February 28, 2024

expert reaction to umbrella review looking at ultra-processed food exposure and adverse health outcomes

A study published in the BMJ looks at UPF exposure and adverse health outcomes. 

Prof Martin Warren, Quadram Institute Chief Scientific Officer and Group Leader in Synthetic biology and biosynthetic pathways, said:

“The paper by Lane et al reinforces something we have known for some time – that, broadly speaking, certain ultra-processed foods are bad for human health.  In this study the authors used a statistical technique to combine the results of multiple independent studies on the association between ultra-processed food and poor health, to provide a more comprehensive understanding of the overall effect.

“The authors have critically appraised the evidence and highlighted that increased consumption of ultra-processed food is directly linked to elevated risks of negative health outcomes, particularly those related to cardiovascular and metabolic health, as well as common mental well-being problems and mortality.

“There is a primary need to better understand the mechanistic processes at play that result in the damage to health and there remain problems associated with the definition of ultra-processed food.  Food is processed to help preserve it, make it safer, make it more convenient and to improve its palatability – and hence food processing is generally an important way of ensuring a growing population can be fed.  Not all ultra-processed foods are bad, as the authors highlight.

“What is clear, however, is that high energy, low nutrient-density foods in excess are causing problems and ways to mitigate this issue need to be found.  This paper is another salutary reminder of the scale of the public health challenge facing the UK which has amongst the shortest healthy-life expectancy in western Europe.”

Prof Pete Wilde, Emeritus Fellow, Quadram Institute Bioscience, said:

“This is a review of previous studies.  This review essentially supports the epidemiological evidence that UPFs when consumed in high quantities have a negative impact on health.  However the paper also supports the need for further research to determine the different mechanisms by which these foods impact health.  UPFs cover a very wide range of food types and compositions, so the impact on health will be varied, and so we need to identify the mechanisms by which different foods (UPFs or not) influence health, in either a negative or positive way.  It is also important to consider that most foods contain components that can have health benefits as well as components that can be detrimental to health.  Furthermore, the structure of the foods we eat can also have additional impacts above and beyond the nutrient composition.  Together, this calls for further, mechanistic (not epidemiological) studies to identify the impact of processing on health.”

Prof Amelia Lake RD RNutr (Public Health), Professor of Public Health Nutrition, Teesside University, said:

“This is an important review giving us high level recent data that calls for clear policy discussion and ultimately action to make it clear to the population what foods are ultra processed and harmful to health.  This is a live and lively debate but we have strong knowledge around the harmful effects of diets high in fat, high in sugar, high in salt on our health.

“This is good quality research bringing together recent evidence (within 3 years), there are always issues around how dietary data is collected but the authors have reviewed the evidence and graded its quality.

“This is important and is going to help shape future research and policy direction around ultra processed foods and our population health.”

Dr Duane Mellor, Registered Dietitian and Senior Lecturer, Aston Medical School, Aston University, said:

“This is a review of reviews, reporting on the potential health impacts associated with the consumption of ultra-processed foods.  This highlights the significant volume of research published on ultra-processed foods, according to PubMed in the last 10 years the numbers of paper has tripled from around 700 per year in 2013 to 2400 in 2023.

“It is important to note, just because there is a lot of research does not necessarily mean that there is a lot of quality in the research, meaning reviews are only as good as the research they are based on.  It is possible that the combination of the relatively easy criteria used to define ultra-processed foods with NOVA classification and large number of observational studies reporting food intake and health outcomes means that it has been relatively easy for researchers to publish research in this area.  This highlights the problem of umbrella reviews like this, as it can be insensitive to the limitations of the methods in the original research.  In this case it cannot consider the limitations resulting from using data based on food frequency questionnaire carried out 10-20 years ago which might not be accurate enough to measure intake of ultra-processed foods.  Additionally this study did not or was not able to consider the individual effects of categories or types of ultra processed foods within what the NOVA category considers to be ultra-processed.  From a number of the studies included there is clear evidence of associations between sweetened drinks and negative health effects and between processed red meat and negative health effects, but studies tend to show no risk or even reduced risk associated with breads and cereals – the problem is NOVA considers all these foods to be ultra-processed.

