2019-01-16 Food in the Anthropocene: the EAT–Lancet Commission on healthy diets from sustainable food systems
Prof Walter Willett, MD
Prof Johan Rockström, PhD
Brent Loken, PhD
Marco Springmann, PhD
Prof Tim Lang, PhD
Sonja Vermeulen, PhD
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Published: January 16, 2019 DOI:https://doi.org/10.1016/S0140-6736(18)31788-4
Food systems have the potential to nurture human health and support environmental sustainability; however, they are currently threatening both. Providing a growing global population with healthy diets from sustainable food systems is an immediate challenge. Although global food production of calories has kept pace with population growth, more than 820 million people have insufficient food and many more consume low-quality diets that cause micronutrient deficiencies and contribute to a substantial rise in the incidence of diet-related obesity and diet-related non-communicable diseases, including coronary heart disease, stroke, and diabetes. Unhealthy diets pose a greater risk to morbidity and mortality than does unsafe sex, and alcohol, drug, and tobacco use combined. Because much of the world's population is inadequately nourished and many environmental systems and processes are pushed beyond safe boundaries by food production, a global transformation of the food system is urgently needed.
The absence of scientific targets for achieving healthy diets from sustainable food systems has been hindering large-scale and coordinated efforts to transform the global food system. This Commission brings together 19 Commissioners and 18 coauthors from 16 counties in various fields of human health, agriculture, political sciences, and environmental sustainability to develop global scientific targets based on the best evidence available for healthy diets and sustainable food production. These global targets define a safe operating space for food systems that allow us to assess which diets and food production practices will help ensure that the UN Sustainable Development Goals (SDGs) and Paris Agreement are achieved.
We quantitatively describe a universal healthy reference diet to provide a basis for estimating the health and environmental effects of adopting an alternative diet to standard current diets, many of which are high in unhealthy foods. Scientific targets for a healthy reference diet are based on extensive literature on foods, dietary patterns, and health outcomes. This healthy reference diet largely consists of vegetables, fruits, whole grains, legumes, nuts, and unsaturated oils, includes a low to moderate amount of seafood and poultry, and includes no or a low quantity of red meat, processed meat, added sugar, refined grains, and starchy vegetables. The global average intake of healthy foods is substantially lower than the reference diet intake, whereas overconsumption of unhealthy foods is increasing. Using several approaches, we found with a high level of certainty that global adoption of the reference dietary pattern would provide major health benefits, including a large reduction in total mortality.
The Commission integrates, with quantification of universal healthy diets, global scientific targets for sustainable food systems, and aims to provide scientific boundaries to reduce environmental degradation caused by food production at all scales. Scientific targets for the safe operating space of food systems were established for six key Earth system processes. Strong evidence indicates that food production is among the largest drivers of global environmental change by contributing to climate change, biodiversity loss, freshwater use, interference with the global nitrogen and phosphorus cycles, and land-system change (and chemical pollution, which is not assessed in this Commission). Food production depends on continued functioning of biophysical systems and processes to regulate and maintain a stable Earth system; therefore, these systems and processes provide a set of globally systemic indicators of sustainable food production. The Commission concludes that quantitative scientific targets constitute universal and scalable planetary boundaries for the food system. However, the uncertainty range for these food boundaries remains high because of the inherent complexity in Earth system dynamics.
Diets inextricably link human health and environmental sustainability. The scientific targets for healthy diets and sustainable food systems are integrated into a common framework, the safe operating space for food systems, so that win-win diets (ie, healthy and environmentally sustainable) can be identified. We propose that this framework is universal for all food cultures and production systems in the world, with a high potential of local adaptation and scalability.
Application of this framework to future projections of world development indicates that food systems can provide healthy diets (ie, reference diet) for an estimated global population of about 10 billion people by 2050 and remain within a safe operating space. However, even small increases in consumption of red meat or dairy foods would make this goal difficult or impossible to achieve. Within boundaries of food production, the reference diet can be adapted to make meals that are consistent with food cultures and cuisines of all regions of the world.
