Could what’s on your dinner plate tonight be quietly shaping the future of your family?
That question sounds dramatic — but after reading what a new study from Rotterdam found,
it doesn’t feel so far-fetched.

Welcome, dear reader. Here at FreeAstroScience.com, we believe that
science is for everyone — not just those in white coats. Every week, we take complex
research and break it down into plain, honest language, so you can make sense of the
world around you. Today, we’re doing exactly that with a groundbreaking study just
published on March 24, 2026, in the prestigious journal
Human Reproduction.

This study is the first of its kind to look at how both parents’ diets —
specifically their consumption of ultra-processed foods — affect their ability to conceive
and how well the embryo develops in those critical first weeks of life. The results are
eye-opening, even a little uncomfortable. And we think you deserve to know them.
Stick with us to the end — there’s a lot more to this story than headlines tell you.

When Junk Food Affects Not Just You — But the Life You’re Trying to Create

What Are Ultra-Processed Foods, Exactly?

Before we get into the science, let’s get clear on what we’re talking about.
Ultra-processed foods (UPFs) are products that go far beyond simple
cooking. They’re manufactured with industrial ingredients — artificial colors, emulsifiers,
preservatives, stabilizers, and flavor enhancers — that you’d never find in a home kitchen.

Think: packaged chips, instant noodles, sugary breakfast cereals, pre-made frozen meals,
fizzy soft drinks, fast food burgers, and mass-produced pastries.
Scientists classify them using the NOVA food classification system,
which groups foods into four categories based on how much processing they undergo.
NOVA Group 4 — the ultra-processed tier — is what this study focuses on.

UPFs now make up a frightening share of daily calories in many countries.
In this study’s Dutch cohort, women got 22% of their total food intake
from UPFs, while men consumed even more — about 25%.
Those aren’t extreme numbers. That’s pretty normal for modern life. And that’s exactly
what makes these findings so relevant to you.

What Did This New Study Actually Find?

Researchers at Erasmus University Medical Center in Rotterdam, the
Netherlands, led by Dr. Romy Gaillard — a paediatrician and associate
professor of developmental epidemiology — conducted what is now the first study to examine
the combined dietary impact of both parents on conception and early embryonic
development.

The team analyzed data from 831 women and their 651 male
partners, all enrolled in the Generation R Study Next Programme,
a long-term Dutch cohort study that has followed families from before conception into
their children’s early years.
Couples joined between 2017 and 2021.
Diet was assessed around the 12-week mark of pregnancy using a detailed
food questionnaire.

The study also used transvaginal ultrasound scans to measure embryo
size and yolk sac volume at weeks 7, 9, and 11 of pregnancy.
That level of detail is rare. Most fertility research looks at just one factor — sperm
count, say, or birth outcomes. This one connected the dots from the dinner table to the
womb, in real time.

Why Are Men’s Fertility Numbers So Alarming?

A 63% Higher Risk — Is That Number Real?

Yes, it is. Men who ate higher amounts of UPFs were 63% more likely
to experience subfertility — defined as taking 12 months or longer to conceive,
or needing assisted reproductive technology like IVF. They also took longer, on average,
to achieve pregnancy with their partner.

First author Celine Lin, a PhD student at Erasmus University Medical
Center, explained it clearly: “In men, we observed that higher UPF consumption
was related to a higher risk of subfertility and a longer duration until pregnancy was
achieved.”
Sperm, it turns out, is remarkably sensitive to what a man eats.

This tracks with earlier research, too. A 2024 study in
Human Reproduction Open — involving 200 healthy men of
reproductive age — found that higher UPF consumption was directly linked to
reduced total sperm count, lower sperm concentration, and decreased sperm motility
(the sperm’s ability to swim). Swap those UPFs for minimally processed foods?
Semen quality improved. The pattern is consistent.

And another 2025 study confirmed that the Mediterranean diet — rich in vegetables, fish,
whole grains, and olive oil — was associated with better sperm quality parameters,
including viability and typical morphology. The contrast with UPF-heavy diets is stark.

How Does a Mother’s Diet Shape Early Embryo Growth?

For women, the story is different — but equally striking.
Higher maternal UPF consumption didn’t consistently affect whether a woman could
conceive. What it did affect was what happened once she did.

At 7 weeks of gestation, women with higher UPF diets had embryos
that were measurably smaller than those of women eating fewer ultra-processed foods.
Their yolk sacs were also smaller. These differences faded somewhat by weeks 9 and 11,
but the early window clearly matters.

As Celine Lin put it: “Maternal UPF consumption may directly influence the environment
in the womb in which the embryo develops from the start of life onwards.”
Think of it like soil quality. The embryo can only grow as well as the environment
around it allows. A nutrient-poor, additive-laden environment in those first weeks
may leave early marks — even if they’re difficult to see clearly yet.

What Is the Yolk Sac and Why Does It Matter So Much?

Most people have heard of the yolk of an egg. In human embryology, the
yolk sac plays a similar role — it’s the embryo’s first source of
nourishment before the placenta takes over. It forms in the very first weeks of pregnancy,
typically visible by ultrasound around week 5 or 6.

