The global food security challenge is less about providing sufficient food quantities and calories than about ensuring an adequate supply of essential nutrients, including quality protein and various minerals and vitamins. Meat, dairy, eggs, fish, and seafood offer convenient and comprehensive nutrient packages that support both healthy growth and aging. For pregnant and lactating women, infants, and young children, they provide vital nutrients such as iron, vitamin A, zinc, and calcium, which are essential for proper development. In older adults, they help combat undernutrition, functional impairment, cognitive decline, and sarcopenia. Adequate protein intake, especially from animal sources, becomes more critical with age. Additionally, animal source foods are valuable for individuals with metabolic health issues. While meat consumption is often associated with better mental health, its avoidance parallels a higher risk of certain mental disorders. Furthermore, intervention trials demonstrate that incorporating animal source foods into diets can prevent deficiencies, support growth, development, and overall health in various population groups.
This subsection addresses the following five questions:
- What is the global food security challenge and how do animal source foods fit in?
- Which vulnerable populations benefit from animal source foods, and how?
- How are animal source foods associated with nutritional adequacy?
- What is the relationship between animal source foods and mental health?
- What do intervention studies tell us about the nutritional contributions of animal source foods?
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What is the global food security challenge and how do animal source foods fit in?
Many populations, including in high-income countries, struggle to meet recommendations for several priority nutrients. Animal source foods contribute to the solution by enhancing nutrient sufficiency beyond staple foods and biofortification. Eggs and milk are accessible options for low-resource populations and contribute to healthy growth. Despite an increase in ASF intake among children and adolescents globally, Sub-Saharan Africa still faces disproportional deficiencies in key nutrients that are particularly bioavailable in ASFs, such as iron, zinc, iodine, and vitamin B12.
Further reading (summary of the scientific literature):
The mid-century food security challenge may relate less to the provision of sufficient food quantities, carbohydrates, or energy (even if hunger remains a problem) than to adequate essential nutrition [see elsewhere], i.e., quality protein and a spectrum of minerals (iron, calcium, zinc, iodine) and vitamins (A, D, E, B9, B12) [Nelson et al. 2018; Smith et al. 2018]. This problem is not unique to the Global South. Even in high-income countries, substantial percentages of the populations of women of childbearing and menopausal age fail to meet recommendations for many of these nutrients [Devarshi et al. 2021; Godfrey et al. 2023]. In the Netherlands, for instance, large parts of the population consume less calcium, iron, zinc, and vitamins A, B6, B9, D, and E than the estimated average requirements; with Dutch adolescents and women most at risk of inadequate intake [Bird et al. 2023].Animal source foods (ASFs) provide a powerful option to reach nutrient sufficiency by increasing the intake of limiting nutrients [Leroy & Barnard 2020; Nordhagen et al. 2020], creating robustness beyond an increase in staples and biofortification [Zhang et al. 2016; Adesogan et al. 2020; Paul et al. 2021; Zaharia et al. 2021], whereas even optimized local plant-based solutions may leave some of the needs insufficiently addressed [Osendarp et al. 2016]. Eggs and milk are accessible options to low-resource populations, providing 'holistic packages of nutrients and bioactive factors to support healthy growth' [Iannotti 2018]. Even in the US, ASFs generate adequate food patterns at the lowest cost [Chungchunlam et al. 2020]. Worldwide, intake of ASFs has been increasing for children and adolescents, but not in Sub-Saharan Africa, where deficiencies in iron, zinc, iodine, folate, and vitamins B12, and D are disproportionally high [Miller et al. 2023]. In high-income countries, the increasing advocacy to reduce the intake of meat and dairy has led some authors to express concern related to nutrient adequacy in vulnerable populations, especially pregnant women [Godfrey et al. 2023].
Which vulnerable populations benefit from animal source foods, and how?
Special attention is needed for pregnant and lactating women, infants, children, adolescents, and older adults due to their susceptibility to suboptimal micronutrient levels. Strict vegetarian diets can lead to severe consequences, as evidenced by clinical case reports for both young individuals and adults. Proper nutrition during early childhood is crucial for lifelong health, and complementary foods should include nutrient-rich options like meat, poultry, fish, or eggs. In older adults, animal source foods play a vital role in healthy aging, addressing undernutrition, cognitive decline, functional impairment, and sarcopenia. People with metabolic health issues also benefit from sufficient intake of animal source foods. Given the associated health care costs, the societal impact of addressing these nutritional needs is substantial.