“This study also tends to lean heavily on a non-universally accepted credibility score, where the more accepted AMSTAR2 approach to assess quality of the systematic reviews used in the study was only reported in the supplementary materials and briefly mentioned toward the end of the results section.  The quality assessment highlighted that many of the studies included were not pre-registered on databases, which is standard practice and required by many academic journals, and not all the reviews were clear how they selected their papers.  This combined with the GRADE score, which is highlighted in the commentary will tend to down rate observational data compared with clinical trials – as the reviews included in this review were all observational, it meant that the evidence was rated as mostly having a low or very low level of certainty, meaning the findings of this analysis might not represent what the real effect actually is.  This could mean that the results reported in this paper could be a significant over or underestimate of what the true associated linked between ultra-processed foods and health might be.  So, the claims in the paper that the results are credible need to be balanced with the low or very low certainty and the limitations in quality of the studies included, and may represent an over-estimate of any risk reported.

“Overall, this only consolidates findings from previous papers that suggest an association between ultra-processed food and disease.  As such it still does not answer what is in ultra-processed foods that could be associated with the increased health risks and if any associated increase in risk is seen with all foods classified by NOVA as ultra-processed.  Given that some ultra-processed foods such as sweetened drinks and processed red meat have been linked with increased risk for decades, and bread especially wholegrain bread (which can still be classed as ultra-processed) has been associated with a reduced risk of disease, suggests that NOVA classification is too broad.  It is also still unclear if NOVA is a better way of classifying foods than foods high in fat, salt and sugar and low in fibre, vitamins and minerals.

“It also does not distract from the messages on healthy eating – encouraging people to eat plenty of vegetables, fruit, legumes, nuts, seeds and wholegrain with modest amounts of dairy and unprocessed meats, as studies on ultra processed foods do not tell us what we should be eating, only suggesting that at least some of the foods included in a very broad category which includes foods already accepted to be associated with ill health are associated with poor health.  It also does not address the limitations of how dietary intake was measured in original studies.”

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“This review attempts to summarise the association between estimates of ultraprocessed food (UPF) consumption and health outcomes from published studies.  The credibility of the evidence was low for most outcomes (meaning they cannot be trusted).  Moderate grade evidence was for a 2% increase in all cause mortality, a lack of association with prostate cancer and a 3% increase of being overweight or obese as well as a 12% increased risk of type 2 diabetes.  The associated increase in risk of diabetes is tiny compared to the known effects of a lack of physical activity and even 1 unit increase in body mass index.  A limitation of this study is that it is not a systematic review and so is subject to publication bias.  A further limitation is that less healthy diets are usually associated with unhealthy lifestyle (smoking, lack of exercise etc) as well low social status and it is difficult to control for this in statistical adjustments.”

Prof Gunter Kuhnle, Professor of Nutrition and Food Science, University of Reading, said:

“The latest meta-analysis on ultra-processed foods in the BMJ is providing a useful summary on mainly epidemiological data investigating the links between ultra-processed food intake and health.  While the results suggest that a higher intake of ultra-processed foods is associated with adverse health effects, the authors admit that the data does not allow us to establish causality and admit that there might be a number of reasons beyond ultra-processed foods that can explain the results.

“The results of the meta-analysis are interesting and confirm the opinion of many mainstream scientists: the quality of the evidence for a link between ultra-processed food intake and adverse health outcomes is weak (GRADE criteria low and very low).  Although the press release mentions associations with many disease outcomes – moderate (not strong, as the editorial implies) evidence for a very small increase in all cause mortality and a positive association with type 2 diabetes and obesity/overweight – this is not surprising considering that soft-drinks are ultra-processed food.

