What role should the commercial food system play in promoting health through better diet?BMJ 2020; 368 doi: https://doi.org/10.1136/bmj.m545 (Published 17 March 2020) Cite this as: BMJ 2020;368:m545
- Martin White, professor of population health research1,
- Emilie Aguirre, Earl B Dickerson fellow2 3,
- Diane T Finegood, professor4,
- Chris Holmes, independent consultant5,
- Gary Sacks, associate professor6 ,
- Richard Smith, professor of health economics7
- 1Centre for Diet and Activity Research, MRC Epidemiology Unit, Institute of Metabolic Sciences, University of Cambridge, UK
- 2University of Chicago Law School, Chicago, IL, USA
- 3Harvard Business School, Boston, MA, USA
- 4Morris J Wosk Centre for Dialogue, Simon Fraser University, Vancouver, BC, Canada
- 5Aldershot, Surrey, UK
- 6Global Obesity Centre, Deakin University, Burwood, VIC 3125, Australia
- 7College of Medicine and Health, University of Exeter, Exeter, UK
- Correspondence to: M White
Populations across the globe are highly dependent on commercial food systems for daily nourishment
Commercial food systems rely heavily on high volume sales of foods high in unhealthy ingredients to generate profits and value for shareholders
The commercial food system does not adequately take account of the high costs of its activities for societies, health, or the environment
Profit could be made from a healthier and more sustainable food system, in ways that are consistent with prevention of non-communicable diseases, but whole system change will be needed
Governments need to increase their efforts to catalyse rapid change in commercial food systems, through fiscal and regulatory policies and development of metrics for the health, environmental, and social impacts of food companies
The commercial food system is of increasing concern to those responsible for improving population health.1 The transition in global nutrition is rapidly changing agricultural practices and increasing the consumption of nutritionally poor processed foods, which are associated with increases in non-communicable diseases.2 The growth of childhood obesity, in particular, continues largely unchecked, risking enormous burdens of future disease, health system costs,3 and intergenerational inequalities.4
A number of aspects of nutritionally poor processed foods, especially ultra-processed foods, are unhealthy (eg, excess salt or sugar).2 The mechanisms that lead to associations between processed foods and poor health remain largely unknown.5 Processed foods have some advantages—for example, their longer shelf life and convenience—and they may not inherently need to be unhealthy. Nevertheless, how to achieve healthier processed foods remains unclear.5
Food processing, and associated marketing, adds value to raw ingredients6 and is a key driver of profits for the commercial food system. Large, and especially publicly listed, food companies operate in an economic environment that demands continual growth of profits. This drive for profits leads to a range of emergent behaviours, such as aggressive marketing, the avoidance of regulation that could impede profits (eg, through lobbying), and the generation of huge external health, social, and environmental costs associated with the high volume sales of processed foods. These behaviours amplify the direct adverse effects of processed foods and result in poor alignment between commercial food production, environmental sustainability, societal wellbeing, and population health goals.7 This imbalance is unsustainable and needs urgent attention. The syndemic crises of climate change and global obesity8 need to be treated as emergencies now to avoid catastrophic costs and consequences for future generations.
In this article, we examine two questions. How can social, public health, and sustainability goals achieve parity with profit in the commercial food system? And, what leadership is needed to support this challenge globally? Although we briefly discuss the commercial food system as a whole, given the breadth, scale, and complexity of the system, our main focus is on the elements closer to consumers (manufacturing, retailing, and food service).
Commercial food systems, diet, and health
Our tastes and desires for foods are both physiologically driven and culturally embedded within societies.9 Dietary risks are among the greatest predictors of disease burden, leading to increased incidence and mortality from non-communicable diseases. These dietary risks include foods high in energy, salt, or added sugar and diets low in fruits, vegetables, legumes, nuts, seeds, and whole grains.10 Commercial food systems must, therefore, be considered one of the most important influences on population health globally.11
The commercial food system delivers largely affordable food to whole populations and has become vital to national economies, providing considerable employment and contribution to export trade.12 Global agricultural trade is valued at around $1tn (£0.78tn, €0.88tn) and food retail sales at around $4tn annually.13 The commercial food system produces sufficient food to adequately nourish the global population of around 7.5 billion but has two key defects.