Further reading (summary of the scientific literature):
Pregnant and lactating women, infants, children, and adolescents deserve particular attention as they often suffer from suboptimal micronutrient levels [see elsewhere]. In case nutrient adequacy is not met, consequences can be severe for individuals on (strict) vegetarian diets, as documented by clinical case reports for both (very) young individuals [see elsewhere for a literature overview] and adults [Hines 1966; Carmel 1982; Milea et al. 2000; Brocadello et al. 2007; De Rosa et al. 2012; Noh et al. 2013; Førland & Lindberg 2015; Hsu et al. 2015; Nimmagadda et al. 2018; Bachmeyer et al. 2019].Because appropriate feeding in early childhood is critical for health throughout the course of life, 'complementary foods should be rich in nutrients and given in adequate amounts [so that] young children should receive a variety of foods including meat, poultry, fish or eggs as often as possible' [WHO 2011]. In young children, the top food sources of commonly lacking micronutrients in low- and middle-income countries are all animal sourced: iron (chicken liver), vitamin A (ruminant liver), zinc (ruminant meat or small dried fish), folate (chicken liver), vitamin B12 (ruminant liver), and calcium (small fish) [Beal et al. 2021; White et al. 2021]. For example, compared with ruminant liver, children 6–23 months would need more than 100 times the portion size of pulses to achieve a similar level of adequacy of these critical micronutrients [Beal et al. 2021; White et al. 2021].In older adults, the role of ASFs in healthy aging is of particular importance and more research is needed to weigh potential benefits against harms [Kouvari et al. 2016]. Recent studies indicate that a higher intake of ASFs contributes to addressing the wide prevalence of undernutrition [Borkent et al. 2020], functional impairment [Yuan et al. 2020; Miyazaki et al. 2023], cognitive decline [Gao et al. 2022], and sarcopenia [Rondanelli et al. 2015], and may parallel lower mortality [Meroño et al. 2021]. Low intake of protein is of particular concern [Langsetmo et al. 2020; Borkent et al. 2023]. Observational studies favour the intake of animal protein over plant protein to combat sarcopenia [Campbell et al. 2023]. A vegan diet should not be recommended without protein supplementation as it may lead to lower muscle mass and a higher risk for loss of physical function due to sarcopenia [Domić et al. 2022]. The Irish Food Safety Authority specifically recommends ASFs and, to a lesser extent, legumes and nuts to supply older adults with sufficient high-quality protein [FSA Ireland 2021]. Avoiding ASFs increases the risk of inadequate protein intake, as strategies to improve the anabolic properties of plant-based foods are often not feasible for older adults [Domić et al. 2022]. In addition, elderly are more reliant on the few dietary sources of vitamin D (oily fish, eggs, liver, butter, meat), since their capacity to form 7-dehydrocholesterol in the skin is decreasing with advancing age [Bender 2002]. They especially benefit from high-quality protein supply [Bauer et al. 2013; Paddon-Jones et al. 2015; Medonça et al. 2020], which is more complicated when using plants only [Berrazaga et al. 2019]. Aging populations also become more vulnerable to B12 deficiency [Green et al. 2017]. Morever, it is known that higher levels of total cholesterol and iron serve as biomarkers for longevity in Swedish centenarians [Murata et al. 2023].Finally, the metabolically unhealthy are an important target population group that would benefit from sufficient ASF intake. They suffer from inflammatory conditions and perturbed endocrine responses (in particular hyperinsulinemia), which can at least be partially mediated via higher protein bioavailability [cf. Wolfe et al. 2008]. In Ireland, for instance, >80% of older adults are abdominally obese, while >50% are at high risk of cardiometabolic disease [FSA Ireland 2021]. The societal impact is gigantic, also because of the very high costs related to the treatment of such diseases.
How are animal source foods associated with nutritional adequacy?
