A recent, large-scale review of 45 meta-analyses of almost 10m people found that eating ultra-processed foods vastly increases the risk of developing or dying from dozens of adverse health conditions.
“There was consistent evidence linking higher intakes of ultra-processed foods with more than 70% of the 45 different health outcomes we assessed,” said senior author Wolfgang Marx, a senior research fellow at the Food & Mood Centre at Deakin University in Geelong, Australia.
A higher intake was considered about one serving or about 10% more ultraprocessed (UPF) foods per day, said Heinz Freisling, a scientist in the nutrition and metabolism branch of the World Health Organisation’s International Agency for Research on Cancer.
“This proportion can be regarded as ‘baseline’ and for people consuming more than this baseline, the risk might increase,” said Freisling, who was not involved in the study.
CNN reports that researchers graded each study as having credible or strong, highly suggestive, suggestive, weak or no evidence. All of the studies in the review had been published in the past three years, and none was funded by companies involved in the production of UPF.
“Strong evidence shows that a higher intake of ultra-processed foods was associated with a 50% higher risk of cardiovascular disease-related death and common mental disorders,” said lead author Dr Melissa Lane, a postdoctoral research fellow at Deakin.
Cardiovascular disease encompasses heart attacks, stroke, clogged arteries and peripheral artery disease.
The findings – published in The BMJ – showed convincing evidence that a high versus low intake of UPF could increase the risk of anxiety by up to 53%, and the risk of an early death from any cause by 20%.
“It’s not surprising that a lot of studies point to a positive association between ultraprocessed food consumption and the risk of various disease outcomes,” said cancer epidemiologist Fang Fang Zhang, associate professor and chair of the division of nutrition epidemiology and data science at Tufts University in Boston, USA, who was not involved in the new research.
“Ultraprocessed foods are high in calories, added sugar, sodium and low in fibre. All of these have already been known to contribute to cardiometabolic health outcomes, weight gain, obesity, type 2 diabetes and hypertension.”
However, Zhang questioned the findings on studies of anxiety and depression, which tend to be done only on those who have already been diagnosed with those conditions.
“People with depressive symptoms or anxiety may seek out UPF for various reasons such as self-comfort,” she said. “It may not be that eating ultraprocessed food puts you at high risk for depression – we cannot tell.”
Mixed impact on some conditions
The researchers also found highly suggestive evidence that eating more ultraprocessed foods raised the risk of obesity by 55%, sleep disorders by 41%, development of type 2 diabetes by 40% and the risk of depression by 20%.
However, evidence was limited for an association between UPF and asthma, gastrointestinal health and cardiometabolic risk factors like high blood fats and low levels of “good” high-density lipoprotein, or HDL, cholesterol, according to the analysis.
In addition, the study found only suggestive or no evidence for an association between ultraprocessed foods and cancer. That’s surprising, according to Zhang, who has previously researched the role such a link.
“Obesity is a risk factor for 13 types of cancers. Ultraprocessed foods increase weight gain, and obesity increases cancer,” she said. In an August 2022 study she co-authored, Zhang found men who ate the most UPF of any type had a 29% higher risk of developing colorectal cancer.
One reason for the unexpected finding is that research on ultraprocessed foods is still in its infancy, said study co-author Mathilde Touvier, research director at the French National Institute of Health and Medical Research, a public research organisation.
“We definitely need more studies to be able to upgrade the weight of evidence for cancer, for instance,” she added.
Touvier is also the principal investigator of the NutriNet-Santé cohort, a long-term study of the relationship between nutrition and health.
“So it’s not because there’s nothing there, it’s just because we need additional research,” she said.
The making of ultraprocessed foods
Ultraprocessed foods are much more than simply “modified” foods, said nutrition researcher Dr Carlos Monteiro, head of the Centre for Epidemiological Studies in Health and Nutrition at the University of São Paulo in Brazil. He was not involved in the study.
“They are formulations of often chemically manipulated cheap ingredients like modified starches, sugars, oils, fats, and protein isolates, with little if any, whole food added.”
Monteiro coined the term ultraprocessed food in 2009 when he developed NOVA, a system of classifying foods into four categories. Group one consists of unprocessed or minimally processed foods like fruits, vegetables, eggs and milk. Group two includes culinary ingredients such as salt, herbs, oils and the like. Group three are processed foods that combine groups one and two – canned goods and frozen vegetables are examples.