1 Unhealthy and unsustainably produced food poses a global risk to people and the planet. More than 820 million people have insufficient food and many more consume an unhealthy diet that contributes to premature death and morbidity. Moreover, global food production is the largest pressure caused by humans on Earth, threatening local ecosystems and the stability of the Earth system.
2 Current dietary trends, combined with projected population growth to about 10 billion by 2050, will exacerbate risks to people and planet. The global burden of non-communicable diseases is predicted to worsen and the effects of food production on greenhouse-gas emissions, nitrogen and phosphorus pollution, biodiversity loss, and water and land use will reduce the stability of the Earth system.
3 Transformation to healthy diets from sustainable food systems is necessary to achieve the UN Sustainable Development Goals and the Paris Agreement, and scientific targets for healthy diets and sustainable food production are needed to guide a Great Food Transformation.
4 Healthy diets have an appropriate caloric intake and consist of a diversity of plant-based foods, low amounts of animal source foods, unsaturated rather than saturated fats, and small amounts of refined grains, highly processed foods, and added sugars.
5 Transformation to healthy diets by 2050 will require substantial dietary shifts, including a greater than 50% reduction in global consumption of unhealthy foods, such as red meat and sugar, and a greater than 100% increase in consumption of healthy foods, such as nuts, fruits, vegetables, and legumes. However, the changes needed differ greatly by region.
6 Dietary changes from current diets to healthy diets are likely to substantially benefit human health, averting about 10·8–11·6 million deaths per year, a reduction of 19·0–23·6%.
7 With food production causing major global environmental risks, sustainable food production needs to operate within the safe operating space for food systems at all scales on Earth. Therefore, sustainable food production for about 10 billion people should use no additional land, safeguard existing biodiversity, reduce consumptive water use and manage water responsibly, substantially reduce nitrogen and phosphorus pollution, produce zero carbon dioxide emissions, and cause no further increase in methane and nitrous oxide emissions.
8 Transformation to sustainable food production by 2050 will require at least a 75% reduction of yield gaps, global redistribution of nitrogen and phosphorus fertiliser use, recycling of phosphorus, radical improvements in efficiency of fertiliser and water use, rapid implementation of agricultural mitigation options to reduce greenhouse-gas emissions, adoption of land management practices that shift agriculture from a carbon source to sink, and a fundamental shift in production priorities.
9 The scientific targets for healthy diets from sustainable food systems are intertwined with all UN Sustainable Development Goals. For example, achieving these targets will depend on providing high-quality primary health care that integrates family planning and education on healthy diets. These targets and the Sustainable Development Goals on freshwater, climate, land, oceans, and biodiversity will be achieved through strong commitment to global partnerships and actions.
10 Achieving healthy diets from sustainable food systems for everyone will require substantial shifts towards healthy dietary patterns, large reductions in food losses and waste, and major improvements in food production practices. This universal goal for all humans is within reach but will require adoption of scientific targets by all sectors to stimulate a range of actions from individuals and organisations working in all sectors and at all scales.
Because food systems are a major driver of poor health and environmental degradation, global efforts are urgently needed to collectively transform diets and food production. An integrative framework combined with scientific targets can provide essential support for a sustainable and healthy food transformation. This Commission concludes that global food systems can provide win-win diets to everyone by 2050 and beyond. However, achieving this goal will require rapid adoption of numerous changes and unprecedented global collaboration and commitment: nothing less than a Great Food Transformation.
We focus mainly on environmental sustainability of food production and health consequences of final consumption. However, the food system consists of much more than these factors. A transformation of the global food system should ultimately involve multiple stakeholders, from individual consumers to policy makers and all actors in the food supply chain, working together towards the shared global goal of healthy and sustainable diets for all.
However, humanity has never aimed to change the global food system on the scale envisioned in this Commission; this objective is uncharted policy territory and the problems outlined in this Commission are not easily fixed. Three lessons can be learned from other examples of societal responses to global changes. First, no single actor or breakthrough is likely to catalyse systems change. Second, science and evidence-gathering are essential for change. Third, a full range of policy levers, from soft to hard, will be needed. Together, these lessons guide the thinking that will be necessary to transform the global food system.
