What are the effects of food processing on health?
Food processing is the process by which food is altered to add or remove chemical properties. The level of processing is graded according to the NOVA system (Monteiro et al., 2019) and is done to increase food palatability, increase shelf life, prevent pathogen growth, preserve the food, increase the convenience of the food, cook it, reduce allergens, replace animal products, remove or replace a macronutrient (fat/sugar eg), increase a food attractiveness or change its texture or to fortify a product with missing nutrients. The level of processing affects its energy-giving capacity, effects on appetite and hormonal secretions, nutrient bioavailability, and ability to protect against or cause disease. There is considerable evidence (Hall et al., 2019) that ultra-processed foods can increase excess calorie intake and weight gain, metabolic disease (Lane et al., 2021), irritable bowel syndrome, (Narula et al., 2021) and impact diabetes and cardiovascular disease (Juul et al., 2021), sleep (Delpino et al., 2023) and cancer risk (Schnabel et al., 2019).
What are the effects of food processing on health?
Food processing is the process by which a food is altered to add or remove chemical properties. The level of processing is graded according to the NOVA system (Monteiro et al., 2019) and is done to increase food palatability, increase the shelf life, prevent pathogen growth, and preserve the food, increase the convenience of the food, cook it, reduce allergens, replace animal products, remove or replace a macronutrient (fat/sugar eg), increase a food attractiveness or change its texture or to fortify a product with missing nutrients. The level of processing effects its energy giving capacity, effects on appetite and hormonal secretions, nutrient bioavailability, and ability to protect against or cause disease. There is considerable evidence (Hall et al., 2019) that ultra-processed foods can increase excess calorie intake and weight gain, metabolic disease (Lane et al., 2021), irritable bowel syndrome, (Narula et al., 2021) and impact diabetes and cardiovascular disease (Juul et al., 2021), sleep (Delpino et al., 2023) and cancer risk (Schnabel et al., 2019).
Studies, including analysis of the National Health and Nutrition Examination Survey by Juul et al, (Juul et al., 2022) of 40,937 19-year-olds in the USA and (Wang et al., 2021) Wang et al, have both shown that more and more young people are consuming processed foods. The strengths of these studies are that they have large cohort sizes, and the weaknesses are that they rely on cross-sectional analysis from 24-hour dietary recall questionnaires which may be subject to recall bias and where correlations may not mean causation due to the level of potential confounders. Juul analysed based on the NOVA framework and found that US adults consumed more ultra ultra-processed foods between 2017–2018 to 2001–2001 with a 53.5kcal percentage to 57.0 calorie percentage increase, (P- < 0.001<0.05 ). It was found that this trend existed within all sociodemographic populations except Hispanics. Juul also found that minimally processed consumption decreased significantly over the same period from 32.7–27.4 calories (P-trend < 0.001) within every sociodemographic group. The same trends were found in the study by Wang, showing that more and more dietary calories are now coming from processed foods.
The NOVA classification system classes foods based upon the NOVA classification system which states that minimally or unprocessed foods are ones obtained directly from plants or animals that are wholefoods, often still within the intact food matrix which do not undergo any alteration following their removal from nature (fruit and vegetables, nuts and seeds, eggs, meat and fish and dairy without additives or spices, fermented vegetables (sauerkraut, kimchi, miso), heated food or frozen from fresh foods. Then there are the processed cooking ingredients (table vinegar, honey, maple syrup, table sugar and salt, flour, butter etc) which are to add flavour, the processed food: (such as smoked salmon, bread, commercial stock, fresh pizza, canned vegetables and fish, beer and wine, cured meats, smoked cheeses, olives). Finally, there is the ultra-processed food (UPFs) which include heavily processed French fries, chips, ready meals, most flavoured yoghurts, most sweets, chocolates, crisps, ice creams, burgers, most vegan protein substitutes, most cereal bars, most oven pizzas, most sugar-sweetened beverages (Monteiro et al., 2018).