Group four are ultraprocessed foods, which Monteiro said are made flavourful and enticing by using combinations of artificial flavours, colours, thickeners and other additives that have been “linked by experimental and epidemiological evidence to imbalances in gut microbiota and systemic inflammation”.
“No reason exists to believe that humans can fully adapt to these products,” he said. “The body may react to them as useless or harmful, so its systems may become impaired or damaged, depending on their vulnerability and the amount of ultra-processed food consumed.”
Since Monteiro’s definition of ultraprocessed food appeared, nutritionists, researchers and public health officials have grown concerned about the increasing prevalence of such foods in the United States, Australia, the United Kingdom, Canada and many developing nations.
“Two-thirds of the calories children consume in the US are ultraprocessed, while about 60% of adult diets are ultraprocessed,” Zhang said.
Study details
Ultra-processed food exposure and adverse health outcomes: umbrella review of epidemiological meta-analyses
Published in The BMJ on 28 February 2024
Melissa Lane, Elizabeth Gamage, Wolfgang Marx et al.
Abstract
Objective
To evaluate the existing meta-analytic evidence of associations between exposure to ultra-processed foods, as defined by the Nova food classification system, and adverse health outcomes.
Design
Systematic umbrella review of existing meta-analyses.
Data sources
MEDLINE, PsycINFO, Embase, and the Cochrane Database of Systematic Reviews, as well as manual searches of reference lists from 2009 to June 2023.
Eligibility criteria for selecting studies
Systematic reviews and meta-analyses of cohort, case-control, and/or cross sectional study designs. To evaluate the credibility of evidence, pre-specified evidence classification criteria were applied, graded as convincing (“class I”), highly suggestive (“class II”), suggestive (“class III”), weak (“class IV”), or no evidence (“class V”). The quality of evidence was assessed using the GRADE (Grading of Recommendations, Assessment, Development, and Evaluations) framework, categorised as “high,” “moderate,” “low,” or “very low” quality.
Results
The search identified 45 unique pooled analyses, including 13 dose-response associations and 32 non-dose-response associations (n=9 888 373). Overall, direct associations were found between exposure to ultra-processed foods and 32 (71%) health parameters spanning mortality, cancer, and mental, respiratory, cardiovascular, gastrointestinal, and metabolic health outcomes. Based on the pre-specified evidence classification criteria, convincing evidence (class I) supported direct associations between greater ultra-processed food exposure and higher risks of incident cardiovascular disease related mortality (risk ratio 1.50, 95% confidence interval 1.37 to 1.63; GRADE=very low) and type 2 diabetes (dose-response risk ratio 1.12, 1.11 to 1.13; moderate), as well as higher risks of prevalent anxiety outcomes (odds ratio 1.48, 1.37 to 1.59; low) and combined common mental disorder outcomes (odds ratio 1.53, 1.43 to 1.63; low). Highly suggestive (class II) evidence indicated that greater exposure to ultra-processed foods was directly associated with higher risks of incident all cause mortality (risk ratio 1.21, 1.15 to 1.27; low), heart disease related mortality (hazard ratio 1.66, 1.51 to 1.84; low), type 2 diabetes (odds ratio 1.40, 1.23 to 1.59; very low), and depressive outcomes (hazard ratio 1.22, 1.16 to 1.28; low), together with higher risks of prevalent adverse sleep related outcomes (odds ratio 1.41, 1.24 to 1.61; low), wheezing (risk ratio 1.40, 1.27 to 1.55; low), and obesity (odds ratio 1.55, 1.36 to 1.77; low). Of the remaining 34 pooled analyses, 21 were graded as suggestive or weak strength (class III-IV) and 13 were graded as no evidence (class V). Overall, using the GRADE framework, 22 pooled analyses were rated as low quality, with 19 rated as very low quality and four rated as moderate quality.
Conclusions
Greater exposure to ultra-processed food was associated with a higher risk of adverse health outcomes, especially cardiometabolic, common mental disorder, and mortality outcomes. These findings provide a rationale to develop and evaluate the effectiveness of using population based and public health measures to target and reduce dietary exposure to ultra-processed foods for improved human health. They also inform and provide support for urgent mechanistic research.
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Another study links ultra-processed food to higher cancer risk
Wake-up call for governments as studies flag high risk of ultra processed foods