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A core question in discussions of replacing animal foods with plant-based substitutes is whether plant-based substitutes can adequately satisfy nutrition requirements. As omnivores, humans tend to satisfy some nutrients more readily from plant sources while other nutrient requirements are generally better satisfied by consumption of animal foods. For example, our vitamin C and magnesium requirements are much more readily fulfilled by plant than animal foods. In addition, plant-based diets are often higher in folate, manganese, thiamin, potassium, and vitamin E (Davey et al., 2003). Plant foods also provide a wide array of phytochemicals that have important regulatory roles in human health (Briskin, 2000). The findings of extensive in vitro and in vivo experimental data, furthermore, suggest that plant compounds can antagonize some of the deleterious effects of compounds found in cooked red meat (e.g., heterocyclic amines, nitroso compounds, malondialdehyde, advanced glycation end products etc.) (Pierre et al., 2003; Vulcain et al., 2005; Gorelik et al., 2008; Hur et al., 2009; Li et al., 2010; Van Hecke et al., 2017a).

These findings may represent a mechanistic explanation—but certainly not the only one—for why high quality omnivorous diets (also rich in plants) do not show the typical associations between red meat consumption and negative health outcomes (Key et al., 2003; Schulze et al., 2003; Kappeler et al., 2013; Lee et al., 2013; Roussell et al., 2014; Wright et al., 2018; Deoula et al., 2019) that are often observed in population studies of individuals consuming a typical Standard American/Western Diet (Wang and Beydoun, 2009; Chan et al., 2011; Pan et al., 2011; Micha et al., 2012; Abete et al., 2014), though more work is needed to firmly establish this hypothesis.

On the other hand, vitamins A (retinol), B₁₂ (adenosyl- and hydroxocobalamin), D (cholecalciferol), K₂ (menaquinone-4), minerals such as iron and zinc, and long-chain polyunsaturated fatty acid (PUFAs) (e.g., docosahexaenoic acid [DHA] and eicosapentaenoic acid [EPA]) are more readily, or exclusively, obtained from animal sources as opposed to plant sources. These nutrients play essential roles in tissue development and regeneration (Georgieff, 2007; van Vliet et al., 2018). While plant foods often contain precursors to these nutrients, considerable portions of the population experience a poor in vivo enzymatic conversion of plant-precursors into forms usable by the human body (Brenna, 2002; Burdge, 2006; Tang, 2010). For example, the conversion of carotenoids (provitamin A) to retinol (vitamin A) is in the range of ~3.5 to 28%, depending on the genetic variability between individuals, and highlights that “poor converters” are unable to obtain sufficient retinol when relying on plant foods only. Retinol deficiency is especially prevalent in the developing world, particularly in young children and women of childbearing age, who largely depend on the consumption of provitamin A (primarily β-carotene) in vegetables and fruit to satisfy their vitamin A needs, with many failing to do so (Sommer and Vyas, 2012).

Of course, individual genetic differences related to nutrient metabolism (Brenna, 2002; Burdge, 2006; Stover and Caudill, 2008; Tang, 2010), at the same time, also explain why some individuals can thrive on plant-based diets, while others following a vegan/vegetarian diet report health problems associated with nutrient deficiencies. For example, there are five times more former vegans/vegetarians than current vegans/vegetarians in the US, of which 53% reported that they followed the diet <12 months (Faunalytics, 2015). While many factors contribute to the difficulties in adhering to plant-based diets (including social factors and food options), intra-individual differences in nutrient metabolism (Brenna, 2002; Burdge, 2006; Stover and Caudill, 2008; Tang, 2010; van Vliet et al., 2015) make it highly unlikely that everyone can thrive on a plant-based diet. The same is likely true for those on “carnivorous” diets (mostly or exclusively animal foods) (Mcclellan and Du Bois, 1930), though more work is needed to confirm this hypothesis.