Very low intake of animal source foods among vulnerable populations is often linked to decreased nutrient intake and compromised health. In contrast, various studies highlight the associations between the consumption of animal source foods and improved nutrient intake and health outcomes in different groups with elevated needs. Higher meat consumption can be linked to reduced anaemia among elderly, as well as decreased stunting in young children. Dairy consumption is, for instance, associated with an improved status of B-vitamin and vitamin-D biomarkers in older adults. Intake of fish is linked to improved nutritional outcomes, including a better vitamin D status in maternal diets and children's diets. Egg consumption is associated with higher intake of various nutrients, including choline. It is important to underline, however, that such associational data is not necessarily proof of causal relationships.
Further reading (summary of the scientific literature):
Low intake of ASFs in vulnerable populations parallels decreased nutrient coverage and health [Adesogan et al. 2020]. For instance, blanket advice to reduce the consumption of red meat (<40 g/d) may reduce nutrient intake to problematic levels in British females [Derbyshire 2017]. In meat-avoiding young Australian women, a decrease has been observed in the intake of n-3 fatty acids, vitamin B12, selenium, iron, and zinc [Fayet et al. 2013]. Adhering to the EAT-Lancet recommendation to limit meat intake was associated with a higher risk of deficiencies in protein, zinc, iron, selenium, and folate in young adults in the UK [Young 2022]. A higher intake of ASFs in pregnancy was associated with a lower risk of adverse birth outcomes in urban Tanzania [Kamenju et al. 2022] and an increase in placenta weight in the US [Meng et al. 2024]. Although, as such, not able to prove a causal link with actual health improvement (for instance due to confounding by poverty), various associations between ASF consumption and improved nutrient intake and/or health in vulnerable populations deserve to be mentioned [Otsuka et al. 2014; Miller et al. 2016; Derbyshire 2017; Balehegn et al. 2019; Zaharia et al. 2021; Kaur & Kaur 2021; Meroño et al. 2021; Gao et al. 2022]:
- Meat, as higher consumption parallels less anemia in Japanese elderly [Kito & Imai 2020] and Ethiopian diabetic patients [Engidaw & Feyisa 2020], as well as less stunting in young children worldwide [Adesogan et al. 2020]. More frequent childhood meat eating was associated with better cognition to old age in China [Heys et al. 2010]. In an Irish study (age groups 5–90 years), consumption of red meat was associated with higher intakes of protein, niacin, vitamins B6, B12, zinc, and potassium [Kehoe et al. 2023]. In US adolescents, beef consumers had a higher intake of calcium, iron, zinc, phosphorus, potassium, choline, and vitamin B12 than non-consumers [Fulgoni & Fulgoni 2023].
- Dairy, being associated with more protein, calcium, B vitamins, and vitamins A and D in the diets of children [Bao Khanh et al. 2016; Cifelli et al. 2017] and less stunting in low- and middle-income countries [Headey et al. 2024], better bone health in post-menopausal females [Yuan et al. 2023], and improved status of B-vitamin and vitamin-D biomarkers [Laird et al. 2017] and CLA [Wannamethee et al. 2018] in older adults (60+).
- Fish intake is associated with improved nutrition outcomes, including a lower risk of anaemia and an improved vitamin D status in maternal diets and diets of children [Byrd et al. 2022]. In Polish female adolescents, fish consumption leads to a higher intake of vitamin D in a region where the intake of this vitamin is alarmingly low in general and constitutes a key nutritional challenge [Lachowicz & Stachon 2022].
- Eggs, of which the consumption parallels higher protein, choline, B12, selenium, and phosphorus in the diet, and lower intake of sugar, regardless of poverty-income-ratio [Papanikolaou & Fulgoni 2018; Papanikolaou & Fulgoni 2023].
What is the relationship between animal source foods and mental health?
