A Systematic Review of Worldwide Consumption of Ultra-Processed Foods: Findings and Criticisms

1Food processing includes all the processes needed to transform raw or harvested foodstuffs into new products, ensuring their safety, palatability, and shelf-life. However, in recent decades, food processing has drastically changed to address consumer preferences. The demand for food items with longer shelf-life and improved palatability has led to other natural or artificial ingredients being added to processed foods, which may, to some extent, impact the nutritional quality of these foods, which are often characterized by high sugar, fat, and salt contents. For this reason, interest is growing in elucidating whether the high consumption of these foods negatively impacts diet quality and, in turn, human health.

2One of the main limits to the evaluation of the role and impact of food processing on health status is the lack of a proper definition and classification of “processed food”. In 2009, the European Prospective Investigation into Cancer and Nutrition (EPIC) proposed a classification of foods into three main categories: highly processed, moderately processed, and non-processed foods. A Brazilian group of researchers coordinated by Monteiro instead proposed the NOVA classification, which classifies foods into four main categories based on their degree of processing, without providing any indication of their nutritional content: (i) unprocessed and minimally processed foods such as fruit and vegetables, milk, eggs, and meats; (ii) processed culinary ingredients, including oils, butter, lard, sugar, and salt; (iii) processed foods such as canned fish or legumes, typically produced by adding salt, oil, sugar, or other substances from group 2 to group 1 foods, and using preservation methods such as canning and bottling; and (iv) ultra-processed foods (UPF). The latter comprises formulations of ingredients, mostly for exclusive industrial use, produced through a series of industrial processes that, for instance, include the fractioning of whole foods into substances, the assembly of unmodified and modified food substances, and the frequent use of cosmetic additives, often added to improve the sensory characteristics of the final product. UPF include, amongst others, carbonated soft drinks; sweet, fatty, or salty packaged snacks; candies; ice creams; pastries; margarines; and many others.

3The Siga classification further attempts to categorize foods based on processing, which was developed by combining the four holistic NOVA groups with four additional new reductionist subgroups that consider the impact of processing on the food/ingredient matrix; the contents of added salt, sugar, and fat; the nature and number of markers of ultra-processing; and the levels of at-risk additives.

4Despite the different types of food classification systems based on the degree of processing, the NOVA classification is the most widely used worldwide by researchers. Since it was proposed, the NOVA classification has been used in many epidemiological studies to investigate the association between the levels of UPF consumption and diet quality and/or the potential effect of UPF consumption on human health. For instance, a narrative review summarized the main findings from observational studies reporting a higher risk of all-cause mortality with high consumption of UPF. In another narrative review, high UPF consumption was associated with an increased risk of all-cause mortality including cardiovascular diseases, coronary heart diseases, cerebrovascular diseases, cancer risk, and numerous other metabolic diseases. More recently, a systematic review and meta-analysis of observational studies highlighted that increased UPF consumption is associated with a worse cardiometabolic risk profile and a higher risk of cardiovascular diseases and all-cause mortality. Furthermore, the results of a randomized controlled trial showed that a two-week intervention with a diet rich in UPF consumed ad libitum resulted in significantly increased weight gain amongst American adults compared to a diet of unprocessed foods.

5The criteria used in these types of classification are often ambiguous, only based on a chaotic conception of processing that is not only related to technical processes. Notably, the dietary habits of different populations may vary widely based on tradition, culture, and individual characteristics; in turn, the consumption of UPF in terms of type and amount may differ across target populations and countries.

6Based on these premises, understanding the implications of increasing UPF consumption for global human health is of upmost importance, together with the identification of the cause-effect relationship. In order to pursue this important goal, it is first of all crucial to estimate/quantify the amount of UPF consumed adequately. The aim of the present review was to investigate the levels of UPF consumption systematically—as defined by the NOVA system—across countries around the world. The summarized information will be useful to provide a clear overview of the actual consumption of UPF in different countries, of their contribution to total energy intake also in diverse target groups (i.e., children, adolescents, adults), but also to bring out possible criticisms in the estimation of UPF intake and to underline eventual gaps that need to be considered in future studies.

7This study was conducted according to the Preferred Reporting Items for Systematic Reviews Meta-Analysis (PRISMA) guidelines. To identify pertinent articles, we searched the PubMed and SCOPUS databases up to March 2021 using the combination of the following keywords: (“ultraprocessed food*” OR “ultra-processed food*” OR “NOVA system” OR “NOVA classification” OR “minimally processed food”) AND (“intake” OR “consumption”). Reference lists of included manuscripts and relevant reviews were examined for any possible unidentified study.

