728

3,090

3,581

2,781

3,074

3,590

4,171

3,154

3,489

PAL (> 1.0 < 1.4), 1.11 for low active PAL (> 1.4 < 1.6), 1.25 for active PAL (> 1.6 < 1.9), and 1.48 for very active PAL (> 1.9 < 2.5).

d EER for women calculated as: EER = 354 - (6.91 X age [y]) + PA X (9.36 X weight [kg] + 726 X height [m]), where PA is the physical activity coefficient of 1.00 for sedentary PAL, 1.12 for low active PAL, 1.27 for active PAL, and 1.45 for very active PAL.

In late gestation, the anti-insulinogenic and lipolytic effects of human chorionic somatomammotropin, prolactin, cortisol, and glucagon contribute to glucose intolerance, insulin resistance, decreased hepatic glycogen, and mobilization of adipose tissue (Kalkhoff et al., 1978). Although levels of serum prolactin, cortisol, glucagon, and fatty acids were elevated and serum glucose levels were lower in one study, a greater utilization of fatty acids was not observed during late pregnancy (Butte et al., 1999). On the contrary, higher mean respiratory quotients (RQs) were observed for BEE and TEE compared with the postpartum period. Higher basal RQs have been observed in pregnancy by several (Bronstein et al., 1995; Denne et al., 1991; Knuttgen and Emerson, 1974; van Raaij et al., 1989), but not all (Spaaij et al., 1994b) investigators. These observations are consistent with persistent glucose production in fasted pregnant women, despite lower fasting plasma glucose concentrations. After fasting, the total rates of glucose production and total gluconeogenesis were increased, even though the fraction of glucose oxidized and the fractional contribution of gluco-neogenesis to glucose production remained unchanged (Assel et al., 1993; Kalhan et al., 1997). In pregnant women, the sustained energy expenditure and higher RQ may reflect the obligatory oxygen consumption of the fetus and the contribution of glucose as the primary oxidative substrate of the fetus. In late gestation, the fetus is estimated to use 17 to 26 g/d of

190 DIETARY REFERENCE INTAKES

TABLE 5-23 Cumulative Changes in Basal Energy Expenditure (BEE) Throughout Pregnancy

Reference

n

Pregravid Weight (kg [lb])

Gestation Interval

Durnin et al.,

88

57.3±7.5

Prepregnancy to 40 wk

1987

(126.1±16.5)

van Raaij et al.,

57

62.5±8.1

3 wk to term

1987

(137.5±17.8)

Forsum et al.,

22

61.0± 9.9

Prepregnancy to 40 wk

1988

(134.2±21.8)

Goldberg et al.,

12

61.7±8.8

Prepregnancy to 40 wk

1993

(135.7±19.3)

Kopp-Hoolihan

10

NA

Prepregnancy to 35 wk

et al., 1999

a The Douglas bag technique of indirect calorimetry was used to estimate BEE.

a The Douglas bag technique of indirect calorimetry was used to estimate BEE.

glucose (Hay, 1994), well within the increment of carbohydrate oxidation observed in pregnancy.

Thermic Effect of Food. In studies of pregnant women, TEF has been shown to be unchanged (Bronstein et al., 1995; Nagy and King, 1984; Spaaij et al., 1994b) or lower (Schutz et al., 1988) than values of nonpregnant women.

Physical Activity. Until late gestation, the gross energy cost of standardized nonweight-bearing activity does not significantly change. In the last month of pregnancy, the energy expended while cycling was increased on the order of 10 percent. However, when corrected for increased BMR the increased energy expenditure due to the activity of cycling was 6 percent (Prentice et al., 1996b). The energy cost of standardized weight-bearing activities such as treadmill walking was unchanged until 25 weeks of gestation, after which it increased by 19 percent (Prentice et al., 1996b). Standardized protocols, however, do not allow for behavioral changes in pace and intensity of physical activity, which may occur and conserve energy during pregnancy.

Growth of Maternal and Fetal Tissues. Gestational weight gain includes the products of conception (fetus, placenta, and amniotic fluid) and accretion of maternal tissues (uterus, breasts, blood, extracellular fluid, and adipose). The energy cost of deposition can be calculated from the amount of protein and fat deposited. Hytten (1991b) made theoretical

ENERGY

Cumulative Increase in BEE (kcal)

Cumulative Increase in BEE (kcal/d)

Method Used to Estimate BEE

30,114 34,416 50,300 29,636 36,089

108 133 180 106 147

Indirect calorimetry"

Indirect calorimetry"

calculations based on a weight gain of 12.5 kg and birth weight of 3.4 kg. The energy equivalents for protein and fat deposition were assumed to be 5.6 kcal/g and 9.5 kcal/g, respectively. The energy cost of tissue deposition was equivalent to 3.32 kcal/g gained (Table 5-24).

