This subsection discusses the limitations and biases of observational studies that associate plant-based diets with better health outcomes and red/processed meat consumption with negative health effects. Nutritional studies that rely on observational data are typically insufficient to establish clear causal relationships or strong dietary recommendations, as they tend to come with many limitations and biases. The problem may be compounded by the selective reporting of data that support a particular narrative, while dismissing outcomes that contradict a priori expectations and beliefs. There are many instances where vegetarian and vegan diets have been linked to poorer health outcomes and lower quality of life.
This subsection lists the following points and reasons for caution when dealing with observational data (additional commentary on the specific case of the Blue Zone argument can be found elsewhere):
- Introduction: what is the case against animal source foods?
- Argument 1: weak associations are only indicative
- Argument 2: beware of problematic input data
- Argument 3: lifestyle confounding and healthy-user bias
- Argument 4a: cherry picking - dismissal of neutral outcomes
- Argument 4b: cherry picking - dismissal of protective outcomes
_________________________________
Introduction: what is the case against animal source foods?
Observational evidence has linked 'plant-based' eating to a lower risk of an impressive series of health issues, including obesity, cardiovascular disease, diabetes, diverticular disease, eye cataract, cancer, and vulnerability to coronavirus infection. However, such data are largely insufficient from a methodological perspective to support dietary recommendations away from animal source foods. This applies to the case against
red and/or processed meats as well, despite reported associations
between their intake and various
illnesses, including intestinal disease, asthma, pneumonia, kidney
disease, type-2 diabetes, cardiometabolic disease, and cancer. These associations do not
necessarily imply that animal source foods are intrinsically unhealthy,
and more rigorous research is needed to draw definitive conclusions.
Further reading (summary of the scientific literature):
Although part [but certainly not all; see below] of the evidence from observational studies has linked 'plant-based', vegetarian diets to a lower risk of obesity and illnesses such as ischemic heart disease, diabetes, diverticular disease, eye cataract, and cancer [Appleby & Key 2016; Kim et al. 2022], as well as vulnerability to coronavirus infection [Kim et al. 2021], this is not a valid reason to assume that vegetarian diets as such are effectively and uniquely protecting against disease. Neither do these studies prove that animal source foods (ASFs) are intrinsically unhealthy. Below we argue that such data are not a solid basis for causal interpretations or dietary recommendations, for a variety of reasons.The same concern is valid for the claim that red and/or processed meats are unhealthy food choices, despite numerous reported associations between their intake and mortality [Pan et al. 2012; Larsson & Orsini 2014; Etemadi et al. 2017; Schwingschackl et al. 2017; Zheng et al. 2019; Wang et al. 2020], including 'accidental death' [Sinha et al. 2009], as well as a variety of illnesses, including intestinal disease [Cao et al. 2018; Papier et al. 2021], asthma [Adrianasolo et al. 2019], pneumonia [Papier et al. 2021], kidney disease [Kelly et al. 2017], cardiometabolic diseases [Pan et al. 2011; Kaluza et al. 2012; Chen et al. 2013; Feskens et al. 2013; Johnson et al. 2013; Abete et al. 2014; Rohrmann & Linseisen 2016; Yang et al. 2016; Wolk 2017; Ekmekcioglu et al. 2018; Kim & Je 2018, Al-Shaar et al. 2020; Papier et al. 2021a, 2021b; Wang et al. 2022; Shi et al. 2023], some cancers [Norat et al. 2002; Huncharek & Kupelnick 2004; Larsson et al. 2006; Bandera et al. 2007; Faramawi et al. 2007; Larsson & Wolk 2012; Wang & Jiang 2012; Yang et al. 2012; Huang et al. 2013; Qu et al. 2013; Xu et al. 2013; Zhu et al. 2013; Fallahzadeh et al. 2014; Farvid et al. 2015; Caini et al. 2016; Carr et al. 2016; Vieira et al. 2017; Zheng et al. 2017], and depression [Nucci et al. 2020].
