Macronutrients Energy

Energy needs during pregnancy vary according to a woman's basal metabolic rate, prepregnancy weight, amount and composition of weight gain, stage of pregnancy, and physical activity level. It is estimated that on average a pregnant woman requires a total of 85,000 additional calories over the course of 40 weeks of pregnancy, which extrapolates to approximately 300 extra calories per day [3]. For most women, however, energy needs in the first trimester of pregnancy are minimal. While the first trimester is characterized by rapid development of fetal organs and tissues, these processes are not very energy intensive. Maternal basal metabolic rate, for example, does not measurably increase until the fourth month of pregnancy when notable increases in growth of the uterus, mammary glands, placenta and fetus, and increases in blood volume and the work of the heart and respiratory system begin. As a woman's weight increases, she also requires more energy to accomplish the same amount of physical work such that even if physical activity levels remain unchanged from prior to pregnancy, the energy costs of these activities increase.

When the new DRIs for macronutrients were released in 2005 [4], a new approach was used to estimate the energy requirements of pregnancy. Since total energy expenditure (TEE) had been measured using doubly labeled water in several hundred pregnant women, those data were used as the basis for the recommendation. The Estimated Energy Requirement (EER) for pregnancy is derived, therefore, from the sum of the TEE in nonpregnant women plus a median change in TEE of 8 kcal/week plus 180 kcal/day in the second and third trimesters to account for the energy deposition in tissue gained. At 20 weeks' gestation, the additional energy required totals 340 kcal/day; at 34 weeks gestation the additional energy need is 450 kcal/day. Table 1.2 illustrates how energy needs for pregnant women vary with body mass index (BMI) and physical activity level.

Because energy needs are influenced by a variety of factors, they can vary dramatically between individuals. For this reason, monitoring weight gain during pregnancy is the best way to ensure adequacy of energy intake [5]. The IOM [3] released recommendations for

Table 1.2

Estimated Energy Requirements (EER) for Women 30 Years of Age During Pregnancy. (Adapted from [4])

Table 1.2

Estimated Energy Requirements (EER) for Women 30 Years of Age During Pregnancy. (Adapted from [4])

Prepregnancy BMI

Prepregnancy BMI

Height m (in)

PAL

of 18.5 kg/m2

of24.99 kg/m2

First trimester

1.50 (59)

Sedentary

1,625

1,762

Low active

1,803

1,956

Active

2,025

2,198

Very active

2,291

2,489

1.65 (65)

Sedentary

1,816

1,982

Low active

2,016

2,202

Active

2,267

2,477

Very active

2,567

2,807

1.80 (71)

Sedentary

2,015

2,211

Low active

2,239

2,459

Active

2,519

2,769

Very active

2,855

3,141

Second trimester

1.50 (59)

Sedentary

1,965

2,102

Low active

2,143

2,296

Active

2,365

2,538

Very active

2,631

2,829

1.65 (65)

Sedentary

2,156

2,322

Low active

2,356

2,542

Active

2,607

2,817

Very active

2,907

3,147

1.80 (71)

Sedentary

2,355

2,551

Low active

2,579

2,799

Active

2,859

3,109

Very active

3,195

3,481

Third trimester

1.50 (59)

Sedentary

2,075

2,212

Low active

2,253

2,406

Active

2,475

2,648

Very active

2,741

2,939

1.65 (65)

Sedentary

2,266

2,432

Low active

2,466

2,652

Active

2,717

2,927

Very active

3,017

3,257

1.80 (71)

Sedentary

2,465

2,661

Low active

2,689

2,909

Active

2,969

3,219

Very active

3,305

3,591

For each year below 30, add 7 kcal/day; for each year above 30 subtract 7 kcal/day PAL physical activity level aDerived from the following regression equation based on doubly labeled water data: EER = 354 - 6.91 x age (years) + PA x (9.36 x wt [kg] + 726 x ht [m]), where PA refers to coefficient for PAL

PAL = (total energy expenditure) / (basal energy expenditure) PA = 1 if PAL > 1 < 1.4 (sedentary) PA = 1.12 if PAL > 1.4 < 1.6 (low active) PA = 1.27 if PAL > 1.6 < 1.9 (active) PA = 1.45 if PAL > 1.9 < 2.5 (very active)

For each year below 30, add 7 kcal/day; for each year above 30 subtract 7 kcal/day PAL physical activity level aDerived from the following regression equation based on doubly labeled water data: EER = 354 - 6.91 x age (years) + PA x (9.36 x wt [kg] + 726 x ht [m]), where PA refers to coefficient for PAL