Secondly, distribution of food products is uneven, resulting in substantial inequalities in physical and economic access to healthy and nutritious foods.12 Thus in many parts of the world people remain undernourished, yet, often in the same countries, people overeat affordable, energy dense foods and have associated chronic non-communicable diseases, leading to a “double burden” of malnutrition.17
The drive to increase production of food calories to feed the world’s growing population over the past 70 years (“calorie fundamentalism”) has been criticised18; globally we produce enough food energy but insufficient essential nutrients to ensure healthy diets. This challenge will be compounded by predicted global population growth over the next 50 years; it simply will not be viable, owing to the costs to the environment, health, and societies, to expand production based on dietary energy requirements alone.
Small retailers and multinational companies
All parts of commercial food systems are interconnected through supply and value chains, trade, and integration within large, often multinational, companies. Many multinational companies have broad portfolios, including both relatively healthy and unhealthy foods. The overall balance, however, is in favour of highly processed foods, the distribution of which is growing, especially in low and middle income countries.14 Although multinational companies command large market shares for specific foods or in particular sectors (eg, grocery retailing), the much larger numbers of smaller enterprises are also critically important in food provision, driving industry innovation and growth. For example, although the largest fast food chain in the UK commands a significant market share, it has just 1200 outlets compared with, for example, 10 500 independent fish and chip shops19 and a total of around 64 000 independent takeaways across the UK.20
Multinational food companies have been increasingly criticised for their focus on maximising short term profits from less healthy food products, their negative effects on health and the environment, and their manipulation of markets and unduly influencing consumers. All these factors together shape policy and public opinion in relation to non-communicable disease prevention.21
Within the commercial food system a common pattern of “corporate political activities” aimed at influencing policy and public opinion has emerged. These activities are also seen in other “harmful commodity industries”—for example, tobacco, alcohol, and gambling.22 This pattern includes framing information to suit corporate objectives (including manipulation of science); lobbying and providing financial incentives to policy makers; building pro-industry constituency among policy makers, community groups, and health organisations; deploying legal strategies to oppose public health measures; extensive use of voluntary industry codes of practice to avoid government regulation; and efforts to fragment and destabilise groups likely to counter industry arguments.23
High profile examples of the influence of the food industry include efforts to change food labelling regulations in Europe24 and to repeal health related food taxes (eg, the soda tax in Cook County, Chicago, Illinois, USA and the Danish fat tax).25 The range of corporate political activities presents huge challenges for public health and is an important barrier to progress towards a healthier, more sustainable, and equitable food system.
Complex and adaptive
Commercial food systems encompass huge, complex, and interdependent networks of entities involved in agriculture and fisheries, food processing and production, storage and distribution, wholesaling and retailing, and preparation and marketing of raw, processed, and ready to eat foods. They are underpinned by global and national logistics, finance, trade agreements, and regulatory frameworks.26
To understand the commercial food system, it is helpful to view it as a set of inter-related complex adaptive systems. These systems are unpredictable, self-organising, and display behaviour patterns that result from interactions within the whole system but are not necessarily predictable by the behaviours of component entities.27 Such systems respond to external stimuli, such as new regulations, but readily adapt and achieve a new equilibrium, developing new structures, rules, and behaviours.
Complex adaptive systems tend to be governed by simple “rules” that lead to emergent properties. For example, supermarkets generally abide by an implicit, self-imposed simple rule—namely, that shelves must be plentifully stocked because consumers make a high proportion of purchasing decisions in front of shelves. This rule retains customers and drives sales but also creates logistic challenges that can result in overstocking and the emergent property of waste, especially of fresh produce.28
An example of the food system adapting is the emerging commercial response to the UK’s soft drinks industry levy, which was introduced in 2018. This levy applies a graded tax structure to soft drinks, with three tiers according to sugar levels: higher tier (£0.24/L for drinks with >8 g of sugar/100 mL), lower (£0.18p/L for drinks with 5-8 g/100 mL), and no levy (for drinks with <5 g/100 mL). Manufacturers of higher sugar drinks can choose not to change their drinks and absorb the cost or pass it on to customers by increasing prices; reduce sugar content to avoid the levy; or make other changes, such as diversifying their product ranges and the mix of product volumes and prices. All these responses have been seen since the announcement of the levy, yet the pattern of reactions was not predictable.29 Furthermore, change is continuing, accompanied by extensive marketing,30 indicating that the industry is continually testing many strategies in a quest to find the “sweet spot”—a new equilibrium where they maintain profits, comply with the law, and satisfy customers, albeit with a different commercial offer.
