Diet and disease

The Global Burden of Disease analysis estimates that poor diet is responsible for approximately 11 million deaths and 255 million disability-adjusted life years annually around the world⁽¹⁾. Both over- and undernutrition are common. In many countries, diets are too low in fruits, vegetables and wholegrain and too high in fats, sugars and Na leading to higher rates of overweight and obesity. Rising rates of obesity over the past 3–4 decades have contributed to increased risk of common non-communicable diseases that are the major causes of morbidity and mortality globally including type 2 diabetes mellitus (T2DM), CVD, some cancers and mental health issues⁽²⁾. In 2021, the WHO declared that over 1·9 billion people aged 18+ years were overweight with 650 million of these being obese⁽³⁾. In the WHO European Region, overweight and obesity affect almost 60 % of adults. In higher income countries, overweight and obesity are more common among less-advantaged sections of the community. However, in contrast, in most countries of sub-Saharan Africa, obesity prevalence increases with wealth^{(Reference Yaya, Anjorin and Okolie4)} and therefore requires different approaches. The rise in childhood obesity is of particular concern as it increases the risk of adulthood obesity^{(Reference Ward, Long and Resch5)}, cardio-metabolic diseases and premature mortality. Nearly one in three children (29 % of boys and 27 % of girls) in the WHO European Region are overweight or obese⁽⁶⁾ although there are huge variations by country.

Related to high obesity rates is the concomitant high rate of T2DM in many countries. In 2021, 537 million people were living with any type of diabetes, estimated to be one-in-ten people aged 20–79 years, and similar numbers were living with impaired glucose tolerance⁽⁷⁾. This prevalence varies substantially by ethnicity^{(Reference Goff8)} with high prevalence in South Asians^{(Reference Sattar, Welsh and Leslie9)}. The increase in prevalence of T2DM is mainly due to populations gaining weight, at younger ages. T2DM is a nutritional disease of fat storage and just one of many chronic disease outcomes which commonly coexist as ‘multi-morbidity’. Its disabling, painful, life-shortening complications (in increasingly younger populations) now dominate many healthcare budgets as highly expensive drugs are prescribed to try to modify complications^{(Reference Hex, Bartlett and Wright10)}.

Hidden hunger, which refers to micronutrient deficiencies, is also common and may be present with or without a deficit in total energy intake and is therefore present in both over- and undernutrition. Micronutrient deficiencies affect growth as well as physical and cognitive development in children, and impaired immune function in adults, leading to increased morbidity and susceptibility to communicable as well as non-communicable diseases^{(Reference Hawkes, Ruel and Salm11,Reference Calder12)} .

Specific micronutrients have well-known antioxidant and immunomodulatory properties and specific deficiencies in vitamins A, B₁₂, C, D, E, folic acid, and minerals including Fe, Zn, Se, Mg and Cu can lead to immune dysfunction and increased susceptibility to microbial infections^{(Reference Gombart, Pierre and Maggini13)}. In addition, metabolites of n-3 fatty acids play an important role in immune function based on their anti-inflammatory properties^{(Reference Calder12,Reference Maggini, Pierre and Calder14)} . The COVID-19 pandemic has further highlighted the importance of good nutrition for health in relation to communicable diseases identifying inflammation, hyperglycaemia, hyperlipidaemia, obesity and chronic disease as risk factors for more serious infection, more invasive procedures and a higher mortality rate in patients^{(Reference Sawadogo, Tsegaye and Gizaw15)}, and these outcomes may be independently predicted by malnutrition^{(Reference Vong, Yanek and Wang16)}. Research is ongoing into specific nutrients and COVID-19. Immune-boosting properties of vitamins C, D, E, Zn, Se and n-3 fatty acids^{(Reference Shakoor, Feehan and Al Dhaheri17)} and healthy diet patterns such as the Mediterranean diet^{(Reference Mirzay-Razaz, Hassanghomi and Ajami18)} could provide possible benefits to patients with COVID-19, particularly in elderly people, but results are inconsistent. A review of the evidence by the UK Scientific Advisory Committee on Nutrition (SACN) supports following a balanced diet and complying with dietary recommendations to achieve optimal immune function, but not the intake of any specific nutrients, including vitamin D, above current recommendations⁽¹⁹⁾. More research is needed to better understand the clinical importance of diet and micronutrient supplementations in prevention and management of SARS-CoV-2 patients^{(Reference Diyya and Thomas20,Reference Beran, Mhanna and Srour21)} .

