Non-communicable diseases account for 41 million deaths each year. The two leading non-communicable diseases are cardiovascular diseases (CVDs) and cancer. Chronic disease and inflammation are influenced by environmental factors, with diet playing a significant role (Fritsche, 2015; World Health Organization, 2018; Sanchez-Rodriguez et al., 2019). Based on epidemiological studies, red meat consumption is often associated with increased risks of diabetes, CVDs, and cancer (Wolk, 2017). These claims led health organizations, such as the American Heart Association (AHA), to make public health recommendations to reduce red meat consumption (Arnett et al., 2019). However, epidemiological studies do not differentiate between production systems and types of red meat which are important factors affecting the nutritional profile (Provenza et al., 2019). Beef from grass-fed production systems is more consistent with nutritional recommendations, especially regarding n−3 PUFAs and phytochemicals (Vannice and Rasmussen, 2014; Omaye and Omaye, 2019; Van Vliet et al., 2021b). Omega-3 FAs are important compounds in foods that are linked to health benefits regarding reducing inflammation, blood triacylglycerols, and the risk of CVDs, depression, and arthritis (Calder, 2015; Saini and Keum, 2018). Further, phytochemicals including phenolic compounds also have multiple cardiovascular health benefits including protection against oxidative stress and modulation of blood pressure (Medina-Remón et al., 2015; Omaye and Omaye, 2019). Though public health recommendations suggest a decrease in red meat consumption to prevent chronic diseases, GFB addresses some of the nutritional concerns.

The typical Western diet is usually high in SFAs and n−6 PUFAs and deficient in n−3 PUFAs, related to an increased risk of developing CVDs, diabetes, obesity, and cancer (Simopoulos, 2002). However, FAs need to be considered individually to assess their effects on human health (Calder, 2015; Bloomfield et al., 2016). Saturated FAs as a whole are thought to promote inflammation and increase total low-density lipoprotein (LDL) cholesterol and insulin resistance. This is significant because LDL cholesterol is linked with incidence of coronary heart diseases (Billingsley et al., 2018). Therefore, SFAs increase the risk of CVDs, type 2 diabetes, and inflammation (Fritsche, 2015; Billingsley et al., 2018). However, not all SFAs have the same effects. Stearic acid, for example, has a neutral effect on LDL cholesterol, while myristic acid and palmitic acid have a total cholesterol-raising effect (FAO, 2010). Reduction of SFA consumption is usually linked to a replacement with other nutrients. When SFAs are replaced with refined carbohydrates, total serum cholesterol increases, along with the risk of developing CVDs (Dinicolantonio et al., 2016). Dietary intake of monounsaturated fatty acids (MUFAs) is thought to be beneficial for human health, especially when the increase of MUFAs is coupled with a decreased intake of SFAs. Oleic acid intake is associated with a lower risk of CVD and CVD mortality, while palmitoleic acid may increase insulin sensitivity and improve the blood lipid profile (Calder, 2015). Two important PUFAs are linoleic acid (LA) and ALA. The human body cannot synthesize these essential FAs, but they are important to human health as they are precursors for other long-chain PUFAs of interest including arachidonic acid, EPA, DPA, and DHA (Saini and Keum, 2018). Omega-3 PUFAs have anti-inflammatory effects while n−6 PUFAs do not (Simopoulos, 2006). The n−3 PUFAs DHA and EPA are linked to healthier cardiovascular function and can be synthesized from the precursor ALA (Parolini, 2019; Mendivil, 2021). However, the conversion from ALA to long-chain n−3 PUFAs remains low and is influenced by sex and LA concentrations (Harnack et al., 2009; Welch et al., 2010; Zhou et al., 2019). The n−6:n−3 ratio in the Western diet is estimated to be between 15:1 and 20:1 compared to 1:1 in wild animals or traditional human diets (Simopoulos, 2002, 2006). A lower n−6:n−3 ratio is considered important to prevent chronic diseases (Simopoulos, 2006; Husted and Bouzinova, 2016). Overall, because each FA has a different effect, and the relative proportions of each FA can change health outcomes, it is important to analyze the FA profile of beef to understand its effects on human health.