Argument 1: weak associations are only indicative
Methodological quality assessments have revealed that the evidence currently used to relate the intake of animal source foods, such as red meat, to an increase in mortality or morbidities is uncertain. Such low-certainty evidence is suggestive at best. For the general population, it does not strongly support the dietary recommendation to reduce consumption beyond current levels. In contrast, other risk factors linked to the Western diet, like visceral fat and the metabolic syndrome, show much stronger and plausible associations with certain health outcomes now allegedly ascribed to ASFs. The use of Bradford-Hill criteria and GRADE-based assessments concludes that the evidence incriminating red meat for increased mortality and morbidities is of low to very-low certainty. It may as well be classified as merely suggestive. For the general population, the evidence does not strongly support the recommendation to reduce consumption beyond current levels.
Further reading (summary of the scientific literature):
Observational studies looking into the protective and harmful associations between plant-based eating or animal source food consumption, respectively, typically comes with low relative risk (RR) levels, if any. Moreover, the absolute risk (AR) is usually trivial and often not reported [cf., Johnston et al. 2019]. Taking into account that there can be an abundance of false-positive findings [Bofetta et al. 2008; Young & Karr, 2011], and because of the large bias and uncertainties [see below], such low risk levels would not be considered as strong evidence in most epidemiological research outside nutrition. Even if a threshold theoretically depends on the risk prevalence in the reference group [Sainani 2011], RR values <2 should be considered as poorly informative [Shapiro 2004]. They should not be used to infer strong causal claims, especially when there is a strong suspicion of confounding [McAfee et al. 2010; Alexander & Cushing, 2011; Alexander et al. 2015; Klurfeld 2015; Feinman 2018; Leroy et al. 2018; Händel et al. 2021]. Hazard ratios (HR), specifically, come with their own issues regarding causal inference [Hernán 2010; Uno et al. 2014].To put things in perspective, the association of colorectal cancer with visceral fat is coupled to a RR of 5.9 for the highest compared to the lowest tertile [Yamamoto et al. 2010], overshadowing the value for meat eating (RR of 1.2 per 100g/d of red meat or 50g/d of processed meat). Likewise, the presence of the metabolic syndrome at baseline is to be seen as meaningful as it is associated with increased risk of colorectal cancer (HR 2.2) in postmenopausal women [Kabat et al. 2012], acting as a prognostic factor [Shen et al. 2010] and driven by hyperinsulinemia (e.g., via angiogenesis) [Liu et al. 2014]. It is within this gradient, created by differences in strength of association and the absence or presence of plausible mechanisms, that certainty of evidence should be established. To do so, methodological frameworks are needed, such as the Bradford-Hill criteria and GRADE protocol [BMJ Best Practice].Application of Bradford-Hill criteria led to the conclusion that the causality of the associations between red and processed meat intake and cardiovascular disease can not be inferred due to weakness of associations and a lack of coherence with experimental evidence (although potential causality was mentioned for type-2 diabetes in the case of processed meats) [Hill et al. 2020, 2022]. The alleged link of processed meat with colorectal cancer has been criticized for demonstrating serious or critical risks of bias (risk of confounding, missing data, selective outcome reporting bias) [Händel et al. 2020] and in the case of red meat for displaying an unclear dose-response effect and weakening evidence over time [Alexander et al. 2015].After the most comprehensive assessment of the evidence, the observational evidence used to incriminate red and processed meats for increased mortality or a variety of morbidities was deemed to be of 'low-' to 'very-low-' certainty [Han et al. 2019; Johnston et al. 2019; Vernooij et al. 2019; Zeraatkar et al. 2019; see elsewhere]. In support of this finding, another GRADE-based approach concluded that the recommendation to reduce the consumption of processed meat and meat products in the general population to lower the risk of cancer 'seems to be based on evidence that is not methodologically strong' [Händel et al. 2021]. Likewise, an umbrella review classified evidence for the link between red and/or processed meats and colorectal cancer as merely 'suggestive' (i.e., above 'weak' but below 'highly suggestive' and 'strong' [Papadimitriou et al. 2021]. Use of 'burden of proof risk function' methodology similarly indicated that the evidence is 'weak' for the link between unprocessed red meat and colorectal cancer, breast cancer, type-2 diabetes, and ischemic heart disease, and absent for stroke [Lescinsky et al. 2022].
