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OCR for page 137
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
OCR for page 138
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
OCR for page 139
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OCR for page 165
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.
OCR for page 166
166
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OCR for page 167
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.,
OCR for page 168
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
OCR for page 169
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
OCR for page 170
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.
OCR for page 171
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).
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Representative terms from entire chapter:
energy intake