The commercial food system has achieved continual economic growth through a range of actions: increased agricultural productivity reducing the cost of inputs; increased processing that simultaneously reduces the costs of production and distribution, lowers prices, and increases palatability and convenience of foods to consumers31; intensive and targeted marketing of foods with the greatest added value from processing32; and increased economies of scale, consolidation, and extension of markets across nations. Economies of scale have been achieved through acquisitions, mergers, vertical and horizontal integration across the supply chain, proliferation of multinational companies, and using low wage economies (fig 1 and table 1).11
Highly processed foods are palatable and satisfy human taste for salty and sweet foods.9 Despite their convenience, palatability, longer shelf life, improved food safety, endless choice, and affordability for consumers,33 highly processed foods are widely criticised for not contributing to a healthy diet.34 Aggressive marketing of such foods, often accompanied by health and nutrition claims (for example, “high in vitamins”) that can obscure potential harms, drives and distorts consumer demand.35 Processed foods thus present a dilemma for public health, food policy, and consumer choice.
Recent growth in the sales of processed food, especially soft drinks, in low and middle income countries has been extraordinarily rapid.36 In many countries, a small number of food companies and retailers hold substantial economic power, owing to their size and the collective efforts of their trade associations.37 This power translates into substantial political influence nationally and internationally.1 Where the profitability of such companies is reliant on high volume sales of processed foods, their influence is often in direct conflict with health and sustainability efforts. In such circumstances, profits usually come first, resulting in food governance and public health policy that does not adequately balance public and commercial interests.22 Critically, the commercial food system does not adequately account for external costs, such as the environmental effects of intensive farming and food processing, the social costs of relying on low wage economies, and the effect on health of overconsumption of foods high in unhealthy ingredients and low in healthy ingredients (fig 1 and table 1).37 Food prices are therefore often artificially low, particularly for less healthy foods and those that have greater cost to the environment.38
Healthier, more sustainable, yet commercially viable food systems
When a market generates artificially low prices that do not account for environmental, social, and health externalities, government intervention is necessary. Furthermore, while food companies pursue profits through sales of unhealthy foods, they will maintain efforts to ensure that the regulatory environment favours the status quo.39 In this case, governments will need to do more to limit the influence of companies on health policy—for example, through trade agreements, regulation of advertising, fiscal policies, mandating nutrition labelling and transparency on food ingredients, and, possibly, use of competition laws. Advocacy groups, health professionals, and consumers will need to do more to recognise and counter unacceptable commercial tactics and encourage greater transparency of policy making processes and decisions (table 1).
Commercial food companies can voluntarily shift their focus towards expanding the market for healthier and more sustainable foods, while reducing the availability of less healthy foods. This shift would require a significant will to change as well as technical and business model innovations within commercial food systems (fig 2). The challenges of incorporating a larger proportion of healthy ingredients into shelf stable foods are considerable, but companies that can successfully overcome them should attain significant competitive advantage.
Although the predominant economic model of the commercial food system is poorly aligned with social, health, and environmental goals, recognition of this challenge and an appetite for change are emerging. Much of this effort is peripheral, such as the development of corporate social responsibility initiatives, rather than involving change in core business models.
Small but growing movements are emerging, such as impact investing and alternative “social” business models.40 Some of these alternative models use full cost accounting based on the triple bottom line, which proportionally or equally weights profit, people (social good), and the planet (environment).41 These models also include community interest companies and “B corporation” certification, which requires companies to pursue public benefit in conjunction with profit.42 The drive for such social purpose generally focuses on social or environmental causes, such as workers’ rights and carbon reduction, and rarely on health. Thus certified B corporations can include companies that are famous for their environmental and social credentials but market unhealthy food products.42 If health externalities were included in B corporation certification criteria, this would offer a new lever for change.
Much of this pro-social commercial activity has been dismissed by critics as unenforceable, as green or health washing, or as failing to demonstrate a meaningful commitment by industry to reduce its untenably high external costs.43 As things stand, trends are in the wrong direction, with the highest profits globally coming from unhealthy, processed food.44 Increasing evidence shows, however, that companies that place more emphasis on social goals can outperform competitors over the long term,45 and that healthier foods are now driving sector innovation and growth. Indeed, there is some evidence that offering consumers healthier food has commercial potential, both in grocery retailing and for ready to eat takeaway or fast food (boxes 1 and 2). Whether this will also translate more widely into improved healthiness of food and associated sales remains to be seen.
