Comparative analysis of temporal trends of obesity and physical inactivity in Brazil and the USA (2011–2021)

In our study, we have comparatively analyzed the temporal trends of obesity in Brazil and the USA in parallel with the temporal analysis of physical inactivity in these countries. To the best of our knowledge, this is the first study analyzing temporal trends of obesity between Brazil and the USA and simultaneously considering its association with the temporal trend of physical inactivity. The main findings showed a different tendency of temporal trends between obesity and physical inactivity if we compare the two variables within each country. While obesity tended to increase over time, physical inactivity tended to stabilize between 2011 and 2021. Comparing the two countries, we found a correlation between temporal trends of obesity. The obesity prevalence trend in Brazil in the last decade was almost identical to the USA, noting that the current difference of about 11 p.p. already existed at the beginning of the period. Also, despite a more significant oscillation of the prevalence curve of physical inactivity in the USA as compared to Brazil, during the last decade, in both countries, the trend of physical inactivity showed no association with the trends of obesity. In other words, the tendency of stability in physical inactivity prevalence estimates was not associated with the tendency of obesity, which increased in both countries in the same period.

Our results contradict previous studies analyzed in a recent systematic review demonstrating an association between obesity and physical inactivity [23]. Also, relatively old British epidemiological data suggest that low levels of physical activity may play an essential role in obesity [24]. However, apart from this British study, none of these associations reported in the above-mentioned review study considered the temporal trend analysis. A possible explanation for obesity showing a growing trend, even with a trend towards stability in physical inactivity, is the multifactorial determinants of obesity and the fact that other factors may have a more substantial impact on obesity than physical inactivity alone, such as sedentary behavior, diet, genetics, sleep patterns [25], and mental health [26].

In Brazil, a national study carried out in 2019 revealed that 30,1% of adults spent 6 or more hours per day in screen-based sedentary behaviors like watching TV and using computer or other screens [27]. Over a period of 10 years, between 2008 and 2018, it was observed an increase in the percentage of energy intake from ultra-processed foods and a decrease from plant-based natural/minimally processed foods in Brazilian adults [28]. Similar results were found among US adults, in which a study with accelerometers revealed median time of 8 h per day in sedentary behaviors [29]. Also, there is an increase in consumption of ultra-processed foods, which has been rising in the last two decades [30].

Although sedentary behavior is a phenomenon interrelated to physical activity, both are conceptually different [31] and can manifest independently, with the individual being able to reach the physical activity recommended by the WHO criterion while presenting high levels of sedentary behavior [32]. Notably, there is still much to understand about the independent detrimental effect of sedentary behavior on cardiometabolic diseases, such as obesity. At the same time, physical activity might be an effect modifier of the association between sedentary behavior and cardiometabolic health outcomes, making the interpretation of obesity trend analyses even more complex [33]. After that, our data do not support the understanding that physical activity does not affect populational obesity prevalence, which would imply the denial of solid evidence-based public health recommendations. However, our findings do support the interpretation that public policies or health programs aimed at controlling obesity should not be exclusively based on the promotion of physical activity.

Despite the finding that other factors may be more associated with the increase in obesity, the result of the stabilization trend of physical inactivity in both countries reveals a need to increase efforts so that this trend is reduced [34]. In addition, considering a different approach to our results, we cannot estimate the impact of the obesity trend in both countries if the physical inactivity trend had increased between 2011 and 2021. However, based on current evidence, it is reasonable to admit that if physical inactivity had experienced an increased trend in the analyzed period, the obesity prevalence would have probably been even higher [23]. In other words, decreasing the trend of physical inactivity could potentially help to reduce or stabilize the increasing trend of obesity.

The growing trend of obesity in both countries had already been confirmed in previous studies carried out individually in both countries [7, 8, 13], but our study found that these trends are correlated. In this sense, actions need to be taken in Brazil so that the prevalence of obesity does not reach values as high as those currently presented in the USA. Our findings are likely generalizable to other middle-income countries, similar to Brazil. Suppose no action is taken, obesity will continue to increase, mainly in low- and middle-income countries. In that case, the World Obesity Atlas projects a prevalence of 33% for women and 26% for men in Brazil, placing the country among the 11 with more women and 9 with more men with obesity by 2030 [35].

Research analyzing temporal trends of risk and protective behaviors related to chronic diseases is essential for understanding certain phenomena and predicting population behaviors that may be encouraged or discouraged to improve people’s health. Comparing temporal trends from two different contexts is also essential, especially when one of them, the USA, is the biggest economy in the world, in which we observe one of the highest prevalence estimates of obesity. Importantly, our data demonstrate that the Brazilian obesity trend in the last decade is very similar to one of the leading countries in obesity prevalence. This concerning finding imposes, per se, an urgent and collective call to action aiming to revert this scenario.

Of note, our findings must not be a disincentive to physical activity promotion. Apart from all the health benefits associated with an active lifestyle [36], our results suggest that physical inactivity alone could not explain the obesity trend in both countries. On the other side, the stability trend of the high prevalence of physical inactivity in both countries demonstrates the need to create public policies that consider physical activity as an essential component in the fight against obesity and other chronic diseases, together with other factors such as healthy eating and reducing sedentary behavior (potentials). In this way, initiatives to promote physical activity implemented in Brazil, such the Health Academy Program (Programa Academia da Saúde) [37], and Healthy People 2030 [38], in the USA, could include specific aims focusing on reducing obesity through physical activity. Beside that, cities need to increase the opportunities for physical activity practices that are also attractive to obese people, considering their limitations and needs [39, 40].

This study has some limitations. VIGITEL uses representative data from the capitals of the Brazilian states, disregarding the prevalence of the interior, which has its particularities. Because of this, the sample size in the USA is larger than in Brazil. However, due to the similarity of the data collection methods, and because the sampling from both countries are representative of the target population of each country, both surveys are comparable. Also, an intrinsic limitation in comparing health indicators between central and peripheral economies could be raised. However, we did not compare causal relationships or associated factors frequently modified by economic factors. We aimed to reflect on the Brazilian reality based on a comparison with a leading country in obesity worldwide, which previously went through an epidemiological transition. Another limitation is that the definition of physical inactivity in Brazil considers the absence of physical activity in the last three months in leisure-time, work, transport, and domestic domains. In contrast, the USA considers the absence of physical activity only in the last month in the leisure-time domain. As differences remain across years, trend comparison minimizes cross-country differences. Another limitation that might be pointed out is that many other factors besides physical inactivity, especially diet, stress, sleep disorders, and sedentary behavior, interfere with obesity. However, the impact of different obesity-associated factors is beyond the scope of the study, and physical inactivity was analyzed in isolation. The causes of obesity, both individual and socioeconomic, were also beyond our aims. Furthermore, the present study did not consider other socioeconomic factors that could explain differences mainly between the two countries.