Attention included two areas: dietary fat and sugar. Early ecological studies and small, short term interventions, most prominently by Ancel Keys, Frederick Stare, and Mark Hegsted, contributed to the widespread belief that fat was a major contributor to heart disease.
At the same time, work by John Yudkin and others implicated excess sugar in coronary disease, hypertriglyceridemia, cancer, and dental caries. Ultimately, the emphasis on fat won scientific and policy acceptance, embodied in the US Senate committee report Dietary Goals for the United States, which recommended low fat, low cholesterol diets for all.
This was not without controversy: in , the US National Academy of Sciences Food and Nutrition Board reviewed the data and concluded that insufficient evidence existed to limit total fat, saturated fat, and dietary cholesterol across the population. Some interpret these controversies as evidence of industry influence, and others as natural disagreement and evolution of early science. Unfortunately, as subsequent research would establish, such reductionist models translated poorly to non-communicable diseases. In less wealthy countries, the main objectives of nutrition policy and recommendations during this period remained on increasing calories and selected micronutrients.
In many ways, foods became viewed as a delivery vehicle for essential nutrients and calories. Accordingly, agricultural science and technology emphasised production of low cost, shelf stable, and energy dense starchy staples such as wheat, rice, and corn, with corresponding breeding and processing to maximally extract and purify the starch. As in high income nations, these efforts were accompanied by fortification of staple foods 10 11 12 13 as well as food assistance programmes to promote survival and growth of infants and young children in vulnerable populations.
Other scientists supported the primary role of calorie insufficiency and believed that protein enriched formulas and foods should not replace breast milk.
5. Population nutrient intake goals for preventing diet-related chronic diseases
This conclusion influenced subsequent efforts to tackle malnutrition in developing countries. However, the earlier decades of uncertainty had fostered a multinational industry that continued to promote formula and baby foods in low income countries based on their protein content and nutrient fortification. In addition, nutrient supplementation strategies remained effective at preventing or treating endemic deficiency diseases.
Thus, despite the shift in scientific thinking to focus on economic development, substantial emphasis remained or even accelerated on providing sufficient calories, most often as starchy staples, plus vitamin fortification and supplementation. Accelerating economic development and modernisation of agricultural, food processing, and food formulation techniques continued to reduce single nutrient deficiency diseases globally.
Coronary mortality also began to fall in high income countries, but many other diet related chronic diseases were increasing, including obesity, type 2 diabetes, and several cancers. In response, nutrition science and policy guidelines in high income nations shifted to try to deal with chronic disease. Building on the Senate report, the Dietary Guidelines for Americans was one of the earliest such national guidelines. More importantly, these studies followed the deficiency disease model, largely considering isolated single nutrients. At the same time the global community prioritised action to eliminate hunger and micronutrient deficiency in lower income nations.
Major micronutrient targets during this period were iron, vitamin A, and iodine. Evidence was increasing that vitamin A supplements could prevent child mortality from infection, such as measles, as well as preventing night blindness and xerophthalmia. Based on these priorities, the UN, national governments, and other international groups adopted portfolios for preventing micronutrient deficiencies through supplementation and fortification and integration of the growing relevant evidence.
Thus, in both lower and higher income nations, for partly overlapping reasons, a nutrient specific focus continued to shape both scientific inquiry and policy interventions. Among the most important scientific development of recent decades was the design and completion of multiple, complementary, large nutrition studies, including prospective observational cohorts, randomised clinical trials, and, more recently, genetic consortiums. Cohort studies provided, for the first time, individual level, multivariable adjusted findings on a range of nutrients, foods, and diet patterns and a diversity of health outcomes.
Clinical trials allowed further testing of specific questions in targeted, often high risk populations, in particular effects of isolated vitamin supplements and, more recently, specific diet patterns. Genetic consortiums provided important evidence on genetic influences on dietary choices, gene-diet interactions affecting disease risk factors and endpoints, and Mendelian randomisation studies of causal effects of nutritional biomarkers. These advances were not without controversy, in particular the general discordance of findings between cohort studies and those of supplement trials for specific vitamins on cardiovascular and cancer endpoints.
