A team of researchers from the University of São Paulo Medical School in Brazil followed a diverse sample of more than 10,000 Brazilians for up to 10 years. The subjects filled out food frequency questionnaires to note how often they were eating foods including: unprocessed or minimally processed ingredients (aka whole foods like fresh, dry or frozen fruits, vegetables, whole grains, meat, fish and milk that underwent minimal processing, like pasteurization); processed foods (canned fruits, artisanal bread and cheese, and salted, smoked or cured meat or fish); and ultra-processed foods (industrial formulations of processed food substances like oils, fats, sugars, starch, artificial flavors and colorings, but containing little or no whole foods). 

The subjects also took cognitive tests up to three times a year, including memory tests and word recognition tests, to monitor their cognitive functioning; aka, mental abilities such as learning, thinking, reasoning, remembering, problem-solving, decision-making and attention. They also took regular verbal fluency tests to track their executive functioning; aka the mental skills that help an individual plan, monitor and successfully meet their goals. 

The findings? Those who ate 20% or more of their daily calories from ultra-processed foods had a 28% faster rate of cognitive decline, and a 25% faster rate of executive function decline, compared to the subjects in the study who ate the least amount of processed foods. In other words, someone following a 2,000-calorie-a-day diet who consumed 400 of their daily calories from ready-to-eat frozen meals, processed meats, breakfast cereals and sugar-sweetened beverages each day saw a faster rate of cognitive decline. 

Opinion: Your diet isn’t just making you obese, it could be speeding up cognitive decline

And many of us are fueling ourselves with these ultra-processed foods. The researchers noted that a whopping 58% of the calories consumed by U.S. citizens come from ultra-processed foods. We’re not alone; 56.8% of the calories consumed by British citizens, 48% of the calories consumed by Canadians, and up to 30% of the calories eaten by Brazilians also typically come from these ultra-processed foods, the researchers added. And despite the rise in plant-based alternatives (some of which are highly processed, themselves) and poultry consumption — and a dip in buying and eating unprocessed red meat — another recent report noted that Americans are still eating as much processed food as they did two decades ago, particularly deli meats, sausage, hot dogs, ham and bacon.

Related: Putting less sugar in packaged foods could prevent millions of Americans from getting sick — and save the U.S. over $160 billion

But there was an interesting catch in the cognitive decline study: If the overall quality of a subject’s diet was otherwise very high (meaning they ate a lot of unprocessed whole foods like fruits and vegetables, whole grains and lean proteins), then this association between ultra-processed foods and dementia disappeared. So the good news is, you can counter consuming these often cheap and easily-accessible ultra-processed foods by cooking more at home (which can also save you money) and preparing your food with whole foods like fresh or frozen produce, whole grains and lean meats and proteins. 

“Limiting ultra-processed food consumption, particularly in middle-aged adults, may be an efficient form to prevent cognitive decline,” the researchers wrote in their findings published in the journal JAMA Neurology this week. Indeed, this aligns with what health officials such as the American Heart Association have been saying: rather than calling out “good” or “bad” individual foods, folks should focus on eating an overall healthy diet that is high in fruits and vegetables, whole grains and lean/high-fiber proteins that are minimally processed. 

Read more: No more ‘good’ vs. ‘bad’ foods: 10 healthy eating ‘patterns’ to prevent heart disease and death

But brain health isn’t the only concern when it comes to ultra-processed foods. Here are four other ways that these ready-made meals and snacks can hurt your health. 

Processed foods raise your risk of heart disease

An analysis of almost 30,000 people published in the JAMA Internal Medicine journal in 2020 suggested that eating two servings of red meat and processed meat each week – such as two hot dogs or four pieces of bacon – was “significantly associated” with heart disease.

“It’s worth trying to reduce [consumption of] red meat and processed meat like pepperoni, bologna and deli meats,” wrote senior study author Norrina Allen, associate professor of preventive medicine at the Northwestern University Feinberg School of Medicine.

Researchers from the University of Paris collected data on the diets and health of more than 105,000 people aged 18 and up over the course of five years for a 2019 report. They found that those who ate the most “ultra-processed” foods had a greater risk of heart attack, stroke and other cardiovascular issues.

The American Heart Association also released a new scientific statement last year focusing on overall healthy eating habits to protect your ticker, which included choosing minimally-processed foods (such as a bag of salad or roasted, unsalted nuts) rather than ultra-processed foods (such as sugary cereal, potato chips or smoked sausage) as much as possible. The dietary guidelines also recommended limiting the consumption of food and beverages with added sugars. And it suggested choosing or preparing foods with little or no salt.

Processed foods increase cancer risk

People who had a 10% higher intake of ultra-processed foods saw more than a 10% increase in risk for cancers including breast cancer, according to a 2018 study published in the peer-reviewed British Medical Journal.

So when the American Cancer Society updated its diet recommendations to prevent cancer in 2020, cutting out processed foods was high on the list – along with curbing the consumption of sugar-sweetened drinks, red meat and alcoholic beverages. The American Cancer Society recommended piling your plate with a variety of whole, unprocessed foods and vegetables, instead; particularly dark green, red and orange veggies, as well as fiber-rich legumes like beans and peas. The guide also promoted whole grains, whole fruits in a variety of colors, and overall foods that are “high in nutrients in amounts that help achieve and maintain a healthy body weight.”

Processed foods lower life expectancy 

So considering the reports suggesting processed foods are associated with a host of chronic health conditions like cancer, heart disease and dementia – not to mention obesity, as those who follow an ultra-processed diet could consume up to 500 more calories per day compared with those who consume whole foods – it shouldn’t come as too much of a surprise that research has also found a link between eating these foods and early death.

Researchers at the University of Navarra in Pamplona, Spain documented the dietary habits of more than 20,000 Spanish college graduates between 1999 and 2014. They found that people who frequently consumed heavily processed foods (as in, more than four servings of each per day) had a 62% increased risk for early death compared to those who indulged in these foods less often.

And the 2020 study that noted eating two servings of red meat and processed meat each week was linked with heart disease also found that consuming these tasty but risky foods was also “significantly associated” with death. In fact, people who ate two servings of red meat or processed meat a week — but not poultry or fish — were linked with a 3% higher risk of all causes of death.

Processed foods hurt the planet – and come back around to bite you  

Favoring the growth and production of processed foods – which often rely on the same handful of staple ingredients such as sugar cane, corn, rice and wheat – has resulted in killing off more diverse plant offerings. This impacts agrobiodiversity—or the variety and variability of animals, plants and microorganisms used directly or indirectly for food and agriculture, which affects soil health and farming’s long-run profitable resilience, according to research published in BMJ Global Health earlier this year. What’s more, producing ultra-processed food uses large quantities of land, water, energy, herbicides and fertilizers, which hurts the environment by emitting greenhouse gas and creating tons of packaging waste.

Read more: Processed foods like ramen packets and frozen pizza can hurt your heart — and the globe, study says