In addition, we outline five specific and implementable strategies, which are supported by a strong evidence base. Our modelling and analysis shows their effectiveness for achieving a Great Food Transformation. These strategies are:
Seek international and national commitment to shift towards healthy diets. The scientific targets set by this Commission provide guidance for the necessary shift, which consists of increasing consumption of plant-based foods and substantially reducing consumption of animal source foods. Research has shown that this shift will reduce environmental effects and improve health outcomes. This concerted commitment can be achieved by investment in public health information and sustainability education, and improved coordination between departments of health and environment.
Re-orient agricultural priorities from producing high quantities of food to producing healthy food. Production should focus on a diverse range of nutritious foods from biodiversity-enhancing food production systems rather than increased volume of a few crops, most of which are used for animal production.
Sustainably intensify food production to increase high-quality output. The current global food system is unsustainable and requires an agricultural revolution that is based on sustainable intensification and driven by sustainability and system innovation. This change would entail reducing yield gaps on cropland, radical improvements in the efficiency of fertiliser and water use, recycling phosphorus, redistributing global use of nitrogen and phosphorus, implementing climate mitigation options, including changes in crop and feed management, and enhancing biodiversity within agricultural systems.
Strong and coordinated governance of land and oceans. Such governance includes implementing a zero-expansion policy of new agricultural land into natural ecosystems and species-rich forests, management policies aimed at restoring and re-foresting degraded land, establishing mechanisms of international land-use governance, and adopting a Half Earth strategy for biodiversity conservation to safeguard resilience and productivity in food production. The world's oceans need to be effectively managed to ensure that fisheries do not negatively affect ecosystems, fish stocks are used responsibly, and global aquaculture production is expanded sustainably given its effect on and linkage to both land and ocean ecosystems.
At least halve food losses and waste, in line with global sustainable development goals. Substantially reducing the amount of food lost and wasted across the food supply chain, from production to consumption, is essential for the global food system to stay within its safe operating space. Technological solutions will need to be applied along the food supply chain and public policies implemented to achieve a 50% reduction in food loss and waste.
An opportunity exists to integrate food systems into international, national, and business policy frameworks aiming for improved human health and environmental sustainability. Establishing clear, scientific targets to guide food system transformation is an important step in realising this opportunity.
Food, planet, and health
In the past 50 years, global food production and dietary patterns have changed substantially. Focus on increasing crop yields and improving production practices have contributed to reductions in hunger, improved life expectancy, falling infant and child mortality rates, and decreased global poverty. 1, 2
However, these health benefits are being offset by global shifts to unhealthy diets that are high in calories and heavily-processed and animal source foods. These trends are driven partly by rapid urbanisation, increasing incomes, and inadequate accessibility of nutritious foods.3, 4
Transitions to unhealthy diets are not only increasing the burden of obesity and diet-related non-communicable diseases, but are also contributing to environmental degradation.5 , 6
Food in the Anthropocene represents one of the greatest health and environmental challenges of the 21st century.
The international community has taken steps in recent decades to reduce hunger and improve nutrition through global agendas such as the Millennium Development Goals, the Sustainable Development Goals, and the Decade of Action on Nutrition. However, wide-scale undernutrition still exists alongside increasing prevalence of overweight, obesity, and non-communicable diseases. Low dietary quality contributes to undernutrition, overweight, and obesity, and has caused persistent micronutrient deficiencies. Globally, more than 820 million people remain undernourished,7151 million children are stunted, 51 million children are wasted,8and more than 2 billion people are micronutrient deficient.9
Concurrently, prevalence of diseases associated with high-calorie, unhealthy diets are increasing, with 2·1 billion adults overweight or obese10 and the global prevalence of diabetes almost doubling in the past 30 years.11, 12
Unhealthy diets are the largest global burden of disease and pose a greater risk to morbidity and mortality than does unsafe sex, alcohol, drug, and tobacco use combined.4 Because much of the global population is inadequately nourished (ie, undernutrition, overnutrition, and malnutrition), the world's diets urgently need to be transformed.
