First of all, let us commend you on the fact that you’re even reading this article! You’re some woman!

Worries you may have (let's put your mind at rest)

Milk supply issues:

Milk supply and its nutritional content is not affected by breastfeeding. No. Studies have shown no difference in the volume or composition of the milk or babies' weight gain. One study showed a slight increase in milk supply for the women who exercised regularly, but because of the small size of the study this increase may not be significant.

Physical exercise and the lactating woman: a qualitative pilot study of mothers' perceptions and experiences.

Breastfeed Rev. 2004 Jul;12(2):11-7.

Research has not shown a noticable increase in lactic acid buildup after moderate exercise (50% & 75% intensity). The lactic acid in breastmilk does increase somewhat if the mother exercises to maximum intensity. This increase may be present up to 90 minutes post-exercise. There are no known harmful effects for the baby.

• Most studies have found no difference in acceptance of the breast, even after maximum intensity exercise.

Although a highly publicized 1992 study indicated that baby might fuss or refuse expressed milk from a mother who had been exercising at 100% intensity, the results were questionable because the babies were fed the milk by dropper (unfamiliar to these babies), and the mothers reported that the babies had not had problems with nursing after exercise in the past. A more recent study showed no change in infants' acceptable of mom's milk an hour after exercise, even for the mothers who exercised at maximum intensity (and thus did have a slight increase in lactic acid in their milk).

(taken from kellymom)

• Dr. Ruth Lawrence, in her most recent volume (Breastfeeding, A Guide for the Medical Profession, 1999 edition) says that there is no reason to wait to nurse after exercising.

The Research:

The benefits of exercise for healthy adults include a lower risk for many chronic diseases such as cardiovascular disease, diabetes, osteoporosis and certain cancers. Exercise has been shown to be beneficial for maintenance of self-esteem, immune function and weight control (Commonwealth of Australia 1998). The effects of exercise on milk production, maternal and infant health has been less widely studied. Women who are lactating are sometimes given confusing advice regarding exercise and may be unsure as to the effects on themselves and their babies. This review examines the safety of exercise during lactation. The studies suggest that exercise during lactation is not only safe for the infant but also beneficial for the mother.

Effect on mum and baby

Lovelady et al (1995) examined the effects of a twelve week exercise program on lactation performance and metabolism of previously sedentary women. The results show that exercise during lactation improves cardiovascular fitness. Weight loss was the same for the exercise and the control group, with the exercise group compensating for increased energy expenditure by eating more. The exercise group showed a small increase in the beneficial HDL-cholesterol, a change in insulin response, and an increase in maximal oxygen consumption that, in the general population, is suggestive of a protective effect for cardiovascular disease and diabetes. Sampselle et al (1999) described reported patterns of postpartum physical activity to identify the benefits and risks of physical activity at 6 weeks postpartum. The results of this exploratory investigation were that the women who exercised vigorously postpartum benefited physically and psychologically. Breastfeeding was not adversely affected by vigorous exercise. The authors would like to see evidence based care plans developed for new mothers and call for further research in order for these care plans to be developed. Research cited by Sampselle et al (1999) from the United State Department of Health and Human Services shows that at all ages women are less likely than men to participate in vigorous physical or regular leisure time exercise. This is particularly important in view of the finding that the effect of exercise in decreasing symptoms of anxiety and depression are stronger in women than in men (Stephens 1998). Sampselle et al (1999) found in their study that the association between exercise and indicators of well-being is consistent with research conducted on non-childbearing women. Exercise has been shown to be beneficial for lactating women wishing to lose weight as the combination of exercise and diet enhanced fat loss without reducing lean body mass. (McCrory 1999).

Bone Density

Two studies (Drinkwater & Chestnut 1991, Little & Clapp 1998) were unable to detect an effect of exercise which the authors attribute to the short duration of the study, low number of subjects and lack of consistency of type of exercise. Given that lactation and weight bearing exercise are protective for osteoporosis the authors call for better prospective studies with larger numbers of subjects to determine whether exercise adds a protective effect to lactation as hypothesized.

Milk composition

Studies that have caused concern to some mothers have examined levels of lactic acid in breastmilk after maximal or exhaustive exercise. Maximal exercise is at the extreme limit of exercise intensity. Lactic acid is produced by anaerobic respiration and can be measured in the blood after maximal exercise. Wallace et al (1992) studied infants’ post exercise acceptance of their mothers’ breastmilk and measured levels of lactic acid in their breastmilk. The babies were offered the breastmilk from a medicine dropper.