It was shown in the randomised controlled trial (a strength of this study as it used a control group, randomisation and meals were isocaloric matched to limit confounding, however, the cohort size was small at only 20 which may not be populationally representative), by Kevin Hall and team, that ultra-processed foods (Hall et al., 2019) increased calorie intake of carbohydrates (increased 80 ± 54 calories a day (P < 0.0001<0.05) and fat (increased 230 ± 53 calories a day; P= 0.0004<0.05), but not protein (P = 0.85). This trend in increased carbohydrate and fat was positively associated with weight gain and increased metabolic diseases such as diabetes and cardiovascular disease. This evidence is supported by the findings by (Rico-Campà et al., 2019) Rico-Campa and Juul (Juul et al., 2021) who showed in two independent metanalyses (Juul from the Framingham Offspring study) which showed a positive association between ultra-processed food intake (with energy-adjusted servings per day) and the risk of CVD, CHD and CVD mortality. The Framingham Offspring study showed that for every portion increase of ultra-processed food, there was a 7% increase in hard CVD with confidence limits 1.03–1.12. The strengths of this study are that it was a large (3003 participants) study over time, and the weaknesses are that it relied on anthropometry recordings and food frequency questionnaires which are subject to recall bias and potential for confounders as there is no randomisation or controls.
Ultra-processed food was also shown in the study to impact inflammatory bowel disease, (Narula et al., 2021), with the Prospective cohort study (n=467) by Narula showing an increased risk of IBD (RR:1.82) with a shown dosal relationship when adjusted for confounders. The weaknesses of this study are that it relied on questionnaires with the potential for bias and confounding.
There is also considerable evidence that food processing affects nutrient bioavailability and that this may impact health. Food processing was shown in a review by (Shahidi & Pan, 2022) Shalhidi of studies including animal (a weakness of the review) studies that breaking down the food matrix alters phytochemical Bioaccessibility and their chemical interactions. Cooking methods such as cooking, cooling and reheating have also been found to alter the health capacity of food as Wang et al (Wang et al., 2015) found that cooking and cooling starch caused starch retrogradation where the starch changed from non-resistant to resistant starch. Additionally, studies have shown that breaking down cell structures such as the cellulose cell wall in foods (for example almonds) alters their post-prandial response (glycaemic index) and nutrient release. The blinded randomised cross-over (no control) study by (Grundy, Grassby, et al., 2015) Grundy (n=15 so small cohort which may not be populational representative and is subject to much potential confounding), found that breaking down the cell wall of almonds impacted the amount of lipid released from the almonds. This impacts food processing as it showed that whole almonds will have a different glycaemic and lipemic health response to those that are milled in products such as nut butter or ground almonds, impacting their effect on metabolic disease. Further studies by (Grundy, Wilde, et al., 2015) Grundy showed that particle size had an increased rate and extent of lipolysis and fat digestion. It was found in a study by Bajka that oatmeal particle size impacts the rate glucose is absorbed, the gastric emptying, gut hormones and subjective hunger and fullness sensations. This study (not randomised or with control and subject to recall bias and potential for selection bias) showed that food processing impacts the appetite and gut hormone response which impacts food consumption, weight and metabolic disease risk. Milling of oats was shown in a metanalysis of randomised controlled trials (a huge strength of the study as it used controls and peer-reviewed many RCTs) by (AbuMweis et al., 2010) AbuMweis showed that alternative dietary and processing approaches to oats, such as wholegrain round oats versus milled oats versus oat beverages like oat milk, affected the beta-glucan lipid-lowering benefits of the oats, with the milled out being shown to have less lipid-lowering effect than round wholegrain oats in RCTs. This is important as this beta glycan LDL-reducing effect has impacts on cardiovascular health and hypertension risk.
Round wholegrains, with the cellulose and aleurone layer of the grain intact, also was found to alter the iron, calcium, copper and other metal mineral and B vitamin nutrients content of the grain, with the majority of these being milled away when the grain is refined in food processing to make white flour and rice. This is especially important, as studies by Aune et al, (Aune et al., 2016; Tang et al., 2015) and Tang et al, show that wholegrains reduce the risk of CVD, cancer and all cause mortality. The meta-analysis of prospective studies (a weakness of the study as no control and subject to potential recall and selection bias) study by Aune shows a dose relationship with wholegrain intake and reduce risk of cardiovascular disease and all cause mortality.
