by Allison Hu
Due to rising incomes and urbanization, traditional diets are being replaced by diets that are higher in refined sugars, refined fats, oils, and meats. By 2050, if these dietary trends are unchecked, they can become a major contributor to an estimated 80% increase in global agricultural greenhouse gas emissions from food production and global land clearing, which can result in species extinction (Tilman et al. 2014). Additionally, these dietary shifts are greatly increasing the incidence of type II diabetes, coronary heart disease, and other chronic non-communicable diseases that lower global life expectancies. Because the global dietary transition directly links and negatively affects human and environmental health, it is one of the greatest challenges facing humanity. If alternative diets that offer substantial health benefits are widely adopted, there is potential to reduce global agricultural greenhouse gas emissions, reduce land clearing and resultant species extinctions, and even help prevent such diet-related chronic non-communicable diseases. Therefore, the implementation of dietary solutions to the tightly linked diet-environment-health trilemma, although a global challenge, is an important and valuable opportunity to improve the environment and human health. Impactful solutions will not be easily achieved and will require analyses of the quantitative linkages between diets, the environment, and human health. Tilman et al. focus their study on these solutions, along with the efforts of nutritionists, agriculturists, public health professionals, educators, policy makers, and food industries.
In this study, Tilman et al. compile and analyze global-level data in order to quantify relationships between diet, environmental sustainability, and human health, to evaluate potential environmental impacts of the global dietary transition, and to explore prospective solutions to the diet-environment-health trilemma. Their methods to do so include expanding on earlier food lifecycle analyses (LCAs) by compiling all published LCAs of GHG emissions of food crop, livestock, fishery, and aquaculture production systems. They then use 50 years of data for 100 of the world’s most populous nations to analyze global dietary trends and their motivators and use this information to forecast future diets assuming these past trends continue.
Although diets differ within and among nations and regions for a variety of climatic, cultural and historic reasons, diets have been changing in fairly consistent ways as incomes and urbanization have increased globally during the past five decades. Data obtained by Tilman et al. indicate several trends amongst global diets. As annual incomes (per capita real gross domestic product, GDP) increased from 1961 to 2009, total protein per capita demand increased 750% in the 15 richest nations relative to the 24 poorest nations, but legume protein demand decreased as animal protein demand increased. A second trend within and among economic groups is the income-dependent increase in demand for calories from refined fats, refined sugars, alcohols and oils. The last trend is that total per capita caloric demand also increased with income. These three trends show that global dietary changes and associated with increased income, which in itself is associated with urbanization and industrial food production. Combining these trends with forecasts of per capita income for the future decades, Tilman et al. estimate that relative to the average global diet of 2009, the 2050 global-average per capita income-dependent diet would have 15% more total calories and 11% more total protein, with dietary composition shifting to having 61% more empty calories, 18% fewer servings of fruits and vegetables, 2.7% less plant protein, 23% more pork and poultry, 31% more ruminant meat, 58% more dairy and egg and 82% more fish and seafood.
Diet has a significant impact on human health. Many of the world’s poorest people have inadequate diets, and would have improved health were their diets to include more essential fatty acids, minerals, vitamins and protein from fish and meats and added calories and protein from other nutritionally appropriate sources. In contrast, diets of many people with moderate and higher incomes are shifting towards diets that are high in processed foods; refined sugars, refined fats, oils, and meats have contributed to 2.1 billion people becoming overweight or obese. These dietary shifts and resulting increases in body mass indicies (BMI) are further associated with increased global incidences of chronic noncommunicable diseases, especially type II diabetes, coronary heart disease, some cancers, and with higher all-cause mortality rates. These diseases are predicted to become two-thirds of the global burden of disease if these dietary trends persist.
In order to quantify the effects of alternative diets on mortality and these chronic noncommunicable diseases, Tilamn et al. compiled and summarized results of studies encompassing ten million person-years of observations on diet and health. The results demonstrate that relative to conventional omnivorous diets, across the three alternative of Mediterranean, pescetarian, and vegetarian diets, incidence rates of type II diabetes were reduced by 16%–41% and of cancer by 7%–13%, while relative mortality rates from coronary heart disease were 20%–26% lower and overall mortality rates for all causes combined were 0%–18% lower. This summary illustrates the magnitudes of the health benefits associated with some widely adopted alternative diets. Furthermore, though these patterns do not necessarily indicate that healthier diets are necessarily more environmentally beneficial, not that more environmentally beneficial diets are healthier, they do, however, demonstrate that there are alternative dietary options that should substantially improve both human and environmental health.
Dietary composition also strongly influences greenhouse gases (GHGs) as global agriculture and food production release over 25% of all GHGs. GHG emissions were found to vary widely among foods – relative to animal-based foods, plant-based foods have lower GHG emissions. Diet-driven increases in global food demand and increases in population are also leading to pollution of fresh and marine waters with agrochemicals and clearing of tropical forests, savannas, and grasslands – threatening species with extinction. Using LCA emission data, Tilman et al. calculated annual per capita GHG emissions from food production (‘cradle to farm gate’) for the 2009 global-average diet, for the global-average income-dependent diet projected for 2050, and for Mediterranean, pescetarian and vegetarian diets. Global-average per capita dietary GHG emissions from crop and livestock production would increase 32% from 2009 to 2050 if global diets changed in the income-dependent ways. All three alternative diets could reduce emissions from food production below those of the projected 2050 income-dependent diet, with per capita reductions being 30%, 45% and 55% for the Mediterranean, pescetarian and vegetarian diets, respectively. However, minimizing environmental impacts does not necessarily maximize human health. For example, prepared items high in sugars, fats, or carbohydrates can have low GHG emissions but be less healthy than foods they displace. Solutions to the diet–environment–health trilemma should seek healthier diets that have low GHG emissions rather than diets that might minimize only GHG emissions.
Changes towards healthier diets can also have globally significant GHG benefits. From 2009 to 2050, the global population is projected to increase by 36%. When combined with the projected 32% increase in per capita emissions from income-dependent global dietary shifts, the net effect is an estimated 80% increase in global GHG emissions from food production. In contrast, there would be no net increase in food production emissions if by 2050 the global diet had become the average of the Mediterranean, pescetarian, and vegetarian diets.
The analyses by Tilman et al. demonstrate that there are plausible solutions to the diet–environment–health trilemma, diets already chosen by many people that, if widely adopted, would offer global environmental and public health benefits. Unless the nutrition transition that is under way is changed, diabetes, chronic heart disease and other diet-related chronic non-communicable diseases will become the dominant global disease burden, often affecting even the poorer members of poorer nations for whom appropriate health care is unavailable. Furthermore, the dietary choices that individuals make are influenced by culture, nutritional knowledge, price, availability, taste and convenience, all of which must be considered if the dietary transition that is taking place is to be counteracted. The evaluation and implementation of dietary solutions to the tightly linked diet–environment–health trilemma is a global challenge, and opportunity, of great environmental and public health importance.
Tilman, D., Clark, M., 2014. Global diets link environmental sustainability and human health. Nature, 515, 518-522.