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Energy requirements of pregnant and lactating women

Introduction
Pregnancy
Recommendations for pregnancy
Lactation
Recommendations for lactation
References
Discussion
References

AM Prentice¹, CJK Spaaij², GR Goldberg¹, SD Poppitt¹, JMA van Raaij², M Totton¹, D Swann¹ and
AE Black¹

¹ MRC Dunn Clinical Nutrition Centre, Hills Road, Cambridge CB2 2DH; ² Department of Human Nutrition
Agricultural University of Wageningen, The Netherlands

Descriptors: pregnancy, lactation, energy requirements

Introduction

The 1985 FAO/WHO/UNU recommendations for energy and protein requirements were based on a meeting of an expert panel held in October 1981 as the culmination of a review process initiated soon after the publication of the 1973 guidelines (FAO/WHO/UNU, 1985). Since this time a considerable amount of new data have been collected in the fields of pregnancy and lactation. Much of the research, particularly with respect to pregnancy, has been specifically directed towards the definition of recommended dietary allowances and therefore permits a thorough review of the 1985 recommendations.

In this position paper we review the new data in some detail, and attempt to resolve outstanding areas of controversy especially those relating to the apparent mismatch between estimated incremental needs and observed energy intakes. We explore alternative methods for expressing the incremental requirements for reproduction to bring them closer into line with the use of physical activity levels (PALs) as applied to other adults.

The existing FAO/WHO/UNU recommendations for pregnancy and lactation are summarised in Tables 1 and 2 and compared with some other recent guidelines from affluent nations.

Pregnancy

The 1985 values were based on a general acceptance of Hytten's estimate that the total energy needs of pregnancy amount to 335 MJ (80000 kcal) or about 1.2 MJ/ day (285 kcal/day; Hytten & Chamberlain, 1980). There was a clear recognition that this rather small increment could be greatly influenced by possible changes in physical activity, and that a reduction in activity might explain why 'many recent studies of food intakes of well nourished pregnant women indicate that the extra energy requirements for tissue deposition are not always accompanied by commensurate increases in intake'. The recommended increment of 1.2 MJ/day was applied evenly across pregnancy because 'some fat should be deposited early in pregnancy, and because appetite and periodic work requirements vary greatly'. It was considered reasonable to reduce the average additional allowance to 0.84 MJ/day (200 kcal/day) where healthy women reduce their activity. Table 1 highlights the wide differences in allowances between various reports. These reflect both differences in interpretation of the available data and in underlying philosophy. Most reports published after 1985 have recommended lower increments than the FAO/WHO/UNU figure.

Correspondence: AM Prentice.

Lactation

The 1985 recommendations were based on the median milk consumption of breast-fed Swedish infants for the first 6 months and on more limited data from a number of populations for later periods. It was assumed that milk energy was 2.9 kJ/g (0.7 kcal/g) and the efficiency of conversion of dietary to milk energy was 80%. Furthermore it was assumed that the average woman would start lactation with 150 MJ (36000 kcal) of additional fat reserves (laid down in pregnancy) and that these would be used to subsidise the cost of lactation over the first 6 months thus yielding about 0.84 MJ/day (200 kcal/day). It was stated that allowances 'will need to be adjusted according to maternal fat stores and patterns of activity', but no additional figures were provided.

It can be seen from Table 2 that there is a much greater international consensus regarding recommended allowances for lactation than for pregnancy (Table 1) There has not been such a pronounced trend towards lowering allowances for lactation as there has been for pregnancy.

Recent advances in understanding the links between maternal nutrition and the well-being of her offspring

Since 1985 there have been major advances in our understanding of the potential influence that a mother's nutrition can have on the health of her children. In particular, the work of Barker (1992) and his colleagues on the fetal origins of adult disease has demonstrated that the pattern of fetal growth is a strong predictor of later susceptibility to diseases of affluence such as cardiovascular disease, non-insulin dependent diabetes, hypertension and hyperlipidaemia (Goldberg & Prentice, 1994). These findings re-emphasise the importance of ensuring optimal maternal nutrition, and indicate an urgent need to revise the previous assumption that a pregnancy had been successful if it resulted in a baby of viable birthweight. In our opinion such findings point to a need to err on the side of plenty when setting allowances.

Table 1 Existing FAO/WHO/UNU recommendations for pregnancy and comparison with UK, USA and Dutch values

From FAO/WHO/UNU (1985), COMA (1991), NAS (1989), Dutch Expert Committee (1981).

Table 2 Existing FAO/WHO/UNU recommendations for lactation and comparison with UK, USA and Dutch values

From FAO/WHO/UNU (1985), COMA (1991), NAS (1989), Dutch Expert Committee (1981).

Psychological impact of setting 'minimalist' allowances for pregnancy

The trend towards reduced allowances in pregnancy has been fuelled by the desire to ensure that recommended allowances are not at variance with observations of increased food intake. The apparent paradox between estimates of needs and estimates of intake has been explained away by assuming that physical activity naturally decreases in pregnancy or that women are capable of energy-sparing alterations in metabolism. We recommend that such arguments are introduced only with great caution since women in developing countries may be prevented from reducing their activity by the constraints of a subsistence livelihood. Furthermore it must be made quite clear that, although energy-sparing metabolic adjustments may help women to carry a pregnancy to term under harsh nutritional conditions, such adjustments almost certainly result in health costs to both the mother and the baby. They should never be equated with optimal performance. To this end we recommend that allowances should clearly reflect the full costs of pregnancy and lactation, and that conditional reductions should receive less prominence than in the past.

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