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close this bookMaternal Diet, Breast-Feeding Capacity, and Lactational Infertility (UNU/WHO, 1983, 107 pages)
close this folder3. Effect of diet on maternal health and lactational performance
View the document(introductory text...)
View the documentBody size and composition
View the documentProtein status of the mother
View the documentMaternal vitamin status
View the documentDiet and breast-milk composition
View the documentDiet and the quantity of milk produced
View the documentThe effect of maternal dietary supplementation on milk output and composition
View the documentGeneral conclusion
View the documentReferences

Diet and breast-milk composition

Proximal Constituents

3.8. Generally speaking, it would appear that, except in extreme maternal undernutrition, the concentrations of total energy and protein in breast-milk are maintained at remarkably normal levels. In the Gambia, for example, where even during good times of the year dietary mean intake is only 1,700 kcal/d, the average energy content of the mother's milk is maintained at 72 kcal/100 ml, which compares well with the mean content of British mothers' milk, 69 kcal/100 ml. Even when mean intake was 1,100-1,200 kcal/d the energy content only dropped by about 10 per cent.

3.9. It is not easy to be precise about the effect of maternal diet on fat content, because concentration varies during the course of a feed - the fore-milk being more dilute than hind-milk. Most studies have been based on expressed milk, but more cannot be sure that this reproduces the same value that integrated measurements during actual breast-feeding would. In the Gambia, an estimate of the average fat content as consumed by the baby is 3.86 9/100 ml(14), in comparison with a value for British women of 4.2 9/100 ml(15). Whether the differences truly reflect maternal dietary differences, or whether they are due to different collection methods, is not known.

Hambraeus has reviewed the literature on the fatty acid composition of mothers' milk(16). It would seem that the milk fat resembles that of the mother's diet when her plane of energy intake is good, but when there is a shortage of food energy the milk fatty acid pattern resembles more that of the mother's subcutaneous fat stores. Maternal fat intake has no effect on the total triglyceride content, however, as illustrated by the Gambian data. The fat content of the Gambian diet is no greater than 10 per cent of the total energy, while in United Kingdom it is over 40 per cent, yet the fat concentrations are essentially the same.

3.10. The lactose content of human milk is high, around 7 9 per 100 ml. This component seems very stable in concentration as illustrated in table 7, which show that the milk of non-privileged Ethiopian mothers has very much the same lactose content as their Swedish and privileged Ethiopian counterparts (17).

TABLE 7. Lactose Content in Human Milk (9/100 ml, Means and SD)

Duration of lactation (months)

Swedish mothers

Ethiopian mothers

Privileged

Non-privileged

0-0.5

5.9 + 0.6

6.5 + 0.9

 
0.5-1.5

7.0 + 0.6

6.6 + 0.6

7.4 + 0.5

1.5-3.5

7.3 + 0.5

7.6 + 0.2

7.4 + 0.5

3.5-6.5

7.6 + 0.4

7.5 + 0.3

 
> 6.5

7.8 + 0.5

   

Source: ref. 17.

3.11. The overall protein content of human milk also seems remarkably stable to despite changes in the maternal diet, as illustrated in table 8. Once again there is a remarkable similarity between the two sets of data from Swedish and non-privileged Ethiopian mothers(17). In the Gambia also, total protein content was essentially maintained at British levels despite an intake of marginal adequacy. During the period of the year when food intake was especially poor, some fall in milk total nitrogen content was observed, but this was by no more than 10 per cent. It must also be remembered that not all the protein in milk is a dietary source. Some of the fractions have specific functions as protective factors. The effect of diet on these components has still to be evaluated, a task complicated by the need to integrate the effects of dietary change with intercurrent infections afflicting both the mother and her baby.

TABLE 8. Nitrogen and Protein Composition of Mature Human Milk (mg per ml, Means and SD)

 

Swedish Mothers

Non-privileged Ethiopian mothers

Total nitrogen

1.61 + 0.21

1.77 + 0.33

Non-protein nitrogen

0.41 + 0.04

0.36 + 0.05

alfa-lactalbumin

2.78 + 0.49

2.76 + 0.29

Lactoferrin

1.65 + 0.29

1.67 + 0.51

Serum albumin

0.39 + 0.04

0.36 + 0.07

Source: ref. 17.

