Estimated Energy Requirements

The incremental energy cost of lactation is determined by the amount of milk produced (exclusivity and duration), the energy density of the milk secreted, and the energy cost of milk synthesis [6]. The Estimated Energy Requirements (EERs) for lactation, or the average daily energy intake predicted to maintain energy balance in a healthy lactating woman, of a given age, weight, height, and level of physical activity can be estimated by a factorial approach from the sum of the (1) EER of a nonpregnant, nonlactating woman (of a given age, weight and activity level), plus (2) estimated milk energy output, plus (3) energy mobilization from tissue stores (i.e., weight loss) [7]:

  1. The EER of a nonpregnant nonlactating woman can be calculated using information provided in Table 18.1. The current age, weight and relative physical activity level must be known.
  2. Milk energy output is tabulated by multiplying the volume of milk produced by its energy density (Table 18.2). The figure used by the Institute of Medicine to estimate the daily volume of milk produced from birth to six months is 0.78 l/day [7]. From 7 to 12 months, mean milk production is estimated to be 0.6 l/day, reduced with the introduction of solid foods. While the daily volume of breast milk produced among exclusively breastfeeding mothers is remarkably consistent from woman to woman and country to country, it varies considerably, of course, if a woman is partially or totally breastfeeding [6]. The US Institute of Medicine reviewed studies where human milk energy density was measured by bomb calorimetry and found an average value of 0.67 kcal/g.
  3. Energy mobilization from tissue stores is the energy derived from the weight lost in the first six months postpartum (Table 18.2). For the purposes of calculating the EERs for lactation this value was set at 0.8 kg/month [7].

Research shows that women meet most of the incremental energy requirements of lactation by eating more calories, decreasing physical activity early postpartum, and mobilizing fat stores laid down during pregnancy [6]. Mobilization of fat stores laid down during pregnancy is not obligatory, and the extent to which they are used to support lactation depends on the nutritional status of the lactating mother and the amount of weight gained during pregnancy. A well-nourished woman will mobilize approximately 0.72 MJ/day (~170 kcal/day) of fat stores to help support breastfeeding in the first 6 months postpartum. Physical activity tends to be lower in the early postpartum period among women in the developed world, as daily activities change in response to caring for a newborn. While the expectation of many women is that they will lose weight rapidly by breastfeeding, weight changes postpartum are highly variable, though they are greater and more consistent for women who breastfeed exclusively. Some women may actually gain weight postpartum. Generally, well-nourished women will lose on average 0.8 kg/month (1.8 pounds/month) for the first 6 months postpartum; undernourished women can expect to lose 0.1 kg/month.

The reported energy intakes of lactating women in the literature are generally lower than that recommended by the Institute of Medicine [7]. Under-reporting may be a reason for these low energy intakes or the EER is set too high. Alternatively, mobilization of fat stores may play a greater role in energy balance or energy expenditure is lower than expected. There is little evidence to suggest energy conservation in the lactating woman, i.e., more efficient metabolism due to a change in the hormonal milieu, for example. Most research data do not suggest that an individual's basal

Table 18.1

Calculating the Estimated Energy Requirement (EER) for a Nonpregnant, Nonlactating Woman 30 Years of Agea [7]

Table 18.1

Calculating the Estimated Energy Requirement (EER) for a Nonpregnant, Nonlactating Woman 30 Years of Agea [7]

Weight for BMI

Weight for BMI

EER, women (kcal/day)c

of 18.5 kg/m2

of24.99kg/m2 kg

BMI of

BMI of

Height m (in)

PALb

kg (lb)

(lb)

18.5 kg/m2

24.99 kg/m

1.45 (57)

Sedentary

38.9 (86)

52.5 (116)

1,563

1,691

Low active

1,733

1,877

Active

1,946

2,108

Very active

2,201

2,386

1.50 (59)

Sedentary

41.6 (92)

56.2 (124)

1,625

1,762

Low active

1,803

1,956

Active

2,025

2,198

Very active

2,291

2,489

1.55 (61)

Sedentary

44.4 (98)

60.0 (132)

1,688

1,834

Low active

1,873

2,036

Active

2,104

2,290

Very active

2,382

2,593

1.60 (63)

Sedentary

47.4 (104)

64.0 (141)