Others believed it showed the limitations of single nutrient approaches to chronic diseases as well as potentially reflecting the different methodological designs, with trials often focused on short term, supraphysiological doses of vitamin supplements in high risk patients, while observational studies often focused on habitual intake of vitamins from food in general populations.
In contrast to single nutrients, physiological intervention trials, large cohort studies, and randomised clinical trials provided more consistent evidence for diet patterns, such as low fat diets few significant effects or Mediterranean and similar food based patterns consistent benefits. Together, these advances suggested that single nutrient theories were inadequate to explain many effects of diet on non-communicable diseases.
This pushed the field beyond the RDA framework and other nutrient metrics designed to identify thresholds for nutrient deficiency diseases, and towards complex biological effects of foods and diet patterns.
Prospective cohorts and dietary intervention trials showed that a focus on total fat, a mainstay of dietary guidelines since , produced little measurable health benefit; conversely, nutrient based recommendations for specific foods such as eggs, red meats, and dairy products eg, based on dietary cholesterol, saturated fat, calcium belied the observed relations of these foods with health outcomes.
These recent scientific shifts help explain many uncertainties and controversies in nutrition today. After decades of focus on simple, reductionist metrics such as dietary fat, saturated fat, nutrient density, and energy density, the emerging true complexities of different foods and diet patterns create genuine challenges for understanding influences on health and wellbeing.
For several categories of foods, meaningful numbers of prospective observational or interventional studies have become available only recently. Many of these patterns have specific aims eg, general health, weight loss, anti-inflammation and are based on differing interpretations of current evidence.
In lower income countries, concerns about vitamin supplementation have emerged, such as harms associated with higher dose vitamin A supplements, risk of exacerbating infections such as malaria with iron, and safety concerns about folic acid fortification of flour, which might exacerbate neurological and cognitive deficits among people with low vitamin B 12 levels. These dual global burdens are increasingly found within the same nation, community, household, and even person. Yet, after decades of focus in the international nutrition community on vitamin supplements, food fortification, and starchy staples to provide calories, the necessary shift towards diet quality is slowed by considerable inertia.
This is seen, for example, in the reductionist, single nutrient focus of many of the UN sustainable development goals. Building on the evidence for multifaceted effects of different foods, processing methods, and diet patterns, 32 33 new priorities for research are emerging in nutrition science. These include optimal dietary composition to reduce weight gain and obesity; interactions between prebiotics and probiotics, fermented foods, and gut microbiota; effects of specific fatty acids, flavonoids, and other bioactives; personalised nutrition, especially for non-genetic lifestyle, sociocultural, and microbiome factors; and the powerful influences of place and social status on nutritional and disease disparities.
For lower income nations and populations, rigorous investigation is required to understand the optimal dietary patterns to jointly tackle maternal health, child development, infection risk, and non-communicable diseases. Our understanding of diet related biological pathways will continue to expand fig 1 , 33 57 61 highlighting the limitations of using single surrogate outcomes to determine the full health effects of any dietary factor.
In addition, future conclusions about diets and health should be based on complementary evidence from controlled interventions of multiple surrogate endpoints, mechanistic studies, prospective observational studies, and, when available, clinical trials of disease outcomes. Given the large and continuing global rise in agribusiness and manufactured foods, nutrition science must keep pace with and systematically assess the long term health effects of new food technologies.
Relatively little rigorous evaluation has been done on potential long term health consequences of modern shifts in agricultural practices, livestock feeding, crop breeding, and food processing methods such as grain milling and processing; plant oil extraction, deodorisation, and interesterification; dairy fat homogenisation; and use of emulsifiers and thickeners.
