Several studies in the past have looked at how the mother's weight develops in the first year or two after giving birth, depending on whether she breastfeeds.
Researchers at the University of Oslo have now also looked at what happens to her weight in the longer term, up to 50 years after she has stopped breastfeeding. They will use these findings in further research on mothers' risk of cardiovascular disease.
And the findings are clear: for many women, breastfeeding each child for at least three months has a positive long-term effect on weight.
The researchers used data from the Women and Health Study, in which over 170,000 women in Norway have taken part. The study was recently published in the American Journal of Clinical Nutrition.
Greatest difference among women with overweight
The researchers found the greatest difference among those who had overweight or obesity as young adults, before pregnancy.
"We compared women in this group who were otherwise similar in terms of education level, physical activity and smoking. We then found that those who breastfed for three to 15 months gained on average up to 6.5 kilos less from young adulthood to middle age, compared with those who breastfed little," says PhD candidate Thorbjørn Brun Skammelsrud. He is doing his doctorate at the Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo.
For women with normal weight, the difference was up to 3 kilos
For those who had been of normal weight as young adults, the difference was up to 3 kilos if they breastfed for three to 15 months. For women who had been underweight, breastfeeding made little difference to later weight.
Skammelsrud explains that the extent to which breastfeeding affects weight will in any case vary from woman to woman.
"Breastfeeding increases energy expenditure, so in theory breastfeeding should contribute to weight loss. But precisely because energy expenditure increases, some women will also experience increased appetite when they are breastfeeding," he says.
Breastfeeding patterns traced back to the 1940s
The women who took part in the study had children as early as the 1940s. The association between breastfeeding and lower weight was clearest among women who had children after 1980. These women are also more representative of today's mothers in terms of breastfeeding patterns and diet.
Breastfeeding is positive for public health
Norwegian guidelines generally recommend that mothers partially breastfeed for one year or more if both mother and baby are comfortable with it. Skammelsrud points out that Norwegian women breastfeed for longer compared with many other countries.
"This is positive for public health. At the same time, the study shows that some women may need extra follow-up after giving birth, particularly those with overweight or obesity," he says.
"In this study, we see that breastfeeding for at least three months has a positive effect on women's weight later in life. It is therefore important that breastfeeding is facilitated, and that women who wish to breastfeed are offered qualified support," the researcher emphasises.
Reference:
Skammelsrud TB et al: Breastfeeding duration and maternal weight change through adulthood in a population-based cohort study