Potential for healthier grocery retailing
Supermarkets range from small, local stores with thousands of product lines to mega stores with tens of thousands of products. The nature of the business and the possible changes at these different levels vary considerably. Much of the food available in supermarkets is highly processed and of poor nutritional quality.14 But, is all processed food bad? And, what evidence is there that manufacturers and supermarkets can produce and promote healthier alternatives? Although overall trends are worrying, they conceal a range of nutritional values; not all packaged foods are nutritionally poor. For example, 83% of “convenience foods” in Australia and New Zealand were eligible to carry health claims according to their nutrient profile.46 In a study in the UK, although the profile was poor overall, one fifth of ready meals available in supermarkets were low in fat, saturated fat, salt, and sugar, and two thirds of these were labelled as “healthier” ready meals.47
In response to consumer and government pressures, supermarkets have introduced policies to restrict less healthy foods and promote healthier food—for example, by limiting “junk foods” at checkouts.48 Supermarket retailers in the US have also indicated some interest in healthier food retailing, but their willingness is constrained by perceived consumer demand, product availability, and price points. Further constraints include the complex competitive arrangements whereby strategic placement of products in supermarkets is governed by “listing” or “slotting” fees and dominated by industry “category captains.”49
The Food Foundation is an independent UK think tank aiming to stimulate a healthier food system. Its flagship initiative, “Peas Please,” aims to reverse the decline in vegetable consumption in the UK by seeking company pledges to achieve goals that could increase consumption.50 Historically, compliance of food companies with voluntary pledges has been poor (eg, in the UK government’s public health responsibility deal),51 except for salt reduction during the early 2000s, which was a concerted effort by non-governmental organisations and government and seems likely to have resulted in health benefits.52 Voluntary actions by commercial food companies offer valuable publicity and opportunities for corporate social responsibility, but further evaluation is needed to understand better why some voluntary pledges affect population diet while others fail to deliver meaningful change.RETURN TO TEXT
Potential for healthier eating out
Eating out has increased considerably over recent decades.53 Food prepared out of the home tends to be less healthy than food prepared at home, and its consumption has been associated with higher energy, saturated fat, and salt intakes and excess body mass.5455 In the UK, more than a quarter of adults and one fifth of children eat out more than once a week, and one fifth of both adults and children eat takeaway meals at home once or more a week.56 With the ability to order online and continued expansion of the sector, these trends seem unlikely to be reversed in the short term. So, what scope is there for improving the nutritional quality of food eaten outside the home?
Research has focused mainly on the calorie content of food eaten outside the home. Recent papers in TheBMJ have illustrated this focus in the UK57 and six other middle and high income countries.58 A range of interventions has been proposed and evaluated.5960 Foremost among these have been interventions that mandate calorie labelling on menus or at point of sale to help consumers make informed choices.61
A potentially more powerful action with greater effects on the population is to stimulate reformulation within the sector.62 Structural interventions such as the promotion of smaller portion sizes using packaging or tableware,63 adaptations to food dispensers (such as salt shakers that deliver less salt) in takeaways,64 and levies on the price of less healthy foods in restaurants65 have also been shown to promote healthier purchases, consumption, or diets. A growing number of companies now combine the convenience of home delivery with providing all the ingredients needed to prepare healthier meals in recipe boxes. These boxes are limited in their reach and profitability but could be scaled up to have a greater effect on the health of the population, although their effects on the environment will need to be carefully assessed. All such interventions could, without too many problems, be led by industry without external regulation or, in the absence of action, could be subject to legislation.RETURN TO TEXT
Accompanying this emerging market for healthier food products is an increase in the financing and incentivising of healthy food ventures. For example, venture capital investment in early stage healthier start-up companies is increasing. Multinational companies are creating their own in-house venture capital arms to deploy early stage investments and are also taking part in later stage acquisitions of healthier food companies to generate greater innovation and growth. These trends could expand the market for healthier food, although there is no guarantee that brands will maintain their healthy credentials once acquired.66 Bolstered by shifting millennial consumer preferences towards healthier foods—in particular, in higher income groups67— multinational companies could continue to expand further into healthier offerings, leveraging their commercial expertise, economies of scale, robust supply chains, and distribution channels to ensure profitability. Whether, and how, these trends are harnessed to improve diet, especially for lower income consumers, may have substantial implications for the global food supply and population health.