The infants’ acceptance of this milk was rated by the mother using a double blind design. Wallace et al concluded from this study that mothers should modify their feeding to take into account a rise in lactic acid in breastmilk after maximal exercise. In contrast Carey et al (1997) and Quinn (1999) found levels of lactic acid in breastmilk after maximal exercise were approximately half of that found by Wallace (1994). Carey and Quinn question whether the exercise intensity may have been underestimated in Wallace’s study. Small milk samples (1-3ml) were collected by Wallace and then frozen before assay. Because milk composition can vary greatly within a feeding, in Carey and Quinn’s 1999 study both breasts were emptied of milk at each collection time, the milk was then analysed immediately. Wallace et al tested for maximal exercise only and used a medicine dropper to provide milk to the infant. This method of testing for taste response or infant acceptance has not been validated. Carey and Quinn (2001) in their review article conclude that while lactic acid can increase in breastmilk following maximal exercise, mild or moderate exercise does not cause lactic acid to accumulate in milk. Most mothers only wish to exercise to a submaximal level to lose weight and improve fitness therefore Carey et al (2001) questions the practical significance of studies using maximal exercise.

In a recent study by Wright, Carey and Quinn (2002) composition and infant acceptance of postexercise breastmilk was reexamined. The tests were conducted after a period of maximal intensity exercise, moderate exercise and a resting control session. One hour before and one hour after each session participants fully expressed their milk and fed their infants the milk from a familiar bottle. Infant acceptance of the milk showed no differences pre session or post session although there was a significant but slight increase in lactic acid levels in the milk after the maximal exercise. Moderate exercise did not produce an increase in lactic acid.

Another study which received some publicity was by Gregory et al (1997) that showed a decrease in breastmilk immunoglobulin A (IgA) after maximal exercise. IgA helps to prevent and fight infection and with light to moderate exercise IgA activity is thought to increase. Maximal exercise was studied in order to mimic physical stress and to then observe the most severe scenario. Gregory et al also noted that women seldom exercise to maximal capacity, that the decrease in breastmilk IgA concentrations was transient and returned to control values within one hour. Another interesting finding was that lactating women have an increase in IgA after emptying their breasts with or without maximal exercise. Carey (1998) criticizes the study for stating that exercise depresses milk IgA when it is only maximal exercise that had this effect. Carey also points out that if a baby receives one feed in 24 hours that has a slightly lower level of IgA it is likely to have very little effect overall on the protective effect of breastmilk.

Fly et al (1998) showed that major mineral concentrations - calcium, phosphorous, magnesium, potassium and sodium were unchanged after maximal exercise. Maximal exercise was chosen for this study as it was reasoned that if maximal exercise did not change milk composition then moderate exercise would not.

Dewey et al (1994) studied the effects of moderate aerobic exercise four or five times a week on breastmilk composition (lipid, protein, lactose concentration, and energy density) and volume. They confirmed the results of their earlier study (Lovelady et al 1990) and found that there were no significant differences between the exercise and control group in maternal body weight, volume or composition of the breastmilk, the infants weight gain, or maternal prolactin levels. None of the mothers reported any difficulties breastfeeding after the exercise.

Baby's health/ growth

The study by Lovelady et al (2000) showed that even when on a diet and exercise program overweight women could safely lose approx .5kg per week without affecting their infants’ growth. Gains in weight and length were the same for infants in the control group (no diet, no exercise) as in the diet and exercise group. McCrory et al (1999) randomly assigned exclusively breastfeeding women to three groups: - Diet only; diet plus exercise and a control group. Change in milk volume, composition, energy output and infant weight did not differ significantly between the three groups. However in the diet only group, milk energy output increased in fatter women and decreased in leaner women. It appears that exercise protects lactation when there is an energy deficit that may be due to the enhanced fat utilization and the ability to stabilize blood glucose concentrations that occurs with exercise. Lovelady et al in 1990 showed that a self selected group of exercising mothers compared with controls had the same plasma hormones, milk energy, lipid, protein, and lactose content. Many of these women were highly trained athletes. Therefore the authors suggest that while there was no adverse effect of vigorous exercise on these women’s lactation performance it may not be applicable to the general population. The 1994 study by Dewey and Lovelady overcame this limitation by randomly assigning a group of previously sedentary women to an exercise or a control group. Once again there were no significant differences between the two groups for breastmilk composition, volume, or the infants weight gain. The exercise had no adverse effect on lactation and significantly improved the mothers’ cardiovascular fitness.

