Over 1.9 billion adults worldwide are overweight or obese, and by 2025 this is projected to increase to 2.7 billion. Obesity significantly raises the risk of developing 11 different types of cancer, stroke, type 2 diabetes, heart disease and non-alcoholic fatty liver disease (1, 2).

New research in The Journal of Physiology found a possible explanation for the benefits of maternal exercise on fetal development, in obese mothers: it's down to improved placental function, which prevents the fetus from growing too big, and also better metabolism in the mothers.

The placenta performs nutrient and oxygen exchanges between the mother and her fetuses, and placental function is impaired due to maternal obesity, which likely alters nutrient and oxygen delivery to the fetus. Exercise during pregnancy is known to be beneficial for both maternal health and fetal development. This study found that exercise both improved the function of the placenta, but also the metabolism of the mother. Importantly, they found that the babies were not born larger (which is frequently associated with obesity and metabolic diseases in later life) when the obese mothers exercised.

In this study, female mice were fed a healthy diet (10% energy from fat) or a high-fat diet to become obese and then mated. Each of the maternal groups was further divided into two subgroups: those that did and did not perform exercise during gestation. Mice were exercised from 0 to 18.5 days of pregnancy (the term is 20.5 days) and placental function, and maternal and fetal changes were analysed.

Further studies will focus on identifying mechanisms explaining the beneficial effects of exercise on placental development of obese mothers. Researchers will define the possible role of chemicals secreted during exercise, on blood vessel development in placenta, which is critical for delivery of nutrients and oxygen to fetuses, as well as their long-term impacts on the health of next generation. Prof Min Du, senior author on the paper said:

"Understanding how maternal exercise might help prevent offspring from becoming obese or developing metabolic diseases will help us best guide mothers so they can ensure their babies are as healthy as possible."