To effect meaningful dietary change in populations requires structural and system-wide action. Some food company executives have stated that they prefer regulation to voluntary change as then all competitors must follow the same rules.68 Regulation in conjunction with commercial innovation and appropriate tax and incentive structures for unhealthy and healthy foods, respectively, supported by voluntary actions, could enable the commercial food system to move more rapidly towards supplying healthy foods.69 Such a change is likely to require a cultural adjustment, in which companies place similar weight on social, health, and environmental goals as they do on profits.
Implications for policy, practice, and research
Change within the food industry will depend on economic, regulatory, and political factors, shifting public attitudes, and willingness of corporations to accept this change. The pursuit of social, health, and environmental goals together with economic goals will also require cultural and organisational change within companies.70 Viewing the commercial food sector as a complex adaptive system helps us to understand how it may be shaped in the interests of population health and suggests ways to intervene.27 Possible interventions range from achieving a fundamental change in approach (most difficult but having the greatest effect) to changing system substructures (easier but less effective).71 The kinds of interventions proposed in the UK’s childhood obesity plan (eg, mandating calorie labelling and restricting price promotions for unhealthy foods)72 seek leverage at the substructural level and are thus relatively weak levers for system change, although they may act synergistically to be more powerful. Evaluation of multiple synergistic actions will add vital new evidence.
Governments will need to act as both catalyst and regulator.73 Catalytic activities include information brokerage, coordination, and mobilisation of resources. These activities need to be supported by accountability systems to better promote company valuation beyond profit , which in turn requires change in accounting practices and improved metrics for measuring social, health, and environmental impacts, which are currently being explored.74
Governments can help to develop metrics and incentivise or mandate their use—for example, through securities or corporate law. Examples of accountability systems include those developed by the Access to Nutrition Foundation, which assesses the progress of major food companies towards healthier and more transparent product portfolios.75 Another example is the INFORMAS initiative (International Network for Food and Obesity/Non-communicable Diseases Research, Monitoring and Action Support), which offers tools for governments and civil society to benchmark food environments globally.76 A global “framework convention on healthy and sustainable food systems” (using the model of the WHO Framework Convention on Tobacco Control),77 with which national governments would be required to comply, would provide a legal basis to drive action by all sectors and could powerfully underpin such tools.8
Achieving closer alignment between business and public health will require a major cultural shift.78 Coproducing solutions to public health challenges with businesses carries risks and also benefits. Creating “safe spaces” to negotiate and agree outcomes using strong governance frameworks will be important. This would be aided by a common language for these discussions, agreeing and setting clear expectations, building trust, and identifying opportunities for mutual learning.79 One stepping stone to this goal would be to develop a shared understanding of what a healthy, vibrant, and sustainable commercial food system looks like—namely, one that balances and optimises outcomes for the environment, people, and profit.80 The discussion started to generate UK government’s forthcoming national food strategy, which involves deliberative events with citizens,81 could provide such a template.82
To achieve such closer alignment of commercial and public health goals will require strong leadership from governments and international organisations. It will also require some bravery, humility, and willingness to change from both public health and commercial stakeholders. Progress is likely to be limited while the relation between public health and the commercial food system, and processed food companies in particular, remains adversarial and a huge imbalance of power exists. Governments need to recognise this imbalance of influence on the policy process and ensure a more appropriate balance of public and commercial interests in policy making that affects health.4 They then need urgently to drive change towards healthier commercial food systems to reverse costly global trends in non-communicable diseases and their disastrous consequences for intergenerational inequalities in diet and health.4 To achieve the pace of change in the food system needed to deal with syndemic climate and obesity emergencies will require commitment of the food industry to a new business model, in which unsustainable growth is replaced by commitments to long term business value, people, health, and the environment.38
Interdisciplinary research should have a pivotal role in setting the agenda for this change. Research is urgently needed to understand the potential of food systems to achieve change that aligns with population health and sustainability goals. Important unanswered questions are set out in table 1 together with key challenges. The food industry needs to contribute to such efforts, but it will be vital to ensure that, in doing so, conflicts of interest arising from its potential for commercial gain are managed. Frameworks to guide governance of interactions between researchers and commercial organisations are being developed.8384
