Does exercise intensity or diet influence lactic acid accumulation in breast milk? Med. Sci. Sports Exerc., Vol. 31, No. 1, pp. 105-110, 1999.
Purpose: This study examined the relationships among diet, exercise intensity, and breast milk composition in lactating women.
Methods: Twelve lactating women were randomly assigned to either a high (N = 6; 5.03 g carbohydrate (CHO)·kg body mass (BM)−1) or moderate (N = 6; 3.89 g CHO·kg BM−1) carbohydrate diet. Milk and blood samples were collected before and after a nonexercise session (control) and maximal, lactic acid-threshold (LAT), and 20% below the LAT (LAT-20) intensities.
Results: The 30-min exercise LAT bout was more stressful than the 30-min LAT-20 bout (rating of perceived exertion (RPE) = 15 vs 12, respectively, P < 0.05). Milk LA was significantly higher at 0 min following maximal exercise in the high and moderate CHO groups (1.27 ± 0.56 and 1.52 ± 0.49 mM, respectively) and following LAT exercise (0.19 ± 0.16 and 0.25 ± 0.12 mM, respectively), when compared with the control session (0.08 ± 0.03 and 0.09 ± 0.05 mM, respectively). This was not observed following the LAT-20 exercise in the high and moderate CHO groups (0.11 ± 0.04 and 0.12 ± 0.08 mM, respectively). Elevated milk LA persisted in the 30-min collection point after maximal exercise only. There was no significant effect of dietary treatment on milk or blood LA at any of the collection points.
Conclusions: In lactating women whose caloric needs are being met: 1) dietary CHO intake, within a practical range, does not influence LA levels in breast milk at rest or after exercise; 2) LA appearance in the milk is a function of exercise intensity; and 3) moderate intensity exercise (RPE = 12) will not increase breast milk LA levels.
Department of Kinesiology and Department of Animal and Nutritional Sciences, University of New Hampshire, Durham, NH 03824
Submitted for publication August 1997.
Accepted for publication February 1998.
Thanks are due to Medela, Inc., for generously lending our subjects electric breast pumps. Thanks are also due to Alex Bates and Susan Goodwin who assisted with nutrition counseling, data collection, and laboratory measurements. Lastly, thank you to all of our subjects for their willing and time-consuming participation.
This work was supported by the Gatorade Sports Nutrition Award from the American College of Sports Medicine Foundation.
Address for correspondence: Timothy J. Quinn, Ph.D., University of New Hampshire, Department of Kinesiology, Field House - #35, Durham, NH 03824. E-mail: firstname.lastname@example.org.