American journal of clinical nutrition

     
tinycollege.edu.vn 2018; 361 doi: https://doi.org/10.1136/tinycollege.edu.vn.k2392 (Published 13 June 2018) Cite this as: tinycollege.edu.vn 2018;361:k2392
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A timeline of nutrition retìm kiếm, from the era of vitamin discovery in the early 20th Century, through current research on complex effects of dietary patterns, and onwards to lớn the future possibilities for nutrition research và public health implementation


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Food for thought

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Dariush Mozaffarian và colleagues describe how the history of modern nutrition science has shaped current thinking


Although food và nutrition have been studied for centuries, modern nutritional science is surprisingly young. The first vitamin was isolated & chemically defined in 1926, less than 100 years ago, ushering in a half century of discovery focused on single nutrient deficiency diseases. Retìm kiếm on the role of nutrition in complex non-communicable chronic diseases, such as cardiovascular disease, diabetes, obesity, & cancers, is even more recent, accelerating over the past two or three decades & especially after 2000.

Historical summaries of nutrition science have sầu been published, focusing on dietary guidelines, general scientific advances, or particular nutritional therapies.1234 Carl Sagan said, “You have khổng lồ know the past khổng lồ understvà the present;” và Martin Luther King, Jr, “We are not makers of history. We are made by history.” This article describes key historical events in modern nutrition science that form the basis of our current understanding of diet và health và clarify contemporary priorities, new trends, & controversies in nutrition science and policy.


1910s lớn 1950s: era of vitamin discovery

The first half of the 20th century witnessed the identification và synthesis of many of the known essential vitamins and minerals và their use to lớn prsự kiện and treat nutritional deficiency related diseases including scurvy, beriberi, pellagra, rickets, xerophthalmia, & nutritional anaemias. Casimir Funk in 1913 came up with idea of a “vital amine” in food, originating from the observation that the hulk of unprocessed rice protected chickens against a beriberi-like condition.5 This “vital amine” or Vi-Ta-Min was first isolated in 1926 & named thiamine, and subsequently synthesised in 1936 as Vi-Ta-Min B1. In 1932, Vi-Ta-Min C was isolated và definitively documented, for the first time, to lớn protect against scurvy,6 some 200 years after ship’s surgeon James Lind tested lemons for treating scurvy in sailors.7

By the mid-20th century all major vitamins had been isolated and synthesised (fig 1). Their identification in animal and human studies proved the nutritional basis of serious deficiency diseases và initially led lớn dietary strategies khổng lồ tackle beriberi (vitamin B1), pellagra (vitamin B3), scurvy (Vi-Ta-Min C), pernicious anaemia (vitamin B12), rickets (vitamin D), & other deficiency conditions. However, the chemical synthesis of vitamins quickly led to food based strategies being supplanted by treatment with individual Vi-Ta-Min supplements. This presaged modern day use and kinh doanh of individual & bundled multivitamins to lớn guard against deficiency, launching an entire Vi-Ta-Min supplement industry.


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This new science of single nutrient deficiency diseases also led to lớn fortification of selected staple foods with micronutrients, such as iodine in salt and niacin (vitamin B3) and iron in wheat flour and bread.8910 These approaches proved khổng lồ be effective sầu at reducing the prevalence of many comtháng deficiency diseases, including goitre (iodine), xerophthalmia (vitamin A), rickets (vitamin D), và anaemia (iron). Foods around the world have sầu since been fortified with calcium, phosphorus, iron, and specific vitamins (A, B, C, D), depending on the composition of local staple foods.10111213

As one of the great accidents of nutrition history, this new science and focus on single nutrients và their deficiencies coincided with the Great Depression và second world war, a time of widespread fear of food shortages. This led lớn even further emphasis on preventing deficiency diseases. For example, the first recommended dietary allowances (RDAs) were a direct result of these concerns, when the League of Nations, British Medical Association, and the US government separately commissioned scientists to generate new minimum dietary requirements to lớn be prepared for war.14 In 1941, these first RDAs were announced at the National Nutrition Conference on Defence, providing new guidelines for total calories and selected nutrients including protein, calcium, phosphorus, iron, và specific vitamins.15 These historical events established a precedent for nutrition research & policy recommendations lớn focus on single nutrients linked lớn specific disease states.