Global action to improve diet and health

WHO and the World Cancer Research Fund (WCRF) have both recommended actions to improve dietary behaviour. The EAT-Lancet report^{(Reference Willett, Rockstrom and Loken22)} took into account planetary boundaries as well as health-related factors and strongly recommended improvements to the food system in order to optimise diet and planetary health, to feed 10 billion people sustainably while saving an estimated 11 million lives per year. WHO have put forward the best value (in health economic terms) national policies for countries to follow named ‘best buys’, which include taxes on sugary drinks and reformulation to eliminate trans fats⁽²³⁾, while the changing behaviour framework from WCRF for healthy populations recommends a range of actions from education to labelling, fiscal policies, marketing and food supply⁽²⁴⁾. However, these policies generally are not implemented well enough^{(Reference Allen, Wigley and Holmer25)}.

For population-scale interventions to improve undernutrition, fortification and bio-fortification offer the most practical solutions. Fortification of salt with iodine has been a global success story in terms of international reach and the global impact on iodine deficiency disorders^{(Reference Zimmermann and Andersson26)}. However, effective national or regional monitoring of the fortification process is needed to ensure that the target level of added micronutrient in the food product is consistently achieved. Bio-fortification involves the enhancement of the nutrient content of the staple crops through traditional selective breeding techniques, genetic modification and/or agronomic methods such as the application of micronutrient fertilisers. It has the potential to be sustainable and highly cost effective because the high nutrient varieties can be released to farmers, replacing standard varieties over time, and thus raising the micronutrient intakes of the population. Some success has already been demonstrated around the world, for example, the release of vitamin A-rich maize in Zimbabwe, Fe-rich beans in Uganda and Zn-rich wheat and rice in Bangladesh⁽²⁷⁾.

Further challenges relate to evaluation of intervention programmes. Fe is a ‘type 1’ nutrient, meaning that a deficiency results in specific, measurable biochemical and metabolic consequences. As such, the diagnostic criteria for Fe deficiency (and similarly for iodine) are well defined and provide a robust indicator of an individual’s Fe (or iodine) status^{(Reference Lynch, Pfeiffer and Georgieff28)}. In contrast, Zn is a type 2 nutrient, meaning that the consequences of deficiency are general and non-specific, making diagnosis challenging^{(Reference King, Brown and Gibson29)}. The identification of novel, sensitive biomarkers of Zn status is a research priority, and recent studies suggest that blood fatty acid ratios^{(Reference Massih, Hall and Suh30)} and indices of oxidative stress, such as DNA damage^{(Reference Zyba, Shenvi and Killilea31)}, may be responsive to small changes in dietary Zn intake.

Despite extensive recommendations and action from global organisations such as WHO and the FAO of the United Nations, countries struggle to optimise dietary behaviour. Sadly, global malnutrition is on the rise due to conflict and climate change⁽³²⁾, despite the United Nations (UN) decade of action for nutrition (2016–2025), and the drive to meet the UN sustainable development goal for zero hunger⁽³³⁾. The current situation in Türkiye and learnings from approaches in the UK and Finland are discussed in the next sections.

The current status of nutrition and health in Türkiye

In common with many countries, Türkiye is focused on improving the health and nutritional status of its population. Türkiye is suffering a larger burden of disease than most countries in Europe in terms of T2DM⁽⁷⁾ and obesity⁽⁶⁾, and major causes of death are CVD and lung cancer⁽³⁴⁾. Furthermore, the population is younger than elsewhere and therefore the burden is likely to increase in the future. TURDEP-I (1997–8) and TURDEP-II (2010) are two comprehensive population-based field surveys conducted by Istanbul University in collaboration with the Ministry of Health and under the monitoring of WHO in the same 540 centres throughout Türkiye and providing key information on diet and health^{(Reference Satman, Yilmaz and Sengül35,Reference Satman, Omer and Tutuncu36)} . In addition, in 2019 the Republic of Türkiye Ministry of Health published a comprehensive report on the Türkiye Nutrition and Health Survey undertaken in 2017, highlighting areas of concern⁽³⁷⁾. The key public health priorities in Türkiye are to reduce tobacco and alcohol use, to increase physical activity and to improve poor diets.