 

Vitamins and Minerals

3.12. In contrast to the proximal constituents, vitamin content - particularly of the water-soluble vitamins - is very sensitive to dietary intake. In the Far East a maternal diet deficient in thiamin can result in infantile beri-beri(18). Riboflavin content is also affected by maternal diet, as illustrated in table 9 (1). In the Gambia, milk values are only two-thirds of those in the United Kingdom and only about half the reported American ones. Thus, despite the existence of mechanisms that favour the foetus and the suckling child at the expense of maternal stores, the baby is born biochemically deficient; because the breast-milk has a low riboflavin content, and any traditional supplementary food an even lower one, the baby remains deficient throughout infancy (19).

The vitamin C content of milk also parallels closely the monthly variations in vitamin intake and plasma ascorbic acid levels (see



FIG. 8. Seasonal Changes in Breast-milk Ascorbic Acid in the Gambia (Source: ref. 8)) (8). Likewise, folic acid content is also affected (table 9). In the Gambian dry season, mean concentrations were 54 ng/ml, while in the wet season these had dropped to 38 ng/ml. A comparison of breast-milk concentrations of other water-soluble vitamins during the two seasons is shown in table 9.

TABLE 9. Seasonal Variations in Breast-milk Composition in the Gambia

 

Dry season (N = 22)

Wet season
(N = 21)

Mean stage of lactation (days)

149

132

Energy (kcal/100 ml)

69 ± 2

65 ± 2

Protein (9/100 ml)

1.10 ± 0.05

0.98 ± 0 07

Fat (9/100 ml)

4.36 ± 0.25

3.45 ± 0.22a

Lactose (9/100 ml)

6.35 ± 0.09

7.17 ± 0.09b

Biotin (ng/ml)

10.3 ± 0.87

8.97 ± 0.69

Pantothenic acid (µg/ml)

2.71 ± 0.14

2.04 ± 0.11b

Thiamin (µg/ml)

0.175 ± 0.005

0.157 ± 0.006

Riboflavin (µg/ml)

0.23 ± 0.01

0.21 ± 0.01

Vitamin B6 (µg/ml)

0.091 ± 0.004

0.115 ± 0.005b

Vitamin B12 (ng/ml)

0.290 ± 0.046

0.163 ± 0.040

Nicotinic acid (µg/ml)

1.49 ± 0.098

1.13 ± 0.111

Folic acid (ng/ml)

54.3 ± 5.7

38.2 ± 2.9a

Values are means SEM.
a. p < 0.02
b. p < 0.001
N = number of subjects
Source: ref. 1.

3.13. The situation with the fat-soluble vitamins is less dramatic but nevertheless clear-cut. A comparative study of breast-milk samples from well nourished Swedish mothers and underprivileged Ethiopian ones has shown a significantly higher vitamin A level in the former and a greater concentration of 9-carotene in the latter(20).

The fat-soluble vitamin D content of breast-milk is generally low even in well-nourished mothers. Recently, however, there has been a report of a water soluble conjugate, vitamin D sulphate, in human milk (21 ) but the biological activity of this derivative is still in question (22).

3.14. The mineral content of human breast-milk in relation to diet has been insufficiently studied. The calcium content is variable and there have been suggestions that malnourished mothers do produce milk with a lower average calcium content, but there is no concrete evidence to support this statement. Since calcium is crucial to both bone development and growth, this is an uncertainty that surely should be clarified. Most mothers in developing countries from poor socio-economic circumstances consume considerably less than the RDA, only about one-third of their counterparts in the Western world (see section 2.6).

The iron content of milk is very low in concentration, but it appears that it is absorbed with a very high degree of efficiency (23). This is partly, but by no means completely, because of the association of milk iron within a lacto-ferrin protein complex. It has been demonstrated in Ethiopia (17) that mothers on a high iron intake have particularly high concentrations of lacto-ferrin in their milk, even when they are living under poor circumstances. It seems therefore, that the synthesis of this protein is protected, at least under the dietary circumstances prevailing in Ethiopia. The response of lacto-ferrin to a diet low in both iron and protein is not known, however, and there is an obvious need for the effects of maternal iron balance on the various iron components of human milk to be further elucidated.