Food production is the largest cause of global environmental change. Agriculture occupies about 40% of global land,13and food production is responsible for up to 30% of global greenhouse-gas emissions14 and 70% of freshwater use.2, 15
Conversion of natural ecosystems to croplands and pastures is the largest factor causing species to be threatened with extinction.16
Overuse and misuse of nitrogen and phosphorus causes eutrophication and dead zones in lakes and coastal zones.17
Environmental burden from food production also includes marine systems. About 60% of world fish stocks are fully fished, more than 30% overfished, and catch by global marine fisheries has been declining since 1996.18
In addition, the rapidly expanding aquaculture sector can negatively affect coastal habitats, freshwater, and terrestrial systems (related to the area directly used for aquaculture and feed production).19
Faced with the challenge of feeding about 10 billion people a healthy and sustainable diet by 2050, and with a rising number of environmental systems and processes being pushed beyond safe boundaries by food production, methods of food production need to be urgently reviewed.
Integrated agenda for food systems
Diets are a major link between human health and environmental sustainability.5, 6 Lose-lose diets20 (ie, unhealthy and environmentally unsustainable) are often characterised as being high in calories, added sugars, saturated fats, processed foods, and red meats. In addition, environmental degradation resulting from these lose-lose diets might further exacerbate poor health. Negative effects include premature deaths caused by poor air quality from biomass burning for agriculture and land clearing,21 reduced food security resulting from low yields due to changing climatic conditions,22diminished nutrient content of some crops due to rising atmospheric carbon dioxide concentrations,23and famine exacerbated by extreme weather events such as drought.7
This Commission focuses mainly on the link between diet, human health, and environmental sustainability, whereas other Lancet Commissions have explored additional areas.1, 24, 25
The global food system needs to be transformed to reduce its effect on human health and environmental stability and begin reversing current trends. However, this transformation will not be achieved without people changing how they view and engage with food systems. This change in thinking should recognise the inextricable link between human health and environmental sustainability and integrate these separate concerns into a common global agenda to achieve healthy diets from sustainable food systems. The call for an integrated agenda began in the 1980s,26 whereas the concept of healthy and sustainable food, the focus of this Commission, has only emerged in recent years.
Two major global agendas focus on human health and environmental sustainability. The UN Sustainable Development Goals (SDGs)27 seek to end poverty, protect the planet, ensure prosperity for all, and eradicate hunger and malnourishment. This ambitious and inclusive international policy framework includes human health or environmental sustainability in most of its goals. The Paris Agreement, although focused on climate change, also addresses the effects of climate change on human health. Furthermore, reaching the Paris Agreement of limiting global warming to well below 2°C, aiming for 1·5°C, is not possible by only decarbonising the global energy system. Transitioning to food systems that can provide negative emissions (ie, function as a major carbon sink instead of a major carbon source) and protecting carbon sinks in natural ecosystems are both required to reach this goal. A revolutionary change in food systems to support human health and environmental sustainability is essential to the Paris Agreement.28
Given the disproportionate effect of food systems on human health and environmental sustainability, these global agendas provide an unprecedented opportunity for catalysing the change in thinking that will be necessary to transform the global food system.
Safe operating space for food systems
An integrated agenda of human health and environmental sustainability alone will not be enough to achieve the SDGs and Paris Agreement. Clear scientific targets that define healthy diets and sustainable food production are necessary to guide policy makers, businesses, and all food system actors. The Intergovernmental Panel on Climate Change (IPCC) has set scientific targets for climate, defining ranges of maximum carbon dioxide emissions allowed to remain within different levels of average global temperature rise. These emission targets have provided estimates of remaining carbon budgets and climate risks for societies, which have formed the basis for the Paris Agreement, by 195 nations. However, the 1·5–2°C Paris range is a science-based target (panel 1), agreed on through negotiations and political consensus and based on the latest scientific understanding. For the global food system, clear scientific targets do not exist. This absence of targets is a barrier for policy makers and businesses looking for guidance in achieving their food-related SDG goals and commitments under the Paris Agreement.
