Scientists stress ‘uncertainties’ in links between ultra-processed food and health problems

By Flora Southey

- Last updated on GMT

Studies suggest links between ultra-processed food consumption and increased risk of health problems, but scientists have observed 'uncertainties' surrounding the quality of evidence available. GettyImages/monticello
Studies suggest links between ultra-processed food consumption and increased risk of health problems, but scientists have observed 'uncertainties' surrounding the quality of evidence available. GettyImages/monticello

Related tags NOVA classification Ultra-processed food Nutrition Obesity

In the UK, government scientists have pointed to ‘uncertainties’ surrounding the quality of evidence linking consumption of ultra-processed foods with adverse health outcomes.

This week, the Scientific Advisory Committee on Nutrition (SACN) published its independent report on ultra-processed foods.

In serving to advise the UK Government on nutrition and related health matters, the SACN sought to review the available evidence on associations between processed food consumption and health outcomes.

Most systematic reviews analysed reported that increased consumption of processed food – and specifically ultra-processed food (UPF) – was associated with an increased risk of adverse health outcomes.

But at the same time, the independent scientific experts pointed to ‘uncertainties’ surrounding the quality of evidence available.

What are the uncertainties?

The review comes as UPF finds itself the focus of more nutrition-based studies. In recent years UPF consumption has been linked to a greater risk of developing cancer​ and a higher mortality rate​.

In the SACN’s analysis, scientists assessed systematic reviews linking UPF with a range of adverse health outcomes, ranging from overweight and obesity to chronic non-communicable diseases, depression, maternal and child health outcomes, and mortality risk.  

Although such links were mostly identified, SACN members stressed ‘important’ limitations, including that the available evidence is ‘almost exclusively’ observational in nature.

They also noted inconsistent adjustment for covariables as well as inconsistency between systematic reviews regarding which are they key covariables. This means that although adverse health associations were consistently reported, it is ‘unclear’ whether these associations are due to – or independent of – the ‘unhealthy’ nutrient contents often typical of many UPFs, such as salt, saturated fat, or free sugars.

Other ‘uncertainties’ surround the systematic reviews, according to the government advisory group, include limited available information on the impact on population subgroups as well as socially and ethnically diverse groups.

“Studies are almost exclusively observational and confounding factors or key variables such as energy intake, body mass index, smoking and socioeconomic status may not be adequately accounted for,” ​noted the scientists, who contend more research in this field is required.

NOVA ‘potentially suitable’, but not perfect

Other limitations outlined by the SACN relate to the classification of UPF. In the absence of a universally agreed definition of processed food, several classification systems have been developed around the world.

The most common definition of UPF comes from the so-called NOVA food classification system. Developed in 2009, the NOVA system splits levels of food processing into four classifications, from raw and minimally processed foods; to processed culinary ingredients; processed foods; and ultra-processed foods.

Of all the classification systems examined by the SACN, NOVA was found to be the only one that met its initial screening criteria as being potentially suitable for use on home-soil. However, assessment of the NOVA approach did identify some concerns around its practical application in the UK.

Most notably, the classification of some foods is discordant with nutritional and other food-based classifications. The scientists therefore recommend further assessment and development of an (ultra-) processed foods classification system that can reliably be applied to estimate consumption of processed foods in the UK.

Why process food?

The SACN’s review acknowledges that food processing plays a number of key roles in food production and can offer some major benefits in terms of food safety and acceptability.

Food processing can:

  • Ensure foods that would otherwise be inedible without processing are edible;
  • Ensure foods that would be unsafe to eat are safe;
  • Increase the shelf life, preservation and retention of nutrients for some foods;
  • Modify the nutrient composition or bioavailability;
  • Increase palatability; and
  • Increase convenience

Putting ‘often-outrageous’ claims into context

The SACN’s review has been welcomed by nutrition scientists, some of whom are pleased to see new focus on ‘uncertainties’ surrounding the quality of evidence available linking UPF consumption to health issues.

“There have been a lot of discussions about the health impact of ultra-processed foods, and these discussions have unfortunately been dominated by hyperbole and unnecessary generalisations,” ​according to Gunter Kuhnle, professor of nutrition and food science at the University of Reading.

“The statement makes it clear that processed and ultra-processed foods are a much more complex issue than previous reports suggest – and clearly not as dangerous as often implied.”

The professor continued: “The SACN statement puts many of the often-outrageous claims about ultra-processed foods into context.”

The SACN report concluded by suggesting that consumption of (ultra-) processed foods may be an indicator of other unhealthy dietary patterns and lifestyle behaviours. UPFs are often energy dense, high in fat, salt or sugar (HFSS), high in processed meat, and/or low in fruit and vegetables and fibre.

According to Tom Sanders, professor emeritus of nutrition and dietetics at King’s College London, such a view is ‘simplistic’, since it does not differentiate between foods that are nutrient dense from those that provide energy and little else.

He also stresses that modern food processing has helped reduce micronutrient deficiencies through fortification. Folic acid fortification of cereals, for example, has prevented neural tube defects.

Food processing therefore plays a ‘critical role’ in feeding the population, he noted. “SACN concludes that further research is needed to evaluate whether the regular consumption of specific highly processed foods is harmful.”

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