A healthy, properly-sized yolk sac is linked to better early development outcomes.
A smaller or irregularly formed yolk sac, on the other hand, is associated with
a higher risk of miscarriage and developmental complications.
Impaired yolk sac development in the first trimester has also been connected to
adverse birth outcomes — including premature birth, low birth weight,
and even cardiovascular issues in childhood.

We’re talking about differences measured in fractions of a standard deviation
(–0.14 SDS per unit increase in UPF intake, to be precise). Small? Yes.
Irrelevant? Far from it. At a population level, small shifts in embryo development
can translate into large public health implications.

Key Study Numbers at a Glance

We’ve pulled the most important numbers together in one place.

Why Might UPFs Cause This Kind of Damage?

Is It the Empty Calories, or Something More Sinister?

Honestly? We don’t know yet. And the researchers are the first to admit that.
There are two leading theories, and they’re not mutually exclusive.

The first is simple: UPFs tend to crowd out nutritious foods.
When 25% of a man’s diet is chips and packaged snacks, that’s 25% not spent on
zinc-rich legumes, antioxidant-packed vegetables, or omega-3 fatty acids from fish —
all nutrients known to support sperm quality and reproductive hormone levels.
Poor nutritional density alone could explain a lot.

The second theory is more unsettling.
UPFs contain a cocktail of food additives — emulsifiers, artificial
sweeteners, colorings, and preservatives — whose long-term reproductive effects are
largely unknown. Some researchers also point to microplastics,
which contaminate packaging and have been found in human sperm, blood, and placental
tissue. Whether these microplastics actively disrupt sperm production or embryonic
signaling is still an open question.

Sperm cells are particularly vulnerable. They take roughly 74 days
to fully mature — and during that entire window, they’re being shaped by diet, toxins,
and environment. Every chip bag, every soda, every microwave meal a man consumes during
those three months could theoretically nudge his sperm quality in one direction or another.
That’s a sobering thought.

Should We Trust These Results? Limitations and Nuances

Good science always names its limits. This study is no exception, and we’d be doing
you a disservice if we glossed over them.

First: this is an observational study. That means it can identify
associations between UPF intake and fertility outcomes — but it cannot prove direct
causation. People who eat more UPFs may also sleep less, exercise less, smoke more,
or live in more stressful environments. Disentangling all those variables is genuinely hard.

Second: diet was assessed at 12 weeks of pregnancy, not at the time
of conception. It’s reasonable to assume eating habits hadn’t changed dramatically,
but we can’t be certain. Also, the study cohort consisted entirely of couples who
did eventually conceive — so the impact on couples who never got pregnant at all
may be even larger than these numbers suggest.

A parallel study, published in the journal Nutrition and Health around the
same time, analyzed data from over 2,500 American women in the US
National Health and Nutrition Examination Survey. That study included women
who were unable to conceive — and found the same direction of effect:
lower UPF consumption was linked to a higher likelihood of pregnancy. That consistency
across two independent datasets, using different methodologies, is meaningful.

What Can We Realistically Do About This?

We’re not here to shame anyone’s eating habits. Modern life is busy.
Food is expensive. And whole foods take time to prepare.
But if you’re trying to conceive — or even just thinking about it — these findings
give you a real, evidence-based reason to look at what’s in your shopping trolley.

Here’s what the science points to, without being preachy about it:

• Both partners should think about diet in the pre-conception window — not just the woman.
• A diet closer to the Mediterranean model (vegetables, fish, olive oil, legumes, whole grains) is consistently linked to better reproductive health in both sexes.
• Swapping UPFs for minimally processed alternatives — even gradually — appears to improve sperm quality parameters in men.
• The pre-conception period and first trimester are especially sensitive windows. Early exposure matters enormously.
• If you’re concerned about fertility, speak to a doctor. Diet is one piece of a complex picture.

Dr. Romy Gaillard put it well when she said: “Our research shows that we should
think more broadly about fertility and early pregnancy. Our results highlight the need
to pay more attention to male health in the preconception period, which has traditionally
been overlooked.”
We at FreeAstroScience couldn’t agree more.

Final Thoughts from FreeAstroScience

What this research really tells us is that the body is not a sealed machine.
It’s a living system, constantly in conversation with its environment — including
the food we feed it. A man’s sperm, a woman’s embryonic womb, the yolk sac
quietly nourishing a new life: all of it responds to the world outside.
That’s both humbling and empowering.

We know there are people reading this who are in the middle of difficult fertility
journeys. You are not alone. Science is beginning to look at factors that for too long
were invisible — including male diet — and that matters. These findings aren’t a
verdict; they’re a direction. A reason to ask better questions.

At FreeAstroScience.com, we write for you — the person on the train,
the parent-to-be scrolling late at night, the curious mind who refuses to accept easy
answers. We believe knowledge protects you. It shields you from misinformation,
from fear-mongering, and from the kind of half-truths that circulate on social media
masquerading as science.

We live by one principle here: never turn off your mind. Keep it active,
keep it questioning, keep it open — because, as Goya warned us more than two centuries
ago, the sleep of reason breeds monsters.

Come back to FreeAstroScience.com
— where complex science is explained simply, every single day.
Your knowledge is your superpower. Don’t waste it.