A geological epoch that is characterised by humanity being the dominating driver of change on Earth.
All parts of the Earth where life exists, including the lithosphere (solid surface layer), hydrosphere (water), and atmosphere (air). The biosphere plays an important part in regulating the Earth system by driving energy and nutrient flow between components.
Thresholds set at the low end of the scientific uncertainty range that serve as guides for decision makers on acceptable levels of risk. Boundaries are baselines, unchanging, and not time-bound.
Earth's interacting physical, chemical, and biological processes consisting of land, oceans, atmosphere, and poles, and includes Earth's natural cycles— ie, carbon, water, nitrogen, phosphorus, and other cycles. Life, including human society, is an integral part of the Earth system and affects these natural cycles.
All elements and activities that relate to production, processing, distribution, preparation, and consumption of food. This Commission focuses on two endpoints of the global food system; final consumption (healthy diets) and production (sustainable food production).
Great Food Transformation
The unprecedented range of actions taken by all food system sectors across all levels that aim to normalise healthy diets from sustainable food systems.
Long-term diseases, also known as chronic diseases, which are caused by a combination of genetic, physiological, environmental, and behavioural factors. The main types of non-communicable diseases are cardiovascular diseases, cancers, chronic respiratory diseases, and diabetes.
Nine boundaries, each representing a system or process that is important for regulating and maintaining stability of the planet. They define global biophysical limits that humanity should operate within to ensure a stable and resilient Earth system—ie, conditions that are necessary to foster prosperity for future generations.
Safe operating space for food systems
A space that is defined by scientific targets for human health and environmentally sustainable food production set by this Commission. Operating within this space allows humanity to feed healthy diets to about 10 billion people within biophysical limits of the Earth system.
Targets that are reached through international scientific consensus, based on the latest available science, and are time-bound. The Intergovernmental Panel on Climate Change has provided scientific targets defining ranges of maximum carbon dioxide emissions allowed to remain less than different levels of average mean global temperature rise. This Commission is providing global scientific targets defining ranges of the amount and types of food groups necessary for human health and boundaries we should stay within to reduce environmental degradation due to food production at all scales.
Targets developed through collaboration and negotiation that build on expertise and rigor used to reach international scientific consensus on an issue (eg, scientific targets set by the Intergovernmental Panel on Climate Change). These targets are used, for example, to allocate a proportion of the required global emissions reduction targets, in line with the Paris Agreement, to an individual company in a fair and transparent way. These targets differ from scientific targets because they are based on science but factor in feasibility and viability.
We can conceptualise an integrated agenda of human health and environmental sustainability for the global food system that has clear scientific targets using the concept of a safe operating space for food systems. The concept of a safe operating space for humanity, proposed by Rockström and colleagues in 2009,29 originates from the planetary boundaries framework and is defined as “the safe operating space for humanity with respect to the Earth system and are associated with the planet's biophysical subsystems or processes”. We use the planetary boundaries framework as a guide to propose a safe operating space for food systems that encompasses human health and environmental sustainability. This space is defined by scientific targets that set ranges of intakes for food groups (ie, 100–300 g/day of fruit) to ensure human health (table 1) and planetary boundaries for food production to ensure a stable Earth system. These boundaries include the total global amount of cropland use, biodiversity loss, water use, greenhouse-gas emissions, and nitrogen and phosphorus pollution that can be due to food production (table 2). These boundaries for human health and food production identify the safe operating space within which food systems should jointly operate to ensure that a broad set of universal human health and environmental sustainability goals are achieved.
Table 1 Healthy reference diet, with possible ranges, for an intake of 2500 kcal/day
Macronutrient intake (possible range), g/day Caloric intake, kcal/day
Rice, wheat, corn, and other
† 232 (total gains 0–60% of energy) 811
Tubers or starchy vegetables
Potatoes and cassava 50 (0–100) 39
All vegetables 300 (200–600) ..
