In a recent study published in the journal Nature Medicine, researchers used a novel risk assessment model to estimate absolute and proportional burdens of new type 2 diabetes (T2D) cases globally among adults in 184 countries, especially direct and body weight-mediated effects of 11 dietary factors, separately and jointly.
Study: Incident type 2 diabetes attributable to suboptimal diet in 184 countries. Image Credit: Lightspring / Shutterstock
T2D is a leading cause of mortality globally and has vast socio-economic repercussions. Between 1980 and 2021, the number of people living with diabetes (90% T2D cases) surged from 108 to 537 million globally, with corresponding increases in obesity among adults.
The incidence of T2D has only increased globally in the past 40 years and is on the rise continuously; if left unchecked, T2D will deteriorate human health and economic productivity even further, thus exerting immense pressure on healthcare systems worldwide.
Studies have evidenced direct- and weight gain-mediated effects of several dietary factors on the etiology of T2D. Yet, absolute and proportional contributions of suboptimal diet or specific dietary factors on the global T2D incidence remain unclear.
About the study
In the present study, researchers estimated the effects of 11 dietary factors, viz., inadequate intake of whole grains, fruits, nuts, yogurt, seeds, and vegetables (non-starchy) and excessive consumption of refined wheat and rice, unprocessed red meat, processed meat, sugar-sweetened beverages (SSBs), fruit juices, and potatoes on global T2D incidence.
They made these estimates using dietary data from the Global Dietary Database (GDD) for adults in 184 countries. The team presented the absolute change in the proportional burden of T2D attributable to suboptimal diet and each risk factor between 1990 and 2018 globally stratified by world region.
GDD delineated all 184 countries into world regions, which helped the researchers specifically discuss T2D trends in the 30 most populous countries for four dietary factors, inadequate fruit, nuts, seeds, and non-starchy vegetable intake, and excessive intake of fruit juices based on effects mediated through weight gain.
They stratified their findings by age, gender, urbanicity, and education of participating individuals. In addition, they stratified country-wise findings by sociodemographic index (SDI), a measure of a country’s development. SDI is expressed on a scale of zero to one based on the average rankings of educational fulfillment, per capita income, and fertility rates.
The researchers used proportional multiplication to estimate the burden due to a suboptimal diet, assuming that 50% benefit of whole-grain intake is due to substituting it with refined wheat and rice intake. They modeled the effects of refined rice and wheat intake separately but combined this using proportional multiplication.
The team compared T2D incidence trends between 1990 and 2018 and reported all data as a median and the corresponding 95% UI, based on the quantification of uncertainty using 1,000 multiway probabilistic Monte Carlo simulations.
The study model estimated that, in 2018, suboptimal intake of 11 dietary factors led to 14.1 million new T2D cases globally. Excessive consumption of harmful dietary factors contributed towards a higher percentage of this burden than inadequate consumption of protective dietary factors (60.8% vs. 39.2%). Insufficient whole grain intake led to most T2D cases globally (26.1%), followed by excessive intake of refined wheat & rice (24.6%), processed meat (20.3%), and unprocessed red meat (20.1%).
The researchers noted marked heterogeneity in T2D incidence due to an overall suboptimal diet and individual dietary factors at the country level and worldwide. In addition, they observed an inverse correlation between diet-attributable T2D incidence and age. However, the absolute T2D burden, assessed per million population, was highest at middle age, i.e., between 45 and 60 years, indicating an interplay between variations in dietary habits vs. absolute T2D risk at varying ages.
Further, some of the dietary factors showed substantial regional heterogeneity. Regionally, the most increases and decreases in diet-attributable T2D incidence occurred in sub-Saharan Africa (+9.3 in absolute percentage points) and high-income countries (−1.5%), respectively.
For instance, in the Middle East, North Africa (+4.1%), and sub-Saharan Africa (+3.3%), refined wheat and rice intake increased T2D incidence, whereas T2D cases attributable to excess refined rice declined in South Asia, Central-eastern European regions and Central Asia but increased due to excessive refined wheat intake in the same regions.
The diet-attributable T2D incidence was higher in men vs. women, for individuals with higher vs. lower education, and in urban vs. rural settings; however, in high-income countries, Central Asia, and Central and Eastern Europe, its diet-attributable T2D incidence was higher in less educated people. In populous countries, e.g., Poland and Russia, excessive unprocessed red & processed meat and potato intake mainly drove relatively higher T2D burdens. Since the 1990s, the correlation between country-level diet-attributable T2D incidence and socio-economic development turned less robust. Latin America and the Caribbean stood second in diet-attributable T2D burden, especially Colombia and Mexico, where excessive SSBs, processed meats intake, and inadequate whole grains intake drove increased T2D incidence.
In regions with higher diet-attributable T2D burdens in people with higher education, e.g., high-income countries, educational and social safety intervention programs should target a nutritious diet to reduce T2D-related health inequities. Conversely, in regions where diet-attributable T2D burdens were highest in highly educated adults, e.g., South Asia, other approaches, such as proper package labeling, might be more effective. Financial markets could significantly contribute to global human health and equity by investing in the producing, marketing, and selling products aligned with societal goals.
Data suggests that body mass index (BMI) is increasing rapidly in rural regions of low- and middle-income countries due to more supply of processed foods in these areas. Thus, managing these nutritional and health-related inequities will require interventions and public health policies customized to regional circumstances. Notably, the T2D incidence attributable to direct etiologic effects of dietary factors was generally higher than their separate BMI-mediated effects. In light of these findings, multisectoral strategies to improve diet quality throughout life would remain vital, especially during childhood and adolescence, when people often form lifetime dietary habits.
While in 2018, there was a modest correlation between diet-attributable T2D burden and SDI (r = 0.29) that varied by world region. The authors noted a positive correlation in sub-Saharan African countries, South Asia, and high-income countries and a negative correlation in Latin American, Central Asian, Central and Eastern European nations, the Caribbean, and Southeast and East Asia. However, this correlation turned more robust in 1990 (r = 0.53) than in 2018, and these trends became comparable across all world regions. These findings pointed out that while diet quality worsened in lower-SDI countries; however, there was no sociodemographic development alongside.
The study highlighted carbohydrate quality as an area that needs immediate attention. In particular, excessively refined rice and wheat intake and inadequate consumption of whole grains, as the top two dietary drivers of T2D globally, albeit trends varied temporally and by world region. In proportional diet-related T2D burden, of all 11 dietary- factors assessed, excessive intake of unprocessed red meat contributed the most to the global increase in T2D incidence. To conclude, these findings should inform clinical and public health planning to improve dietary quality globally to reduce the global T2D burden.