Breastfeeding moms can exercise moderately without diminishing the amount of vital fatty acids in their breast milk, a new study suggests.

In fact, researchers found, the concentration of certain fats may temporarily increase right after a bout of moderate activity.

Some questions have been raised about the effects exercise could have on the composition of a woman's breast milk. One study, for instance, found that when women exercised to exhaustion, their breast milk showed short-term dips in immune-boosting proteins that are passed on to infants through breastfeeding.

Further research of mothers who exercised moderately found no such effects, however.

Long-chain polyunsaturated fatty acids, or PUFAs, are among the natural components of breast milk that promote infant growth and development. The concentration of these fats in a woman's breast milk depends in large part on her body fat stores. It also depends on adequate intake of foods rich in the fats, including canola oil and some other vegetable fats, nuts and seeds.

In theory, exercise could diminish the supply of essential fatty acids in breast milk because the fats could be diverted toward mom's energy needs and away from breast milk production, Dr. Cheryl Lovelady, one the new study's authors, explained in an interview.

But she and her colleagues found no difference in breast milk PUFA concentrations between new mothers who regularly exercised and those who were inactive.

'If anything, there was a rise'

The study, published in the Journal of the American Dietetic Association, included 30 mothers who exercised at least 3 days a week, for 30 minutes per day, and 23 moms who exercised infrequently or not at all.

A subgroup of the women underwent exercise tests to see whether there were any temporary effects on PUFA levels. The researchers found no evidence of a dip in breast milk fatty acids after 30 minutes of exercise; rather, two fatty acids -- alpha-linolenic acid and linoleic acid -- tended to increase in concentration.

"If anything, there was a rise, rather than a decrease," said Lovelady, a researcher at the University of North Carolina Greensboro . "So we think (exercise) could be beneficial."

She stressed, however, that the women in the study had a healthy PUFA intake, adequate body fat and moderate exercise habits. It's unknown whether the findings would hold true for underweight women or those with low PUFA intakes. Rigorous exercise could also have different effects than moderate activity.

Those questions aside, the current findings, according to Lovelady, provide reassurance that two major public health recommendations -- that infants be breastfed for at least the first 6 months of life, and that adults get regular, moderate exercise -- are indeed "compatible."