While human omnivory should arguably not be interpreted as true optionality for either plant or animal foods, concerns regarding the negative effects of animal foods on human and environmental health have led to widespread suggestions to replace traditional animal foods with plant-based foods to meet the vast majority of our nutritional needs (Godfray et al., 2018; Willett et al., 2019). The shift toward replacing animal foods with plant substitutes is, furthermore, enabled by modern food technologies that allow for the production of plant-sourced foods that are able to match the macronutrient, vitamin and mineral content of animal foods by using isolated plant proteins, bioengineered ingredients, and/or synthetic vitamins and minerals (Figure 1).

Moreover, a potential reason why the novel plant-based meats that look, feel, and taste like meat are of interest to consumers is that they may be able to better satisfy the “intrinsic desire” that humans have for eating meat (Piazza et al., 2015). For example, despite an aversion in vegetarians toward animal foods at the subjective level, the intrinsic motivational salience (desire for meat) was preserved on the neural level similar to that of omnivores (Giraldo et al., 2019). Noteworthy, is that this “subconscious motivation for eating meat” was observed already after a single overnight fast, which is far from a starvation-like state. Given the close resemblance of novel plant-based meat alternatives to meat, in the following section we address the following question: Can plant-based alternatives meet the nutritional requirements traditionally fulfilled by eating animal foods?

The recommended dietary allowance (RDA) for protein in adults is 0.8 g protein/kg bodyweight per day (~56 g for a 70 kg individual) (Institute of Medicine, 2005). However, this amount should be viewed as the minimum to prevent deficiency in young adulthood rather that an amount that promotes optimal health (Wolfe and Miller, 2008; Phillips et al., 2016). Furthermore, the protein RDA is considered too low for middle-aged and older adults (>50 y) (Bauer et al., 2013; Deutz et al., 2014), and for adults who seek to maximize cellular adaptations from regular physical activity/exercise (Kato et al., 2016; Morton et al., 2018).

Animal foods such as meat are often recommended to meet protein needs because they provide dietary protein at a modest caloric load, and are considered of higher protein quality when compared to plant sources (FAO/WHO/UNI, 2011). The protein digestibility-corrected amino acid score (PDCAAS) and digestible indispensable amino acid score (DIAAS) are the two major standards used to evaluate the quality of dietary protein sources. Plant proteins often have lower scores (ranging from 0.4 to 0.9) than animal proteins (> 0.9). The lower PDCAAS/DIAAS of plant sources is, in part, due to their reduced digestibility as a result of the presence of “anti-nutrients”—phytates and trypsin inhibitors that interfere with digestion and absorption of protein (Sarwar Gilani et al., 2012). The advantage of novel meat alternatives is that they use concentrates and/or isolates of soy, pea, and other plant proteins. These purified protein sources are lower in anti-nutritional factors and, therefore, have comparable PDCAAS/DIAAS to most animal proteins including meat (Rutherfurd et al., 2014; Hodgkinson et al., 2018).

Based on their respective PDCAAS/DIAAS, one could expect that isolated plant proteins would result in a similar anabolic response when compared to animal sources. However, a number of studies have demonstrated that purified plant proteins have a lower skeletal muscle anabolic response when compared to isonitrogenous amounts of animal proteins with similar PDCAAS/DIAAS (Wilkinson et al., 2007; Tang et al., 2009; Phillips, 2012; Yang et al., 2012; Gorissen et al., 2016). Plant proteins tend to be particularly low in either lysine or methionine as well as leucine, which are essential amino acids that cannot be synthesized in vivo and need to be obtained through the diet (van Vliet et al., 2015). For instance, both soy and pea protein, the most commonly used protein sources in novel plant-based alternatives, are particularly low in methionine when compared to beef, in addition to being slightly lower in lysine as well (Figure 2).

The issue of an unbalanced amino acid profile can be solved by combining isolated plant proteins that are lower in lysine yet higher in methionine (e.g., wheat, rice, hemp, and maize) with plant proteins that are higher in lysine yet lower in methionine (e.g., soy, potato, and pea) in a single product or by adding crystalline amino acids to the product (van Vliet et al., 2015). While a popular pea-based alternative contains some isolated rice protein, which is complementary to pea protein, it is unlikely (based on the listed order of ingredients) that the amount is sufficient to increase the methionine content of the product. Similarly, a popular soy-based alternative has a limited amount of potato protein (<2% of total ingredients), but potato, like soy, is low in methionine and high in lysine. While we have previously theorized that blending different complementary plant sources is a promising strategy to improve the skeletal muscle anabolic response to ingested plant protein (van Vliet et al., 2015), no studies have yet determined if this brings the muscle anabolic response from plant sources up to the level of animal proteins. Of note is recent work that showed that consumption of complementary plant proteins still resulted in 30–40% lower circulating essential amino acid availability when compared to a leucine-matched amount of whey protein (Brennan et al., 2019). These data suggest that, despite the blending of plant-based sources to make a complete amino acid profile, the anabolic potential may still be reduced when compared to animal-based protein.