Argument 2: beware of problematic input data
Epidemiological research usually relies on surveys and food frequency questionnaires – imperfect, and sometimes fatally flawed methods of data collection. The input data suffer from categorization issues, errors due to memory-based reporting, social desirability bias, and survivorship bias (including individuals who fare well on certain diets, while overlooking those who do not). Studies on
vegetarian diets may also be problematic because of misclassifications, combining true
vegetarians with semi-vegetarians, leading to potential errors in the
results.
Further reading (summary of the scientific literature):
The input information for epidemiological assessments is usually obtained from surveys and food frequency questionnaires, providing an often seriously problematic way of data collection [Schatzkin et al. 2003; Archer et al. 2013, 2015, 2018; Händel et al. 2021; Young et al. 2022; Brown et al. 2023]. For instance, whereas actual intake of sucrose based on biomarker assessment is positively related with being obese, self-reported intake tends to be negatively associated [Kuhnle et al. 2015]. Whereas the actual intake of fruits and vegetables (based on vitamin C as a biomarker) is associated with less obesity, this is not the case when intake is self-reported [Bingham et al. 2007]. The use of pre-defined food categories also comes with problems. In the case of meat, the categories and descriptors used for muscle foods display heterogeneity and often do not match those of public regulatory definitions [O'Connor et al. 2020]. Processed and (red) meats are often grouped together in 'all meat' even though they may lead to very different results [Männistö et al. 2010]. The same reservation is sometimes valid for plant-based foods as well, displaying a gradient from 'healthy' to 'unhealthy' options [Elliott et al. 2023].Furthermore, memory-based self-reporting issues undermine data robustness, while social desirability bias may cause underreported intake of meat in self-defined vegetarians and other health-conscious groups [Haddad & Tanzman 2003]. In a UK survey, only 1/4 respondents who considered themselves to be reducing meat consumption had cut down on a variety of meats over the year [Richardson 1993]. Moreover, some of the studies claiming to look at 'vegetarian diets' are in reality combining true vegetarians with semi-vegetarians to avoid low sample sizes. Therefore, the term 'vegetarian' in self-reports requires caution [Juan et al. 2015]. In the Oxford Vegetarian Study, 23% of 'non-meat-eaters' ate meat occasionally but less than once a week, or ate fish, or both [Appleby et al. 1999].
Survivorship bias is also likely, since many vegans and vegetarians (up to 70-80%) rapidly revert to eating ASFs, a third even within three months of their change of diet [Faunalytics 2014, 2015]. Only 12- 24% of current vegans may be in the diet for >5 years [Kerschke-Risch 2015; FCN 2018; VOMAD 2019], 7% for >10 years, and 3% for >20 years [VOMAD 2019]. Studies looking into 'plant-based' diets may have a selection bias for the minority of subjects that do well on such diets. Several genes, especially those with functions in lipid metabolism and brain function, are associated with vegetarianism and may underlie the ability to subsist on a vegetarian diet [Yaseen et al. 2023].
Disentangling specific dietary effects from the complexity of overall diets and lifestyles in observational data is challenging. Context is crucial when interpreting statistical associations between food intake levels and health outcomes. The relationships are obscured by the overall diet quality, lifestyles, socio-demography, etc. The healthy user bias poses specific challenges. In high-income countries, associations tend to capture what the generally healthier middle-classes believe is healthy, rather than revealing the true biological effects. Studies indicate that both healthier vegetarians and meat eaters have lower risks compared to less healthy meat eaters. Population-specific factors need to be considered when interpreting the results of observational studies on meat consumption.
