Planning a baby? Here's why you should watch your weight

Excess weight and obesity in pre-pregnancy period bring changes in breast milk that can impact infant growth, a study claims.

The study was published in the journal 'PLOS ONE'.

"The importance of this study is that it demonstrates that breast milk contents can vary depending on mother's weight status at the time of conception and further impact the growth and development of breastfeeding infants," said Henry Nuss, lead author of the study.

"Childhood obesity rates in the United States have increased significantly in recent decades," noted Melinda Sothern, professor of Behavioral & Community Health Sciences at Louisiana State University Health Sciences Center.

"Although many studies have shown that breastfeeding may be protective against excessive weight gain during early life, we do not fully understand why," Sothern added.

Breast milk contains pro-inflammatory proteins such as tumour necrosis factor alpha (TNF-a) and interleukin-six (IL-6), as well as hormones like insulin and leptin, and anti-inflammatory polyunsaturated fatty acids, such as omega-3 (DHA) and omega-6 (EPA). If and how their interaction may influence infant growth has been unknown.

The research team set out to discover the interrelationships between these compounds in the blood and breast milk in early postpartum women with normal BMI and with overweight/obesity before pregnancy to determine if these components correlated to infant growth measures at age 4-8 weeks.

They compared polyunsaturated fatty acids, inflammatory markers, and hormones to infant weight, length, head circumference, and per cent fat mass at 4-8 weeks postpartum in the same group of 33 women.

The researchers found that pro-inflammatory qualities of breast milk were associated with infant growth measures regardless of maternal pre-pregnancy BMI.

However, infants born to women with overweight or obesity demonstrated less responsive growth to breast milk.

"Infants who are born to mothers of unhealthy weight status may be metabolically programmed to have a less favourable growth response to breast milk," said Dr Nuss.

"These findings suggest that women of childbearing age who anticipate having a child should consider their weight status as a potential risk factor for adverse growth outcomes," Dr Nuss added.