Many studies have indicated an inverse association between meat intake and mental health issues, although the causal direction is uncertain. Two potential explanations arise: 1) vegetarianism might serve as a cover for underlying mental disorders and eating pathologies, 2) poor mental health could result from nutrient deficiencies or low cholesterol levels. For example, low prenatal meat consumption has been linked to an increased risk of substance abuse in adolescence, potentially linked to vitamin B12 malnutrition. Some studies have found higher rates of depressive episodes among vegetarians compared to meat consumers. While (semi-)vegetarian women might demonstrate positive factors like physical activity and lower body mass indices, they could also report more menstrual problems and poorer mental health. The complex nature of the relationship is underscored by findings that semi-vegetarians with strong orthorexic tendencies tend to exhibit more depressive symptoms than both omnivores and vegetarians. In the elderly population, very low meat consumption has been connected to a higher incidence of dementia and Alzheimer's disease. Overall, the intricate interplay between meat consumption, vegetarianism, and mental health necessitates further comprehensive investigation to elucidate the underlying mechanisms and relationships.
Further reading (summary of the scientific literature):
In adolescents, vegetarianism is a fast-growing phenomenon observed in a majority of patients with anorexia nervosa [Albertelli et al. 2024]. It has been suggested that individuals that are prone to mental disorders and problematic eating behaviour may have to pay attention to the meat levels in their diets, as both are inversely associated [O’Connor et al. 1987; Neumark-Sztainer et al. 1997; Perry et al. 2001; Lindeman et al. 2002; Klopp et al. 2003; Bas et al. 2005; Bardone-Cone et al. 2012; Michalak et al. 2012; Burkert et al. 2014; Herranz Valera et al. 2014; Zuromski et al. 2015; Asanova 2017; Zhang et al. 2017; Kapoor et al. 2017 Barthels et al. 2018; Forestell & Nezlek 2018; Hibbeln et al. 2018; Matta et al. 2018; Nezlek et al. 2018; Li et al. 2019; Dobersek et al. 2020, 2021; Iguacel et al. 2020; Parra-Fernández et al. 2020; Paslakis et al. 2020; Sergentanis et al. 2020; Ocklenburg & Borawski 2021]. For instance, in a cohort of 14,000+ Brazilians aged 35-75 years, a two-fold higher prevalence of depressive episodes was found for vegetarians, after correction of socioeconomic, lifestyle factors, and nutrient deficiencies [Kohl et al. 2022]. Also, closer adherence to meat restriction based on EAT-Lancet recommendations was associated with poorer mood, while leading to a risk of being deficient in certain nutrients [Young 2022].The more rigorous the study, the more positive and consistent the association between meat consumption and better mental health, although the causal direction is not clear (if causality is to be assumed in the first place, which remains uncertain given the limitations of observational research) [Dobersek et al. 2021]. On the one hand, vegetarianism could be used as a smokescreen for mental disorders and eating pathologies [Lindeman et al. 2000; Zickgraf et al. 2020; Albertelli et al. 2023]. Eating disorders are affecting at least 10% of the European adolescents and young adults [Smink et al. 2012; Keski-Rahkonen & Mustelin, 2016]. Between 50-85% of the anorexic nervosa patients are known to adhere to vegetarian diets [Bardone-Cone et al. 2012; Albertelli et al. 2023]. On the other hand, poor mental health could also be the result of nutrient deficiencies or low cholesterol [Fiedorowicz & Haynes, 2014; Balehegn et al. 2019]. For instance, low prenatal meat consumption is associated with increased risk of substance abuse in adolescence, possibly involving vitamin B12 malnutrition [Hibbeln et al. 2017]. Psychiatrists have therefore advised investigating for vitamin B12 deficiency in psychiatrically ill patients, especially if they are vegetarian [Jayaram et al. 2013].Although the level of physical activity and body mass indices of (semi-)vegetarian women suggest a health bonus compared to non-vegetarians, an Australian study showed that the former may more often report menstrual problems and poor mental health [Baines et al. 2007]. In contrast, diets of the omnivore type are associated with reduced psychological disorders [Salehi-Abargouei et al. 2019]. In any case, the complex nature of the diet-depression requires further investigation, as semi-vegetarians with strong orthorexic tendencies tend to show more depressive symptoms than omnivores and vegetarians [Hessler-Kaufmann et al. 2020]. Finally, in the elderly, low meat consumption parallels increased incidence of dementia and Alzheimer's disease [Ngabirano et al. 2019].
