Ultra-processed foods and women’s fertility: what the study reveals

A new study takes a critical look at ultra-processed foods – the very products found in most shopping trolleys. Researchers in Canada have identified a clear link between the share of these products in women’s everyday diets and their fertility. The issue is not simply calories or excess weight, but hidden chemical exposure and disruption to the hormonal system.

What the study specifically examined

The McMaster University research team drew on data from the large US National Health and Nutrition Examination Survey. The analysis included 2,582 women aged 20 to 45.

All participants reported whether they had unsuccessfully tried to become pregnant for at least one year. This created two groups: women with and without indications of infertility.

The women also completed two detailed 24-hour dietary records. This enabled researchers to track relatively precisely what they had eaten and how much of it came from ultra-processed products.

Key finding: the greater the proportion of ultra-processed foods, the higher the risk of reduced fertility.

On average, these products accounted for around 27 per cent of daily energy intake. Among women experiencing infertility problems, the proportion was approximately 30 per cent. Although the difference may appear small, it showed a statistically clear association with fertility.

What counts as an “ultra-processed” food?

Ultra-processed foods are much more than conventional ready meals. They go through numerous industrial processing stages and often contain additives that would not normally be used in a home kitchen.

Typical examples include:

• packaged snacks such as crisps, cheesy puff snacks, biscuits and bars
• sugary drinks such as fizzy drinks and energy drinks
• frozen pizza and other ready meals
• processed meat such as sausages, nuggets and salami
• sweet breakfast cereals with long ingredient lists

A defining feature is that these products barely resemble their original ingredients. Instead, they are usually dominated by combinations of sugar, refined flour, cheap fats, flavourings and preservatives.

Why ready-made foods may harm fertility

The researchers found that the relationship between ultra-processed foods and reduced fertility remained even after taking age, lifestyle and body weight into account. This means the simple argument that these are merely “empty calories” does not explain the findings.

Instead, attention turns to another concern: chemical substances associated with processing and packaging.

Hormone disruptors in the food chain

Many industrially manufactured foods can contain substances capable of affecting the hormonal system. These include, for example:

• Phthalates – plasticisers used in plastics, including packaging and tubing
• BPA (bisphenol A) – a component of plastics and can coatings
• Acrylamide – formed when starchy foods are heated intensely, for instance during frying

These substances can transfer into food from packaging or processing equipment. They are described as “endocrine disruptors”, meaning substances that can interfere with the hormonal system.

Hormones control the entire cycle – from the maturation of the egg cell to the implantation of the fertilised egg. If this finely balanced system is disrupted, the chances of pregnancy decrease.

Inflammation and gut flora as further influencing factors

The study also points to two further possible mechanisms:

• More inflammation in the body: Ultra-processed products often contain high levels of sugar, trans fats and an unfavourable balance of omega-6 and omega-3 fatty acids. This can encourage inflammatory processes, which may in turn disrupt egg maturation and the preparation of the uterine lining.
• Disrupted gut flora: A diet low in fibre and high in sugar can weaken beneficial gut bacteria. These microbes affect not only the immune system but also hormonal balance, including oestrogen metabolism.

The researchers stress that several of these factors may act together. The issue is therefore not just snacks that “make you fat”, but an accumulation of subtle effects that can build up over years.

The role of a Mediterranean-style diet

The team also examined the extent to which a Mediterranean-style diet affects fertility. This refers to an eating pattern rich in:

• vegetables and fruit
• wholegrain foods
• nuts and seeds
• olive oil and other high-quality plant oils
• fish and pulses

Women whose diets more closely followed this pattern initially performed better in terms of fertility. However, once body weight was included in the calculations, the effect became weaker. This suggests that part of the benefit comes from this diet helping to prevent excess weight and metabolic disorders.

Nevertheless, one finding remained notable: women struggling to conceive had lower overall Mediterranean diet scores than fertile women. This is a clear indication that eating habits play a measurable role.

Why processing matters more than nutritional values alone

A key point from the study is that conventional nutrition labels do not go far enough. Two products with similar amounts of calories, fat and protein may affect health very differently depending on how extensively they have been processed.

Processing determines not only flavour and shelf life, but also chemical exposure – and it often displaces fresh foods from the plate that would otherwise protect our bodies.

People who eat many ultra-processed products generally consume less fibre, vitamins and trace elements. Nutrients such as folate, iron and certain B vitamins, however, are important for ovulation, egg quality and a stable pregnancy.

What women can do in practical terms

The encouraging news is that nobody needs to transform their diet perfectly overnight. The researchers emphasise that even small changes to everyday routines can make a difference.

Practical everyday tips when trying to conceive

• Choose more “real” foods: At each shop, deliberately reach for fresh fruit, vegetables, plain yoghurt, nuts or pulses.
• Use a wooden spoon rather than a microwave: Replace ready meals with simple home-cooked dishes, such as roasted vegetables, soups or one-pan meals.
• Check the ingredient list: Leave products with long lists of E numbers, flavourings and processing aids on the shelf.
• Change your drinks: Gradually swap fizzy drinks and energy drinks for water, unsweetened tea or diluted fruit juice drinks.
• Reduce packaging: Where possible, buy food in glass, paper or loose rather than in plastic packaging.

Anyone unsure where to begin can set a simple goal: replace two typical ready meals each week with freshly cooked alternatives. This can be increased over time.

What “ultra-processed” means in detail

For context, it is useful to look briefly at the common classification of foods by their level of processing:

For fertility, experts advise clearly prioritising levels 1 and 3, while reducing level 4 to the lowest possible level.

Why the focus on fertility is so significant

Until now, much of the research into ultra-processed foods has concentrated on excess weight, diabetes and cardiovascular disease. The data now available shifts attention to a sensitive area: the ability to become pregnant.

The study was observational, so it cannot prove a direct cause-and-effect relationship. Even so, it reveals a clear trend that fits well with existing knowledge about hormone disruptors and inflammation.

For women trying to conceive, this offers a practical factor they can influence: choosing more fresh, minimally processed foods early on and cutting back on ultra-processed products creates better starting conditions for their own fertility, while also benefiting the heart, metabolism and long-term health.