• Exercise may help a mother feel more energetic, preserve her health and well-being, and help to contribute to her child’s health.

• It is uncommon for women to exercise to maximal level. Moderate exercise will not increase milk lactic acid levels.

• Moderate exercise that produces a significant improvement in a mothers’ cardiovascular fitness will not affect volume or composition of breastmilk or affect infant growth.

• Exercise is beneficial to a mothers’ mental health and can be recommended as part of a postnatal care plan.

• Infant refusal to breastfeed after exercise is rare.

Tips for fit breastfeeding mothers!

REFERENCES

• Commonwealth Department of Health and Family Services. Developing an Active Australia: A Framework For Action For Physical Activity and Health. Commonwealth of Australia 1998.
• Carey GB, Quinn TJ, Gregory RL, Wallace JP 1998, Effect of exercise on milk and nursing babies (letters). Med Sci Sports Exercise 30(11): 1659-1660.
• Carey GB, Quinn TJ, Goodwin SE 1997, Breast milk composition after exercise of different intensities. J Hum Lact 13: 115-120.
• Carey GB, Quinn TJ 2001, Exercise and lactation: are they compatible? Can J Appl Phys 26(1): 55-74
• Dewy K, Lovelady C, Nommsen–Rivers L, McCrory M, Lonnerdal B 1994, A randomised study of the effects of aerobic exercise by lactating women on breast-milk volume and composition. New Engl J Med 330: 449-453.
• Drinkwater BL, Chestnut CH 1991, Bone density changes during pregnancy and lactation in active women: a longitudinal study. Bone Miner 14: 153-160.
• Fly AD, Uhlin KL, Wallace JP 1998, Major mineral concentrations in human milk do not change after maximal exercise testing. Am J Clin Nutr 68(2): 345-349.
• Gregory RL, Wallace JP, Gfell LE, Marks J, King BA 1997, Effect of exercise on milk immunoglobulin A. Med Sci Sports Exerc 29(12): 1596-1601.
• Little KD, Clapp JF 1998, Self –selected recreational exercise has no impact on early postpartum lactation – induced bone loss. Med Sci Sports Exerc 30: 831-836.
• Lovelady CA, Lonnerdal B, Dewey KG 1990, Lactation performance of exercising women. Am J Clin Nutr 52: 103-109.
• Lovelady CA, Nommsen-Rivers LA, McCrory MA, Dewey KG 1995, Effects of exercise on plasma lipids and metabolism of lactating women. Med Sci Sports Exerc 27(1): 22-28.
• Lovelady CA, Garner K, Moreno KL, Williams JP 2000, The effect of weight loss in overweight, lactating women on the growth of their infants. N Engl J Med 342: 449-453.
• McCrory MA, Nommsen-Rivers LA, Mole PA, Lonnerdal B, Dewey KG 1999, Randomised trial of the short term effects of dieting compared with dieting plus aerobic exercise on lactation performance. Am J Clin Nutr 69: 959-967.
• NMAA Members 2000, Breastfeeding and strenuous exercise. NMAA Newsletter 36(4): 19-21,26
• NMAA 1998, Looking After Yourself. NMAA, East Malvern
• Quinn TJ, Carey GB 1999, Does exercise intensity or diet influence lactic acid accumulation in breast milk? Med Sci Sports Exerc 31(1): 105-110.
• Sampselle CM, Seng J, Yeo SA, Killion C, Oakley D 1999, Physical activity and postpartum wellbeing. JOGGN 28: 48-49.
• Stephens T 1988, Physical activity and mental health in the United States and Canada: evidence from four population surveys (abstract). Prev Med 17(1): 35-47.
• Wallace JP, Inbar G, Ernsthausen K 1992, Infant acceptance of postexercise breast milk. Paediatrics 89(6): 1245-1247
• Wright KS, Quinn TJ, Carey GB 2002, Infant acceptance of breast milk after maternal exercise. Pediatrics 109(4): 585-589.