Dark green vegetables 100 23
Red and orange vegetables 100 30
Other vegetables 100 25
All fruit 200 (100–300) 126
Whole milk or derivative equivalents (eg, cheese) 250 (0–500) 153
Beef and lamb 7 (0–14) 15
Pork 7 (0–14) 15
Chicken and other poultry 29 (0–58) 62
Eggs 13 (0–25) 19
§ 28 (0–100) 40
Dry beans, lentils, and peas
* 50 (0–100) 172
Soy foods 25 (0–50) 112
Peanuts 25 (0–75) 142
Tree nuts 25 149
Palm oil 6·8 (0–6·8) 60
¶ 40 (20–80) 354
Dairy fats (included in milk) 0 0
Lard or tallow
‖ 5 (0–5) 36
All sweeteners 31 (0–31) 120
For an individual, an optimal energy intake to maintain a healthy weight will depend on body size and level of physical activity. Processing of foods such as partial hydrogenation of oils, refining of grains, and addition of salt and preservatives can substantially affect health but is not addressed in this table.
* Wheat, rice, dry beans, and lentils are dry, raw.
† Mix and amount of grains can vary to maintain isocaloric intake.
‡ Beef and lamb are exchangeable with pork and vice versa. Chicken and other poultry is exchangeable with eggs, fish, or plant protein sources. Legumes, peanuts, tree nuts, seeds, and soy are interchangeable.
§ Seafood consist of fish and shellfish (eg, mussels and shrimps) and originate from both capture and from farming. Although seafood is a highly diverse group that contains both animals and plants, the focus of this report is solely on animals.
¶ Unsaturated oils are 20% each of olive, soybean, rapeseed, sunflower, and peanut oil.
‖ Some lard or tallow are optional in instances when pigs or cattle are consumed.
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Table 2 Scientific targets for six key Earth system processes and the control variables used to quantify the boundaries
Control variable Boundary (uncertainty range)
Climate change Greenhouse-gas (CH4and N2O) emissions 5 Gt of carbon dioxide equivalentper year (4·7–5·4)
Nitrogen cycling Nitrogen application 90 Tg of nitrogen per year (65–90; *90–130 †)
Phosphorus cycling Phosphorus application 8 Tg of phosphorus per year (6–12; *8–16 †)
Freshwater use Consumptive water use 2500 km3per year (1000–4000)
Biodiversity loss Extinction rate Ten extinctions per million species-years (1–80)
Land-system change Cropland use 13 million km2(11–15)
* Lower boundary range if improved production practices and redistribution are not adopted.
† Upper boundary range if improved production practices and redistribution are adopted and 50% of applied phosphorus is recycled.
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Boundaries that define a safe operating space for food systems are difficult to set in complex systems, and need to be refined over time. The Earth system and human biology are complex adaptive systems, characterised by interactions and feedback loops. All scientific targets for a safe operating space for healthy diets and sustainable food production are therefore associated with uncertainty. By applying a precautionary and risk perspective, boundaries are placed at the lower end of the scientific uncertainty range, establishing, with a high likelihood, a safe space in which food systems can operate. 30
These boundaries should be viewed as guides for decision makers on acceptable levels of risk for human health and environmentally sustainable food production. Operating outside this space for any Earth system process (eg, high rates of biodiversity loss) or food group (eg, insufficient vegetable intake) increases risk for harm to the stability of the Earth system and human health. When viewed together as an integrated human health and environmental sustainability agenda, win-win diets,20 that fall within the safe operating space for food systems, will help to achieve global human health and environmental sustainability goals.