8Studies were included if they: (i) provided information on UPF consumption expressed as the percentage of energy for each NOVA category with respect to total dietary intake; (ii) provided information for the general population or for at least one target group; (iii) were published in the English language. Conversely, studies were excluded if they: (i) were published before 2009; (ii) did not use the NOVA classification; (iii) were systematic reviews or meta-analyses; (iv) expressed UPF intake as tertiles/quartiles without providing information about the net consumption.

9Data from included papers were extracted by two reviewers (M.M. and F.P.). Any discrepancy between the reviewers was resolved through consultation with a third independent author (C.D.B) to achieve consensus. The following information is reported: (i) authors and year of publication; (ii) country; (iii) characteristics of the population under study; (iv) method of dietary assessment; (v) results expressed as a percentage of energy from UPF compared to total energy intake. Studies are summarized in different tables showing the percentage of energy intake (TEI) from UPF compared to total energy intake, considering the main factors such as age, sex, and BMI. Data are reported as the mean or median value followed by the standard deviation (SD), standard error of the mean (SEM), confidence interval (CI), or interquartile range (IQR). When available, the statistical significance is reported.

10A total of 1051 studies, conducted between 2009 and 2021, were identified using the PubMed and SCOPUS databases. After eliminating 414 duplicates, 434 articles were excluded based on the titles and abstracts, and 97 studies were removed based on the full-text assessment. A total of 106 articles met the inclusion criteria so were included in the final analysis. Among these, five studies led to two different articles each, which were therefore considered as unique studies. Thus, at the end of the process, a total of 99 unique studies were included (Figure 1).

11Among the 99 studies, a total of 1,378,454 subjects were considered, with the number of subjects ranging from 40 to 110,260. On average, the age of participants was 38.9 years, although half of the studies did not report this information. Fifteen studies focused only on children, seven on adolescents, five on pregnant women, and three on older subjects, whereas others focused on an adult population or on ≥2 target groups. Overall, 58.8% of participants were women.

12The number of studies performed in different countries is reported in Figure 2. As shown, Brazil had the highest number of studies (n = 38), followed by the United States (n = 15), France (n = 8), the United Kingdom (n = 6), Canada (n = 6), and Spain (n = 4). Fewer studies were performed in Malaysia, (n = 3), and in other countries such as Mexico, Italy, Australia, Korea, and Portugal (n = 2); only one study each was conducted in Chile, Japan, Indonesia, Lebanon, Israel, the Netherlands, Colombia, Belgium, and New Zealand.

13Regarding the method of dietary assessment, the 24 h recall was the most-used tool (n = 62), followed by food-frequency questionnaires (FFQs) (n = 28) and food diaries (n = 10).

14The levels of consumption of UPF shown in the retrieved studies are reported in Table 1, while results stratified for specific target groups are provided in Table 2, Table 3 and Table 4.

15The data revealed a high variability in terms of the percentage (%) of energy provided by the consumption of food belonging to group 4 based on the NOVA classification. Similar findings were observed both intra- and inter-country. The highest levels of consumption were observed in the United States and the United Kingdom with the percent of energy intake generally higher than 50% with respect to TEI. Conversely, the lowest levels were observed in Italy, in which the two studies identified reported about 10% energy obtained from UPF.

16Regarding the variability within the same country, Brazil showed levels of UPF consumption ranging from 7.7% in 64 subjects aged 25–57 years to 51.2% of total energy intake in over 4200 subjects. A lower variability was identified in studies performed in the United States, with levels of intake ranging from 50% to 70%, with the only exception being a study observing an energy intake of 35.5% in almost 92,000 subjects aged 55–74 years.

17Several studies stratified data based on different characteristics, such as age, sex, and BMI. The level of UPF consumption stratified for these parameters is reported in Table 2, Table 3 and Table 4. Slight differences between the sexes were observed in UPF intake, with men having often an overall higher intake compared to women. However, in most of the studies, the levels of UPF intake appeared comparable (Table 2). Regarding age, studies generally reported large variations amongst the age groups. However, UPF intake generally decreased with increasing age, with the highest levels of UPF intake observed in children and adolescents, and the lowest in older subjects (Table 3). Only five studies also stratified results based on body mass index (BMI) of the participants, generally finding a slight, but higher, UPF intake in subjects with the highest BMI (e.g., greater than 30 kg/m2) (Table 4).

18Two studies evaluated the intake of UPF during pregnancy, reporting conflicting results. Silva et al. reported no difference between second and third trimester. Conversely, Gomes et al. reported a significant difference in the second and third trimesters between the intervention and control group. This latter consumed more UPF compared to the intervention group that received training for the application of healthy food practices during prenatal care appointments (see Supplementary Table S1). Finally, Gehring and colleagues compared UPF intake in subjects adhering to different dietary patterns, observing a higher UPF intake in vegans and vegetarians than pesco-vegetarians and meat eaters (Supplementary Table S1).

