Grass Fed Beef and Saturated Fat

A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef

Cynthia A Daley

¹College of Agriculture, California State University, Chico, CA, United states of america

Amber Abbott

¹College of Agriculture, California State University, Chico, CA, USA

Patrick S Doyle

¹Higher of Agriculture, California Land University, Chico, CA, United states

Glenn A Nader

²University of California Cooperative Extension Service, Davis, CA, USA

Stephanie Larson

ⁱⁱUniversity of California Cooperative Extension Service, Davis, CA, U.s.

Received 2009 Jul 29; Accepted 2010 Mar 10.

Abstract

Growing consumer involvement in grass-fed beefiness products has raised a number of questions with regard to the perceived differences in nutritional quality betwixt grass-fed and grain-fed cattle. Research spanning iii decades suggests that grass-based diets tin can significantly improve the fatty acid (FA) composition and antioxidant content of beefiness, albeit with variable impacts on overall palatability. Grass-based diets have been shown to enhance total conjugated linoleic acid (CLA) (C18:2) isomers, trans vaccenic acid (TVA) (C18:ane t11), a precursor to CLA, and omega-3 (north-3) FAs on a g/g fat basis. While the overall concentration of full SFAs is not dissimilar between feeding regimens, grass-finished beefiness tends toward a higher proportion of cholesterol neutral stearic FA (C18:0), and less cholesterol-elevating SFAs such equally myristic (C14:0) and palmitic (C16:0) FAs. Several studies suggest that grass-based diets elevate precursors for Vitamin A and E, besides as cancer fighting antioxidants such every bit glutathione (GT) and superoxide dismutase (SOD) activeness equally compared to grain-fed contemporaries. Fat witting consumers will besides prefer the overall lower fat content of a grass-fed beef production. Even so, consumers should be aware that the differences in FA content will also requite grass-fed beefiness a singled-out grass flavor and unique cooking qualities that should be considered when making the transition from grain-fed beefiness. In improver, the fat from grass-finished beef may have a yellowish advent from the elevated carotenoid content (precursor to Vitamin A). It is too noted that grain-fed beef consumers may achieve like intakes of both north-3 and CLA through the consumption of higher fat grain-fed portions.

Review Contents

i. Introduction

2. Fat acid contour in grass-fed beef

3. Impact of grass-finishing on omega-iii fatty acids

4. Affect of grass-finishing on conjugated linoleic acrid (CLA) and trans-vaccenic acid (TVA)

5. Impact of grass-finishing on β-carotenes/carotenoids

6. Impact of grass-finishing on α-tocopherol

seven. Impact of grass-finishing on GT & SOD activeness

viii. Impact of grass-finishing on flavour and palatability

9. Conclusion

10. References

Introduction

There is considerable back up amongst the nutritional communities for the diet-eye (lipid) hypothesis, the idea that an imbalance of dietary cholesterol and fats are the chief cause of atherosclerosis and cardiovascular affliction (CVD) [1]. Health professionals earth-broad recommend a reduction in the overall consumption of SFAs, trans-fatty acids (TAs) and cholesterol, while emphasizing the need to increase intake of n-3 polyunsaturated fats [1,two]. Such wide sweeping nutritional recommendations with regard to fatty consumption are largely due to epidemiologic studies showing strong positive correlations betwixt intake of SFA and the incidence of CVD, a condition believed to result from the concomitant ascent in serum low-density-lipoprotein (LDL) cholesterol as SFA intake increases [three,4]. For example, it is generally accepted that for every 1% increase in energy from SFA, LDL cholesterol levels reportedly increase by 1.iii to one.7 mg/dL (0.034 to 0.044 mmol/L) [five-vii].