PAL = (total energy expenditure) / (basal energy expenditure) PA = 1 if PAL > 1 < 1.4 (sedentary) PA = 1.12 if PAL > 1.4 < 1.6 (low active) PA = 1.27 if PAL > 1.6 < 1.9 (active) PA = 1.45 if PAL > 1.9 < 2.5 (very active)

weight gain during pregnancy based on prepregnancy weight status. For women classified as being within a normal weight range prior to pregnancy (BMI 19.8-26 kg/m2), the recommended weight gain is 11.3-15.9 kg (25-35 lbs.), and the recommended rate of weight gain is 0.9-1.8 kg (2-4 lbs.) in the first trimester and about 0.5 kg (1 lb.)/week thereafter. A slightly higher total gain of 12.7-18.1 kg (28-40 lbs.) is recommended for underweight women (BMI < 19.8). A slightly lower total gain of 6.8-11.3 kg (1525 lbs.) and at least 6.8 kg (15 lbs.) is recommended for women who, prior to pregnancy, are overweight (BMI > 26-29) and obese (BMI > 29), respectively. Even among obese women, inadequate weight gain during pregnancy can lead to increased risk of preterm delivery [6].

The additional energy requirements of pregnancy are small relative to the needs for many other nutrients. While an extra 340-450 kcal could be consumed by simply adding a glass of 2% milk and a small sandwich, this would not meet increased nutrient needs for pregnancy. The fact that the relative increase for many other nutrients is more dramatic than for energy indicates the importance of emphasizing nutrient-dense foods during pregnancy. Following the dictum of "eating for two" may result in excessive maternal weight gain. Further, for obese women, sedentary women, and women whose activity levels decline during pregnancy (e.g., bed rest) the recommendations of 340-450 kcal/day may be too high. On the other hand, underweight women, young adolescent mothers who are still growing (<14 years), and women carrying multiple fetuses may need 500 kcal/day or more [7].

The goal is to avoid both ends of the spectrum, both excessive energy intake as well as inadequate energy intake. Overnutrition and excess weight gain in pregnancy impart risk of gestational diabetes, macrosomia, delivery complications such as shoulder dys-tocia, cesarean delivery and post operative problems, difficulty initiating breastfeeding, and risk of subsequent maternal and child obesity [8-10]. Conversely, undernutrition and inadequate weight gain during pregnancy can lead to impaired intrauterine growth and consequent low birth weight of the newborn. In addition to complications at birth, intrauterine growth retardation has been associated with metabolic abnormalities in adulthood, such as hyperlipidemia, hypertension, cardiovascular disease, glucose intolerance, and type 2 diabetes [10, 11].

1.2.1.2 Protein

During pregnancy, additional dietary protein is used for fetal growth, placental development, production of amniotic fluid, increased maternal blood volume, and gain of other maternal tissues. Increases in protein needs mirror maternal and fetal growth rates; early in pregnancy, the requirements for extra protein are relatively small, but increase progressively as pregnancy proceeds. Approximately 82% of the total demand for the 925 g of protein required for maternal and fetal needs is accumulated over the last half of gestation [12]. Inadequate maternal protein intake incurs risk of low birth weight.

A factorial approach was used to calculate the protein DRI during pregnancy. The summation of the additional lean tissue accumulated in pregnancy and the additional protein required to maintain an increased body weight were estimated as outlined in Table 1.3. By the second half of pregnancy, this translates into a 25-g/day increased requirement for a total of approximately 70-75 g/day (or 1.1 g protein per kg of body weight per day) [4].

Table 1.3

Derivation of Protein Requirements During Pregnancy. (Adapted from [4])

Maintenance of increased body weight

Fetal and maternal tissue deposition

Estimated average Average weight requirement Additional protein gain (kg)a (gfkg/dayf required(g/day)

Protein Utilization Additional deposition efficiency of protein required (g/day) dietary protein (g/day)c

Total increase in protein required for pregnancy (g/day)J

12.8 0.66 8.5

5.4 0.43 12.6

25

'Average for trimesters 2 and 3; protein requirements in trimester 1 are estimated to be minimal bEstimated average requirement for maintenance of protein in adults cBased on slope of regression line of protein intake versus nitrogen balance (recalculated from [13]) 11 Adjusted for normal variation to meet the needs of 97.5% of pregnant women

The relative increased need above nonpregnancy is greater for protein (54% increase) than for any other nutrient. However, because protein intakes tend to be high relative to needs in the nonpregnancy state, averaging approximately 60 g/day for nonpregnant women [4], inadequate protein intake is not common in the United States, even among pregnant women. However, vegans and women carrying multiple fetuses may need to pay close attention to their protein intakes.

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