Breastfeeding moms may be able to regularly exercise without hindering their babies' growth, a meta-analysis published suggests.
"Based on what we know at the moment, babies of mums who exercise do not gain less weight than babies of mothers who do not exercise," lead researcher Dr Amanda J Daley, of the University of Birmingham in the UK, said.
Some questions have been raised about the effects exercise could have on the components of a woman's breast milk. One study, for instance, found that when women exercised intensely, their breast milk showed short-term dips in immunogenic proteins.
It's also possible that heavy exercise could raise lactic acid levels in breast milk – and make it less palatable for babies. Some studies have suggested that's true, but others have not.
No evidence of slowed infant weight gain
The ultimate question is whether exercise during breastfeeding affects babies' growth and development. For the new study, researchers pooled data from the few clinical trials that have measured growth in breastfed babies of women who exercised.
When they combined the results of those trials, they found no evidence that exercise slowed infants' weight gain.
On average, babies of exercising moms gained slightly more than breastfed babies of inactive women – 18.6 grams, or about 17 grams, more. That difference was not statistically significant, the researchers reported in Paediatrics.
Dr Daley said there are caveats, however. Her team could find only four trials to include in their analysis, and those trials included only 170 mothers – so the evidence that exercise during breastfeeding is safe is limited, Dr Daley and her colleagues say.
More research needed for confirmation
The four trials were done between 1994 and 2009. In each, researchers recruited sedentary breastfeeding moms, and then randomly assigned them to either start a moderate exercise routine or remain inactive. In two studies, the women also cut kilojoules to help cut some post-pregnancy kilograms. And the follow-up time was limited: three trials ran for 10 to 16 weeks, and the fourth for only 11 days.
On the other hand, the evidence that it could be harmful is also quite limited, according to Dr Daley.
Overall, she and her colleagues conclude, "It appears that mothers can exercise and breastfeed without detriment to the growth of their infants, but this is based on limited evidence, and more research is required before this finding is confirmed."
(Amy Norton, Reuters Health, June 2012)
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