A potential alternative strategy to overcome the lower anabolic effects of plant vs. animal proteins is to simply eat more plant proteins. Consuming 40 g of soy protein results in a similar muscle anabolic response as 20 g of whey protein (Yang et al., 2012). Adding a high dose of rice protein (48 g) to an omnivorous diet is also as effective as a protein-matched amount of whey protein in augmenting resistance-exercise induced gains in muscle mass. This is in contrast to studies that show a superior training-induced skeletal muscle gains after consuming lower doses of animal vs. plant proteins (ranging from 17.5 to 25 g) (Hartman et al., 2007; Volek et al., 2013). Nonetheless, it may reasonably be expected that the consumption of plant-based meat alternatives as part of an omnivorous diet is unlikely to negatively impact skeletal muscle mass or affect protein requirements.

The cobalamins (vitamin B12) are the best-known members of the group of compounds collectively known as corrinoids. Cobalamin (vitamin B₁₂) is an essential nutrient that plays a role in DNA synthesis, myelin formation, red blood cell production, and maintenance of central nervous system function (Yamada, 2013). Humans must obtain vitamin B₁₂ from the foods they eat or via supplementation. While gut bacteria in our large intestine still produce some corrinoids, including small amounts of active forms of cobalamin (Kirmiz et al., 2020), evolutionary pressures likely resulted in preferential absorption of B₁₂ in the small intestine as a result of regular animal consumption (Seetharam and Alpers, 1982). This has resulted in a dependence on exogenous B₁₂ that has likely persisted for at least 1.5 Ma (Dominguez-Rodrigo et al., 2012). Indeed, the receptors necessary for absorbing B₁₂ are found only in the small intestine in modern-day humans, upstream of the site of bacterial corrinoid production (Seetharam and Alpers, 1982).

Biologically active B₁₂ is found predominantly as adenosyl cobalamin in animal flesh (Czerwonka et al., 2014) and as hydroxocobalamin in eggs and dairy (Matte et al., 2012). These active forms of vitamin B₁₂ bioaccumulate in animal products predominantly through microbial synthesis in the gut of ruminants, through consumption of soil and feces in non-ruminant herbivores, and through phytoplankton consumption in aquatic animals (Watanabe and Bito, 2018). A common misperception is that the majority of cattle receive supplemental B₁₂ and that humans are essentially consuming B₁₂ supplements via a “middle-man.” While there is some evidence that high-producing dairy cows need more B₁₂ than their microbes produce (Girard and Matte, 2005; Akins et al., 2013), the reality is that B₁₂ is seldom fed to cattle, which is likely due to its high cost and limited benefits for production (Akins et al., 2013).

Although limited amounts of B₁₂ are also found in some plant foods, such as mushrooms and fermented vegetables, the majority of B₁₂ in plants are biologically inactive corrinoids (i.e., B₁₂ analogs) (Stupperich and Nexø, 1991) that may compete with transport of biologically active B12, thus potentially aggravating a B₁₂ deficiency (Dagnelie et al., 1991). Several plant-based foods, particularly those meant to replace animal foods—cereals, non-dairy milks, vegan spreads, and plant-based meat replacements—are often fortified with supplemental B₁₂ to counteract deficiency. The common supplemental form of B₁₂ used in these products is cyanocobalamin which is relatively inexpensive to produce and has stability to heat exposure (Goldstein and Duca, 1982).