Modern Nutrition in Health and Disease
Additional complexity may arise in nutritional recommendations for general wellbeing versus treatment of specific conditions. For example, dietary recommendations for treating obesity are now particularly controversial. These long term effects will be especially relevant as anti-obesity efforts shift from secondary prevention weight loss in people with obesity towards primary prevention avoidance of long term weight gain in populations.
Recognition of complexity is a key lesson of the past. This is common in scientific progress whether in nutrition, clinical medicine, physics, political science, or economics: initial observations lead to reasonable, simplified theories that achieve certain practical benefits, which are then inevitably advanced by new knowledge and recognition of ever-increasing complexity. Like nutrition science, policy needs to move from simplistic reductionist strategies to multifaceted approaches.
Nutrition policy to reduce non-communicable diseases has so far generally relied on consumer knowledge—simply inform the public through education, dietary guidelines, product nutrition labels, etc, and people will make better choices. However, it is now clear that knowledge alone has relatively limited effects on behaviour, and that broader systems, policy, and environmental strategies are needed for effective change. Compounding these challenges, many current strategies remain focused on reductionist constructs such as total fat or total saturated fat, 41 68 overlooking the importance of food type and quality, processing methods, and diet patterns.
Another example of policy lag involves energy balance. Policy makers continue to promote total calorie labelling laws for menus and packaging and other calorie reduction policies, rather than aiming to increase calories from healthy foods and reduce calories from unhealthy foods.
The public is understandably bewildered by these evolving dietary messages. Public uncertainty is amplified by competing nutritional messages from varied media sources, online and social networks, cultural thought leaders, and commercial outlets, whose messages vary depending on underlying goals, expertise, perspectives, and competing interests. Although reductionist policies may have some value to reduce specific additives—eg, trans fats, sodium, added sugar—whole food based policies will be crucial to fully address diet related illnesses.
Most policy innovation has focused on sugar sweetened drinks, following the model of the WHO Framework Convention on Tobacco Control: tax, restrict places of sale, restrict marketing, use warning labels. This construct breaks down for incentivising consumption of healthy foods. Integrated policy, investment, and cultural strategies are needed to create change in food production and manufacturing, worksites, schools, healthcare systems, quality standards and labelling, food assistance programmes, research and innovation, and public-private partnerships.
To be effective, future nutrition policy must unite modern scientific advances on dietary priorities specific foods, processing methods, additives, diet patterns with trusted communication to the public and modern evidence on effective systems level change.
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This includes a shift from the global medicalisation of health towards addressing the interconnected personal, community, sociocultural, national, and global determinants of food environments and choices. This will require substantially more funding for research, both from government sources and through appropriately fashioned, transparent public-private partnerships.
Modern nutrition science is young: It is less than one century since the first vitamin was isolated in The first half of the 20th century focused on the discovery, isolation, and synthesis of essential micronutrients and their role in deficiency diseases. This reductionist approach was extended to address the rise in diet related non-communicable diseases—eg, focusing on total fat, saturated fat, or sugar rather than overall diet quality. Recent advances in nutrition science have shown that foods and diet patterns, rather than nutrient focused metrics, explain many effects of diet on non-communicable disease.
Nutrition policy should prioritise food based dietary targets, public communication of trusted science, and integrated policy, investment, and cultural strategies to create systems level change across multiple organisations and environments. Contributors and sources: All three authors have widely studied, reported on, and served in policy advisory roles on nutrition and health issues. DM had the idea for the article and drafted it with IR. All authors contributed to revising the draft and approved the final version.
The authors selected the literature for inclusion in this manuscript based on their own expertise and knowledge, discussions with colleagues, and editorial and reviewer comments. The funders had no role in the design or conduct of the study; collection, management, analysis, or interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication. This article is one of a series commissioned by The BMJ.
Open access fees for the series were funded by Swiss Re, which had no input into the commissioning or peer review of the articles. Skip to main content. Food for thought Click here to read other articles in this collection.