Nursing moms can participate in frequent, moderate aerobic exercise without compromising the quantity or content of their breast milk -- and can significantly boost their cardiovascular fitness, according to a study by UC Davis nutritionists that appeared recently in the New England Journal of Medicine. "After the birth of a child, many women are eager to lose weight, and although exercise has often been considered safer than dieting, there has been little information available about its impact on lactation," says Kathryn G. Dewey, a professor of nutrition and an authority on maternal and child nutrition. The study found that both exercising and non-exercising women lost weight, however the exercisers significantly improved their aerobic fitness. The protein and fat content of the exercising mothers' milk did not decrease, nor was there any indication of nursing difficulties following exercise.