Cyanocobalamin is a man-made form of Vitamin B₁₂ that normally occurs only in trace amounts in human tissue, particularly in smokers (Paul and Brady, 2017). While all forms of vitamin B₁₂—naturally occurring adenosylcobalamin and hydroxycobalamin and the man-made form cyanocobalamin—are absorbed with similar efficiency (Paul and Brady, 2017), a potential concern with meeting B₁₂ requirements through cyanocobalamin is that its tissue retention rates, and subsequent metabolic activity, are reduced compared to naturally occurring forms of B₁₂ (Glass et al., 1961; Hertz et al., 1964; Okuda et al., 1973; Paul and Brady, 2017). Additionally, the B₁₂ found in animal foods is protein-bound and therefore partially protected from light degradation (Linnell and Matthews, 1984). Nonetheless, eating cyanocobalamin-fortified foods or ingesting cyanocobalamin supplements can improve vitamin B₁₂ status in adults (Tucker et al., 2000, 2004; Damayanti et al., 2018) and children (Sheng et al., 2019), which is also why fortifying meat alternatives with B₁₂ is encouraged. This is especially important for vegans and vegetarians, and the elderly (even omnivores) who often have low B₁₂ status (Herrmann et al., 2003a,b; Andrès et al., 2004), and rely on food fortification and/or supplementation to meet B₁₂ needs. It is important to highlight that only less than a quarter of plant-based meat substitutes are fortified with B₁₂ (Curtain and Grafenauer, 2019).

Dietary iron is found as heme iron in animal foods, particularly in red meat, and as non-heme iron in plant foods, particularly in pulses, grains, green leafy vegetables, and certain fruits. Heme iron is 5-10-fold more bioavailable than non-heme iron (Hurrell and Egli, 2010), and explains why omnivores often have higher serum ferritin levels (a marker of iron status) (Haider et al., 2018). The uptake of iron, particularly non-heme iron, is limited by several plant compounds such as phytates, polyphenols, and calcium, present in both plants and dairy (Hurrell and Egli, 2010).

In contrast to most plant foods, which predominantly contain non-heme iron as part of their natural food matrix, the iron in a market leading soy-based alternative is heme iron purified from yeast that is genetically engineered to express the leghemoglobin protein normally found in the root nodules of soy plants (i.e., soy leghemoglobin) (Fraser et al., 2018). While the amino acid sequence of leghemoglobin is vastly different from animal heme counterparts, iron uptake of leghemoglobin had similar bioavailability as bovine hemoglobin in a human epithelial cell culture model (Proulx and Reddy, 2006). Importantly, initial studies regarding safety of yeast-derived soy leghemoglobin show little concern for genotoxicity and immunogenicity in in vitro and short-term (28-day) in vivo animal studies (Fraser et al., 2018; Jin et al., 2018). Future work should confirm the bioavailability and long-term safety of yeast-derived soy leghemoglobin consumption in vivo in humans, and particularly in children where soy allergy is more common (Savage et al., 2010). While some concern exists with consumers regarding the use of genetically modified ingredients in food products (Scott et al., 2018), a recent consumer survey suggests that the presence of soy leghemoglobin in a popular soy-based meat alternative does not appear to be a barrier to consumption or perceived healthfulness of the product (International Food Information Council, 2020).

A market leading pea-based meat alternative contains non-heme iron naturally present in peas (Figure 1). While the bioavailability of non-heme iron is reduced compared to heme, non-heme iron can still represent an important dietary source of iron (Young et al., 2018). Vitamin C, and ironically meat, are main enhancers of non-heme iron absorption (Hurrell and Egli, 2010), which is why adding meat to plant-based meals improves uptake of non-heme iron from plants (Bjorn-Rasmussen and Hallberg, 1979; Kristensen et al., 2005). Vitamin C also enhances iron uptake by acting as a chelator in the gut (Conrad and Umbreit, 1993). Important to note is that a market leading soy-based meat alternative is supplemented with sodium ascorbate (vitamin C), which presumably counteracts some of the inhibitory effects of the phytates, found in soy protein, on iron absorption (Hurrell et al., 1992).

