The study doesn't prove that breast-feeding will make you slimmer; it merely shows an association between the two. However, the link held even when the researchers took into account smoking, physical activity and other factors that can affect weight.
Researchers have several hypotheses about why breast-feeding helps control weight over the long term. One is the so-called "reset" hypothesis, Bobrow said. It says that breast-feeding ''may be involved in re-setting various metabolic control centers in the brain after childbirth," Bobrow explained.
Erica Gunderson, a research scientist with the Kaiser Permanente Northern California division of research in Oakland, Calif., said the research is unique partly because of the many women studied. "This type of cross-sectional study has never been accomplished with this sample size," she said.
That's a definite strength of the research, she noted. But it would have been helpful to know the women's BMI earlier in life, she added.
For women who have not yet given birth, the study suggests that it's important to consider breast-feeding and to ask your doctor how much weight you should gain.
Getting advice about nutrition is a good idea, too, Gunderson said. "When you get pregnant, get very good advice about what to eat," she suggested.
To learn more about breast-feeding, visit the U.S. Department of Health and Human Services.
SOURCES: Kirsty Bobrow, clinical researcher, University of Oxford, Oxford, U.K.; Erica P. Gunderson, Ph.D., research scientist, Kaiser Permanente Northern California division of research, Oakland, Calif.; July 10, 2012, International Journal of Obesity
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