19Since Monteiro et al. proposed the NOVA classification to categorize foods based on the degree of processing, several studies have been conducted to estimate the level of consumption of UPF and its association with several health markers as well as with disease risk and mortality, adjusting the models for energy intake and other potential confounding factors. It was hypothesized that a high level of UPF consumption may represent a health issue, being associated with weight gain and worsening of cardiovascular risk factors such as high waist circumference and low HDL cholesterol.

20In the present study, we collected 100 unique studies published in 106 manuscripts estimating the UPF levels in different populations from 21 countries around the world. Overall, we found a large variability in the percent of TEI obtained from UPF in the different countries, with the United States and United Kingdom being the countries with the highest percent of TEI from UPF, and Mediterranean countries such as Italy showing the lowest level (~10% of TEI). These results are in line with previous evidence suggesting that adherence to the Mediterranean diet is inversely associated with UPF consumption. This is further confirmed by findings showing that the highest tertiles or quartiles of UPF intake are associated with the lowest adherence to the Mediterranean diet. The low levels of UPF consumption registered in Italy and other Mediterranean countries are those associated with the lowest risks for non-communicable diseases. For instance, da Silva et al. recently observed an association between UPF consumption and the increased presence of high waist circumference, overweight, and peripheral arterial disease when comparing the third and first tertiles of the UPF contribution to energy intake in a Brazilian cohort. Intriguingly, the first tertile corresponded to <10.6% of TEI from UPF, which is similar to the levels registered in the study conducted in the Italian population. These levels are far lower than those detected in the first quartiles in the study by Rauber et al., who observed that participants in the highest quartile (>70.3% and >71.7% of TEI from UPF in women and men, respectively) had a significantly higher risk of developing obesity, and of experiencing a ≥5% increase in BMI waist circumference than those belonging to the lowest quartile (<24.1% and <26.3% of TEI from UPF in women and men, respectively). The type of foods contributing to UPF intake largely varied among countries, but, in accordance with previous findings, the most consumed UPF included: baked goods, dairy products, processed fruit and vegetables, and, among drinks, carbonated drinks.

21In addition to country, the level of UPF intake was found to be inversely associated with the increase in age. In this regard, children generally showed the highest intake of UPF, which led the European Childhood Obesity Group to “a call to action” aimed to inform people about the potential harmful effects of UPF. For example, it was found that in the United Kingdom, 65% of calories eaten by primary and secondary school children derived from white bread, biscuits, carbonated drinks, crisps, and chips. These findings are in line with the observations reported by others. Similarly, the pediatric populations of the United States and Canada reported an intake of UPF above 55% by including breads, cookies, savory snacks, reconstituted meat products, milk-based drinks, breakfast cereals, juices and sodas, and frozen and ready-to-eat meals in the diet. Among U.S. school-aged children and adolescents, UPF provided 66.2% and 66.4% of TEI, respectively, with pizzas, sodas, and juices being the most-consumed products. In this scenario, it was proposed that the levels of UPF intake in the young may reflect, at least in part, their lifestyle. In this regard, a recent study documented that subjects consume more UPF when dining out than when eating at home. Other reasons are related to socio-economic inequalities, including lower education status of the mother or unemployed parents, which may lead to a preference for cheaper and less nutritious foods. A different trend was observed for older subjects who showed a lower intake of UPF compared to younger subjects; the main UPF products included cookies and pastries, but also processed breads, breakfast cereals, and yogurts. Compared to age, a minor variability was found for sex and/or BMI, which might differ for the net amount of UPF consumption but not for the percent of TEI from UPF. Intriguingly, the adherence to specific dietary patterns represented an additional determinant of the levels of UPF consumption. In this context, based on the NOVA classification, vegans and vegetarians reported higher UPF consumption compared to pesco-vegetarians and meat eaters, mainly driven by a higher consumption of plant-based meat and dairy substitutes. These results highlight the high variability in the characteristics of these types of diet, which may differ widely for the consumption of several food groups. However, these results were found only in two different publications belonging to the same cross-sectional trial performed in the NutriNet-Santé cohort; thus, a confirmation of such an analysis deserves further investigation, also to comprehend better if all vegetarian diets have the same health benefits regardless of the levels of UPF consumed.

