People who eat ultra–processed plant–based diets face a significantly higher risk of heart disease, worrying new research suggests.

While vegan diets have long been praised for their fibre and nutrient content, scientists say the benefits disappear when those diets rely heavily on ultra–processed foods – which may be just as harmful as other forms of junk food.

The study, published in The Lancet Regional Health journal, tracked more than 63,800 middle–aged adults in France and found that plant–based diets only protect the heart when they are based on whole, minimally processed foods.

Lead author Clémentine Prioux, a nutrition researcher at Sorbonne University, said: 'Our findings reinforce the necessity of advocating not only for a reduction in animal products but also encouraging the consumption of minimally processed plant–based foods to improve cardiovascular health.'

Over an average follow–up of just over nine years, participants who ate a nutritionally complete, largely unprocessed plant–based diet were 44 per cent less likely to develop coronary heart disease – a condition that can lead to chest pain, heart attacks and heart failure.

By contrast, those whose plant–based diets were dominated by ultra–processed foods had a 46 per cent higher risk of coronary heart disease and a 38 per cent increased risk of cardiovascular disease overall – an umbrella term for conditions affecting the heart and blood vessels.

These participants tended to consume more supermarket bread, ready–made pasta dishes, packaged soups and prepared salads with heavy dressings – foods that often contain stabilisers, emulsifiers and added fats.

Previous research suggests people who follow plant–based diets may consume more ultra–processed foods than meat–eaters, largely because of the availability of processed meat substitutes.

Interestingly, people who ate some animal products but avoided ultra–processed foods were no more likely to develop heart disease than those following healthy, whole–food plant–based diets.

The findings suggest food quality and processing mattered more than whether diets were plant or animal–based.

Data came from 63,835 adults enrolled in the French NutriNet–Santé study, which assessed how both the nutritional quality and level of processing of plant–based foods influence heart health.

Participants completed detailed annual health questionnaires, while diet was assessed using repeated 24–hour dietary records completed at the start of the study and then every six months.

Researchers also accounted for smoking status, physical activity and other lifestyle factors.

All foods and drinks – including snacks – were recorded, with portion sizes estimated using photographs or standardised containers. Nutrient intake was calculated using a validated food composition database and cross–checked against blood and urine biomarkers.

Foods were categorised using the NOVA classification system, developed in 2009, which groups foods according to the degree and purpose of processing.

Under NOVA, unprocessed or minimally processed foods include items such as fruit, vegetables, grains, pasta, fresh or frozen meat and fish – foods altered only by basic methods like freezing, drying or pasteurisation.

Processed foods are made by adding ingredients such as salt, sugar or oil to whole foods – for example, cheese, freshly baked bread or canned vegetables.

Ultra–processed foods, by contrast, are industrial formulations made using multiple processing steps and ingredients not typically found in home cooking – such as emulsifiers, flavourings, colourings and preservatives.

These products are often high in energy, added sugar, saturated fat and salt, while being low in fibre and micronutrients.

The researchers found nutritionally healthy plant–based diets built around unprocessed foods offered the greatest protection against coronary heart disease.

No such benefit was seen when plant–based diets relied heavily on processed or ultra–processed foods.

The worst outcomes were seen in people consuming ultra–processed plant–based diets, whose risk of heart disease rose by nearly 40 per cent.

The findings come as NHS data shows a rise in heart attacks among younger adults over the past decade, with the largest increase seen in 25 to 29–year–olds – although experts caution that small absolute numbers can exaggerate percentage changes.

The researchers concluded: 'Our findings indicate that the level of food processing can influence the association between plant–based diets and incidence of cardiovascular disease.

'Taken together, these results highlight the importance of considering three dimensions of diet for cardiovascular prevention – the balance between plant– and animal–based foods, nutritional quality and degree of processing.'

They noted the findings may be particularly relevant to the UK, where a wider range of ultra–processed plant–based products is available than in France.

Previous studies suggest people in the UK consume around twice as many ultra–processed plant–based foods as those in some other European countries.

However, the researchers stressed that ultra–processed animal–based foods were associated with an even higher risk of heart disease.

Heart disease is commonly caused by a build–up of fatty deposits in the arteries, restricting blood flow and increasing the risk of blood clots.

It remains one of the leading causes of death and disability in the UK, though experts say many cases could be prevented through healthier diets and lifestyles.

And obesity and poor diet are thought to be at least partly to blame, particularly for the rise among younger adults under 50. 

It comes as research this year has repeatedly suggested fatty, sugary and additive–laden foods such as crisps and sweets could raise the risk of life–threatening heart issues. 

In response, experts have even called for ultra–processed foods (UPFs) to be slashed from diets. 

Cardiovascular disease is usually associated with a build–up of fatty depositions inside the arteries, which restrict blood flow to the heart, and increase the risk of blood clots. 

It can also be linked to damage to arteries in organs such as the brain, heart, kidneys and eyes.

 It is one of the leading causes of death and disability in the UK, but it can often largely be prevented by leading a healthy life style.