If you're worried about exercising because you're breastfeeding, don't be. "Moderate exercise does not affect the quality or quantity of breastmilk – if anything, it makes it better in terms of volume and calorie levels of the milk," says Sandra Greiner, a prenatal fitness instructor and creator of Healthy Expectations, a fitness and wellness program for pregnant women and new mothers. "However, it is best to nurse before exercise. Researchers found that mothers who exercised had lower levels of an immune protein, IgA, which fights disease. Compared with milk taken at rest, milk after 10 minutes of exercise had 60 percent less IgA, after 30 minutes, there was 73 percent less – although after 60 minutes, the levels were back to normal. Lactating women need to avoid excessive stretching and lifting of heavy weights, since laxity of joints and tissues may continue after the initial six-week postpartum period."