Current recommendations for weight gain during pregnancy are specified for a woman's prepregnancy BMI (IOM, 1990). Total weight gain during pregnancy varies widely among women. For normal-weight women, the mean rate of weight gain is 1.6 kg in the first trimester and 0.44 kg/wk in the second and third trimesters (IOM, 1990). For underweight women, the mean rate of weight gain is 2.3 kg in the first trimester and 0.49 kg/wk in the second and third trimesters. For overweight women, the mean rate of weight gain is 0.9 kg in the first trimester and 0.30 kg/wk in the second and third trimesters.

Fat gains associated with gestational weight gains within the IOM recommended ranges were measured in 200 women with varying prepregnancy BMIs using a four-component body composition model (Lederman et al., 1997). The total energy deposition between 14 and 37+ weeks of gestation was calculated based on an assumed protein deposition of 925 g of protein, and energy equivalences of 5.65 kcal/g of protein and 9.25 kcal/g of fat (Table 5-25).

Empirical data on the longitudinal changes in the body composition of well-nourished, normal weight (prepregnancy BMI from 18.5 up to 25 kg/m2) pregnant women were used to estimate the energy deposition during pregnancy. Studies in which a prepregnancy baseline or first trimester value was available and methodology was appropriately corrected

DIETARY REFERENCE INTAKES

TABLE 5-24 Theoretical Energy Cost of Tissue Deposition During Pregnancy

Protein

Fat

Protein

Fat

Gain

Gain

Total Energy

Gain (g)

Gain (g)

(kcal)

(kcal)

Deposition" (kcal)

Fetus

440

440

2,464

4,180

6,644

Placenta

100

4

560

38

598

Amniotic fluid

3

0

17

0

17

Uterus

166

4

930

38

968

Breasts

81

12

454

114

568

Blood

135

20

756

190

946

Maternal stores

3,345

31,778

31,778

Total

925

3,825

5,180

36,338

41,518

a Based on 5.6 kcal/g for protein gained and 9.5 kcal/g for fat gained. SOURCE: Adapted from Hytten (1991b).

TABLE 5-25 Estimated Energy Deposition During Pregnancy

Prepregnancy

Recommended

Estimated

Body Mass

Gestational

Actual

Fat

Energy

Index (BMI)

Weight Gain"

GWG

Gain

Deposition

(kg/m2)

(GWG) (kg [lb])

(kg [lb])

(kg)

(kcal)

Low (BMI < 19.8)

12.5-18.0 (28-40)

12.6±2.4

6.0±2.6

60,726

(28±5.3)

Normal (BMI =

11.5-16.0 (25-35)

12.1±3.4

3.8±3.5

40,376

19.8-26.0)

(27±7.5)

High (BMI >

7.0-11.5 (15-25)

9.1±3.1

2.8±4.1

31,126

26.0-29.0)

(20±6.8)

Obese (BMI > 29.0)

At least 6.8 (15) c

6.9±4.4

-0.6±4.6

-324

(15±9.7)

b a As recommended by IOM (1990).

b Calculated based on assumed 5.65 kcal/g of protein gained and 9.25 kcal/g of fat gained.

c Lederman et al. (1997), used 7-9.2 kg (15-20 lb). SOURCE: Adapted from Lederman et al. (1997).

b for pregnancy-induced changes in the hydration or density of FFM were used (Table 5-26). Total energy deposition during pregnancy was estimated from the mean fat gain of 3.7 kg from these studies, plus an assumed deposition of 925 g of protein, applying energy equivalencies of 5.65 kcal/g of protein and 9.25 kcal/g of fat. Mean total energy deposition was equal to 39,862 kcal or 180 kcal/d (Table 5-26).

ENERGY 193

Total Energy Expenditure. The DLW method has been employed in four studies of well-nourished, pregnant women to measure free-living TEE (Forsum et al., 1992; Goldberg et al., 1991b, 1993; Kopp-Hoolihan et al., 1999) (Table 5-27). There appeared to be a steady decrease in PAL as pregnancy advanced, primarily due to the increase in the denominator, BEE. In the British (Goldberg et al., 1993) and Swedish women (Forsum et al., 1992) studied, the energy expenditure for activity (TEE - BEE) decreased in the 36th week of gestation; this decrease was not observed in the American women (Kopp-Hoolihan et al., 1999).

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