Check out any forum for expectant mothers online, and you’re apt to find a lot of misinformation about breastfeeding—specifically whether or not engaging in high-intensity exercise while breastfeeding is a good idea. Myths on the subject about, including the hoary old idea that exercise can sour breast milk or cause a woman’s supply to dry up. “There are so many myths about exercise and breast milk. We simply need more knowledge,” says Trine Moholdt, PhD, of the Norwegian University of Science and Technology.
The issue is especially important because early nutrition plays a key role in a child’s health later in life. “In fact, the period from conception to two years of age is considered the most critical period for possible development of obesity later in life,” says Moholdt.
One component of breast milk—adiponectin—may hold the key. This hormone plays a role in glucose and fat metabolism, and low levels have been associated with insulin resistance and type 2 diabetes. Many researchers believe that higher concentrations of adiponectin in breast milk could prevent rapid childhood weight gain.
Previous studies have shown that exercise can raise levels of circulating adiponectin, but no research had been done on exercise’s effects on adiponectin levels in breast milk until Moholdt and her team decided to investigate the matter. Their results were published in the journal Frontiers in Nutrition.
To investigate whether—and what type of—exercise could elevate adiponectin levels in breast milk, Moholdt’s team recruited twenty new mothers who had given birth within the previous 6 to 12 weeks. All of the women had to exclusively breastfeed their infants and be able to walk or run on a treadmill for at least 50 minutes. Women with cardiovascular disease or diabetes were excluded.
The women participated in a baseline fitness assessment and three testing sessions conducted in a laboratory. They were also asked to record the type, amount, and timing of food that ate prior to their sessions to help researchers account for the potential effects of diet on breast milk composition.
For the testing sessions, participants were assigned to complete three different tests in random order:
- a rest condition that involved sitting in a chair for 45 minutes
- a moderate-intensity endurance workout that involved walking or jogging at 70% of heart rate maximum for 48 minutes
- a high-intensity interval workout, which consisted of a 10-minute warmup followed by four 4-minute exercise intervals at 90%-95% heart rate maximum separated by 3 minute recovery periods
Participants were asked to provide breast milk samples taken at four specified points of time—a 7:00 AM the morning of each test; at 11:00 AM the day of each test (immediately after the test session), at noon the day of each test (approximately one hour after testing), and at 4:00 PM that afternoon (approximately four hours after testing).
Analysis showed that mothers who did high-intensity interval training had higher levels of adiponectin in their breast milk one hour after their exercise session. Moderate-intensity exercise produced no effect, and the additional adiponectin wasn’t detected in samples taken later in the afternoon.
“The hormone is secreted from fatty tissue and enters the bloodstream, and much of what is in the blood goes into the milk,” says Moholdt. “We were not that surprised by the findings, but now we know for certain,”
Conclusions
One of the reasons why breastfeeding is recommended during the first six months of life is that breast-fed children are less likely to be overweight and obese than formula-fed children. However, emerging research shows that the composition of breast milk varies between mothers who have high and low body mass indexes—and those differences can play a role in the transfer of obesity from mother to child. Improving the quality of breast milk through exercise may therefore be one simple way to curtail childhood weight gain.
“We therefore suggest further studies investigating both the immediate influence of a single exercise session on breast milk composition, as well as chronic adaptations with regular exercise training,” the researchers wrote in their conclusion. “We also propose that further research should consider the whole breast milk matrix, which is composed of many bioactive components.”
