Breastfeeding could influence a woman's weight later on in life, a new British study has found. Six months of breastfeeding could reduce the risk of obesity as much as 30 years down the road, according to researchers.

In the study, published in the International Journal of Obesity, researchers analyzed data from nearly 750,000 participants in the Million Women Study, a broad ongoing health investigation of women aged 50 to 64 in the United Kingdom. They analyzed responses from women about whether they breastfed their children and for how long.

Overall, breastfeeding was associated with a modest, long-term reduction in body mass index, a measurement of height relative to weight. For every six months the women breastfed, their BMI decreased by about 1 percent on average.

"These are long-term effects," said Kirsty Bobrow, a clinical researcher at the University of Oxford and one of the study's authors. "For women in this study, childbearing and breastfeeding occurred on average 30 years before women's weights and heights were recorded."

Bobrow and her colleagues wrote that their study is among the first to look at whether breastfeeding influences weight over the long term. Typically, researchers have focused on how breastfeeding can affect a woman’s weight immediately after she gives birth. This has become a popular subject for discussion for many celebrities, with some claiming that the practice has helped them quickly shed pounds.

"In the short term, it's very clear that it takes calories to make milk," said Dr. Alison Stuebe, an assistant professor of maternal and child health at the University of North Carolina who has researched the link between breastfeeding and weight loss.

"A breastfeeding mom can burn [as much as] 500 calories per day,” she continued. “That's an hour on a treadmill, or [it's] sitting in a rocking chair and giving Baby breast milk, which has all kinds of benefits."

The link between breastfeeding and weight loss has not gone unnoticed by public health officials, who have toyed with the idea of using the prospect of weight loss to encourage women to eschew giving babies formula. (The World Health Organization recommends exclusively breastfeeding a child for six months. After that, mothers can breastfeed a child until he or she is 2 years old or beyond, supplementing that with appropriate foods, according to WHO.)

Several years back, the New York State Department of Health caused a stir with a TV ad that attempted to promote breastfeeding to low-income women by touting a potential weight loss benefit.

The authors of the new study argued that their findings could indeed have profound implications for public health, even though the differences in weight detected were relatively small.

"Even a modest 1 percent reduction in body mass index in western countries would substantially reduce the number of obesity-related diseases and their costs," they wrote, explaining that a 1 percent weight reduction could correspond to a 1 percent reduction in all-cause mortality.

What the new study did not explain is why breastfeeding could result in weight changes, even years later.

One possible explanation for the long-term weight loss is the "reset hypothesis," Bobrow told The Huffington Post. According to that theory, certain fats accumulate during pregnancy, and insulin resistance increases, along with lipid and triglyceride levels. Lactation might play a key role in reversing these changes, essentially "resetting" maternal metabolism after pregnancy, which could influence a woman's weight later on.

But Stuebe, who came up with that hypothesis, cautioned that the new study did not establish a definitive link between breastfeeding and long-term weight loss. Though the researchers did control for socioeconomic factors, such as smoking and physical activity, they did not have details about the study participants’ BMIs before their pregnancies.

"The question that this kind of study can't answer is, Is it breastfeeding that makes you skinnier? Or is it that the type of person who breastfeeds is also skinnier in her 50s?" Stuebe said.

But ultimately, Steube interprets the new study as good news. If the potential of weight loss helps motivate women to continue trying to breastfeed (particularly in the United States where breastfeeding can be an "uphill battle," as she put it), then that's not a bad thing.

"This joins a whole bunch of literature that says that breastfeeding is not just good for babies; it's good for moms," Stuebe said. "And it's potentially good for moms in the long run."

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