Further reading (summary of the scientific literature):
It is primordial yet very difficult to unambiguously disentangle specific dietary effects from the overall complexity and quality of diets and lifestyles within observational data sets. For example, less healthy vegetarians have no cardiovascular benefits compared with less healthy meat eaters, while both healthier vegetarians and healthier meat eaters have a lower risk than less healthy meat eaters [Petermann-Rocha et al. 2023]. Merely eating ‘plant-based' may not associate with protective shifts in markers of cardiometabolic health unless dietary quality is accounted for [Elliott et al. 2023]. Likewise, higher red meat intake increases cancer risk at low levels of fruit and vegetable intake, yet may show a neutral to protective association in people who also report an increased consumption of fruits and vegetables [Maximova et al., 2020]. This may or may not point to protective interactions, but can as well be indicative of more intricate confounding; in any case, such findings demonstrate that context is primordial. Similarly, for the Women's Health Initiative (WHI) [Zheng et al. 2022], UK Biobank [Petermann-Rocha et al. 2023], and ATTICA cohorts [Damigou et al. 2023], risk elevations seem to be due to dietary patterns rather than to the actual consumption of red meat per se. The Southern European Atlantic diet, as found in parts of Spain and Portugal, was identified as a protective eating pattern despite the fact that it deviates from the Mediterranean model due to the regular inclusion of red meat and pork products [Carballo-Casla et al. 2024]. In a population of adolescent girls, those girls consuming higher levels of both red meat and healthy plant foods (fruits and nonstarchy vegetables) had more favourable lipid markers at the end of adolescence than girls consuming lower levels of both food groups [Bradlee et al. 2013]. The authors concluded that: 'lean red meat may be included in a healthy adolescent diet without unfavourable effects on lipid values'.The overall health status of the investigated populations is also of primordial importance. The association between meat eating and inflammatory response or disease becomes non-significant or is at least substantially attenuated after adjustment for excess body weight [Montonen et al., 2013; Chai et al. 2017; Papier et al. 2021; Wood et al. 2023]. In prediabetic adults, association of processed meat consumption with the deterioration of glycemic markers and triacylglycerol levels disappeared when adjusted for weight increase [Zhu et al. 2022]. In the EPIC-Heidelberg cohort, the main ASFs were not meaningful as determinants for overall, cardiovascular, or cancer-related mortality risk, independently of smoking, alcohol consumption, and excess body weight [Bajracharya et al. 2023]. When medical history and dietary habits were taken into account in the Greek ATTICA cohort, positive association between the consumption of red meat (but not processed meat) and cardiovascular disease became non-significant [Damigou et al. 2023]. Yet, whereas such well-characterized factors as obesity can be statistically accounted for as such, at least to some degree, it is impossible to sufficiently correct for all lifestyle confounders. Even anxiety has recently been mentioned as a potential confounder of the associations between meat eating and colorectal cancer [Beslay et al. 2020]. Socio-demographic elements, in particular, are particularly difficult to account for.In observational studies, the problem of healthy user and related biases (e.g., healthy adherer) is a fundamental one [cf. Shrank et al. 2011]. It explains at least part of the deviations between the results of observational studies and randomized controlled trials [see also elsewhere]. Western upper-middle classes are inclined to eat less meat, as they are susceptible to what is perceived as virtuous eating, obediently following official advice [Leroy & Hite 2020]. Self-declared vegetarians tend to be more health conscious and socioeconomically advantaged [Bedford & Barr 2005], while plebeian eating patterns are less prone to dietary guidance. Meat intake thus parallels a higher intake of ultraprocessed foods, obesity, smoking, and lower physical activity [Alexander et al. 2015; Fogelholm et al. 2015; Grosso et al. 2017; Mihrshahi et al. 2017; Turner & Lloyd 2017; Hur et al. 2019]. Such associations captured by epidemiology then serve as positive feedback to reinforce the dietary recommendations that created them in the first place [Leroy & Hite 2020]. Essentially, the dietary guidelines behave as a self-fulfilling prophecy, reinforcing an animal/plant binary that started out as an ideological construct in the 19th century [see elsewhere].When comparing people with similar socio-demographic characteristics, no differences in mortality are seen between vegetarians and meat eaters [Chang-Claude et al. 2005; Appleby & Key, 2016; Appleby et al. 2016; Mihrshahi et al. 2017]. Also, omission of Seventh-Day Adventist studies, describing a specific subset of communities following healthy lifestyles, from meta-analyses results in the weakening or even disappearance of the beneficial associations between vegetarianism and cardiovascular health [Kwok et al. 2014; Dinu et al. 2017; FCN 2018].To further illustrate this point, lifestyle confounding appears when comparing distinct cultural groups. For processed/red meats, associations found in North-America are not necessarily valid elsewhere, where they may be neutral or protective [see below; O'Sullivan et al. 2013; Wang et al. 2016; Grosso et al. 2017; ACC 2018; Iqbal et al. 2021]. Worldwide, bivariate correlation analyses revealed that meat intake is positively correlated with life expectancies and acted as one of the significant predictors of life expectancy, while carbohydrate crops showed weak and negative correlation [You et al. 2021]. Similarly, associations between egg consumption and type 2 diabetes typify US studies but vanish in European (neutral) and Asian (protective) studies [Djoussé et al. 2016; Tamez et al. 2016; Wallin et al. 2016; Drouin-Chartier et al. 2020].
Argument 4a: cherry picking - dismissal of neutral outcomes
Developing a case against animal source foods is often based on cherry-picked evidence from observational studies. In many studies there is no unambiguous association between their avoidance and improved health. The evidence on unprocessed red meat, for instance, is conflicting, some large studies showing no association. Poultry, eggs, and dairy display mostly neutral or even protective associations with health. Butter's associations
with mortality, cardiovascular disease, and diabetes are relatively
small or neutral. The overall picture is complex, and context plays a
crucial role in interpreting the results from observational studies on animal source foods.
Further reading (summary of the scientific literature):
Developing a case against ASFs, in particular red and processed meats, often leads to a biased selection of evidence. In a critique on an influential meta-analysis favoring vegan and vegetarian diets [i.e., Dinu et al. 2017], it has been shown that such attempts are characterized by selective reporting, exaggerated cause-and-effect statements, and a refusal to refer to studies that find no associations with chronic diseases [Fenton & Gillis 2017]. Also, a critical analysis of studies looking into the link between processed meats and colorectal cancer has shown that '75% of the eligible studies had a moderate to serious risk of missing data, and about half of the studies had issues with bias in the selection of the reported results' [Händel et al. 2021].The German Nutrition Society concluded that there is insufficient evidence for a type-2 diabetes risk increase with higher intakes of animal protein and a risk decrease with plant protein intake, mentioning inconsistency, lack of clear biological plausibility, poor methodological quality, contradictory information from intervention studies, and general uncertainty [Schulze et al. 2023].
Many authors were indeed unable to affirm a clear link between veganism, vegetarianism, or red meat avoidance and lower mortality or morbidity due to various diseases of modernity, or only obtained harmful associations for some meat types (mostly processed ones) but not others, in particular of the unprocessed type [Heilbrun et al. 1989; Thun et al. 1992; Missmer et al. 2002; Flood et al. 2003; Huncharek et al. 2003; Key et al. 2003, 2009; Cho et al. 2004; Sato et al. 2006; Lee et al. 2008; Alexander & Cushing 2009; Alexander et al. 2009, 2010a,b,c; 2011; Wallin et al. 2011; Kappeler et al. 2013; Parr et al. 2013; Lee et al. 2013; Rohrmann et al. 2013; Kwok et al. 2014; Lippi et al. 2015; Mihrshahi et al. 2017; Hur et al., 2019; Mejborn et al. 2020; Wang et al. 2021; Iqbal et al. 2021; Zheng et al. 2022; Zhu et al. 2022; Blackie et al. 2023; Damigou et al. 2023; Silva de Medeiros et al. 2023; Myrmel et al. 2024]. The global PURE study did not find problematic associations between red meat and cardiovascular disease or mortality [Mente et al. 2023; Mozaffarian 2023]. Similarly, the PREVIEW study indicated that only processed meat but not total or unprocessed red meat, poultry, dairy products, or eggs showed an association with weight regain and adverse risk factors [Zhu et al. 2022]. In the MESA study, neither processed not unprocessed forms of red meat were associated with any markers of inflammation [Wood et al. 2023]. In the EPIC cohort, processed meat intake above 20 g/d was associated with all-cause mortality, but this was only significant for men and for smokers and not for females or 'never smokers' [Rohrmann et al. 2013]. A Mendelian Randomization study was unable to find causal effects of red and processed meats on cardiovascular disease outcomes [Hu et al. 2024].