Broad promotion of this correlative data spurred an anti-SFA entrada that reduced consumption of dietary fats, including most animal proteins such as meat, dairy products and eggs over the final 3 decades [eight], indicted on their relatively loftier SFA and cholesterol content. Yet, more recent lipid research would suggest that not all SFAs have the aforementioned touch on on serum cholesterol. For case, lauric acid (C12:0) and myristic acid (C14:0), have a greater total cholesterol raising outcome than palmitic acrid (C16:0), whereas stearic acrid (C18:0) has a neutral issue on the concentration of total serum cholesterol, including no apparent impact on either LDL or HDL. Lauric acid increases total serum cholesterol, although information technology also decreases the ratio of total cholesterol:HDL because of a preferential increase in HDL cholesterol [5,7,nine]. Thus, the individual fatty acid profiles tend to be more instructive than broad lipid classifications with respect to subsequent impacts on serum cholesterol, and should therefore exist considered when making dietary recommendations for the prevention of CVD.

Clearly the lipid hypothesis has had broad sweeping impacts; non only on the fashion we eat, but too on the mode food is produced on-subcontract. Indeed, changes in animal breeding and genetics have resulted in an overall leaner beef product[x]. Preliminary examination of diets containing today's leaner beef has shown a reduction in serum cholesterol, provided that beef consumption is express to a three ounce portion devoid of all external fat [11]. O'Dea's piece of work was the first of several studies to show today's leaner beef products can reduce plasma LDL concentrations in both normal and hyper-cholesterolemic subjects, theoretically reducing risk of CVD [12-15].

Beyond changes in genetics, some producers take also altered their feeding practices whereby reducing or eliminating grain from the ruminant diet, producing a product referred to as "grass-fed" or "grass-finished". Historically, most of the beef produced until the 1940'southward was from cattle finished on grass. During the 1950'due south, considerable inquiry was done to improve the efficiency of beef production, giving nativity to the feedlot industry where high free energy grains are fed to cattle as means to subtract days on feed and improve marbling (intramuscular fatty: Imf). In improver, U.South. consumers have grown accustomed to the sense of taste of grain-fed beef, mostly preferring the flavor and overall palatability afforded by the higher energy grain ration[sixteen]. Yet, changes in consumer need, coupled with new research on the effect of feed on nutrient content, accept a number of producers returning to the pastoral arroyo to beefiness product despite the inherent inefficiencies.

Enquiry spanning three decades suggests that grass-only diets can significantly alter the fat acid composition and improve the overall antioxidant content of beefiness. Information technology is the intent of this review, to synthesize and summarize the information currently available to substantiate an enhanced nutrient merits for grass-fed beef products too as to discuss the effects these specific nutrients have on homo health.

Review of fat acid profiles in grass-fed beef

Ruddy meat, regardless of feeding regimen, is nutrient dense and regarded as an important source of essential amino acids, vitamins A, B_vi, B₁₂, D, E, and minerals, including fe, zinc and selenium [17,eighteen]. Along with these important nutrients, meat consumers also ingest a number of fats which are an of import source of energy and facilitate the absorption of fat-soluble vitamins including A, D, E and M. According to the ADA, animal fats contribute approximately 60% of the SFA in the American nutrition, most of which are palmitic acid (C16:0) and stearic acid (C18:0). Stearic acid has been shown to accept no net bear upon on serum cholesterol concentrations in humans[17,19]. In add-on, 30% of the FA content in conventionally produced beef is composed of oleic acid (C18:1) [twenty], a monounsaturated FA (MUFA) that elicits a cholesterol-lowering effect among other healthful attributes including a reduced risk of stroke and a significant decrease in both systolic and diastolic claret pressure in susceptible populations [21].

Be that as it may, changes in finishing diets of conventional cattle can alter the lipid profile in such a way as to better upon this nutritional package. Although in that location are genetic, age related and gender differences among the various meat producing species with respect to lipid profiles and ratios, the effect of animal nutrition is quite significant [22]. Regardless of the genetic makeup, gender, age, species or geographic location, straight contrasts betwixt grass and grain rations consistently demonstrate significant differences in the overall fatty acrid profile and antioxidant content found in the lipid depots and trunk tissues [22-24].

Table ane summarizes the saturated fatty acid assay for a number of studies whose objectives were to dissimilarity the lipid profiles of cattle fed either a grain or grass diets [25-31]. This table is limited to those studies utilizing the longissimus dorsi (loin eye), thereby standardizing the contrasts to similar cuts within the carcass and limits the comparisons to cattle between 20 and thirty months of age. Unfortunately, not all studies report data in similar units of measure (i.e., thou/one thousand of fat acrid), so direct comparisons betwixt studies are not possible.

