The ongoing nutrition transition thwarts long-term targets for food security, public health and environmental protection

The global nutrition transition, a shift in dietary patterns from predominantly plant-based to diets richer in animal products, processed foods, and added sugars, is a significant driver of changes in global food systems, public health, and the environment. This transition presents a complex challenge, as it is intertwined with issues of undernutrition, overnutrition, and environmental degradation. While undernourishment persists, particularly in developing countries, the rise of diet-related non-communicable diseases (NCDs) such as diabetes and cardiovascular disease poses a growing threat to global health. Suboptimal diets are currently a leading global health risk, causing a considerable loss of disability-adjusted life years (DALYs) annually. The transition also intensifies pressure on natural resources, as increasing food demand drives agricultural expansion, water consumption, and greenhouse gas emissions. Agriculture's contribution to environmental issues like nutrient pollution, biodiversity loss, and antibiotic resistance further exacerbates the situation. This study investigates the complex interplay of undernutrition, overnutrition, and environmental pressures driven by this ongoing nutrition transition. The central research question is: How will the symptoms of this "global syndemic" (the combination of obesity, undernourishment, and climate change) evolve in the coming decades, assuming the nutrition transition continues?

Existing literature highlights the multifaceted nature of the nutrition transition. Popkin's theory of dietary transitions, progressing from famine to receding famine to degenerative diseases, provides a framework for understanding the changing patterns of malnutrition. However, his hypothesis that this would eventually lead to behavioral change and a decline in obesity has not been fully observed. Studies show a persistent rise in obesity even in high-income countries, while the proportion of individuals with a healthy BMI declines. In low- and middle-income countries, the coexistence of underweight and overweight populations is common. The literature also underscores the significant environmental impacts of the food system, including land use change, water scarcity, greenhouse gas emissions, and nutrient pollution. The EAT-Lancet Commission highlights the need for sustainable food systems to support healthy diets, emphasizing the urgent need for policy interventions to address the global syndemic. Previous studies have projected future food demand, but many lack the integration of anthropometric dynamics and the detailed breakdown of dietary components necessary for a comprehensive understanding of the issue. This study improves upon previous work by incorporating a more nuanced approach that considers both anthropometric and socioeconomic factors to forecast future food demands.

This study utilizes a comprehensive open-source food demand model to project various indicators related to the nutrition transition from 1965 to 2100. The model incorporates data from FAOSTAT, WHO, World Bank, and the NCD-RisC consortium. Key variables include population growth, demographic change (age and sex distribution), income levels, body mass index (BMI) distributions, body height, physical activity levels, and household food waste. A novel aspect of the model is its incorporation of anthropometric dynamics, including BMI and height, to estimate food energy requirements and food intake. The model accounts for the varying basal metabolic rates (BMR) of different age and sex groups, using Schofield equations. The model also includes projections based on the five Shared Socioeconomic Pathways (SSPs) which represent different plausible futures. The model estimates the prevalence of underweight, overweight, and obesity, taking into account factors like body height and physical activity levels. It also projects dietary composition, splitting calorie consumption into four key groups: animal-source foods, empty calories (oils, sugar, and alcoholic beverages), vegetables, fruits, and nuts, and staples. The model employs a nested demand model to ensure consistency between individual food groups and total calorie consumption. The data were processed using a data management system called MADRAT, utilizing R programming. Data gaps, especially in historical data, were filled using model estimations which were validated through cross-validation techniques. The accuracy of model predictions were further verified by comparing results with out-of-sample data, and with results from other global food demand projection studies. Finally, the model decomposed food demand into its driving forces, allowing for the analysis of the relative contributions of population growth, ageing, changes in BMI, physical activity levels, and food waste.

The study projects a concerning future trajectory for the nutrition transition. By 2050, it estimates that 45% of the world's population will be overweight and 16% obese, compared to 29% and 9% in 2010, respectively. While underweight prevalence will decrease relatively, absolute numbers will stagnate at 0.4–0.7 billion. Dietary composition will shift towards higher consumption of animal-source foods and empty calories, while the increase in consumption of vegetables, fruits, and nuts will remain insufficient. Global food demand is projected to surge from 30 EJ in 2010 to 45 EJ in 2050, driven by population growth, aging, increasing body mass, and higher levels of food waste. The demand for resource-intensive animal-source foods will increase even faster than total food demand, with the share of animal-source calories in total calories rising from 18% to 24% by 2050. Analysis reveals that increases in food energy requirements (due to population growth, demographic shifts, and increased body height) will have a significant impact on food demand. Reducing food waste and addressing overweight and obesity have the greatest potential to reduce food demand, while eliminating underweight will have a less significant impact. These projections highlight that current efforts to combat undernutrition are insufficient to meet the Sustainable Development Goal 2 (SDG 2) of achieving zero hunger by 2030. The obesity epidemic will continue to worsen, violating SDG 2 targets to end all forms of malnutrition. The study's regional breakdown reveals that India and Africa will be the primary drivers of future food demand increases.

These findings confirm that the nutrition transition is an unchecked global process, contradicting the hope of a shift towards more balanced and sustainable diets. The continued rise of obesity in high-income countries, coupled with the increasing prevalence of both underweight and overweight in many middle-income countries, illustrates the failure of current policies to curb the syndemic. The observed shift towards highly unbalanced diets, with overconsumption of animal-source foods and empty calories and insufficient increases in consumption of nutritious plant-based foods, is particularly concerning. The significant increase in projected food demand, driven by several factors, underscores the need for urgent and comprehensive action. The study demonstrates that reducing food waste and combating obesity offer the highest potential for mitigating the environmental impact of increased food demand, while simultaneously improving public health. The findings support the need for integrated policy interventions that address both undernutrition and overnutrition, alongside environmental concerns.

This study provides strong evidence that current trends in the nutrition transition are unsustainable, jeopardizing the achievement of SDGs related to food security, public health, and environmental protection. The projected increases in overweight and obesity, coupled with persistent undernutrition and escalating environmental pressures, demand a fundamental restructuring of the food system. Future research should focus on investigating the effectiveness of various policy interventions, including taxes on unhealthy foods, marketing restrictions, and public awareness campaigns. International aid priorities should shift towards supporting the production and consumption of nutritious plant-based foods, especially in low-income countries. A coordinated, interdisciplinary approach, involving policymakers, researchers, and the private sector, is crucial to navigating the complex challenges posed by the ongoing nutrition transition.

The study's model relies on several assumptions and simplifications. The anthropometric food intake estimates may exceed FAOSTAT data in some low-income countries, potentially due to data limitations or unaccounted metabolic factors. Projections for high-income countries are subject to uncertainty due to limited data on dietary patterns at extremely high income levels. The model uses per capita income as a primary socioeconomic driver, which is a simplification, potentially overlooking other relevant factors such as inequality, education, and the influence of food marketing. While the model includes anthropometric and demographic dynamics, the effect of technological innovations, social change and policy interventions that might shift trends are not fully captured. The model's projections are more robust for scenarios involving a continuation of materialistic lifestyles, and might underestimate obesity and the change towards more sustainable lifestyles.