Prospective assessment of exclusive breastfeeding in relation to weight change in women

To study prospectively the relation of parity, prepregnancy body mass index (BMI), and exclusive breastfeeding to weight gain.

The cohort of the Nurse's Health Study II, with analysis restricted to women who were aged 24 to 40 y at baseline (1989), who had a history of no more than one past full-term pregnancy at baseline, gave birth to one child between 1990 and 1991, but had no other pregnancies during the follow-up.

1538 of the 33 082 nulliparous women and 2810 of the 20 261 primiparous, in 1989.

Introduction of daily formula/milk was assumed to represent the end of exclusive breastfeeding period. Duration of exclusive breastfeeding was categorized into 0, 1-3, 4-7, 8-11, and 12 months or more.

After adjusting for age, physical activity, and BMI in 1989, lactation was associated with a weight gain from 1989 to 1993 of approximately 1 kg (statistically significant only for women nulliparous in 1989 with a BMI <25 kg/m(2) (P=0.02) and for those women primiparous in 1989, with a BMI >/=25 kg/m(2) (P=0.04)) comparing women who breastfed with women who did not, and duration of lactation was unrelated to the magnitude of weight change (P>0.40 for all comparisons).

Although promotion of breastfeeding has high priority because of its enormous advantages for a newborn child, the associated maternal weight reduction is minimal. Dietary guidelines for pregnant and breastfeeding women should include ways to prevent weight retention after parity.