As a result, the common narrative that red meat causes colon cancer and heart disease becomes messy. Even if vegetarians may display lower mortality from ischemic heart disease than meat eaters in some large prospective studies, no protective associations with mortality from cerebrovascular disease and various cancers were found in those same datasets (including colon cancer) [Key et al. 1999]. Also, no association was found between red meat and heart disease or diabetes (although processed meats paralleled higher risk) [Micha et al. 2010], while a GRADE analysis of the relationship between vegan diets and cardiovascular disease indicated variable associations and weak to very weak quality of evidence [Kaiser et al., 2021]. One very large study within Harvard’s Pooling Project of Prospect Studies of Diet and Cancer did not find a link between red and processed meat intake and colorectal cancer, but was only abstracted and never published [Cho & Smith-Warner 2004], which has raised suspicion given the dietary beliefs prevailing at Harvard's School of Public Health [Butterworth 2007].When arguing for restriction of ASFs based on observational studies, poultry should be exonerated based on neutral [Lupoli et al. 2021; Zhu et al. 2022] or even protective findings [see below]. The same is valid for eggs, with the occasional association being limited mostly to a US context [Rong et al. 2013; Shin et al. 2013; Tran et al. 2014; Alexander et al. 2016; Djoussé et al. 2016; Tamez et al. 2016; Wallin et al. 2016; Dehghan et al. 2020; Xia et al. 2020; Krittanawong et al. 2021; Zhu et al. 2022; Myers & Stevenson Ruxton 2023]. The case against dairy leads to inconsistent yet mostly neutral results [Jayaraman et al. 2019, Zhu et al. 2022] and would overall lead to a net protective effect [Scrafford et al. 2020], while even the persistent narrative stating that it would cause prostate cancer is unlikely [Preble et al. 2019]. Cheese intake, for instance, is neutral for prostate cancer while offering protective associations for various other outcomes (see below) [Zhang et al. 2023]. For butter, a meta-analysis has revealed relatively small or neutral overall associations with mortality, CVD, and diabetes [Pimpin et al. 2016].
With respect to total animal protein, no significant association with all-cause, cardiovascular, or cancer mortality was found, although intake of plant protein was associated with lower all-cause and cardiovascular but not cancer mortality [Nahghsi et al. 2020].
Argument 4b: cherry picking - dismissal of protective outcomes
Embracing observational data to criticize omnivore diets would undermine the notion that vegan diets are always superior for avoiding chronic diseases and death. Those who rely on nutritional epidemiology to argue that we need more ‘plant-based’ eating need to acknowledge that some animal source foods also come with protective associations – implying that their underconsumption may be suboptimal for certain aspects of health. The global PURE study, for instance, has associated the intake of fish, eggs, full-fat dairy, and white meat, along with plant foods, to protective health outcomes. In the PURE cohort, red meat is mostly considered neutral in terms of health outcomes. In some studies, red meat consumption has even been associated with benefits, including lower morbidity, increased telomere length, and decreased risk of depression. Also, some studies have linked vegetarian and vegan diets to poorer health outcomes and lower quality of life. However, it is essential to recognize that both pro-meat and pro-plant studies may have limitations in establishing causal relationships, and they should be considered together in the overall debate about dietary choices.