Studies show that other food processing methods, such as cooking with frying or roasting, can cause lipid oxidation and increase free radical response. This is altered also by (Zhang et al., 2021) the level of antioxidant in the foods, which are often lost in food processing where the aleurone layer containing most phytochemicals is lost. Whilst cooking can sometimes increase nutrient bioavailability (such as carotene content in peas) and reduce the trypsin inhibitors and toxins in food, it can also alter the bioavailability of some vitamins such as vitamin C (which is for example reduced when foods are cooked) (Fardet, 2018).
Overall, food processing is important for improving the taste, appearance, texture safety and profitability of foods, however, ultra-processed foods have been shown to have widespread detrimental effects on health.
References
AbuMweis, S. S., Jew, S., & Ames, N. P. (2010). β-glucan from barley and its lipid-lowering capacity: a meta-analysis of randomized, controlled trials. Eur J Clin Nutr, 64(12), 1472–1480. https://doi.org/10.1038/ejcn.2010.178
Aune, D., Keum, N., Giovannucci, E., Fadnes, L. T., Boffetta, P., Greenwood, D. C., Tonstad, S., Vatten, L. J., Riboli, E., & Norat, T. (2016). Whole grain consumption and risk of cardiovascular disease, cancer, and all-cause and cause-specific mortality: a systematic review and dose-response meta-analysis of prospective studies. Bmj, 353, i2716. https://doi.org/10.1136/bmj.i2716
Delpino, F. M., Figueiredo, L. M., Flores, T. R., Silveira, E. A., Silva Dos Santos, F., Werneck, A. O., Louzada, M., Arcêncio, R. A., & Nunes, B. P. (2023). Intake of ultra-processed foods and sleep-related outcomes: A systematic review and meta-analysis. Nutrition, 106, 111908. https://doi.org/10.1016/j.nut.2022.111908
Fardet, A. (2018). Characterization of the Degree of Food Processing in Relation With Its Health Potential and Effects. Adv Food Nutr Res, 85, 79–129. https://doi.org/10.1016/bs.afnr.2018.02.002
Grundy, M. M., Grassby, T., Mandalari, G., Waldron, K. W., Butterworth, P. J., Berry, S. E., & Ellis, P. R. (2015). Effect of mastication on lipid bioaccessibility of almonds in a randomized human study and its implications for digestion kinetics, metabolizable energy, and postprandial lipemia. Am J Clin Nutr, 101(1), 25–33. https://doi.org/10.3945/ajcn.114.088328
Grundy, M. M., Wilde, P. J., Butterworth, P. J., Gray, R., & Ellis, P. R. (2015). Impact of cell wall encapsulation of almonds on in vitro duodenal lipolysis. Food Chem, 185, 405–412. https://doi.org/10.1016/j.foodchem.2015.04.013
Hall, K. D., Ayuketah, A., Brychta, R., Cai, H., Cassimatis, T., Chen, K. Y., Chung, S. T., Costa, E., Courville, A., Darcey, V., Fletcher, L. A., Forde, C. G., Gharib, A. M., Guo, J., Howard, R., Joseph, P. V., McGehee, S., Ouwerkerk, R., Raisinger, K., . . . Zhou, M. (2019). Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake. Cell Metab, 30(1), 67–77.e63. https://doi.org/10.1016/j.cmet.2019.05.008
Juul, F., Parekh, N., Martinez-Steele, E., Monteiro, C. A., & Chang, V. W. (2022). Ultra-processed food consumption among US adults from 2001 to 2018. Am J Clin Nutr, 115(1), 211–221. https://doi.org/10.1093/ajcn/nqab305
Juul, F., Vaidean, G., Lin, Y., Deierlein, A. L., & Parekh, N. (2021). Framingham Offspring Study-Ultra-Processed Foods and Incident Cardiovascular Disease in the J Am Coll Cardiol, 77(12), 1520–1531. https://doi.org/10.1016/j.jacc.2021.01.047
Lane, M. M., Davis, J. A., Beattie, S., Gómez-Donoso, C., Loughman, A., O’Neil, A., Jacka, F., Berk, M., Page, R., Marx, W., & Rocks, T. (2021). Ultraprocessed food and chronic noncommunicable diseases: A systematic review and meta-analysis of 43 observational studies. Obes Rev, 22(3), e13146. https://doi.org/10.1111/obr.13146
Monteiro, C. A., Cannon, G., Lawrence, M., Louzada, M. d. C., & Machado, P. P. (2019). Ultra-processed foods, diet quality, and health using the NOVA classification system. Rome: FAO, 48.
