Metabolic Flexibility and Weight Status May Contribute to Inter-Individual Changes in Breastmilk Lipid Content in Response to an Acute Bout of Exercise: Preliminary Findings from a Pilot Study

Abstract

The purposes of this pilot study were to describe changes in breastmilk lipid content in response to an acute bout of moderate intensity exercise and to explore maternal metabolic health factors, including metabolic flexibility, which may impact this change. A cross-sectional, observational, pilot study design was performed in 14 women between 4 and 6 months postpartum. Whole body fasting lipid oxidation was assessed, a standardized high-fat breakfast was consumed, and lipid oxidation was again measured 120-minutes post-meal. Metabolic flexibility was determined by comparing the change in lipid oxidation before and after the meal. Women completed 30-minutes of moderate intensity treadmill walking 150-minutes post-meal. Breastmilk was expressed and analyzed for lipid content before and after exercise. Overall, there was no significant difference between pre- and post-exercise breastmilk lipid content (pre-exercise 59.4±36.1 g/L vs. post-exercise 52.5±20.7 g/L, p=0.26). However, five (36%) women had an increase in breastmilk lipid content in response to the exercise bout, compared to nine (64%) that had a decrease in breastmilk lipid content suggesting inter-individual variability. The change in breastmilk lipid content from pre- to post-exercise was positively correlated to metabolic flexibility (r=0.595, p=0.03). Additionally, post-exercise lipid content was positively correlated with body mass index (BMI), body composition, and postpartum weight retention. Preliminary findings from this pilot study suggest that metabolic flexibility and maternal weight status may help explain the inter-individual changes in breastmilk lipid content in response to an acute bout of moderate intensity exercise.

Keywords: Postprandial metabolism; body fat percentage; high-fat meal; lipid oxidation; maternal metabolism; moderate intensity exercise; physical activity; postpartum.

Figure 1

Breastmilk lipid content in response to an acute bout of exercise. There was no significant difference between breastmilk lipid content collected pre-exercise and post exercise (pre-exercise 59.4±36.1 g/L vs. post-exercise 52.5±20.7 g/L, p=0.26).

Figure 2

Changes in breastmilk lipid content in response to an acute bout of exercise. A. Fold changes in breastmilk lipid content in response to an acute bout of exercise for each individual participant. Fold change was calculated by dividing post-exercise lipid content by pre-exercise lipid content. No change is a value of 1, which is represented by the dashed line, with values >1.0 indicative of an increase in breastmilk content in response to the exercise. B. Percent changes in breastmilk lipid content in response to an acute bout of exercise for each individual participant. Percent change was esimated using the following equation: ((post-exercise breastmilk lipid content - pre-exercise breastmilk lipid content) / pre-exercise breastmilk lipid content) * 100.

Figure 3

Fold change in breastmilk lipid content in response to an acute bout of exercise correlated with metabolic flexibility and postprandial lipid oxidation. A. The change in breastmilk lipid content in response to exercise was positively correlated to metabolic flexibility (i.e. the upregulation of lipid oxidation in response to the high-fat meal) (r=0.59, p=0.03). B. There was a trend for the change in breastmilk lipid content in response to exercise to be positively correlated to postprandial lipid oxidation (r=0.52, p=0.06).