Unsaturated trans FAs are an important topic in the connection between FAs and human health. Unsaturated trans FAs have their double bonds in the trans configuration. With the usual configuration of unsaturated FAs being cis; trans FAs are formed either naturally via metabolic processes like microbial activity in ruminant animals or industrially by hydrogenation (Markiewicz-Keszycka et al., 2013; Calder, 2015). Each cis unsaturated FA can give multiple trans isomers, but the major ones include elaidic acid (trans C18:1 n−9), TVA (trans C18:1 n−11), and CLA (c9 t11 C18:2 and c12 t10 C18:2) (Calder, 2015). The c9 t11 CLA isomer is mainly found in bovine milk and meat, while the t10 c12 form is mainly found in processed oils (Lindmark Månsson, 2008; Calder, 2015; Alothman et al., 2019). Unsaturated trans FAs have different biological properties compared to the cis configuration, and their functions differ based on how they were produced. Trans FAs produced by industrial hydrogenation of plant oils are related to higher risks of CVDs compared to other FA classes (Calder, 2015; Del Razo Olvera et al., 2017; Qiu et al., 2018). On the other hand, trans FAs created by biohydrogenation in ruminants (TVA and CLA) are not associated with heart disease (Kalač, 2011). CLA, especially the c9 t11 isomer, and its precursor TVA, are purported to have health benefits, including managing insulin resistance and blood pressure as well as improving lipid metabolism, in moderate doses (Field et al., 2009; Menaa et al., 2013; Da Silva et al., 2015). It is important to note the differences between industrial trans FAs, which should be avoided, and ruminant trans FAs, which confer some health benefits, since the two are structurally similar but have different effects. Despite this distinction, the health benefits of ruminal trans FAs still require investigation. Recent studies exploring ruminal trans FAs found potential negative health effects including increasing cardiometabolic risk factors such as the lipid profile similarly to that of industrial trans FAs (Gebauer et al., 2015; Verneque et al., 2020).

Other than FAs, phytochemicals such as phenolic compounds in foods have numerous beneficial health effects (Serra et al., 2021). Phenolic compounds are secondary metabolites derived from plants, and their chemical structure is characterized by having at least one phenolic group. They can be divided into two categories: non-flavonoids, also called phenolic acids, and flavonoids which include flavonols, flavanones, flavones, flavanols, isoflavones, anthocyanidins, and chalcones. Although they are not essential for major biological mechanisms, they do have important ecological functions and possess antioxidant properties (Cianciosi et al., 2018; Pogorzelska-Nowicka et al., 2018). Phenolic compounds stabilize free radicals by giving up one hydrogen from their hydroxyl group; thus, the degree of antioxidant activity of each compound depends on the number of hydroxyl groups (Kumar et al., 2015; Cianciosi et al., 2018). Carotenoids, including β-carotene and lutein, are another class of phytochemicals found in plentiful amounts in plants. These compounds can act as precursors to vitamin A in humans, have antioxidative effects, and reduce the risk of metabolic diseases (Van Vliet et al., 2021b). Because of the potential of phytochemicals to reduce oxidative stress and inflammation, consumers are looking for foods containing these compounds (Provenza et al., 2019).