Obesity and diabetes in Türkiye

In 2016, Türkiye was ranked number one across the WHO European Region in terms of prevalence of overweight and obesity in adults⁽⁶⁾. The mean age standardised prevalence of combined overweight and obesity was 66·8 % of whom 32·1 % were obese⁽⁶⁾ (using data from the STEPS survey⁽³⁸⁾). The results from the 2017 Türkiye Nutrition and Health Survey using different age ranges reported that the frequency of individuals aged 15 years and over who were overweight was 35·6 % (males: 41·2 %; females:30·1 %), and the frequency of those who were obese was 28·8 % (males: 21·6 %; females: 35·9 %). The situation is worsening and a 44 % overall increase in obesity was observed between TURDEP-1 (1998) and TURDEP-II (2010)⁽³⁹⁾. Obesity is more common in young and middle-age women than in men. However, the rate of increase in obesity was higher in men than in women (107 % v. 34 %). The estimated obesity prevalence in the elderly (65+) is 36·8 % while 4·4 million children under 5 years old (7·9 %) are overweight or obese⁽⁶⁾.

High rates of obesity increase the risk of T2DM and Türkiye ranks first in Europe with a diabetes prevalence of 14·5 % and a diabetes population of over 9 million according to 2020 data⁽⁷⁾. Age-adjusted diabetes prevalence increased by 90 % from 6·6 % in 1998 to 14·1 % in 2010, with 44 % undiagnosed. According to TURDEP-II, in 2010 approximately 30 % of the adult Turkish population had some degree of pre-diabetes (impaired glucose tolerance and/or Impaired fasting glucose (IFG))^{(Reference Satman, Omer and Tutuncu36)}. These rates are likely to worsen with an ageing population, and the need for preventative action is urgent.

Nutrient deficiencies and dietary behaviour in Türkiye

Dietary intakes are currently not optimal for health in Türkiye with under- and overconsumption identified. Specific nutrient deficiencies include Fe deficiency anaemia which remains an important public health problem. All age groups but particularly preschool and school-age children, adolescents and pregnant and lactating women are at risk. Severe vitamin D deficiency (< 10 ng/ml) was found in 3·1 % of men and 12·7 % of women. Furthermore, according to the most recent data, 27·8 % of the population has iodine deficiency. Niacin and vitamin B₁₂ status is also low in sectors of the population⁽³⁷⁾.

Overconsumption of some nutrients is an issue as it is in many countries. Salt consumption is twice that recommended by the WHO⁽³⁷⁾ although it has significantly decreased. Mean intakes of saturated fats are also above recommended, and daily intakes have increased from 9·4 g in 2010 to 11·4 g in 2017⁽³⁷⁾. However, total sugar consumption decreased from 33·0 to 30·6 g in the same time period⁽³⁷⁾. Although Türkiye is one of those rare countries where the four seasons can be experienced simultaneously, consumption of fruits and vegetables is low⁽³⁷⁾. As elsewhere, food waste is also an issue at an estimated 18 million tonnes per annum according to one source⁽⁴⁰⁾. Future policy action must aim to improve nutrient density of the diet and not solely focus on reducing fats, sugars and salt.

Health literacy in Türkiye

A further concern in Türkiye is the low level of HL, that is, the ability to accurately interpret health information. Modern healthcare systems can be difficult to navigate especially for those who are disadvantaged, vulnerable and elderly. Recently, personal HL has been defined as the degree to which individuals have the ability to find, understand and use information and services to inform health-related decisions and actions for themselves and others^(41–43).

In 2014, a Health Literacy Survey devised by the European Union was translated into Turkish^{(Reference Sorensen and Ristolainen44)} and used to investigate the HL level of the adult population^{(Reference TANRIÖVER, YILDIRIM and READY42)}. The mean general HL index of the adult population was estimated as 30·4 over a scale of fifty points. It was determined that 64·6 % of the population fell into the ‘inadequate’ (24·5 %) or ‘problematic’ (40·1 %) HL category, which corresponded to almost 35 million adults. The level of HL was inversely correlated with age and directly correlated with educational level. Furthermore, higher use of healthcare services and a higher incidence of disease were associated with lower HL levels. According to the data, 43·5 % of those with inadequate HL level, 22·6 % of those with problematic HL, 19·7 % of those with adequate HL and only 13·5 % of those with excellent HL have a diagnosed disease.

Strategies to increase the HL in Türkiye should focus on improving the general literacy level of the population, empowering women and establishing a social structure which protects the vulnerable and disadvantaged people, and which attains socio-economic justice.

Actions to improve diet and health in Türkiye

Finland: an example of the power of interventions

In the 1960s, Finland, and especially North Karelia in the eastern part of the country, had the highest rate of cardiovascular mortality in the world. The decision was made to target the whole community to address whether risk factors and behaviours can be changed on a population level and if so, what happens to mortality rates. The North Karelia Project was started as a comprehensive preventive programme to reduce serum cholesterol levels, high blood pressure and smoking. The main aims related to diet were to reduce intake of saturated fats, mainly coming from dairy and meats, and replace them with polyunsaturated fats, as well as to reduce salt intake in the whole population^{(Reference Puska, Vartiainen and Nissinen68)}.