What do intervention studies tell us about the nutritional contributions of animal source foods?
Intervention trials have shown that the incorporation of animal source foods in the diet can enhance nutritional resilience across different life stages, especially when the baseline intake is low. Their administration can help to improve the physical, behavioural, and cognitive outcomes of children, mitigate deficiencies in young females, enhance muscle synthesis in young men, and tackle poor bone health and sarcopenia in older adults. In Kenia, the administration of meat improved the performance of school children. Seafood, rich in long-chain omega-3 fatty acids, protein, and many other nutrients, contributes to improved responses in risk factors for chronic disease and has potential to reduce inflammation. Dairy products have demonstrated various health benefits, including improved vitamin K2 status, enhanced cognitive outcomes in school children in Ghana, and better bone health in various young and adult population groups. In rural Ecuador, it has been shown that eggs contribute to a reduction in stunting and improved plasma levels of essential nutrients like choline and DHA in infants.
Further reading (summary of the scientific literature):
Intervention trials have looked into the use of ASFs as complementary foods in population groups from various stages of life with specific nutritional needs. ASFs thus contribute to maternal nutrition and the physical and cognitive development of infants and children [Neumann et al. 2003, 2007; Hulett et al. 2014; Tang & Krebs 2014; Iannotti et al. 2014, 2017; Kaimila et al. 2019; Mahfuz et al. 2020; Asare et al. 2022], although study design is sometimes suboptimal [Eaton et al. 2019] and the empirical evidence base still needs improvement [Iannotti 2018]. Except when baseline intake is already high [Stewart et al. 2019], increasing ASFs thus help to meet the nutritional needs of young children. In contrast, low ASF intake may increase their health risks [see elsewhere].Intervention studies also illustrate that ASFs can help to prevent deficiencies in young females [Hall et al. 2017], enhance muscle synthesis in young men [van Vliet et al. 2017], and are useful to tackle malnutrition, poor bone health, and sarcopenia in elderly [Pannemans et al. 1988; Rondanelli et al. 2015; Torres et al. 2017; Groenendijk et al. 2019].Examples of intervention studies with ASFs include:
- Meat administration improved the zinc and iron status of infants [Obbagy et al. 2019], and the behavioral, physical, and cognitive outcomes of Kenyan children [Neumann et al. 2007; Hulett et al. 2014]. Also, a pork-containing 'Mediterranean diet' led to positive cognitive outcomes compared to a low-fat diet [Wade et al. 2019]. In older adults, a whole-food meal containing beef resulted in enhanced muscle protein synthesis rates compared to an isonitrogenous whole-food plant-based option [Pinckaers et al. 2023].
- Seafood is rich in long-chain omega-3 fatty acids (EPA/DHA) needed for proper (neural) development in the young and for healthy aging [Makrides et al. 2009; Swanson et al. 2012] and to reduce inflammation, which may beneficially affect rheumatoid arthritis [Lindqvist et al. 2019]. Being rich in protein and nutrients, it can lead to more favourable responses of postprandial blood glucose and incretins [Lin et al. 2020], as well as to improved lipid risk factors [Aadland et al. 2015].
- Dairy products have been shown to improve vitamin K2 status [Knapen et al. 2017], improve cognitive outcomes in Ghanian school children [Lee et al. 2018], and improve bone health in children [Hidayat et al. 2023], overweight adolescent girls [Josse et al. 2020], postmenopausal women [Shi et al. 2020], and older adults [Baek et al. 2023; Skuladottir et al. 2023]. In healthy adults, iso-energetic replacement of a carbohydrate-rich breakfast component with dairy improves postprandial amino acid availability, glycemic control, bone metabolism, and satiety [Hilkens et al. 2023].
- Eggs in complementary feeding of rural Ecuadorian infants reduced stunting [Iannotti et al. 2017a] and improved plasma levels of choline and DHA [Iannotti et al. 2017b]. A meta-analyses has shown that children in the intervention groups experienced improved growth when compared to those in the control groups [Larson et al. 2024]. There is suggestive evidence that eggs may improve body weight management in individuals predisposed to obesity and type-2 diabetes from animal feeding studies [Saande et al., 2019].
