Summary of main results

1. Pregnancy
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).

2. Lactation
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.

FIG 1. Relation between Maternal Energy Intake and Breast-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.

FIG. 2. Relation between Lactation Dietary Energy Increment and Weight Loss over the First Four Months Post Partum

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.

FIG. 2. Relation between Weight retainrd after Pregnancy and Lactation Dietary Energy Increment