Fatty acid profiles in meat vary from species to species and from animal to animal. Poultry is usually leaner and therefore contains less fat, while red meat usually contains more fat (Biesalski, 2005). Because cattle diet has the biggest impact on the nutritional profile of beef, the FA profile differs based on the production system (Berthelot and Gruffat, 2018; Lenighan et al., 2019; Prache et al., 2020). Regardless of feeding regime, SFAs are abundant in beef, with stearic acid accounting for approximately one-third of total SFAs. Previous studies mainly agree that grass-feeding or finishing results in higher levels of SFAs (around 45% total FA) compared to grain-finishing (43%) (Duckett et al., 2009; Daley et al., 2010; Van Elswyk and Mcneill, 2014). Nevertheless, it is important to note that grass-finished beef products are leaner than grain-finished products (Alfaia et al., 2009). Grass-finished beef has 1.4 g less SFAs than grain-finished beef per 100 g (Van Elswyk and Mcneill, 2014). Furthermore, grass-finished beef contains around 3% more stearic acid (C18:0) compared to grain-finished beef; stearic acid is considered neutral in regard to effects on plasma LDL cholesterol (Leheska et al., 2008; Alfaia et al., 2009; Daley et al., 2010; Van Elswyk and Mcneill, 2014). Concentrations of individual SFA were reported in the literature; unfortunately, not all articles report values using the same units, so it is difficult to compare them directly. Many sources report higher concentrations of myristic acid (C14:0) and palmitic acid (C16:0), considered to be detrimental to serum cholesterol levels, in grain-finished beef (Duckett et al., 2009, 2013; Daley et al., 2010; Van Elswyk and Mcneill, 2014). Overall, grass-finished beef has a more favorable SFA profile (Daley et al., 2010).

Monounsaturated fatty acids make up nearly half of beef fat, with oleic acid (cis C18:1 n-9) being the most abundant (Leheska et al., 2008). Oleic acid is the most prevalent cis MUFA in the human diet, and it is widely available in plant and animal products. Its effects on human health include lower LDL cholesterol levels and blood pressure, as well as improved insulin sensitivity. These effects are improved when oleic acid is used as a replacement of SFAs (Calder, 2015). It has been reported that GFB has between 30 and 70% less MUFAs compared to grain-finished beef. More specifically, grain-finished beef has up to 1.8 g more MUFAs per 100 g tissue (2.61 vs. 0.79 g per 100 g meat) (Duckett et al., 2013; Van Elswyk and Mcneill, 2014). These findings are interesting from a human-health standpoint since consumption of high-oleic acid beef was linked to increased plasma high-density lipoprotein (HDL) cholesterol (Gilmore et al., 2011; Van Elswyk and Mcneill, 2014).

The key FAs of interest in GFB are the PUFAs, especially n−3 and n−6 PUFAs. Significant differences in n−6 concentrations have been reported in the literature with grass-finished beef containing less n−6 PUFAs compared to grain-finished beef (Davis et al., 2022; Klopatek et al., 2022). Typically, grass-raised products have higher levels of n−3 PUFAs, leading to a more favorable n−6:n−3 ratio. The n−6:n−3 ratio in GFB is around 1.53:1 while the ratio in grain-fed beef is about 7.65:1 (Daley et al., 2010; Pighin et al., 2016). It has been reported that when the amount of grain in the feed is increased, the concentration of n−3 PUFAs decreases and the concentration of n−6 PUFAs increases. The length of time on feed also influences the PUFA content of meat. Klopatek et al. (2022) found that cattle grazing for 20 months and finished for 45 days on a high concentrate diet displayed a n−6:n−3 ratio of 2.5:1 compared to animals kept on pasture for 20 or 25 months without any concentrate displaying a n−6:n−3 ratio of 1.5:1. This was mainly due to a decrease in n−3 PUFA concentrations and it was confirmed by a n−6:n−3 ratio of 5.5:1 in animals that were fed a concentrate diet for 128 days in a feedlot. Analyzing the effects of various feedstuff on the n−6:n−3 ratio in GFB will help consumers to understand these vast differences and select the healthiest GFB products. Beef from cattle fed diets rich in grass and other forages also have about 2–3 times higher concentrations of c9 t11 CLA and TVA than grain-fed cattle (Leheska et al., 2008; Alfaia et al., 2009). This is mainly due to a more favorable rumen pH which allows for more efficient microbial biohydrogenation (French et al., 2000; Kraft et al., 2008).