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1950s khổng lồ 1970s: fat versus sugar và the protein gap

During the next đôi mươi to lớn 30 years, calorie malnutrition và specific Vi-Ta-Min deficiencies fell sharply in high income countries because of economic development và large increases in low cost processing of staple foods fortified with minerals và vitamins. At the same time, the rising burdens of diet related non-communicable diseases began khổng lồ be recognised, leading to new research directions. Attention included two areas: dietary fat & sugar.16171819

Early ecological studies & small, short term interventions, most prominently by Ancel Keys, Frederiông xã 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 và others implicated excess sugar in coronary disease, hypertriglyceridemia, cancer, and dental caries. Ultimately, the emphasis on fat won scientific & policy acceptance, embodied in the 1977 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 1980, the US National Academy of Sciences Food and Nutrition Board reviewed the data & concluded that insufficient evidence existed lớn limit total fat, saturated fat, & dietary cholesterol across the population.20

Some interpret these controversies as evidence of industry influence, và others as natural disagreement & evolution of early science.16171819 More relevant is that both the dietary fat và sugar theories relied on a nutritional Model developed lớn address deficiency diseases: identify & isolate the single relevant nutrient, assess its isolated physiological effect, và quantify its optimal intake màn chơi to prsự kiện disease. Unfortunately, as subsequent research would establish, such reductionist models translated poorly khổng lồ non-communicable diseases.

In less wealthy countries, the main objectives of nutrition policy & recommendations during this period remained on increasing calories and selected micronutrients. In many ways, foods became viewed as a delivery vehicle for essential nutrients và calories. Accordingly, agricultural science và technology emphasised production of low cost, shelf stable, and energy dense starchy staples such as wheat, rice, and corn, with corresponding breeding và processing to lớn maximally extract và purify the starch. As in high income nations, these efforts were accompanied by fortification of staple foods10111213 as well as food assistance programmes lớn promote survival and growth of infants & young children in vulnerable populations.

Scientists focused on malnutrition disagreed on the relative sầu role of total calories & protein in infant và child diseases such as marasmus và kwashiorkor—also termed “the protein-calorie deficiency diseases.”2122 Support for the “protein gap” concept led to lớn extensive sầu industrial development of protein enriched formulas and complementary foods for developing countries. Other scientists supported the primary role of calorie insufficiency và believed that protein enriched formulas & foods should not replace breast milk. As one prominent scientist wrote in 1966, “Millions of dollars và years of effort… into developing these foods would have been better spent on efforts to lớn preserve the practice of breast feeding... being abandoned everywhere.”22

The debate essentially ended when in 1975 leading scientists in the US và London independently concluded from the scientific evidence that a laông xã of food was the main problem:22 “The concept of a worldwide protein gap… is no longer tenable… the problem is mainly one of quantity rather than chất lượng of food.”23

This conclusion influenced subsequent efforts lớn tackle malnutrition in developing countries. For example, a formal UK advisory committee on international nutrition aid recommended that, “the primary attack on malnutrition should be through the alleviation of poverty… aid should be directed to lớn projects that will generate income among mỏi the poor, even where such projects vày not have sầu any marked effect on the national income of the country concerned.”22

However, the earlier decades of uncertainty had fostered a multinational industry that continued to lớn promote formula and baby foods in low income countries based on their protein nội dung và nutrient fortification. In addition, nutrient supplementation strategies remained effective sầu at preventing or treating endemic deficiency diseases. Thus, despite the shift in scientific thinking lớn focus on economic development, substantial emphasis remained or even accelerated on providing sufficient calories, most often as starchy staples, plus vitamin fortification và supplementation.


1970s to lớn 1990s: diet related chronic diseases & supplementation

Accelerating economic development & modernisation of agricultural, food processing, và food formulation techniques continued lớn 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, & several cancers.

In response, nutrition science và policy guidelines in high income nations shifted lớn try khổng lồ giảm giá khuyến mãi with chronic disease. Building on the 1977 Senate report, the 1980 Dietary Guidelines for Americans was one of the earliest such national guidelines.24 Many of the available data were derived from less robust types of evidence, such as from crude cross-country (ecological) comparisons và short term experiments using surrogate outcomes, mostly in healthy middle aged men. More importantly, these studies followed the deficiency disease Mã Sản Phẩm, largely considering isolated single nutrients. Accordingly, the 1980 dietary guidelines remained heavily nutrient focused: “avoid too much fat, saturated fat, và cholesterol; eat foods with adequate starch and fiber; avoid too much sugar; avoid too much sodium.”24 International guidelines were similarly nutrient focused.25 This led khổng lồ a proliferation of industrially crafted food products low in fat, saturated fat, và cholesterol & fortified with micronutrients, as well as expansion of other nutrient focused technologies lớn reduce saturated fat such as partial hydrogenation of vegetable oils.

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At the same time the global community prioritised action to eliminate hunger & micronutrient deficiency in lower income nations. Major micronutrient targets during this period were iron, vitamin A, and iodine. Evidence was increasing that Vi-Ta-Min A supplements could prsự kiện child mortality from infection, such as measles, as well as preventing night blindness và xerophthalmia.26 Field trials provided a basis for WHO recommendations for widespread micronutrient supplementation, especially during pregnancy, with iron and vitamin A, and for fortification of salt with iodine khổng lồ prevent goitre & developmental abnormalities such as congenital hypothyroidism và hearing loss.

