Eating ultraprocessed foods raises the risk of developing or dying from dozens of adverse health conditions, according to a new Australian review of 45 meta-analyses on almost 10 million people.
"We found consistent evidence linking higher intakes of ultra-processed foods with over 70 per cent of the 45 different health outcomes we assessed," senior author Wolfgang Marx, a senior research fellow at the Food & Mood Centre at Deakin University in Geelong, said.
A higher intake was considered about one serving or about 10 per cent more ultraprocessed foods per day, Heinz Freisling, a scientist in the nutrition and metabolism branch of the World Health Organization's International Agency for Research on Cancer, said in an email.
"This proportion can be regarded as 'baseline' and for people consuming more than this baseline, the risk might increase," Freisling, who was not involved in the study, said.
Researchers graded each study as having credible or strong, highly suggestive, suggestive, weak or no evidence.
All the studies in the review were published in the past three years, and none were funded by companies involved in the production of ultraprocessed foods, the authors said.
"Strong evidence shows that a higher intake of ultra-processed foods was associated with approximately 50 per cent higher risk of cardiovascular disease-related death and common mental disorders," lead author Dr Melissa Lane, a postdoctoral research fellow at Deakin, said.
Cardiovascular disease encompasses heart attacks, stroke, clogged arteries and peripheral artery disease.
There was convincing evidence that a high versus low intake of ultraprocessed foods could increase the risk of anxiety by up to 53 per cent, and the risk of an early death from any cause by 20 per cent, according to the study published Wednesday in the journal The BMJ.
"It's not surprising that there are a lot of studies that point to a positive association between ultraprocessed food consumption and the risk of various disease outcomes," cancer epidemiologist Fang Fang Zhang, associate professor and chair of the division of nutrition epidemiology and data science at Tufts University in Boston, said.
She was not involved in the new research.
"Ultraprocessed foods are high in calories, added sugar, sodium, and low in fibre," Zhang said.
"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 who are having depressive symptoms or anxiety may seek out ultraprocessed foods 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 health conditions
Researchers found highly suggestive evidence that eating more ultraprocessed foods raised the risk of obesity by 55 per cent, sleep disorders by 41 per cent, development of type 2 diabetes by 40 per cent and the risk of depression by 20 per cent.
However, evidence was limited for an association between consuming ultraprocessed food and asthma, gastrointestinal health and cardiometabolic risk factors such as 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 researched the role of ultraprocessed foods and cancer.
"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 coauthored, Zhang found men who ate the most ultraprocessed foods of any type had a 29 per cent higher risk of developing colorectal cancer.
One reason for the unexpected finding is that research on ultraprocessed foods is still in its infancy, study coauthor Mathilde Touvier, research director at the French National Institute of Health and Medical Research, a public research organisation, said.
"We definitely need more studies to be able to upgrade the weight of evidence for cancer, for instance," said Touvier, 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 new research.
"They are formulations of often chemically manipulated cheap ingredients such as modified starches, sugars, oils, fats, and protein isolates, with little if any whole food added," Monteiro, a professor of nutrition and public health, said in an attached editorial.
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 such as 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," Monteiro wrote in the editorial.
"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 Australia as well as the United States, the United Kingdom, Canada and many developing nations.
"Two-thirds of the calories children consume in the US are ultraprocessed, while about 60 per cent of adult diets are ultraprocessed," Zhang said.
"I think it's like when we invented cars," she added.
"Yes, they bring us convenience, but if we use a car for everything and we don't exercise we have problems. We need new strategies to bring down the consumption of ultraprocessed food to a healthier level."
How to reduce the use of ultraprocessed foods
There's an easy solution — buy real food and cook it at home.
It's that simple, experts say.
But experts also agree that in today's fast-paced world, giving up the convenience of ready-to-heat and ready-to-eat foods is difficult.
In addition, it's nearly impossible to avoid temptation, as over 70 per cent of the US food supply is made of ultraprocessed food.
Regulation by public health agencies and governments should be considered, Monteiro said, such as front-of-pack warning labels; restriction of advertising, especially to children; and the prohibition of sales of ultraprocessed foods in or near schools and hospitals, all while making minimally processed foods more affordable and accessible.
In the meantime, Marx and Lane offered the following advice:
1) Read and compare product labels and try to choose less processed alternatives. For example, swap flavored yogurt for plain yogurt with added fruit.
2) What you include is just as important as what you exclude. Focus on what you can add to your diet such as fresh, frozen or tinned fruits, vegetables, beans and legumes.
3) Be mindful of beverages. Sugar-sweetened beverages have no nutritional value. Swap them out for water.
4) When eating out, go to local restaurants and cafés instead of fast-food chains. Local eateries are less likely to make ultraprocessed foods.