Contributors and sources: MW conceived the idea for the article. All authors contributed to developing the arguments, researched the literature, helped to draft the manuscript, and approved the final version. MW is the guarantor. The article is based on our collective professional experience and a review of published material in the public domain. MW is grateful to Anna Taylor, chief executive of the Food Foundation, for extensive and insightful discussions about food system challenges and solutions. MW leads publicly funded research on food systems and public health at the University of Cambridge. EA holds a degree in sociology from Princeton and degrees in law from Harvard and Cambridge. She is presently a doctoral candidate in Health Policy and Management at Harvard Business School and Harvard Graduate School of Arts and Sciences examining how for-profit companies pursue social and economic goals simultaneously. DTF holds degrees in chemical and biomedical engineering, physiology, and biophysics. Through her various leadership roles, including as inaugural scientific director of the Canadian Institutes of Health Research’s Institute of Nutrition, Metabolism and Diabetes, she has developed an academic interest in public-private partnerships and systems approaches to complex problems. After a 15-year commercial career in the food industry, CH has worked to apply behavioural science to social problems with a focus on public health. Until 2018, CH headed Shift Design’s Healthy Food programme, harnessing the competitive dynamics of consumer markets to deliver pro-social outcomes, such as developing products and services that catalyse changes in existing food categories leading to better diets. He now works as an independent consultant. During 2019, he worked on projects to promote healthier nutrition with the Global Alliance for Improved Nutrition (GAIN), Guy's and St Thomas' Charity, Big Society Capital, and the London Borough of Southwark. With degrees in in economics, information systems, health informatics, and public health, GS undertakes research on policies for the prevention of obesity and related non-communicable diseases. GS co-founded INFORMAS,76 a global network of public interest non-government organisations and researchers that aims to monitor, evaluate, and support public and private sector actions to improve food environments and reduce obesity and non-communicable diseases. Research by RS has spanned the monetary value of health, macroeconomic modelling of health, and the political economy of trade and trade agreements. A substantial programme of work in recent years has involved links between agriculture, the environment, and health, and public health economics in the UK and globally.
Competing interests We have read and understood BMJ policy on declaration of interests and declare the following interests: MW is funded as a scientist in the Centre for Diet and Activity Research (CEDAR), MRC Epidemiology Unit, University of Cambridge. CEDAR is a UK clinical research collaboration, public health research centre of excellence, which received funding from the British Heart Foundation, Cancer Research UK, Economic and Social Research Council, Medical Research Council (MRC), National Institute of Health Research (NIHR), and Wellcome Trust. MW is also funded by NIHR as director of its public health research funding programme. MW, with RS, holds a research grant from NIHR to evaluate the UK soft drinks industry levy; a grant from the Canadian Institutes of Health Research to fund the International Food Policy Study; and has held a grant from MRC to develop consensus on the governance of relationships between public health scientists and the food industry. MW is an expert adviser to the Food Foundation and the House of Lords Committee on Food, Poverty Health and the Environment; and a member of the Obesity Health Alliance, Independent Obesity Strategy working group. Between 2008 and 2011, DTF received funds from government, non-profits and the private sector to organise three meetings on building trust to examine the epidemic of obesity. CH receives no income from the commercial sector. In the period 1990-2005, CH was employed, with Nestle and Mondelez, in various commercial roles in the UK and mainland Europe. Since 2005, CH has been studying childhood obesity in various positions across government and the charitable sector. GS reports grants from the Australian Research Council, the National Heart Foundation of Australia, and the National Health and Medical Research Council (Australia); and GS recently conducted a study to benchmark the nutrition related policies of major food and beverage companies in Australia. GS is a researcher involved in a NHMRC-funded trial of healthy supermarket interventions in partnership with IGA (supermarket retailer), City of Greater Bendigo and VicHealth.
Provenance and peer review: Commissioned; externally peer reviewed.
This article is one of a series commissioned by The BMJ. Open access fees for the series were funded by SwissRe, which had no input into the commissioning or peer review of the articles. The BMJ thanks the series advisers, Nita Forouhi and Dariush Mozaffarian, for valuable advice and guiding selection of topics in the series.
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