Before Baby: New study links father's prenatal weight to early growth patterns, obesity risk in children

Children of fathers who were with obesity or overweight around the time of conception are more likely to develop obesity themselves, according to new research from the University of Toronto that is reshaping how we understand paternal influence on child health.

The study, published in the International Journal of Obesity, analyzed data from more than 2,200 Canadian participants in the CHILD Cohort Study, one of the largest prospective pregnancy cohort studies in the country. The study collects information from families starting in pregnancy and at key developmental stages to track the impact of genetic and environmental factors on children’s long-term health.

Researchers found that children of fathers who were with obesity or overweight during pregnancy were nearly twice as likely to follow a rapid body mass index (BMI) growth trajectory up to age five. The pattern is linked to a higher risk of obesity later in life. When both parents had obesity, the child’s risk increased more than fourfold.

“We’ve long known that a mother’s health can influence a child’s growth,” says Kozeta Miliku, an assistant professor of nutritional sciences at U of T’s Temerty Faculty of Medicine and a researcher in the Joannah & Brian Lawson Centre for Child Nutrition. “But our study shows that a father’s health before conception also plays a significant role.”

The team compared parental BMI prior to pregnancy with children's BMI patterns from birth to age five. They accounted for a wide range of variables — including income, screen time, physical activity, breastfeeding and daycare attendance — but none outweighed the influence of parental weight.

What sets the study apart is its rare inclusion of paternal data. “We often overlook fathers in health research,” Miliku says. “But thanks to thousands of Canadian men who took part in this study more than a decade ago — completing surveys, physical tests and providing blood samples — we’re now uncovering just how important their contribution truly is.”

The mechanisms behind the link are still being explored. “There are likely multiple layers at play — genetics, epigenetics and environment,” says Miliku. “We’re investigating whether poor diet and excess weight in men can pass on risk through epigenetic changes in sperm, and how shared behaviours in the home may also contribute.”

Nearly 70 per cent of Canadian men of average fathering age — about 34 — are classified as being with overweight or obesity, yet public health messaging on prenatal health has historically focused on women.

“Women are often told to think about their health before pregnancy — but we rarely give that message to men,” says Miliku, who also holds an adjunct assistant professorship in medicine at McMaster University. “These findings shift some of the responsibility, showing that a father’s health can impact not just their own future, but their partner’s and their child’s too.”

The work was led by Antonio Rossi, an M.Sc. graduate in Miliku’s lab, who notes the findings underscore how parents’ preconception health can shape the early development of their children and continue into adulthood with long-term health consequences.

She believes it’s time to include men in clinical conversations about reproductive and family health. “We need to start thinking about preconception care for men the same way we do for women,” she says. “That means asking about future family plans during routine visits and offering guidance on nutrition, physical activity, and other lifestyle habits.”

Miliku’s team is now taking the work further, analyzing blood samples from thousands of fathers to better understand how modifiable behaviours, like diet, can shape child health.

Ultimately, she says, it’s about broadening the way we think about family wellbeing. “Recognizing the role of fathers in the health of their offspring isn’t just about fairness — it’s about better outcomes for the next generation.”

This study was supported by a Temerty Faculty of Medicine Pathway Grant, Connaught New Investigator Award and the Ontario Regional Centre of the Canadian Statistical Sciences Institute. The CHILD Cohort Study is funded by the Allergy, Genes and Environment (AllerGen) Network of Centres of Excellence, the Canadian Institutes of Health Research, and Genome Canada.