Despite increased awareness, iron deficiency remains one of the most common nutrient deficiencies in both developed and developing countries, and population groups such as children, adolescent females, and older individuals are particularly at risk for deficiency (Patel, 2008; Beck et al., 2014; Gibson et al., 2014). On the other hand, excessive heme iron intake is increasingly linked to the promotion of cardiovascular disease (CVD) (Fang et al., 2015). The association of heme iron intake and CVD is particularly prevalent in US cohorts, but is inconsistent in cohorts outside of the US (Fang et al., 2015). Interestingly, even in the US the association between high heme iron intake and risk of CVD was absent in the first cohort of NHANES, which was studied during the 1970s (Liao et al., 1994) when red meat intake was higher compared to present day (Daniel et al., 2011). This heterogeneity between studies likely suggests that the background diet in which red meat is consumed may be an important modulating factor. In particular, the deleterious effects of red meat consumption may be perpetuated when meat is consumed as part of the Standard American Diet, rich in processed foods and inadequately counterbalanced with whole food plant sources. For example, polyphenols, phytates, calcium, and fibers inhibit heme iron absorption (Hurrell and Egli, 2010; Ma et al., 2010), and this may explain why some epidemiolocal studies find that risk of heme iron intake and CVD disappears with extensive adjustment for diet quality (i.e., diets also high in whole plant foods) (Galan et al., 2009; de Oliveira Otto et al., 2012; Kaluza et al., 2014).

Similar to iron, zinc deficiency can be a concern in both developed and developing countries (Alloway, 2008), and those who restrict animal foods often have lower zinc status (Foster et al., 2013; Foster and Samman, 2015). Uptake of zinc from plant sources can be lower as a result of the presence of anti-nutrients such as phytates, lectins, and certain fibers (Harland and Oberleas, 1987; Welch, 1993). Similar to iron, zinc uptake from plants can be improved when consumed in conjunction with animal foods (Sandström et al., 1989). While soy protein contains limited amounts of zinc, a popular soy-based alternative is fortified with zinc gluconate to bring its level up to that of beef (Figure 1). Nevertheless, zinc absorption from fortified plant foods, at equal zinc content of beef, is lower than that for beef (Zheng et al., 1993; Etcheverry et al., 2006). We note that a well-planned vegan diet rich in legumes, nuts, seeds, and other zinc-rich plant foods can potentially provide adequate amounts of zinc (Eshel et al., 2019). Of further consideration when meeting zinc (and iron) requirements with supplementation is that this practice may reduce the absorption of other minerals such as copper (Yadrick et al., 1989), thus increasing their dietary requirements. The latter can be mitigated by consuming copper-rich (plant) foods (e.g., nuts, seeds, and leafy greens).

The ω-6 fatty acid linoleic acid (C18:2, LNA) and the ω-3 fatty acid alpha-linolenic acid (C18:3, ALA) are essential fatty acids that cannot be synthesized in vivo by humans and must be obtained from dietary sources (Barcelo-Coblijn and Murphy, 2009). ALA is the parent precursor to the long-chain polyunsaturated fatty acids (LCPUFA) eicosapentaenoic acid (C20:5 n-3, EPA) and docosahexaenoic acid (C22:6 n-3, DHA). ALA and LNA are commonly found in plant foods but can also be found in limited quantities in animal foods, while DHA and EPA are found exclusively in animal foods and certain algae.

While ALA can be converted to DHA and EPA through a series of elongation and desaturation steps, this conversion is poor and often <1% (Su et al., 1999; Brenna, 2002; Pawlosky et al., 2003). Moreover, this conversion efficiency also depends on the presence of co-factors such as selenium, zinc, iron and vitamin B₆ (Brenner, 1981), which are less bioavailable from plant foods. For these reasons, vegetarians can have lower levels of DHA and EPA when compared to omnivores (Rosell et al., 2005).

