New ‘Mega-Review’ Finds Ultraprocessed Foods Contribute to More Than 30 Damaging Health Outcomes

Study Shows Processed Foods Can Harm Health: What You Need to Know

microwave dinner artificially colored drink sugary cereal
Ultraprocessed foods have high amounts of added sugars, saturated fat, and salt, as well as artificial colors and flavors — but little or no vitamins, minerals, or fiber.

The study, published in The BMJ, examined data from numerous studies conducted since 2009 to assess the relationship between processed food intake and various health outcomes. The findings revealed a concerning link between processed food consumption and an increased risk of several health conditions, including heart disease, cancer, mental health disorders, and premature death.

“Our study showed a relatively consistent trend in the link between a higher intake of ultraprocessed foods and several adverse health outcomes,” says lead author Melissa Lane, PhD, a post-doctoral research fellow and professor at Deakin University in Melbourne, Australia.

The review highlights the both the need for public health strategies to reduce the amount of ultraprocessed foods people eat and more research to understand how they may be negatively impacting health, according to Dr. Lane.

Ultraprocessed Foods Can Make Up Nearly 60 Percent of a Western Diet

Ultraprocessed foods include mass-produced products that require industrial formulations, like sugar-sweetened beverages, packaged baked goods and snacks, sugary cereals, and ready-to-eat or microwave products. They often contain added artificial colors and flavors, along with high levels of added sugar, fat, and salt, but not much in the way of nutrients, vitamins, or fiber.

For people in wealthier countries, ultraprocessed foods can account for up to 58 percent of the calories consumed every day, according to researchers.

Although there have been many studies looking at how highly processed foods affect health, this is the first comprehensive review to look at all the evidence that’s accumulated since 2009, which is the year that the concept of ultraprocessed foods was introduced in research. The latest umbrella review included 45 distinct pooled meta-analyses from 14 review articles.

The review articles were all published in the past three years and involved almost 10 million participants. None were funded by companies involved in the production of ultraprocessed foods.

All the analyses included observational studies, not randomized controlled studies. That means that researchers didn’t design a trial in which some people ate ultraprocessed foods and were compared with people who didn’t eat them. Rather, the studies typically recorded estimates of exposure to ultraprocessed foods from a combination of food frequency questionnaires, 24-hour dietary recalls, and dietary histories. Participants were then grouped between higher versus lower consumption, additional servings per day, or 10 percent increments.

Researchers graded the studies included as convincing, highly suggestive, suggestive, weak, or no evidence. They also used the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) system to evaluate the quality of evidence for each pooled analysis as high, moderate, low, or very low. According to the GRADE approach, all observational studies are initially considered low quality.

Ultraprocessed Foods Linked With Higher Risk of Heart Disease and Anxiety

According to the authors there was “convincing evidence” that higher ultraprocessed food intake was associated with the following:

  • Close to a 50 percent increased risk of heart disease-related death
  • A 48 to 53 percent higher risk of anxiety and common mental disorders
  • A 12 percent greater risk of type 2 diabetes

“Highly suggestive” evidence also showed that higher ultraprocessed food intake was associated with:

  • A 21 percent greater risk of death from any cause
  • A 40 to 66 percent increased risk of heart disease related death, obesity, type 2 diabetes, and sleep problems
  • 22 percent increased risk of depression

The evidence for the associations of ultraprocessed food exposure with asthma, gastrointestinal health, some cancers, and cardiometabolic risk factors (such as high blood fats and low levels of “good” cholesterol) remains limited and more research is needed in these areas, according to the authors.

“The analysis is an umbrella review, so essentially an attempt to summarize the data that are currently available. A strict interpretation of the quality-of-evidence (GRADE) data would suggest that there is only very limited evidence for an association between ultraprocessed food intake and health, because most associations are rated as of low or very low quality,” says Gunter Kuhnle, PhD, a professor and researcher in the department of food and nutritional sciences at the University of Reading in England, who was not involved in the study.

The authors do not seem to agree with this — although they do not explain the reasons for it — and consider these associations to be relevant enough to be discussed, says Dr. Kuhnle. “But they do agree that the study cannot provide any information on causality,” he adds.

Why Are Most Nutrition Studies Observational?

There are many reasons why there are very few randomized controlled nutrition studies that look at long term health outcomes.
People vary in many ways: sex, race and ethnicity, BMI, food preferences, exercise patterns, and existing health conditions, just to name a few. It’s also hard to get people to stick to a dietary intervention for months or years. Finally, some researchers believe that we already know enough about the harms of ultraprocessed foods to make it unethical to instruct people to eat them in order to study the effects.

The researchers acknowledge that reviews like this one “can only provide high-level overviews” and it’s possible that other unmeasured factors and variations in assessing ultraprocessed food intake may have influenced their results.

However, the fact that the included analyses were observational doesn’t negate the potential associations, especially as more data becomes available in the future, the authors wrote. They also point to the fact that 93 percent of the pooled analyses had very similar findings on the increased risks reported in the review.

“These findings support urgent mechanistic research and public health actions that seek to target and minimize ultraprocessed food consumption for improved population health,” the authors conclude.

Why Are Ultraprocessed Foods Bad for Us?

Ultraprocessed foods are not merely modified foods, wrote Carlos Monteiro, PhD, a professor of nutrition and public health at the School of Public Health at the University of Sao Paulo in Brazil, in an accompanying editorial.

They are formulations of often chemically manipulated, cheap ingredients like modified starches, sugars, oils, fats, and protein isolates, and “no reason exists to believe that humans can fully adapt to these products,” wrote Dr. Monteiro.

Do the potential health risks posed by ultraprocessed foods go beyond their link to being overweight or obese, which is known to increase the risk of many chronic conditions?

Obesity is only one detrimental outcome of diets high in ultraprocessed foods, says Lane. “While high body mass index may be one upstream biological or physical mechanism linking diets high in ultraprocessed foods to other health outcomes, we know that the relationship between unhealthy diets and, for example, mental health outcomes like depression, does not seem to work through body weight,” she says. There needs to be more exploration into the impact of these types of foods on all our body systems, including the immune system and gut microbiome, says Lane.

More Research Is Needed to Understand the Health Risks Posed by Ultraprocessed Foods

“What we need now are trials that improve our understanding of how ultraprocessed foods are linked to chronic diet-related diseases: what physiological processes are affected and what are the precise attributes of ultraprocessed foods that link them to poor health outcomes. Trials are like missing puzzle pieces we need to fill in to strengthen the evidence base,” says Lane.

Kuhnle believes there needs to be a greater understanding of the potential underlying mechanisms. “We would need to identify which specific food groups are associated with ill health beyond their composition,” he says.

For example, would supermarket bread increase the risk of disease compared with homemade bread, he asks. “We would also need a clearer definition of the term ‘ultraprocessed,’” says Kuhnle.

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