Plant foods become unhealthy when they’re ultra-processed, study finds

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Eating a plant-based diet is good for your health, but not if those plant foods are ultra-processed, a new study has found.

The findings show that all plant-based diets aren’t the same, and that plant foods can have very different effects on your health depending on what manufacturers do to them before they reach your plate.

The new research, published on Monday in the journal Lancet Regional Health — Europe, found eating plant-derived foods that are ultra-processed — such as meat substitutes, fruit juices and pastries — increases the risk of heart attacks and strokes. But when plant foods such as fruits, vegetables, whole grains and nuts are only minimally processed, meaning they are cleaned, cut and packaged but served largely as they are found in nature, they have a protective effect against cardiovascular disease.

Ultra-processed foods have faced intense scrutiny from health authorities in recent years. What’s unusual about the new study is that it zeroed in on the health effects of ultra-processed foods that begin as plants, comparing them with minimally processed plant foods. Given that plant-based foods are generally healthy in their natural state, the research suggests that there’s something uniquely damaging about ultra-processing that changes a food in a way that can harm a person’s health long term.

“The artificial and heightened flavors of these foods can lead people to become addicted to these flavors, making it difficult for them to appreciate the natural flavors of real foods such as fruits and vegetables,” said Fernanda Rauber, the lead author of the new study and a researcher at the Center for Epidemiological Research in Nutrition and Health at the University of São Paulo in Brazil.

How ultra-processing distorts plant foods

The new study analyzed data on 118,000 adults who were followed for roughly a decade as part of the UK Biobank, a study that has been tracking the health and lifestyle habits of people throughout the United Kingdom. As part of the long-running study, the participants answered questions about their diets, habits and environments on different occasions and provided biological samples, and health and medical records. The findings included:

  • The more ultra-processed foods people consumed, the higher their likelihood of dying of heart disease.
  • Every 10 percent increase in calories from plant-derived ultra-processed foods was associated with a 5 percent higher likelihood of developing cardiovascular disease and a 6 percent higher risk of coronary heart disease in particular.
  • For every 10 percent increase in the consumption of whole plant-based foods — those that were not ultra-processed — the participants had an 8 percent reduction in their likelihood of developing coronary heart disease and a 20 percent reduction in their risk of dying of it. They also had a 13 percent lower risk of dying of any cardiovascular diseases.

Many of the foods studied were not foods people would typically consider a plant food. But the main ingredients in many junk foods come from plants, such as cane and beet sugars, wheat flour, corn, potatoes, fruit juices and vegetable oils.

In the new study, the plant foods that were defined as ultra-processed included:

  • Wheat and corn: Pastries, buns, biscuits, cakes, packaged breads, cereals, chips and salty snacks.
  • Potatoes: French fries, potato chips.
  • Beet, cane and other sugars: Candy, soft drinks.
  • Fruits and vegetables: Sauces, dressings, juices, beverages, frozen pizza.
  • Soy, wheat, beans, peas: Meat substitutes, including imitation burgers and sausages.

Ultra-processing strips away health-promoting nutrients, replaces them with salt, sugar and fat, and destroys the food’s internal structure or “food matrix,” which causes our bodies to absorb the food more rapidly. This results in less satiety and in some cases higher blood-sugar levels.

During industrial processing, foods are often subjected to extreme pressures and temperatures, which can transform additives into harmful new compounds. Two well-known compounds that are generated during food processing, acrolein and acrylamide, have been found to promote cardiovascular disease.

Plant foods that are not ultra-processed contain fiber, polyphenols, phytosterols and a wide array of compounds that reduce inflammation and promote overall health.

Rauber recommended eating a diet of mostly minimally processed foods and avoiding things that come in packages with long lists of colorants, sweeteners, flavor enhancers, emulsifiers and other additives that you would not use at home in your own kitchen.

“When buying ready-made food or preparations, the best tip is to read the ingredient list,” said Rauber. “If it contains only ingredients that you recognize and commonly have in your kitchen, it is most likely made from real food and is not an ultra-processed food.”

The health risks of ultra-processed plant foods

There is also evidence from previous research that supports the findings about plant-based ultra-processed foods. In one large study published in 2022, scientists examined the diets of 78,000 men and women from a health-conscious community of Seventh-day Adventists, many of whom were vegans and vegetarians. After following them for an average of about eight years, they found that those who ate the most ultra-processed foods had a 14 percent higher mortality rate compared with those who ate the least.

Dozens of studies have linked ultra-processed foods to early death and an increased risk of more than 30 different health conditions, including higher rates of weight gain, obesity, cancer, diabetes and heart disease. A panel that shapes the federal government’s influential Dietary Guidelines for Americans is debating whether a warning against ultra-processed foods should be included in the next edition of the guidelines.

Ultra-processed foods are what scientists call hyper-palatable: They’re industrially manufactured foods that have unusual combinations of flavors and additives, such as salt, sugar, stabilizers, emulsifiers, oils and artificial ingredients that cause us to crave and overeat them. In most cases these foods are stripped of their fiber, vitamins, minerals and other naturally occurring nutrients and crammed full of calories.

The authors of the study cautioned that their research showed a correlation between ultra-processed plant foods and cardiovascular disease, but that it did not prove cause and effect. It’s possible that the participants misreported the types and amounts of foods that they ate, for example, or that other lifestyle factors explained the findings.

Do you have a question about healthy eating? Email [email protected] and we may answer your question in a future column.

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