A new study, published in Nutrition Research, suggests that what fathers eat before pregnancy may influence their baby's birth weight and body fat. Researchers found that fathers who ate more ultra-processed foods were more likely to have babies with higher birth weights and more fat around the thighs and waist. Previous research suggests that a father's diet can influence how this gene functions. Although the study was small, the findings highlight that a father's nutrition matters just as much as a mother's when planning a pregnancy. Nutrition Research.