Monteiro, C. A., Cannon, G., Moubarac, J. C., Levy, R. B., Louzada, M. L. C., & Jaime, P. C. (2018). The UN Decade of Nutrition, the NOVA food classification and the trouble with ultra-processing. Public Health Nutr, 21(1), 5–17. https://doi.org/10.1017/s1368980017000234
Narula, N., Wong, E. C. L., Dehghan, M., Mente, A., Rangarajan, S., Lanas, F., Lopez-Jaramillo, P., Rohatgi, P., Lakshmi, P. V. M., Varma, R. P., Orlandini, A., Avezum, A., Wielgosz, A., Poirier, P., Almadi, M. A., Altuntas, Y., Ng, K. K., Chifamba, J., Yeates, K., . . . Yusuf, S. (2021). Association of ultra-processed food intake with risk of inflammatory bowel disease: prospective cohort study. Bmj, 374, n1554. https://doi.org/10.1136/bmj.n1554
Rico-Campà, A., Martínez-González, M. A., Alvarez-Alvarez, I., Mendonça, R. D., de la Fuente-Arrillaga, C., Gómez-Donoso, C., & Bes-Rastrollo, M. (2019). Association between consumption of ultra-processed foods and all cause mortality: SUN prospective cohort study. Bmj, 365, l1949. https://doi.org/10.1136/bmj.l1949
Schnabel, L., Kesse-Guyot, E., Allès, B., Touvier, M., Srour, B., Hercberg, S., Buscail, C., & Julia, C. (2019). Association Between Ultraprocessed Food Consumption and Risk of Mortality Among Middle-aged Adults in France. JAMA Intern Med, 179(4), 490–498. https://doi.org/10.1001/jamainternmed.2018.7289
Shahidi, F., & Pan, Y. (2022). Influence of food matrix and food processing on the chemical interaction and bioaccessibility of dietary phytochemicals: A review. Crit Rev Food Sci Nutr, 62(23), 6421–6445. https://doi.org/10.1080/10408398.2021.1901650
Tang, G., Wang, D., Long, J., Yang, F., & Si, L. (2015). Meta-analysis of the association between whole grain intake and coronary heart disease risk. Am J Cardiol, 115(5), 625–629. https://doi.org/10.1016/j.amjcard.2014.12.015
Wang, L., Martínez Steele, E., Du, M., Pomeranz, J. L., O’Connor, L. E., Herrick, K. A., Luo, H., Zhang, X., Mozaffarian, D., & Zhang, F. F. (2021). Trends in Consumption of Ultraprocessed Foods Among US Youths Aged 2–19 Years, 1999–2018. Jama, 326(6), 519–530. https://doi.org/10.1001/jama.2021.10238
Wang, S., Li, C., Copeland, L., Niu, Q., & Wang, S. (2015). Starch retrogradation: A comprehensive review. Comprehensive Reviews in Food Science and Food Safety, 14(5), 568–585.
Zhang, Y., Dong, L., Zhang, J., Shi, J., Wang, Y., & Wang, S. (2021). Adverse Effects of Thermal Food Processing on the Structural, Nutritional, and Biological Properties of Proteins. Annu Rev Food Sci Technol, 12, 259–286. https://doi.org/10.1146/annurev-food-062320-012215