Scope and limitations
This Commission brings together scientists from several disciplines to assess the global food system and set global scientific targets for shifting the world towards healthy diets and sustainable food production. Because setting such targets can be difficult, this Commission focuses on two endpoints of the global food system: final consumption (healthy diets) and production (sustainable food production). These factors disproportionately affect human health and environmental sustainability; however, the food system is not only affected by these two endpoints. Throughout the Commission we use the term food system and acknowledge that food systems are not limited to food production and consumption. Food systems are comprised of all the elements (eg, environment, people, inputs, processes, infrastructures, and institutions) and activities that relate to the production, processing, distribution, preparation and consumption of food. 31
By referring to the food system throughout the Commission, our intention is to emphasise that the Great Food Transformation can only be achieved with all actors in all parts of the food system working collectively towards this transformation. Furthermore, we acknowledge that food systems also affect society, culture, economy, and animal welfare. However, given the breadth and depth of the topics discussed, many important issues could not be discussed. These and other issues should be considered to achieve healthy diets from sustainable food systems.
This Commission is not setting actionable science-based targets (panel 1) on behalf of any country, sector, or business, nor does it have a mandate to do so. This Commission is an independent scientific body using the latest available science to make a global assessment of the food system and set global scientific targets for healthy diets and sustainable food production. These targets form the first attempt to provide scientific guidance for a transformation towards healthy diets from sustainable food systems. The goal, in the absence of an intergovernmental scientific panel or comprehensive agreement for food, is for science to continue refining definitions of global scientific targets for human health and environmentally sustainable food production while business and policy makers begin translating these definitions into operational science-based targets for various sectors, regions, and countries.
The planetary boundaries framework expands the definition of sustainable food production to include the global nature of food production's environmental effects, connecting local to global scales. However, this framework does not provide a plan for translating global targets to national and subnational governments, businesses, and other local actors. This approach is intended to inform national, sectoral, and sociopolitical targets and prioritisations, highlighting the global environmental context within which these diverse activity areas should fit. This approach becomes a first step in connecting a planetary perspective with context-specific levels of action.
In this Commission, we do not propose a simple global fix to the problems discussed. The safe operating space for food systems will require implementation of a variety and multitude of solutions and innovations. For food production, we avoid comparing specific production systems (eg, organic vs conventional) because numerous comparisons exist 32 and debates about specific production systems and diets can be overly prescriptive and mask diversity of contexts and available solutions. We give guidance on healthy diets but provide sufficient scope for many global dietary patterns (eg, vegetarian and pescatarian) to be considered. This scope is captured by use of broad food groups and intake ranges that allow for various dietary preferences to be considered. Guaranteed solutions neither exist nor would allow users of this analysis to adopt a holistic concept of a safe operating space for food systems that will be needed.
This Commission does not explore various population growth scenarios, such as the Shared Socioeconomic Pathways. A major driver of increasing requirements for food is a growing global population, which is expected to increase from about 7·6 billion people in 2017, to 9·8 billion people in 2050. Reducing the rate of population growth will therefore be essential for achieving healthy and sustainable diets for the world's population. Universal access to sexual and reproductive health-care services (including family planning), information, and education will be necessary components of this goal. Our analysis follows the Shared Socioeconomic Pathway 2 for a moderate population growth (9·2 billion people), and trends (ie, population growth, GDP) broadly follow historical patterns (appendix p 1).
Lastly, although this Commission uses 2050 as a cutoff, the issues discussed extend beyond 2050. Global population is expected to exceed 11 billion people by 2100 unless actions are taken to stabilise population growth (appendix p 2). Healthy diets from sustainable food systems are possible for up to 10 billion people but becomes increasingly unlikely past this population threshold.
Treatment of uncertainty
Few decisions about diet, human health, and environmental sustainability can be made on the basis of absolute certainty because evidence is incomplete, imperfect, and continually evolving; therefore, certainty should be considered as a continuum. We have attempted to base estimates on the best available science, and we acknowledge that uncertainty exists. Therefore, when possible, we acknowledge this uncertainty and our confidence in the validity of our findings and qualitatively discuss this on the basis of the type, quantity, quality, and consistency of evidence. We have a high level of scientific certainty about the overall direction and magnitude of associations described in this Commission, although considerable uncertainty exists around detailed quantifications. Modelling and sensitivity analysis provide ways to explore the implications of this uncertainty.