A father’s diet doesn’t just affect his own health. It may shape his child’s body composition before the baby is even conceived.
New research shows that fathers who eat more ultra-processed foods tend to have heavier babies. Those babies also accumulate more fat around the thighs and lower back.
The study was coordinated by Daniela Sartorelli, a professor at the Ribeirão Preto School of Medicine at the University of São Paulo.
Researchers followed 43 sets of fathers, mothers, and newborns receiving care through the public healthcare system in Ribeirão Preto, in the Brazilian state of São Paulo.
The overlooked role of fathers
“Maternal nutrition and health before, during, and after the baby’s birth have always received attention, but little is said about the role of the father’s diet. Our study shows that it also matters a great deal for the baby’s health,” Sartorelli said.
This is the first study to demonstrate a direct association between how much ultra-processed food fathers eat and their newborns’ body composition.
Ultra-processed foods are industrial formulations made mostly from substances extracted from foods and synthetic chemical additives. They contain few, if any, whole-food ingredients.
The link starts before conception
The researchers’ working hypothesis centers on sperm formation, which happens well before conception ever occurs.
Study co-author Mariana Rinaldi Carvalho is a PhD student at the University of São Paulo.
“Diets rich in ultra-processed foods can create a pro-inflammatory environment in the body, affecting sperm quality and altering the expression of genes that will be passed on to the baby. This process is known as epigenetics,” said Rinaldi Carvalho.
“Gene activity can be ‘activated’ or ‘deactivated’ depending on the father’s dietary habits.”
One gene the researchers point to specifically is IGF-II, responsible for fetal growth and inherited exclusively from the father.
“Previous studies have shown that a father’s dietary habits can biochemically modify this gene in sperm through a process called methylation [the addition of a methyl group], thereby influencing fetal development,” Carvalho said.
Differences between mothers and fathers
The results revealed a striking contrast between mothers and fathers.
Fathers who ate more ultra-processed foods tended to have babies with higher birth weights. Mothers who ate the same foods, however, tended to have babies with lower birth weights.
The effect appeared early in pregnancy. Mothers who consumed more ultra-processed foods during the first 16 weeks were more likely to have babies with lower birth weights, shorter lengths, and smaller head circumferences at birth.
“We believe that the impact of maternal consumption of ultra-processed foods on the baby’s birth weight and body measurements may be related to placental development, which depends on many nutrients. Ultra-processed foods are, in fact, nutrient-poor,” said Carvalho.
That distinction may help explain why the same category of food produced opposite effects depending on which parent consumed it.
One effect likely stemmed from nutrient deficiency during pregnancy, while the other appeared to originate earlier in the father’s sperm.
Why birth weight matters
A baby’s birth weight ranks among the most important predictors of health across both childhood and adulthood.
Beyond increasing the risk of death, both low and high birth weights increase the likelihood of developing noncommunicable diseases later in life.
These include cardiovascular disease, type 2 diabetes, and certain cancers.
“The study didn’t find an increase in total body fat. Instead, it found greater fat accumulation in specific regions of the baby’s body,” said Sartorelli. “The results suggest that the quality of the father’s diet may also influence fetal development.”
Ultra-processed foods accounted for an average of 30 percent of the total energy consumed by the fathers whose diets were analyzed in the study. Processed meats, sugary drinks, and cookies were the biggest contributors.
Weight isn’t the whole story
This isn’t the first time Sartorelli’s team has traced paternal factors to newborn outcomes. In earlier research, the same group found that overweight fathers tended to have babies with lower birth weights.
This new study adds an important layer to that finding by isolating diet quality specifically, showing that a father’s weight alone doesn’t tell the whole story.
“With these two studies, we’ve shown that it isn’t just a matter of whether the father is overweight. The quality of the father’s diet before conception has a significant impact on the baby’s health,” Sartorelli said.
Small study with broader implications
The researchers are upfront about the study’s limitations, with only 43 families included in the analysis.
Even so, they consider it a pioneering effort to investigate how ultra-processed food consumption affects both paternal and neonatal health.
“The results pave the way for larger studies and reinforce the need to include men, not just women, in family planning guidance,” said Sartorelli.
The study is published in the journal Nutrition Research.
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