“The main limitation of the study is that it has to rely on previously published epidemiological data.  There are two main limitations of epidemiological studies in this context that raise questions about the validity of the results:

“First, it is very difficult to estimate the intake of ultra-processed food as most epidemiological studies do not collect data on processing.  In many cases, food intake is assessed with so-called food-frequency questionnaires which include only a small number of foods – many of which will include processed and ultra-processed foods, and it is up to the researchers to decide how to interpret results.  Without reliable data on ultra-processed food intake, it is impossible to obtain reliable information about links between food intake and health.

“Second, ultra-processed food is very likely an indicator of an overall higher risk of ill-health.  For example, in many countries, people with lower income or lower socio-economic status consume more ultra-processed foods.  Many studies also show that people who consume a lot of ultra-processed foods also have an unhealthy lifestyle and therefore a higher risk of disease.  Although many studies attempt to adjust for this, it is virtually impossible to do so completely.

“In my opinion the results of the study do not justify any change in dietary recommendations or more stringent measures, as the press release, paper and editorial suggests.  They are based on very weak data and – as the authors admit – fail to establish causality.  Some comments found especially in the editorial do not reflect the scientific consensus or the evidence currently available, for example “They also contain additives including colours, emulsifiers, and sweeteners, linked by experimental and epidemiological evidence to imbalances in gut microbiota and systemic inflammation”.  This is based on very weak data, none of which have been accepted by regulators in additives currently available.  Additives are tightly regulated within the UK and the EU, and signals implying any risk are acted upon quickly.  Data suggesting an adverse effect for example of emulsifiers are based largely on animal studies which are not representative of human consumption.

“Public Health messaging needs to proportionate and evidence based.  An excessive focus on weak evidence is unlikely to have any benefit on health but is likely to erode public trust.”

‘Ultra-processed food exposure and adverse health outcomes: umbrella review of epidemiological meta-analyses’ by Melissa M Lane et al. was published in the BMJ at 23:30 UK time on Wednesday 28 February 2024.

DOI: 10.1136/bmj‑2023‑077310

Declared interests

Prof Martin Warren: “No interests to declare.”

Prof Pete Wilde: “I have received no personal funding from the food industry in the past.  I do not have any current funding from industry. The vast majority of my funding has been government (UKRI) or EU.  In the past I have received partial support for my research from a number of food companies in the past, including Unilever, Mondelez, Nestle and Quorn.”

Prof Amelia Lake: “No CoIs.”

Dr Duane Mellor: “I have been asked to speak about the role of food processing in a modern urban environment and how a healthy diet can be encouraged in modern societies for food companies, professional bodies and all party parliamentary group.”

Prof Tom Sanders: “Member of the Science Committee British Nutrition Foundation.  Honorary Nutritional Director HEART UK.

Before my retirement from King’s College London in 2014, I acted as a consultant to many companies and organisations involved in the manufacture of what are now designated ultraprocessed foods.

I used to be a consultant to the Breakfast Cereals Advisory Board of the Food and Drink Federation.

I used to be a consultant for aspartame more than a decade ago.

When I was doing research at King’ College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks.  In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.”

Prof Gunter Kuhnle: “Employment: University of Reading (since 2010) and member of the USS pension scheme which has a portfolio that includes manufacturers of ultra-processed foods; Director of the University of Reading Chemical Analysis Facility with frequent interaction with instrument manufacturers.

Research funding: current funding from BBSRC TUKFS (Co-I, since 2020); past research funding from Mars, Inc (2014-2018); EU Horizon Programme (2012-2016).

Committee membership: Committee on Toxicity (COT) and various working groups, past member of the EFSA ANS panel and the American Academy of Nutrition and Dietetics working group on flavanols; Scientific advisory committee of the British Nutrition Foundation; Organising committee of the International Conference on Polyphenols and Health.

Scientific organisations: British Mass Spectrometry Society, Nutrition Society, Deutsche Gesellschaft für Epidemiologie and Deutsche Gesellschaft für Ernährung; Trinity Hall Alumni Organisation.

Registered Nutritionist.

Trustee of a Parent Teacher Association.

Family Vineyard.”