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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 affordability, convenience and tastiness. 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. 

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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, 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 (4–8). In addition, in a study which 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).

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 are associated with less healthy diets overall (9–11). 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) (12,13).

Observational evidence has linked high intakes of UPFs with higher risk of developing a range of health concerns, including obesity, high blood pressure, heart disease, type 2 diabetes mellitus and cancer (14–17). Being observational in design, it is difficult to pinpoint whether it is the food processing (or use of food additives) in these studies which are 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 (18). 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) (16). Another study, which used data from EPIC, suggests that it may be some specific groups of foods driving the observed associations, rather than all ultra-processed foods (19). Indeed, this study highlighted that intakes of certain groups of UPF (i.e., UPF breads and cereals) were borderline associated with a lower risk of disease. This suggests that, in addition to being impractical, grouping all UPF’s together may not be appropriate or helpful (19). 

A randomised controlled trial has suggested UPFs may facilitate overeating and weight gain (20).  It is not yet known to what extent processing or nutrient differences in diets is driving the association between UPFs and adverse health outcomes. The study researchers note that the nutritional quality of high UPF diets does not appear to fully explain the links found between UPFs and health. Although, the calories per gram (energy density) provided by food vs. drinks 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 (21,22). 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).

Therefore, UPFs is 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 (5,6,23). Extensive follow up research is ongoing, including controlled feeding trials to better establish whether it is the nutrient composition or the processing, that is driving the observed negative health effects attributed to UPF (3).    

References

  1. Monteiro CA, Levy RB, Claro RM, Castro IRR de, Cannon G. A new classification of foods based on the extent and purpose of their processing. Cad Saude Publica. 2010 Nov;26(11):2039–49. 
  2. Monteiro CA, Cannon G, Levy RB, Moubarac JC, Louzada ML, Rauber F, et al. Ultra-processed foods: what they are and how to identify them. Public Health Nutr. 2019 Apr;22(5):936–41. 
  3. Forde CG. Beyond ultra-processed: considering the future role of food processing in human health. Proc Nutr Soc. 2023 Sep;82(3):406–18. 
  4. Sadler CR, Grassby T, Hart K, Raats M, Sokolović M, Timotijevic L. Processed food classification: Conceptualisation and challenges. Trends Food Sci Technol. 2021 Jun 1;112:149–62. 
  5. Gibney MJ. Ultra-Processed Foods: Definitions and Policy Issues. Curr Dev Nutr. 2019 Feb;3(2):nzy077. 
  6. Gibney MJ, Forde CG. Nutrition research challenges for processed food and health. Nat Food. 2022 Feb 7;1–6. 
  7. Braesco V, Souchon I, Sauvant P, Haurogné T, Maillot M, Féart C, et al. Ultra-processed foods: how functional is the NOVA system? Eur J Clin Nutr. 2022 Sep;76(9):1245–53. 
  8. Sadler CR, Grassby T, Hart K, Raats MM, Sokolović M, Timotijevic L. “Even We Are Confused”: A Thematic Analysis of Professionals’ Perceptions of Processed Foods and Challenges for Communication. Front Nutr. 2022 Feb 23;9:826162. 
  9. Steele EM, Popkin BM, Swinburn B, Monteiro CA. The share of ultra-processed foods and the overall nutritional quality of diets in the US: evidence from a nationally representative cross-sectional study. Popul Health Metr. 2017 Feb 14;15(1):6. 
  10. Machado PP, Steele EM, Levy RB, Sui Z, Rangan A, Woods J, et al. Ultra-processed foods and recommended intake levels of nutrients linked to non-communicable diseases in Australia: evidence from a nationally representative cross-sectional study. BMJ Open. 2019 Aug 28;9(8):e029544. 
  11. Moubarac JC, Batal M, Louzada ML, Martinez Steele E, Monteiro CA. Consumption of ultra-processed foods predicts diet quality in Canada. Appetite. 2017 Jan 1;108:512–20. 
  12. Hess JM, Comeau ME, Casperson S, Slavin JL, Johnson GH, Messina M, et al. Dietary Guidelines Meet NOVA: Developing a Menu for A Healthy Dietary Pattern Using Ultra-Processed Foods. J Nutr. 2023 Aug 1;153(8):2472–81. 
  13. O’Connor LE, Martinez-Steele E, Wang L, Zhang FF, Herrick KA. Food Processing, According to the Nova Classification System, and Dietary Intake of US Infants and Toddlers. J Nutr. 2023 Aug 1;153(8):2413–20. 
  14. Lane MM, Davis JA, Beattie S, Gómez-Donoso C, Loughman A, O’Neil A, et al. Ultraprocessed food and chronic noncommunicable diseases: A systematic review and meta-analysis of 43 observational studies. Obes Rev Off J Int Assoc Study Obes. 2021 Mar;22(3):e13146. 
  15. Pagliai G, Dinu M, Madarena MP, Bonaccio M, Iacoviello L, Sofi F. Consumption of ultra-processed foods and health status: a systematic review and meta-analysis. Br J Nutr. 2021 Feb 14;125(3):308–18. 
  16. Morales-Berstein F, Biessy C, Viallon V, Goncalves-Soares A, Casagrande C, Hémon B, et al. Ultra-processed foods, adiposity and risk of head and neck cancer and oesophageal adenocarcinoma in the European Prospective Investigation into Cancer and Nutrition study: a mediation analysis. Eur J Nutr. 2023 Nov 22; 
  17. Lane MM, Gamage E, Du S, Ashtree DN, McGuinness AJ, Gauci S, et al. Ultra-processed food exposure and adverse health outcomes: umbrella review of epidemiological meta-analyses. BMJ. 2024 Feb 28;384:e077310. 
  18. Gibney MJ. Ultra-processed foods in public health nutrition: the unanswered questions. Public Health Nutr. 2023;26(7):1380–3. 
  19. Cordova R, Viallon V, Fontvieille E, Peruchet-Noray L, Jansana A, Wagner KH, et al. Consumption of ultra-processed foods and risk of multimorbidity of cancer and cardiometabolic diseases: a multinational cohort study. Lancet Reg Health – Eur. 2023 Dec 1;35. 
  20. Hall KD, Ayuketah A, Brychta R, Cai H, Cassimatis T, Chen KY, et al. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metab. 2019 Jul 2;30(1):67-77.e3. 
  21. Fazzino TL, Courville AB, Guo J, Hall KD. Ad libitum meal energy intake is positively influenced by energy density, eating rate and hyper-palatable food across four dietary patterns. Nat Food. 2023 Feb;4(2):144–7. 
  22. Srour B, Fezeu LK, Kesse-Guyot E, Allès B, Méjean C, Andrianasolo RM, et al. Ultra-processed food intake and risk of cardiovascular disease: prospective cohort study (NutriNet-Santé). BMJ. 2019 May 29;365:l1451. 
  23. Tobias D, Hall KD. Eliminate or reformulate ultra-processed foods? Biological mechanisms matter. Cell Metab. 2021;(33).

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