Phytochemicals are also variables of interest that differ based on the production system. Grass-finished beef contains higher amounts of common antioxidants including 3 times more α-tocopherol (vitamin E) and 1.5 to 10 times more β-carotene than grain-finished beef (Duckett et al., 2009; Pighin et al., 2016; Bronkema et al., 2019; Logan et al., 2020). Although intrinsic biological factors such as breed and age can affect carcass fat color, grass-fed beef usually has a yellower fat, mainly due to carotenoids found in the lush green forages they are grazing on (Dunne et al., 2009). Yellow carcass fat is generally related to healthier FA profiles and higher antioxidant content (Daley et al., 2010). Even though direct comparison of phenolic compounds in grass-finished and grain-finished beef has not yet been reported in the literature, differences in phenolics were observed in milk based on grass or concentrate diets (Besle et al., 2010; Prache et al., 2020). Furthermore, some findings suggest that cattle finished on forages might showcase higher phenolic content and diversity in their meat (Provenza et al., 2019; Van Vliet et al., 2021a,b). When cattle graze on phytochemically diverse mixture of plants, the sensory and biochemical characteristics of their carcasses are modified (Alothman et al., 2019; Provenza et al., 2019; Van Vliet et al., 2021b). For instance, a study comparing inflammatory responses of subjects after consuming kangaroo meat (eating a mixture of phytochemically diverse plants) or beef meat (fed a high-grain diet) showed that people who consumed the kangaroo meat had lower inflammatory responses (Arya et al., 2010). However, it is important to note that the generic term “grass-fed” or “grass-finished” does not reflect phytochemical diversity of the feed. There are many variations that exist among grass-fed and grass-finished diets, and these differences can greatly influence the nutritional properties of beef (Figure 1).

Increasing demand for GFB and the use of regenerative agriculture practices go hand in hand (Spratt et al., 2021; Van Vliet et al., 2021b). Regenerative agriculture can be defined as a practice that links soil health and livestock management to farm profitability, human, animal, and ecosystem health, as well as food system sustainability (Spratt et al., 2021). Regenerative agriculture might also be referred to as ecological agriculture, conservation agriculture, permaculture, or holistic management and focuses on restoring holistic and regenerative systems supported by ecosystems that allow healthy soils. Farmers and ranchers with livestock typically use a holistic grazing method with the purpose of increasing soil health, moisture retention, and fertility while continuously moving animals between habitats to allow optimal forage conditions (Gosnell et al., 2019). More specifically, regenerative grazing involves rest-rotation cycles: grazing periods followed by forage rest periods to allow plant recovery (Spratt et al., 2021). Regenerative agriculture is known to improve biodiversity and to enhance ecological function (Provenza et al., 2019). Grazing systems used in regenerative agriculture imitate natural ecosystems and improve plant diversity (Van Vliet et al., 2021b). When compared to feedlots or monocultures, soil, animal, and human health are favored when herbivores, including cattle, graze on phytochemically diverse mixtures of grasses and trees (Provenza et al., 2019). However, diverse plant species and grazing systems have varying effects on the nutritional profile of beef (Table 1).

The “grass-fed” label does not always reflect the phytochemical diversity of the diet (Provenza et al., 2019). Large variations are observed among grass-finished beef (Bronkema et al., 2019). Not all GFB graze on the same type of pastures. Forages including grass and clover contain high concentrations of ALA (50–75% of total FAs), which is the essential FA that can be synthesized into beneficial EPA and DHA (Scollan et al., 2014; Bronkema et al., 2019). Chloroplasts contain high levels of PUFAs, explaining why green plants have high concentrations of ALA (Elgersma et al., 2013). Orchard grass, tall fescue, and perennial ryegrass have 2, 4, and 7 more mg of ALA per g of dry matter compared to alfalfa, respectively (Dierking et al., 2010). Schmidt et al. (2013) reported concentrations of main FAs in alfalfa, bermudagrass, chicory, pearl millet, and cowpea. Bermudagrass contained 7% more ALA than cowpea and pearl millet, while pearl millet and chicory contained 8% more LA than alfalfa and bermudagrass. Other forage mixtures including pearl millet, bluegrass, and clovers increased the n−3 content of beef by more than 2% compared to beef fed a concentrate diet (Duckett et al., 2013). Adding different varieties of plants like red clover can help increase levels of ALA and LA (Scollan et al., 2006). Nutritional profiles of plants differ based on the leaf-to-stem ratio, with leaves containing more n−3 PUFAs than stems as Elgersma et al. (2005) found a positive relation between proportion of leaf blades and C18:3. In general, an increase in n−3 PUFAs is observed in diverse pastures compared to perennial ryegrass and lowland pastures.

