|Protein-Energy Requirements of Developing Countries: Evaluation of New Data (UNU, 1981, 268 p.)|
|Recommended dietary amounts of energy for pregnancy and lactation in the United Kingdom|
Summary of main results
Conclusions and comments
R G. Whitehead, A.A. Paul, A.E. Black, and S.J. Wiles
Medical Research Council Dunn Nutrition Unit, Cambridge, England
To obtain information on the dietary energy intakes of British women during pregnancy and lactation, since estimates of the dietary intakes of individuals living in the United Kingdom have shown a consistent downward trend in recent years.
Twenty-five women were recruited near the beginning of the second trimester of pregnancy through the antenatal clinic of the Cambridge Maternity Hospital. They were 21 to 35 years old (mean 29) and belonged to social grades I, II, and III. Twelve were primiparous and worked during most of their pregnancy, mainly in a clerical capacity. None of the multiparous mothers had outside jobs. Their mean height was 161.7 cm (147.5 to 172.5), and the stated pre-pregnant weight was 56.2 (43.5 to 71.7). The validity of the latter measurement was verified by comparison with the initial weight found on recruitment.
2. Dietary Intake
Energy and nutrient intakes were measured over four consecutive days each month throughout pregnancy and lactation by the mother herself, after instruction, weighing the food and drink she consumed. The food intake measurements were interpreted using food composition tables.
3. Weight Changes and Stored Energy
A number of anthropometric measurements were made, including weight, at monthly intervals throughout pregnancy, at two weeks after delivery, and then once again at monthly intervals. Energy stored as fat during pregnancy was estimated from the difference in body weight between two weeks postpartum and the pre-pregnant weight, making the assumption that adipose tissue provides, during lactation, 6.5 kcal/g body-weight change (Thomson et al., Brit,J. Nutr., 24: 565  ).
4. Duration of Pregnancy and Birth Weights
Birth weights, which were all over 2.6 kg, were obtained by the maternity hospital staff. Mean gestational age was 39 completed weeks, range 36 to 43 weeks.
5. Breast-milk Production
Breast-milk intake was also measured by the mother on four consecutive days each month by test weighing, using Salter Baby weigher Model 40 Scales. The test weighing measurements in a number of subjects were checked by the recently developed deuterium oxide method (Coward et al., Lancet, ii: 13 , the milk intakes showing good agreement between the two procedures.
a. The principal pregnancy data are given in table 1. There was no significant difference in energy intake between the second and third trimesters of pregnancy, and both values agreed closely with those for the first trimester reported by
Smithells in Leeds (Brit. J. Nutr., 38:497 11977] ).
TABLE 1. Energy Intakes and Body-Weight Changes of 25 Mothers during the Second and Third Trimesters of Pregnancy (Mean ± S.D.)
|Energy intake, 2nd trimester||(kcal/day)||1,950 ± 380|
|3rd trimester||(kcal/day)||2,005 ± 345|
|2nd & 3rd trimester||(kcal/day)||1,978 ± 350|
|Weight gain during pregnancy*||(kg)||12.6 ± 4 .0|
|Estimated maternal energy store||(kcal)||38,662 ± 28,570|
|Birth weight||(kg)||3.31 ± 0.35|
* To the 36th week.
TABLE 2. Energy Intake and Milk Output of 17 Mothers at Different Stages of Lactation (Mean + S.D.)
|Month of lactation||Energy intake (kcal/day)||Breast-milk output (9/24 hr)|
|2||2,278 ± 458||715 ± 148|
|3||2,300 ± 470||773 ± 140|
|4||2,380 ± 408||755 ± 136|
b. Among the Cambridge mothers, there was no correlation between energy intake in the last trimester of pregnancy and birth weight (r = 0.01).
a. Of the 25 mothers, 4 breast-fed for only 2 to 14 days, and another 4 for less than three months. Seventeen breast-fed at least up to the beginning of the fifth month, 11 exclusively, but the remaining 6 had by then introduced small amounts of other foods, which supplied only an average of 18 per cent of the babies' total energy intake.
b. The basic lactation data are summarized in table 2. Lactation was associated with an increase in food intake, but daily energy consumption was still 450 kcal less than the United Kingdom's DHSS Recommended Daily Amount. In the fourth month, there was little difference in energy intake among the 11 mothers who were exclusively breast-feeding (2,278 ± 431 kcal [mean ± S.D.] ) and the six who were not (2,363 ± 402 kcal), although the mean milk output of the former, 791 ± 93 g/day, was higher than that of the mothers who were using mixed feeding, 688 ± 186 g/day.
c. Figure 1 shows the relationship between dietary energy intake and milk output. The line of best fit (r = 0.76, p < 0.001) was significant(y curvilinear (p < 0.01). Mean milk outputs were not significantly different in mothers with energy intakes of 2,000 to 2,400 kcal/day and in those with intakes over 2,400 kcal-768 ± 63 to 780 ± 148 g/day, respectively. Energy intakes below 2,000 kcal were, however, associated with significantly lower milk outputs: 455 ± 227 g/day (t-4.2, p < 0.001). Three of the mothers who could not breast-feed for more than two months had intakes below 1,720 kcal/day, and they had the three lowest milk outputs. Data for the fourth mother were omitted because she had been complying with advice to eat beyond her appetite-3,338 kcal/day-in an unsuccessful attempt to boost her milk output.
Most points are the mean of dietary energy and milk output measurements over 12 days during the second, third, and fourth months of lactation.
d. There was no important correlation between the average amount of milk that the individual mother produced during the first four months and her corresponding loss of weight (r = 0.20 NS). There was a significant correlation between weight loss and overall energy intake during lactation (r = 0.56, p < 0.02), and the relationship was even stronger (r = 0.78, p < 0.001) when weight change was related to the increase in energy intake that occurred when the mothers passed from pregnancy into lactation.
Figure 2 predicts that at the DHSS recommended daily energy increment for lactation-600 kcal-mothers would lose none of their excess fat, while at the mean increment for the group studied, 281 kcal, the mothers lost weight at an average rate of 570 g/month. e. Figure 3 partly explains why some mothers ate so little extra during lactation. There was a high(y significant negative relationship (r = 0.73, p. < 0.001) between the extra food energy consumed during lactation and the amount of weight a mother had retained after her pregnancy.
We thank Professor C. Douglas, Mr. R.E. Robinson, and Dr. N.R.C. Roberton and the staff of the Cambridge Maternity Hospital for their collaboration, and Miss M.J. Whichelow for her help in recruiting the subjects. This study was financially supported by the Department of Health and Social Security.