Based on established theoretical frameworks for behaviour modification, practical interventions were implemented which included improving knowledge and skills, incorporating social and environmental support and involving community organisations including lay opinion leaders, to promote health innovations in the community. Specific strategies were developed for schools and workplaces^{(Reference Puska, Vartiainen and Laatikainen69)}.

Cross-sectional population surveys were completed every 5 years starting in 1972. Results of the surveys indicated that saturated fats reduced from 20 % of energy intake to 12–14 % from 2007 to 2017 mainly by substitution with polyunsaturated fats^{(Reference Vartiainen, Laatikainen and Tapanainen70)}. Salt intake was reduced from 14 g to 9 g in men and from 11 g to 7 g in women. There was a substantial shift in the concept of what constitutes a healthy diet and smoking also declined from 52 % to 25 % in men.

Both risk factors and health outcomes improved substantially. Between 1972 and 2012, serum cholesterol was reduced from 6·9 mmol/l to 5·5 mmol/l (21 %) in men and from 6·8 mmol/l to 5·4 mmol/l (21 %) in women. Adults were invited once per year to have their blood pressure taken and get advice. Systolic blood pressure reduced from 148 mmHg to 135 mmHg in men and from 153 mmHg to 129 mmHg in women. Premature cardiovascular mortality in men declined by 84 %. After the 1980s, improvement in treatment explained a significant part of the decline^{(Reference Jousilahti, Laatikainen and Peltonen71)}. Many activities were expanded to the rest of the country. The only factor that is worsening is obesity; mean BMI has increased since 1972.

The medical community reached consensus on the role of dietary fats on serum cholesterol and CHD. Political consensus was achieved, and the Finnish Parliament agreed a health policy statement where prevention was key. After that agriculture policy and legislation were developed to support a healthy diet, with farmers encouraged to change from dairy products to berry and rapeseed oil production. Animal feed was also improved to reduce the saturated fat in milk.

The changes in policy also provided an incentive for the food industry to develop healthier products such as transferring to rapeseed oil to reduce trans fats in baked goods. Plant stanol esters, which can lower cholesterol, were incorporated into spreads as a replacement for butter and the use of rapeseed oil for cooking increased. The project continues through the implementation of innovative approaches including village competitions and reality TV programmes.

In conclusion, improved health by dietary changes is feasible at a population level but requires active work and large-scale cooperation between all meaningful sectors in society sustained over long periods of time.

The current status of nutrition and health in the UK

Prevalence of excess weight has increased over the last three decades: in England approximately 28 % children aged 4–5 years are living with overweight or obesity increasing to 41 % by aged 10–11 years⁽⁷²⁾ which worsened during the COVID-19 pandemic. In England, deprivation and obesity are strongly associated^(73,74) ; however, failure to meet dietary recommendations is seen across all income groups. UK diets generally do not meet evidence-based recommendations as depicted in the Eatwell guide⁽⁷⁵⁾ and are high in saturated fat and free sugars and low in fruit and vegetables, fibre and oily fish^{(76,Reference Scheelbeek, Green and Papier77)} . Average energy intakes exceed those for a healthy body weight for adults by an estimated 300–1200 kJ/d (70–300 kcal), for adults living with overweight and obesity by an estimated 1000–1800 kJ/d (250–400 kcal), for children by an estimated 84–418 kJ/d (20–100 kcal) and for children living with overweight and obesity by an estimated 586–2092 kJ/d (140–500 kcal)⁽⁷⁸⁾.

UK policies and strategies to improve diet and health

Tackling obesity has remained on the UK’s health agenda for three decades and involves many organisations in the four regions of the UK (health is devolved to the four regions of England, Scotland, Wales and Northern Ireland in the UK). In England, it includes Office for Health Improvement and Disparities (formerly part of Public Health England) based in the Department of Health and Social Care, community-based health services and charities.

The UK SACN established in 2000⁽⁷⁹⁾ provides independent scientific evidence-based advice to UK government organisations including Office for Health Improvement and Disparities in England, the Food Standards Agency in Scotland and health agencies in Wales and Northern Ireland, on nutrition and related health matters. Suggestions for nutrition priorities for risk assessment come from a variety of sources, including new evidence on possible diet–health interactions, requests from government ministers, UK Health Departments, Non-Government Organisations, Industry and SACN members. SACN must also respond to unexpected nutritional issues of concern, a recent example of which is the COVID-19 pandemic. SACN’s terms of reference include: (i) nutrient content of individual foods, and diet as a whole, and the nutritional status of people; (ii) how nutritional status of people in the UK may be monitored; (iii) nutritional issues which affect wider public health policy issues; (iv) nutrition of vulnerable groups and health inequality issues and (v) research requirements for these areas.