There is an increasing interest in botanically diverse pastures as cattle feed. However, the information available in the literature remains scarce (Scollan et al., 2014). Different plant species have varying effects on the nutritional quality of beef products. The subcutaneous fat n−6:n−3 ratio of cattle grazing on cicer milkvetch was greater compared to cattle grazing on meadow bromegrass or treated in feedlot. The lower subcutaneous fat n−6:n−3 ratio was found in animals grazing on birdsfoot trefoil (Allen, 2021). It is important to note that unsaturated FAs are toxic to rumen bacteria and therefore undergo extensive rumen biohydrogenation. LA and ALA are hydrogenated to the extent of 70–95 and 85–100%, respectively (Lock et al., 2006). Based on this, increasing PUFA concentrations in the diet could lead to more biohydrogenation and formation of stearic acid, but these rates also depend on other factors such as rumen pH, plant secondary metabolites, and the impact of plant cell walls on the availability of free FAs for biohydrogenation (Lock et al., 2006; Fredriksson Eriksson and Pickova, 2007; Jenkins et al., 2008; Lee et al., 2018). These findings emphasize the importance of defining plant species in pasture and how they affect rumen biohydrogenation and beef nutrient profiles.

Herbivores and plants work synergistically, leading plants to produce a wide array of phytochemicals. These phytochemicals accumulate in meat and milk when animals graze on these diverse pastures, but these metabolites remain underdiscussed when assessing the nutritional quality of meat (Van Vliet et al., 2021b). Plant diversity and grazing are important elements of regenerative agriculture; they play major roles in soil and environmental health, as well as contributing health-enhancing phytonutrients for animals and humans (Provenza et al., 2015). However, factors other than pasture diversity contribute to the nutritional properties of cattle feeds.

The diversity of production systems reflects differences in nutritional profiles of beef (Table 1). Significant nutritional differences are observed among grass-finished beef. However, there are more factors affecting the quality of beef including season, geography, and climate (Mathews and Johnson, 2013; Bronkema et al., 2019; Jain et al., 2020). These variations seen in beef are due to variations in feeds. Factors such as plant maturity and development, cutting date, soil, weather, and light exposure play major roles in the nutritional composition of feeds (Dewhurst et al., 2001; Khan et al., 2009; Garcia et al., 2016).

Generally, grasses decline in FA quality faster than legumes or grains, highlighting the importance of seasonal variations (Kilcher, 1981; Glasser et al., 2013). Nutritional quality of feeds varies with plant growth and maturity, as well as the leaf-to-stem ratio (Boufaïed et al., 2003; Glasser et al., 2013). Different growth periods have been identified in fresh grass between May and September in temperate Northern Hemisphere areas. These growth periods are further subdivided into the primary growth, and the first, second, and third regrowth. Based on these cycles, it was found that total FAs and ALA are higher during the primary growth before strongly declining during the second regrowth, which is a stemmy regrowth period, and increasing again during the last regrowth cycle, which is a leafy regrowth period. The opposite trend was true for LA (Bauchart et al., 1984). These growth and regrowth periods emphasize the importance of plant growth and the leaf-to-stem ratio when assessing the nutritional quality of forages since forage lipids are mainly of leaf origin (Boufaïed et al., 2003). Total fat in grasses is usually higher in early spring before gradually declining, while concentrations of the SFA palmitic acid gradually increase throughout the season (Mir et al., 2006). Concentrations of LA, as well as MUFAs such as C16:1 and C18:1 usually follow the same pattern as palmitic acid, while the beneficial n−3 PUFA ALA decreases over time (Garcia et al., 2016). Following the gradual decrease of ALA, increasing concentrations are seen in the late season because of regrowth vegetation cycles (Glasser et al., 2013). Throughout the season, forages have a more beneficial FA profile compared to grains since seeds are higher in n−6 PUFAs while leaves are higher in n−3 PUFAs (Butler, 2014). Forages are also the largest natural source of vitamins for ruminants, but concentrations vary based on species and maturity. A study comparing α-tocopherol and β-carotene in grasses and legumes found that the highest levels of vitamins were found in the fall and were based on regrowth cycles (Danielsson et al., 2008).

