1. ¹Instituto de Medicina Social, State University of Rio de Janeiro, Rio de Janeiro, Brazil
2. ²Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA
3. ³Department of Ambulatory Care and Prevention, Boston, MA, USA
4. ⁴Department of Nutrition, Harvard School of Public Health, Kresge 617, Boston, MA, USA

Correspondence: Dr R Sichieri, Instituto de Medicina Social, State University of Rio de Janeiro, Rua São Francisco Xavier, 524, 70 andar, Bloco E CEP 20550-012, Rio de Janeiro, RJ, Brazil. E-mail: sichieri@uerj.br

Received 23 July 2002; Revised 21 November 2002; Accepted 7 January 2003.

Abstract

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

DESIGN: 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.

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

MEASUREMENTS: 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.

RESULTS: 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/m² (P=0.02) and for those women primiparous in 1989, with a BMI 25 kg/m² (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).

CONCLUSIONS: 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.