SACN publishes reports (https://www.gov.UK/government/groups/scientific-advisory-committee-on-nutrition) which have led to the formation of numerous Government policies on nutrition. For example, in 2015 these include the redefinition and new dietary reference values for dietary fibre (30 g/d) and free sugars (< 5 % total energy per day)⁽⁸⁰⁾, establishing dietary reference values for the intake of vitamin D (10 μg/d or 400 μg/d) for the general population aged 4 years and older in 2016⁽⁸¹⁾, and saturated fat (less than 10 % total energy/d), with guidance for its replacement with unsaturated fats for those 5 years and older in 2019⁽⁸²⁾. In 2017, SACN recommended mandatory fortification of flour with folic acid to reduce the risk of neural tube defects in babies⁽⁸³ ) but this has yet to be implemented. Data from the cross-sectional National Diet and Nutrition Survey rolling programme are used by SACN to identify dietary intake and nutritional status of a representative UK population and to model and develop new dietary recommendations.

New dietary recommendations by SACN are considered and acted upon by government departments leading on public health in the four devolved nations within the UK. Education and health promotion has been a central component of UK Government strategies to improve diet and reduce obesity. Campaigns promoting salt reduction⁽⁸⁴⁾ and sugar reduction⁽⁸⁵⁾, increasing fruit, vegetable and fibre consumption through ‘5-a-day’⁽⁸⁶⁾ and front-of-pack ‘traffic light’ labelling⁽⁸⁷⁾ have received significant investment and have focused on empowering the population to make healthier choices. Food and nutrition education for children in primary and secondary schools has formed part of the curriculum since 1990^{(Reference Owen-Jackson and Rutland88)} and adherence to standards for school food is mandatory in all four devolved nations of the UK (although the standards vary by region)⁽⁸⁹⁾.

While public health campaigns have achieved high levels of awareness and engagement, knowledge of a healthy diet is only one of many factors influencing food choices. The food environment has changed dramatically as obesity prevalence has increased. Less healthy foods, high in saturated fat, salt and sugar, are highly accessible and heavily marketed and promoted⁽⁹⁰⁾. In recent years, the marketing of food delivery apps has become ubiquitous, catalysing a rapid increase in fast-food delivery⁽⁹¹⁾. In the UK, similar food products brought from the out of home sector tend to contain more energy than those from retail^(92,93) .

Tackling obesity requires meaningful reductions in population energy purchases and intakes. Following the SACN report on carbohydrates and health⁽⁸⁰⁾, Public Health England recommended a broad, cohesive programme⁽⁹⁴⁾ to simultaneously reduce the sugar and energy content of foods and drinks, and the effect of environmental drivers of poor diets. Many of these were structural policies that aimed to improve dietary choices at a population level without requiring personal agency or behaviour change.

In 2016, the voluntary sugar reduction and reformulation programme⁽⁹⁵⁾ announced the ambition to reduce the sugar content of foods contributing most to children’s sugar intakes by 20 % by 2020. The programme has had mixed results⁽⁹³⁾ achieving an overall 3 % sugar reduction in retailers and manufacturers food categories. Breakfast cereals and yogurts and fromage frais achieved a 13 % average sugar reduction, but this has been negated by sales increases in high sugar products like chocolate confectionery. Progress has been more mixed in the eating out of home sector for all products. There is more work to be done to drive reformulation and to encourage industry to deliver greater results.

Conversely, the soft drinks industry levy⁽⁹⁶⁾ legislated in 2018 has been successful⁽⁹³⁾. Analysis demonstrates a 43·7 % reduction in the total sugar content of drinks per 100 ml between 2015 and 2019. The positive effect of this policy on dietary behaviour is equally distributed across all socio-economic groups; however, no reductions in rates of childhood obesity have been detected in the UK.

The existence of an independent committee, in addition to health-related government departments, strengthens the nutrition evidence base and ensures a robust system is in place to identify needs, inform nutrition policies and evaluate improvements in diet behaviour. However, the evidence on improvements in health such as reductions in the prevalence of obesity remains elusive, despite concerted efforts, particularly for more vulnerable groups.