22A thorough comparison of the findings from the different studies considered was challenging due to the differences in food classification and to the disparate definitions that were proposed. Descriptions of UPF within the NOVA system vary with distinguishing features including single vs. 2–3 vs. ≥5 more ingredients, or natural/fresh vs. imitation or industrial, and whole foods vs. fractioned substances. This means that different studies may have classified the same food as UPF or not based on the distinguishing feature used for classifying foods.

23Notably, one of the main sources of variation among study protocols is the tools used for estimating UPF intake. Overall, from the present review, it is difficult to provide conclusive findings about the influence of the tools used to determine UPF intake since its estimation was typically performed using a single method. In this regard, most of the studies (n = 49) used the 24 h recall. To reflect the typical diet, this tool needs to be administered several times; however, in some studies, data were derived from a single 24 h recall, which could have affected the significance of the findings. However, this tool has the strength of being able to assess the consumption of all food items since subjects can include/report specific information (e.g., brand), which may help with identifying the NOVA group. However, a lower number of studies assessed UPF intake using FFQs, which are not always specifically created and validated to estimate the consumption of products undergoing different food processing, and the food list cannot cover all the food items consumed, thus leading to underreporting. Among studies using FFQs, some of them used the questionnaire developed within the European Prospective Investigation into Cancer and Nutrition (EPIC), which is not able to distinguish among products belonging to different NOVA groups. This is, for instance, the case for artisanal or industrial breads or cakes that belong to two different NOVA groups (Groups 3 and 4, respectively). Therefore, the use of tools not specifically validated for estimating UPF consumption may potentially lead to the misclassification of foods in the UPF categories, which, in turn, may lead to the misinterpretation of the associations found with markers of health. Only two studies used a questionnaire specifically validated for estimating the levels of UPF consumption in children and adults. The approach to validating and using ad hoc developed FFQs, when possible, created for specific populations to consider the different dietary habits, should be recommended for more accurately estimating the consumption of UPF and the actual impact on health-related outcomes.

24This study has some strengths worth highlighting, the first of which is the rigorous search and selection strategy that identified available studies examining the energy intake from UPF. However, we cannot exclude that the use of further databases may have allowed the identification of additional studies. Secondly, food processing level was always determined according to the criteria of NOVA classification, to facilitate the comparison amongst findings, although it was reported that some NOVA definitions are open to researchers’ interpretation, leading to a not-always-uniform categorization. Finally, we included only studies reporting results as the percent of TEI from UPF and not as grams per day. In our opinion, the ratio of energy intake from UPF compared to total energy intake is more useful for reflecting the impact of these products on the whole diet. However, this method may not be useful for detecting the consumption of energy-free products (such as energy-free drinks with artificial sweeteners); thus, this choice can also be considered as a limitation. Notably, the NOVA system used has been largely criticized for different reasons, mostly because this system focuses on the role of food processing, regardless of the nutritional characteristics of foods, on human health. Thus, further efforts should be directed toward elucidating the impact of the different foods belonging to the same NOVA category but with different nutrient profiles on human health. To conclude, it seems worthwhile to implement a critical and constructive discussion able to clarify the potential and applicability of this type of approach.

25In conclusion, this review showed high levels of UPF consumption, especially in some countries and in specific target groups (i.e., children and adolescents). However, most of the data on UPF consumption have been derived from FFQs and 24 h dietary recall, which are not specifically validated for estimating UPF; thus, such data should be considered with caution. In this scenario, tools specifically validated to estimate the levels of UPF consumption can be useful to avoid misinterpretation of the findings, especially when used to investigate the association with health status. Despite several studies reporting a positive association between UPF and obesity and cardiometabolic health, on the whole, the evidence is not yet totally convincing. In addition, whether this association is dependent on the nutritional characteristics of UPF and/or related to the applied processing is unclear. In this context, despite the NOVA system classifying foods based on the food processing technology without providing any information about the nutritional content of the food, the UPF group has been suggested to be an indicator of poor food quality due to the generally high amounts of free or added sugars, fats, low levels of fiber, and high energy density. For instance, it was recently observed that UPF consumption is associated with a deterioration in diet quality, with UPF intake being negatively correlated with fiber and protein and positively correlated with sugar, fat, and saturated fat intake. This highlights that the concept of UPF may be somehow misleading, with the effect on human health mediated more by the nutritional quality of products rather than the processing. The association between UPF and nutritional adequacy is not surprising, since, for instance, the presence of added sugar or fat is a major element in defining UPF. Finally, the classification systems based on processing are not often aligned with dietary guidelines (e.g., some products considered UPF are recommended within a balanced diet). Thus, confirmation of the results already obtained should be accompanied by an evaluation of the association between UPF consumption and health status, estimating the contribution within different dietary patterns.