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Introduction
Methods
Basic physiology of lactation
Is BMI a useful discriminator of lactation performance in terms of breast-milk quantity?
Is BMI a useful discriminator of lactation performance in terms of breast-milk quality?
Conclusions
References
Discussion
A. M. Prentice, G. R. Goldberg and A. Prentice
MRC Dunn Nutrition Unit, Milton Road, Cambridge CB4 1XJ, UK
Data from the world literature have
been analysed in order to test whether low body mass index (BMI: kg/m2) is a useful
indicator of functional impairment of lactation performance. Forty-one databases
containing 1726 measurements have been identified as having reliable estimates of
breast-milk quantity and/or quality. There is no detectable relationship between maternal
BMI and the volume of milk produced by mothers when analysed according to the mean BMI of
different populations, or of different subgroups stratified by BMI within populations.
This conclusion holds even at BMIs <18.5. The most remarkable feature of the data is
the very high milk volumes produced by very thin mothers. It is accepted that the
composition of breast milk is relatively unaffected by general undernutrition of the type
that would be indicated by a low BMI with the possible exception of milk fat levels and
hence the energy content. Analysis of the available data reveals studies in which there
are weak, but significant, correlations between maternal BMI and milk fat. However, other
studies show no association or even a negative relationship. Inter-country analysis fails
to reveal any detectable association between BMI and milk energy. Milk energy levels seem
adequate even at BMIs <18.5. It is concluded that human lactation performance is
extremely robust and that BMI does not provide a useful indicator of function at the
levels studied so far. Lactation performance must become compromised when undernutrition
is sufficiently severe, but it appears that this must occur only in famine or near famine
conditions.
Lactation imposes a significant additional energy
stress on women. It might therefore be supposed that lactation performance would be
related to a mother's body energy stores as assessed by the body mass index (BMI: kg/m2).
This paper examines the world literature to test whether this is in fact the case. The
surprising conclusion is that there appears to be very little relation between BMI and
breast-milk quantity or quality, even at BMIs. We conclude that BMI is not a sensitive
index of functional capacity in lactation.