University of Oslo Study Finds Breastfeeding Linked to Significant Long-Term Weight Benefits for Mothers

A University of Oslo study reveals women who breastfeed for 3+ months gain up to 6.5kg less weight later in life, with the most benefit for those with high BMI.

By: AXL Media

Published: Apr 9, 2026, 11:09 AM EDT

Source: Information for this report was sourced from the University of Oslo, Faculty of Medicine.

Metabolic Impact Extending Decades Beyond Childbirth

New research from the University of Oslo’s Faculty of Medicine has shifted the focus of breastfeeding benefits from the immediate postpartum period to a woman's lifelong health trajectory. While previous studies primarily analyzed weight changes in the first two years after delivery, this study utilized data from the Women and Health Study—involving over 170,000 Norwegian women—to track weight developments for up to half a century. The findings, published in the American Journal of Clinical Nutrition, demonstrate that breastfeeding for at least three months per child acts as a protective factor against significant weight gain later in life.

The Role of Energy Expenditure and Metabolic Reset

The biological mechanism driving these long-term benefits is rooted in the high energy demands of lactation. Breastfeeding significantly increases a mother's daily energy expenditure to produce milk, which "in theory" contributes to immediate weight loss after pregnancy. However, researchers suggest that breastfeeding may also facilitate a "metabolic reset," helping the mother's body return to its pre-pregnancy state more efficiently. While some women experience an increased appetite that offsets this expenditure, the cumulative effect over multiple children and months of nursing appears to correlate with a leaner body mass in middle age.

Pronounced Benefits for Women with Overweight

The most striking differences were observed among women who had a high Body Mass Index (BMI) as young adults prior to their first pregnancy. In this group, mothers who breastfed for three to 15 months gained an average of 6.5 kilograms less by middle age compared to those who breastfed for shorter durations. This finding was consistent even when accounting for variables such as physical activity, smoking, and education levels. For women who started at a normal weight, the difference was still notable but smaller, at approximately 3 kilograms.