July 29, 2026, 6:34 pm | Read time: 4 minutes

Beware of These Foods

The current analysis suggests that a higher proportion of ultra-processed foods in a father’s diet is associated with certain growth characteristics of the child at birth. Children of these fathers showed a statistically higher birth weight and higher values in certain skinfold measurements, which can provide insights into body composition.

How the Study Was Conducted

Researchers at the University of São Paulo wanted to find out if a father’s diet before birth could affect the physical development of their child. The background is the so-called “Paternal Origins of Health and Disease” hypothesis (POHaD). It assumes that men’s lifestyle and diet could influence their children’s health through biological processes, such as changes to sperm.¹

For the study, 43 mother-father-child trios from Brazil were evaluated. The fathers’ diets were recorded using two dietary protocols. Researchers then calculated the proportion of ultra-processed foods (UPF) in the daily energy intake.

This includes items such as soft drinks, sweets, cookies, processed meats, instant products, or other heavily industrially processed foods. The newborns’ body measurements were taken after birth and statistically compared with the fathers’ dietary data. The scientists considered various influencing factors such as age, education, smoking, alcohol consumption, and physical activity.

Also interesting: The health risks for babies when men become fathers too late

Notable Findings in Newborns

On average, about 30 percent of the fathers’ calorie intake came from ultra-processed foods. The higher this proportion, the higher some measurements of the newborns were. There was a correlation with birth weight, the so-called ponderal index—a measure of the body proportions of newborns—as well as the thickness of certain skinfolds on the hip and thigh. These skinfolds are considered indirect indicators of body tissue distribution.

However, the researchers found no statistically significant correlation for birth length, various standardized size measurements, or the estimated total body fat mass of the newborns.

While the mother’s diet directly affects the unborn child, the father’s influence could be mediated through biological changes in sperm and epigenetic processes. There was also a contrasting correlation in mothers. A higher proportion of ultra-processed foods in early pregnancy was associated with lower birth weight, shorter birth length, smaller head circumference, and a lower ponderal index.

More on the topic

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Strengths and Weaknesses of the Study

The current study from Brazil has several strengths: It was conducted prospectively and used standardized methods. Additionally, it is one of the first investigations into the possible connection between fathers’ consumption of ultra-processed foods and the body development of their newborns.

However, several factors limit its significance. The study included only 43 families and did not allow conclusions about a cause-and-effect relationship. Furthermore, the fathers’ diets were recorded not before conception but during their partners’ pregnancy. Since men’s lifestyle habits often change little when transitioning to fatherhood, the researchers still used this data as an approximation of the pre-conception period.

Also, the body fat percentage of the newborns was not directly measured but estimated using a prediction model. Moreover, only women with a body mass index between 25 and 29.9 participated, so it is unclear whether the results can be generalized to other populations. Further large studies are now needed to confirm the results.

Also interesting: How fatherhood changes men’s brains

A Look at Previous Studies on This Topic

In conclusion, let’s look at two studies that have addressed this topic. The Brazilian study is not alone in this field.

A study published in the journal “Cell Metabolism” in 2025 provided a possible mechanism.² Forty-three young men ate a highly ultra-processed and a largely unprocessed diet for three weeks each—with identical calorie amounts. After the UPF phase, body weight and the LDL/HDL ratio increased. Several hormones also changed, including FSH (follicle-stimulating hormone), which is important for sperm production. The motility of sperm also worsened with a calorie-rich diet. Crucially, the effects occurred independently of calorie intake—it wasn’t just because the men ate more. For transparency: One of the study’s authors is a consultant for companies in the metabolism and fertility sector.

Other data suggest caution. A Finnish analysis of the STEPS cohort with more than 1,500 fathers found no significant correlation between paternal BMI or diet quality and the birth weight or length of the children in 2025.³ However, the researchers also recorded the diet late in pregnancy—the same issue as in the Brazilian study. Research in this area is still in its early stages.