DHA and EPA have been studied extensively for their importance in cardiovascular function, immunomodulation, vision, and cognitive function (Swanson et al., 2012). DHA is a major constituent of the brain phospholipid membrane (30–40% of total fatty acids), and low circulating levels are associated with accelerated brain aging (Tan et al., 2012; Otsuka et al., 2014). Nonetheless, as studies suggest that the human brain only requires 5 mg of DHA per day (Rapoport et al., 2007; Umhau et al., 2009), it is estimated that 1,200 mg of ALA can provide these minimum requirements (Barcelo-Coblijn and Murphy, 2009), though this minimum amount is not considered optimal for health. While no official daily recommended intakes exist for DHA and EPA, numerous studies demonstrate that combined intakes of DHA and EPA ranging from 250 to 1000 mg/day improve cognitive function and other health parameters (Yurko-Mauro et al., 2015; Derbyshire, 2018), and such amounts are therefore often recommended by various health organizations (WHO, 2008; EFSA, 2012).

The ω-3 fatty acid ALA is found in substantial amounts in certain vegetable oils, such as flax seed oil (53 % ALA), chia seed oil (64% ALA), perilla oil (60% ALA), and camelina oil (38% ALA), though consumption of the latter two oils is generally restricted to Asian and Nordic countries, respectively (Barcelo-Coblijn and Murphy, 2009). While the amount of ALA necessary to ensure minimum DHA requirements in the human body can be obtained with modest intake of these oils, the majority of vegetable oils consumed in industrialized countries is in the form of ω-6 LNA-rich seed oils such as soybean, corn, sunflower, and canola oil, which contain <10% ALA. For instance, sunflower oil and canola oil—the main oils in the novel plant-based meat alternatives—contain only 1% (sunflower oil) and 10% (canola oil) ALA. Given the already low conversion rates of ALA to EPA and DHA, respectively, plant-based meat alternatives in their current state likely will not provide meaningful amounts of very long-chain PUFAs in the diet.

Another potential issue is that the ω-6 fatty acids such as LNA directly compete with ALA for enzymes involved in elongation and desaturation, which further diminishes the ability to obtain DHA and EPA from ALA (Sprecher et al., 1999). This is particularly problematic when one considers that the increased consumption of high LNA seed oils in the modern Western Diet has resulted in an ω-6-to-ω-3 fatty acid ratio of 16:1 (Simopoulos, 2002), whereas historical intakes puts this ratio closer to 1:1 (Eaton et al., 1998; Simopoulos, 2002). This high ω-6-to-ω-3 fatty acid ratio is considered an important underlying cause for the increasing incidence of metabolic disease and all-cause mortality in Western countries (Das, 2006; Zhuang et al., 2019). Experimentally substituting ω-6-rich LNA oils with ω-3-rich ALA oils reduces inflammation (Rallidis et al., 2003; Bemelmans et al., 2004), which represent a mechanistic explanation for why consuming ω-3-rich ALA oils may be cardioprotective. Thus, a suitable improvement to the novel plant-based meat alternatives could be to consider the use of high ALA oils, rich in ω-3, instead of high LNA oils rich in ω-6 fatty acids. An important consideration is that high ALA oils are more prone to lipid oxidation (and perhaps represents a reason why high LNA oils are typically used in meat substitutes); however, the addition of natural anti-oxidants (Wang et al., 2018; Lu et al., 2020) as well as entrapment of high ALA oils with isolated plant proteins (Karaca et al., 2013; Bajaj et al., 2015) represent worthwhile opportunities to explore for producers of plant-based meat substitutes that consider the use of high ALA oils in their products, which potentially increases their healthfulness.

It is often stated that ω-3 fatty acids are present in such modest amounts in land animal-sourced foods, such as beef, that they do not represent a valuable dietary source of these essential fatty acids. However, this notion fails to take into account the abundance of the ω-3 fatty acid docosapentaenoic acid (C22:5, DPA) in beef, particularly pasture-raised beef, which raises platelet EPA and DHA levels as a result of in vivo conversion (McAfee et al., 2011). While DHA can also be directly obtained in substantial amounts from offal cuts of meat—for instance, 100 g of grass-fed beef liver provides 80 mg of DHA (Enser et al., 1998)—the consumption of organ meat is not as common anymore in Western diets and marine sources account for the majority of dietary intake of the ω-3 fatty acids DHA and EPA (Bauch et al., 2006; Papanikolaou et al., 2014).