Temperature and weather affect the quality of forages. Higher temperatures during the summer months negatively affect the quality of feeds by increasing plant maturation and cell wall lignification (Revello-Chion et al., 2011). Regarding precipitation, rainfall promotes grass quality and productivity (Mir et al., 2006; Revello-Chion et al., 2011). On the other hand, water deficit decreases forage quality by reducing the proportion of leaves. This is because nutrients migrate to the roots, decreasing the important leaf-to-stem ratio (Revello-Chion et al., 2011). Furthermore, precipitation directly affects the FA biosynthesis in forages; lipid biosynthesis is decreased or even inhibited under water stress (Gigon et al., 2004).

Seasonal differences in feeds ultimately affect the nutritional composition of beef. Jain et al. (2020) reported that cattle finished in the spring exhibit higher levels of n−3 (including ALA, EPA, DPA, DHA) and n−6 PUFAs, stearic acid, and oleic acid. The n−6:n−3 ratio is also significantly lower in the spring compared to the fall. The higher levels of n−3 PUFAs in the spring are most likely due to higher n−3 levels in spring forages but also higher levels of antioxidants protecting n−3 PUFAs from oxidation and biohydrogenation. Sodium, phosphorus, and β-carotene were reported to be significantly higher in the fall, while magnesium, potassium, iron, zinc, selenium, and α-tocopherol were higher in the spring. Even if feed composition is usually self-reported by producers, it has been found that mineral levels in forages are higher in the spring rather than summer and fall (Jain et al., 2020).

Fatty acid content in beef is also affected by the region and the climate. For instance, Southern regions experience hot weather most of the year with some short periods of weather changes, while regions of the Midwest for example experience drastic weather changes based on seasons that last a few months each. Heat stress might be linked to differences in FA profiles (Steiner et al., 2015; Jain et al., 2020).

Seasonal variations are important to consider in the production of GFB. A well-managed grazing system taking into consideration feed nutritional differences based on season and weather conditions is crucial to determine optimal finishing phases to yield the healthiest nutrient profile in beef.

Providing only fresh forage to grass-fed cattle can become difficult for producers, especially since fresh grass is not always readily available in some regions and seasons. During the winter for instance, producers rely on hay or haylage, as well as non-starchy feeds like alfalfa rations, wheat, or oat straws (Gwin, 2009). According to the USDA, “hay, haylage, baleage, silage, crop residue without grain, and other roughage sources” may be added to grass-fed cattle diets, but these feeds are nutritionally different from fresh forage (Food Safety Inspection Service, 2019). Further, in some cases, additional supplementary feeds such as soybean hulls (SH) or grapeseed extracts may be added to forage-fed beef to improve beef quality and utilize byproducts of other industries (Kiesling, 2013; Muñoz-González et al., 2019). It is important to note that the addition of feed supplements described in this section varies by labeling organizations and does not necessarily reflect what is permitted in “grass-fed” labels outside of the U.S. such as certification by A Greener World in the United Kingdom or by the Pasture-fed Cattle Assurance System in Australia (A Greener World; PCAS). Thus, grass-fed cattle diets in the U.S. can be composed of an array of feeds which may lead to differences in nutritional profiles, particularly FA and phytochemical content, of GFB (Table 1).