Based on these priorities, the UN, national governments, & other international groups adopted portfolios for preventing micronutrient deficiencies through supplementation and fortification and integration of the growing relevant evidence. Scientific investigations further focused on other environmental factors that may interact with micronutrients and dietary protein, such as infection và related poor sanitation, leading khổng lồ concepts such as subclinical enteritis or malabsorption called first “tropical enteritis,” then “environmental enteropathy,” và currently “environmental enteric dysfunction.”272829

Thus, in both lower and higher income nations, for partly overlapping reasons, a nutrient specific focus continued to lớn shape both scientific inquiry & policy interventions.


1990s lớn the present: evidence debates, diet patterns, the double burden

Ahy vọng the most important scientific development of recent decades was the thiết kế và completion of multiple, complementary, large nutrition studies, including prospective sầu observational cohorts, randomised clinical trials, và, more recently, genetic consortiums. Cohort studies provided, for the first time, individual level, multivariable adjusted findings on a range of nutrients, foods, và diet patterns & 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 và those of supplement trials for specific vitamins on cardiovascular and cancer endpoints.3031 Some experts interpreted the discordance as evidence for irredeemable shortcomings of observational studies (inherent residual confounding). Others believed it showed the limitations of single nutrient approaches khổng lồ chronic diseases as well as potentially reflecting the different methodological designs, with trials often focused on short term, supraphysiological doses of Vi-Ta-Min supplements in high risk patients, while observational studies often focused on habitual intake of vitamins from food in general populations.

In contrast to lớn 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 và similar food based patterns (consistent benefits).3233 This concordance was supported by advances in retìm kiếm methods và better understanding of the complementary strengths of different study designs.343536373839

Together, these advances suggested that single nutrient theories were inadequate lớn explain many effects of diet on non-communicable diseases. This pushed the field beyond the RDA framework và other nutrient metrics designed to lớn identify thresholds for nutrient deficiency diseases, và towards complex biological effects of foods & diet patterns.4041424344 Such factors were increasingly seen to lớn reflect joint contributions và interactions between carbohydrate unique (eg, glycaemic index, fibre content), fatty acid profiles, protein types, micronutrients, phytochemicals, food structure, preparation và processing methods, and additives.

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Prospective sầu cohorts và dietary intervention trials showed that a focus on total fat, a mainstay of dietary guidelines since 1980, produced little measurable health benefit; conversely, nutrient based recommendations for specific foods such as eggs, red meats, & dairy products (eg, based on dietary cholesterol, saturated fat, calcium) belied the observed relations of these foods with health outcomes.3233 For weight loss và glycaemic control, decades of emphasis on low fat diets were questioned by the results of a series of prospective cohort studies, metabolic feeding studies, and randomised trials, which showed that foods rich in healthy fats produced benefit, while foods rich in starch and sugar caused harm.33454647 This progress was extended lớn recognition of the relevance of diet patterns such as traditional Mediterranean or vegetarian diets that emphasised minimally processed foods such as fruits, vegetables, nuts, beans, whole grains, and plant oils và low amounts of highly processed foods rich in starch, sugar, salternative text, and additives.3233

These recent scientific shifts help explain many uncertainties & controversies in nutrition today. After decades of focus on simple, reductionist metrics such as dietary fat, saturated fat, nutrient density, và energy density, the emerging true complexities of different foods & diet patterns create genuine challenges for understanding influences on health and wellbeing. For several categories of foods, meaningful numbers of prospective sầu observational or interventional studies have become available only recently.3338 Growing realisation of the importance of overall diet patterns has stimulated not only scientific inquiry but also a deluge of empirical, commercial, and popular dietary patterns of varying origin and scientific backing.48 These range, for example, from flexitarian, vegetarian, và vegan lớn low carb, paleo, & gluten-không tính phí. Many of these patterns have specific aims (eg, general health, weight loss, anti-inflammation) & are based on differing interpretations of current evidence.

In lower income countries, concerns about Vi-Ta-Min supplementation have sầu emerged, such as harms associated with higher dose Vi-Ta-Min A supplements, risk of exacerbating infections such as malaria with iron, and safety concerns about folic acid fortification of flour, which might exacerbate neurological và cognitive sầu deficits ahy vọng people with low vitamin B12 levels.49505152 In addition, a precipitous rise in non-communicable diseases in these countries has led to lớn new focus on the “double burden”—both conventionally conceived malnutrition (insufficient calories and micronutrients) leading lớn poor maternal and child health & modern malnutrition (poor diet quality) leading to obesity, type 2 diabetes, cardiovascular diseases, và cancer. These dual global burdens are increasingly found within the same nation, community, household, and even person.535455

Yet, after decades of focus in the international nutrition community on vitamin supplements, food fortification, và starchy staples to provide calories, the necessary shift towards diet unique is slowed by considerable inertia. This is seen, for example, in the reductionist, single nutrient focus of many of the UN sustainable development goals. Even when non-communicable diseases are considered, the predominant focus is on obesity rather than the diverse risk pathways & conditions affected by nutrition—facilitating a misleading concept of “overnutrition” rather than unhealthy dietary composition as the root problem.55


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