1,752

1,907

Low active

1,944

2,118

Active

2,185

2,383

Very active

2,474

2,699

1.65 (65)

Sedentary

50.4 (111)

68.0 (150)

1,816

1,981

Low active

2,016

2,202

Active

2,267

2,477

Very active

2,567

2,807

1.70 (67)

Sedentary

53.5 (118)

72.2 (159)

1,881

2,057

Low active

2,090

2,286

Active

2,350

2,573

Very active

2,662

2,916

1.75 (69)

Sedentary

56.7 (125)

76.5 (168)

1,948

2,134

Low active

2,164

2,372

Active

2,434

2,670

Very active

2,758

3,028

1.80 (71)

Sedentary

59.9 (132)

81.0 (178)

2,015

2,211

Low active

2,239

2,459

Active

2,519

2,769

Very active

2,855

3,140

1.85 (73)

Sedentary

63.3 (139)

85.5 (188)

2,082

2,290

Low active

2,315

2,548

Active

2,605

2,869

Very active

2,954

3,255

1.90 (75)

Sedentary

66.8 (147)

90.2 (198)

2,151

2,371

Low active

2,392

2,637

Active

2,692

2,971

Very active

3,053

3,371

1.95 (77)

Sedentary

70.3 (155)

95.0 (209)

2,221

2,452

Low active

2,470

2,728

Active

2,781

3,074

Very active

3,154

3,489

"For each year below 30, add 7 kcal/day. For each year above 30, subtract 7 kcal/day. bPAL physical activity level.

cEER for women can be calculated as follows: EER = 354 - (6.91 X age [years] + PA X (9.36 X weight [kg] + 726 X height [m]), where PA is the physical activity coefficient of 1 for sedentary PAL, 1.12 for low active PAL, 1.27 for active PAL, and 1.45 for very active PAL.

"For each year below 30, add 7 kcal/day. For each year above 30, subtract 7 kcal/day. bPAL physical activity level.

cEER for women can be calculated as follows: EER = 354 - (6.91 X age [years] + PA X (9.36 X weight [kg] + 726 X height [m]), where PA is the physical activity coefficient of 1 for sedentary PAL, 1.12 for low active PAL, 1.27 for active PAL, and 1.45 for very active PAL.

Table 18.2

Calculating the Estimated Energy Requirement (EER) for a Lactating Woman [7]

  • adult EER
  • milk energy output
  • weight loss

See Table 1(7)

500kcal (1st six months) 400kcal (2nd six months)

170 kcal (1st six months) 0 kcal (2nd six months)

WHY?

WHY?

calculated based = milk production x energy density on a non-pregnant 1st 6 months: 0.78 L/d x woman's weight, 0.67 kcal/g rounded to age, and physical 500 kcal/d 2nd 6 months:

activity level 0.6 L/d x 0.67 kcal/g

Weight loss seen in 1st six months with an average loss of 0.8 kg/month equivalent to 170-kcal/d deficit rounded, to 400 kcal/d metabolic rate is lower during lactation than prepregnancy or that more energy is used to complete a physical task. Basal metabolic rate is the rate of energy expenditure in an individual resting comfortably, awake, and motionless, 12-14 h after last consuming food.

18.2.1.1 A Sample Calculation of the Estimated Energy Requirement for Lactation

Using Tables 18.1 and 18.2, the EER for lactating women may be calculated. Using the example of a "low active," exclusively, for a lactating woman 4 months postpartum who is 35 years of age, and weighs 60 kg and is 1.6 m tall, you would first refer to Table 18.1, and calculate her EER as if she were neither pregnant nor lactating. Alternatively, you could calculate her estimated energy requirement as if she was nonpregnant, nonlactating using footnote a of Table 18.1. Using the table itself, our sample lactating woman would have a nonpregnant, nonlactating estimated energy requirement of 2,083 kcal. To this value, you would add 500 kcal to account for the amount of energy required to produce breast milk, and subtract 170 kcal for the contribution from fat stores laid down in pregnancy (information found in Table 18.2). Hence, our sample lactating woman's EER would be approximately 2,413 kcal (2,083 + 330). It is important to stress this is an estimate of the energy requirements of an average woman only, and follow-up is required to ascertain its appropriateness at an individual level, i.e., some women can gain or lose weight using this recommendation for energy intake.

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