Food processing and health

This content has been reviewed by Professor Ciarán Forde, Division of Human Nutrition and Health, Wageningen University and Research, The Netherlands.

What is food processing?

Food processing is any method or technique used to turn foods or ingredients into another form of food or food product. This can involve various processes including washing, chopping, freezing, packaging, cooking, addition of ingredients, and many more. Food processing can take place at home, out-of-home (e.g., in restaurants), and at an industrial scale. Humans have processed foods for centuries for many beneficial reasons, including making food edible, ensuring food safety, enhancing the nutritional content of food, and prolonging shelf-life. Processed foods are now prevalent in diets worldwide. The popularity of processed foods in today’s diets worldwide is often explained by their convenience, taste and, for some products, affordability. In recent years, foods have been frequently categorised and researched, based not only on their nutritional content, but also on the extent, purpose, and nature of food processing.

The concept of ultra-processed foods

The concept of ultra-processed foods (UPFs) often refers to foods and drinks that would be classified as “ultra-processed” according to the “NOVA classification system”. It defines UPFs as “formulations of ingredients, mostly of exclusive industrial use, made by a series of industrial processes, many requiring sophisticated equipment and technology” (1,2). A central concept of the NOVA system is that foods are classified by whether they are produced for profit, convenience, palatability (taste), affordability and availability, rather than by their nutrient content (3). The UPF classification includes foods such as soft drinks, chocolate, fried snacks, processed meats, packaged whole-grain breads and vegetable-based sauces. However, this definition is not universally agreed, and there is no scientific consensus on the usefulness of UPF classification as a tool to identify healthier products (4–9). In addition, in a study that asked food and nutrition experts to assign foods to NOVA groups, overall consistency among the experts was low, even when ingredient information was available (7). As such, questions have been asked as to the useability of an evidently subjective definition (6,9–12).

UPF and health research

UPFs and health is a new area of research, and it can be difficult to draw conclusions from the currently limited evidence base. Studies conducted across a range of countries have often reported that higher consumption of UPFs is associated with less healthy diets overall (13–15). Though, research conducted in the U.S. suggests some foods classified as UPFs within the NOVA classification system may be beneficial to health and can have a role to play in providing important nutrients (e.g., fibre and iron) (16,17).

Observational evidence has linked high intakes of UPFs with a higher risk of developing a range of health concerns, including obesity, high blood pressure, heart disease, type 2 diabetes mellitus and cancer (18–21). Being observational in design, it is difficult to pinpoint whether it is the food processing (or use of food additives) in these studies that is causing the observed effect or other related factor/s, such as overall diet quality (3). Many studies do not consider nutrient intakes or diet quality, making it difficult to separate the effect of processing and food additives from the effect of a food or drink’s nutritional composition (3). When the nutritional quality of the diet is considered, findings are mixed as to whether there is still an association between UPFs and health (22). In addition, the majority of dietary intake data used in these studies haven’t captured the detail needed to accurately classify foods and drinks according to level of processing (6).

A research study analysing the European Prospective Investigation into Cancer and Nutrition (EPIC) data suggests underlying factors which are unmeasured, inaccurately measured, or uncontrolled for in the analysis may have a part to play (e.g., smoking and alcohol intake) (20). Other studies suggest that it may be some specific groups of foods driving the observed associations, rather than all ultra-processed foods (10,23–27). Moreover, higher intakes of the bread, cereals, yogurt, desserts and savoury snacks UPF subgroups have been associated with lower risk of adverse health outcomes (23,25–27). This suggests that, in addition to being impractical, grouping all UPF’s together may not be appropriate or helpful (10,23,24).

A randomised controlled trial has suggested UPFs may facilitate overeating and weight gain (28). It is not yet known to what extent processing or nutrient differences in diets are driving the association between UPFs and adverse health outcomes. The study researchers note that the nutritional quality of the high UPF diet does not appear to fully explain the links found between UPFs and health. Although the calories per gram (energy density) provided by the food was higher in the UPF diet, compared to the minimally processed diet, which may have had an effect (3). Other factors, such as food texture, speed of eating, or the palatability (tastiness) of the test diets may also play a role (29–34). Research is underway to tease apart the relative influence of processing and nutrients, and establish whether processing alone is having a unique effect on health outcomes reported to date (3).

UPFs are a complex topic. Until we know more about what might be causing the links between UPFs and health, some researchers argue that drastically reducing or eliminating all UPFs in the diet (which would include most breads, breakfast cereals, ready meals, vegetable-based pasta sauces, low fat fruit yogurts, foods with added nutrients and/or pro-biotics) is not appropriate as it may remove potentially good, affordable, sources of nutrition from diets (5,6,35). Extensive follow-up research is ongoing, including controlled feeding trials, to better establish what is driving the observed negative health effects attributed to UPF (3).