While we have highlighted several important individual nutrients thus far, foods in their natural state are considerably more complex than their essential fatty acid, amino acid, vitamin, and mineral content would suggest. Food sources contain hundreds-to-thousands of biochemicals that are important to human metabolism (Barabási et al., 2019). While many of these nutrients are considered non-essential or conditionally-essential based on life-stages, and are often less appreciated in discussions of human nutritional requirements, their ability to impact human metabolism should not be ignored.

For example, creatine has been studied extensively for its ability to enhance athletic performance (Cooper et al., 2012), but creatine also plays an important role in cognition (Avgerinos et al., 2018). As creatine is found only in animal foods, vegans and vegetarians often have lower bodily stores (Burke et al., 2003), and vegetarians provided with supplemental creatine showed substantial improvements in memory tasks (Benton and Donohoe, 2011). Similarly, the antioxidants anserine, carnosine, and taurine are found (almost) exclusively in animal foods (Hou et al., 2019). Increased anserine and carnosine intake provide neurocognitive protection in humans (Szczesniak et al., 2014; Rokicki et al., 2015).

Taurine is an amino acid found almost exclusively in animal foods and though small amounts may be found in some plant foods such as cereals, legumes, and grains (a thousand times less when compared to animals foods) (Pasantes et al., 1989), these amounts are insufficient to meet human requirements (Laidlaw et al., 1990). It is often stated that since taurine can be synthesized in vivo from methionine and cysteine via cysteinesulfinic acid decarboxylase (CSD), taurine requirements can be met by consumption of plant proteins that are rich in methionine and cysteine, which can be found in adequate amounts in several legumes and grains (van Vliet et al., 2015). However, CSD levels in the human body, which allows for the conversion of taurine from methionine and cysteine, are insufficient to maintain tissue concentrations over time (Ripps and Shen, 2012). Taurine impacts nearly every vital organ in the body and plays vital roles in eye health (Froger et al., 2014), brain function (Kilb and Fukuda, 2017), mitochondrial functions (Suzuki et al., 2002), skeletal muscle cell differentiation (Miyazaki et al., 2013), and cardiovascular health (Waldron et al., 2018). Future studies are needed to better understand how these differences in secondary nutrients between plant-based meat alternatives and meat impacts short- and long-term health.

A recurring concern is that natural whole foods are extremely complex and the reductionist approach of trying to “mimic” whole food sources (whether it be meat or other foods) by combining several isolated nutrients likely underestimates the true complexity and health benefits of eating whole foods (Lichtenstein and Russell, 2005; Jacobs and Tapsell, 2007). In particular, fortification of a low-meat diet with zinc and other minerals found in meat did not result in similar zinc status as when these minerals were provided in the diet as part of the natural matrix of meat (Hunt et al., 1995). Moreover, adequate intakes of zinc, copper, and vitamins A and D were associated with decreased risk of cardiovascular disease and all-cause mortality when obtained from foods, but not from supplements, in a recent large population-based study (Chen et al., 2019). Similarly, carotenoid-containing foods are associated with a decreased risk of various cancers (van Poppel and Goldbohm, 1995), retinopathies (Goldberg et al., 1988; Seddon et al., 1994), and cardiovascular disease (Kritchevsky, 1999). However, the results of interventional and epidemiological studies suggest that carotenoid and/or vitamin A supplements do not decrease the risk of cancer or cardiovascular disease, and might even raise the risk for some sub-populations (The Alpha-Tocopherol Beta Carotene Cancer Prevention Study Group, 1994; Omenn et al., 1996; Druesne-Pecollo et al., 2010; Bjelakovic et al., 2012). Similar findings have been made in studies of calcium that show a potential for increased cardiovascular disease risk with supplementation (Bolland et al., 2011; Li et al., 2012), but not when calcium is obtained from food (Xiao et al., 2013). Finally, similar findings have been made for vitamin C and selenium supplements that show no benefits on mortality in a systematic review of RCTs comprised of nearly 300,000 individuals (Bjelakovic et al., 2012). Thus, it appears that simply ingesting these nutrients outside of their natural food matrices may not be an optimal solution for promoting health. Thus, obtaining nutrients from whole food sources as opposed to supplemental forms is emphasized regardless of the individual's diet (Jacobs and Tapsell, 2007; van Vliet et al., 2018).