Further reading (summary of the scientific literature):
Global analysis (based on the PURE study cohort) indicates that the healthiest dietary setups for cardiovascular protection include substantial amounts of ASFs besides plant foods, with whole-fat dairy and fish mentioned among the "protective" components, while meat is referred to as mostly neutral [Mente et al. 2023; Mozaffarian 2023].Embracing observational data to incriminate omnivore diets would at the same time undermine the premise that vegan diets are the best choice to avoid chronic disease and death. Avoidance of ASFs that are associated with benefits would then have to be considered as suboptimal for some populations, as could be argued for fish and seafood [He et al. 2004; Bouzan et al. 2005; Larsson & Orsini 2011; Chowdhury et al. 2012; Zheng et al. 2012; Jiang et al. 2016; Zhao et al. 2016; Schwingschackl et al. 2017; Qin et al. 2018; Rimm et al. 2018; Black et al. 2019; Kim et al. 2019], white meat [Shi et al. 2015; Xu et al. 2020; Lupoli et al. 2021; Alegria-Lertxundi et al. 2022; Damigou et al. 2023] , and eggs [Gopinath et al. 2020; Zhuang et al. 2020; Xu et al. 2020; Krittanawong et al. 2021], and dairy [Shimizu et al. 2003; Aune et al. 2013; Gao et al. 2013; Astrup 2014; Tapsell 2015; Gijsbers et al. 2016; Lovegrove & Hobbs 2016; Wu & Sun 2017; Yoshida et al. 2019; Scrafford et al. 2020; Bhavadharini et al. 2020; Haugsgjerd et al. 2020; Jin et al. 2020; Poppitt 2020; Papadimitriou et al. 2021; Alegria-Lertxundi et al. 2022; Feng et al. 2022; Gaeini et al. 2022; Neisius et al. 2022; Yuan et al. 2022; Kim et al. 2023; Tanpowpong et al. 2023; Yuan et al. 2023; Villoz et al. 2023; Xie et al. 2024]. Within dairy, even cheese intake is associated with a lower risk of all-cause mortality, incident cardiovascular disease, coronary heart disease, stroke, type 2 diabetes, ER-breast cancer, bone fractures, and dementia, while being neutral for other outcomes [Zhang et al. 2023].In contrast to the common narrative, the eating of red meat (or derived products) has in some instances been associated with protective outcomes, including a lower morbidity or mortality [Lee et al. 2013; ACC 2018; Yen et al., 2018; Black et al. 2019a, b], increased telomere length, potentially increasing life span [Kasielski et al. 2016, You et al. 2021], decreased risk of cognitivie decline and neurogenerative disease [Xu et al. 2020; Zhang et al. 2021; Talebi et al. 2023], and lower incidence of depression [Kohl et al. 2022], or the effects of unprocessed red meat on waist circumference [Zandvakili et al. 2024].Several studies have even linked vegetarian and vegan diets to poorer health outcomes and lower quality of life [Sebeková et al. 2001; Krajcovicová-Kudlácková et al. 2002; Ingenbleek & McCully 2012; Burkert et al. 2014; Orzylowska et al. 2016; Buscail et al. 2017; Ghoshal & Singh 2017; Iguacel et al. 2019, 2020; Tong et al. 2018; Vanacore et al. 2018; Acer et al. 2019; Borude 2019]. Outcomes include the reduced healing of postsurgical scars [Fusano et al. 2020], problems of dental health [Smits et al. 2020], and issues related to psychological well-being [Dobersek et al. 2020; Dobersek et al. 2021; Ocklenburg & Borawski 2021; Fazelian et al. 2021; Brytek-Matera 2021]. While meat-containing diets are more frequently linked to ischemic heart attacks, haemorrhagic strokes occur more frequently with vegetarian/vegan diets [Tong et al. 2019; Grüngreiff et al. 2020]. As such studies may be equally criticized for their lack of causal proof, they should at least serve as counter material in the overall debate.