Table 1

Comparing of mean saturated fat acid composition (expressed equally mg/g of fatty acid or as a % of total lipid) between grass-fed and grain-fed cattle.

	Fatty Acid

Author, publication year, breed, treatment	C12:0 lauric	C14:0 myristic	C16:0 palmitic	C18:0 stearic	C20:0 arachidic	Total SFA (units as specified)	Total lipid (units as specified)
Alfaia, et al., 2009, Crossbred steers	g/100 thousand lipid
Grass	0.05	1.24*	18.42*	17.54*	0.25*	38.76	9.76* mg/yard muscle
Grain	0.06	1.84*	twenty.79*	fourteen.96*	0.19*	39.27	13.03* mg/thousand musculus
Leheska, et al., 2008, Mixed cattle	thou/100 g lipid
Grass	0.05	2.84*	26.9	17.0*	0.13*	48.eight*	ii.8* % of muscle
Grain	0.07	3.45*	26.iii	thirteen.ii*	0.08*	45.1*	iv.four* % of muscle
Garcia et al., 2008, Angus 10-bred steers	% of total FA
Grass	na	2.19	23.i	13.1*	na	38.4*	2.86* %International monetary fund
Grain	na	2.44	22.i	x.8*	na	35.three*	3.85* %IMF
Ponnampalam, et al., 2006, Angus steers	mg/100 g muscle tissue
Grass	na	56.9*	508*	272.eight	na	900*	2.12%* % of muscle
Grain	na	103.7*	899*	463.3	na	1568*	iii.61%* % of muscle
Nuernberg, et al., 2005, Simmental bulls	% of full intramuscular fat reported as LSM
Grass	0.04	one.82	22.56*	17.64*	na	43.91	1.51* % of muscle
Grain	0.05	1.96	24.26*	xvi.80*	na	44.49	ii.61* % of muscle
Descalzo, et al., 2005 Crossbred Steers	% of total FA
Grass	na	2.ii	22.0	19.ane	na	42.viii	ii.seven* %IMF
Grain	na	2.0	25.0	18.2	na	45.5	4.seven* %IMF
Realini, et al., 2004, Hereford steers	% fat acid within intramuscular fat
Grass	na	1.64*	21.61*	17.74*	na	49.08	ane.68* % of muscle
Grain	na	2.17*	24.26*	15.77*	na	47.62	3.xviii* % of muscle

*Indicates a significant deviation (at least P < 0.05) between feeding regimens was reported within each corresponding study. "na" indicates that the value was not reported in the original written report.

Table 1 reports that grass finished cattle are typically lower in total fat equally compared to grain-fed contemporaries. Interestingly, there is no consistent difference in total SFA content between these ii feeding regimens. Those SFA's considered to be more detrimental to serum cholesterol levels, i.e., myristic (C14:0) and palmitic (C16:0), were college in grain-fed beefiness as compared to grass-fed contemporaries in 60% of the studies reviewed. Grass finished meat contains elevated concentrations of stearic acid (C18:0), the only saturated fatty acrid with a net neutral affect on serum cholesterol. Thus, grass finished beef tends to produce a more than favorable SFA composition although petty is known of how grass-finished beef would ultimately bear on serum cholesterol levels in hyper-cholesterolemic patients as compared to a grain-fed beef.

Like SFA intake, dietary cholesterol consumption has also become an important outcome to consumers. Interestingly, beef'southward cholesterol content is similar to other meats (beef 73; pork 79; lamb 85; chicken 76; and turkey 83 mg/100 g) [32], and can therefore be used interchangeably with white meats to reduce serum cholesterol levels in hyper-cholesterolemic individuals[11,33]. Studies have shown that brood, diet and sex do not affect the cholesterol concentration of bovine skeletal muscle, rather cholesterol content is highly correlated to IMF concentrations[34]. As IMF levels rise, and so goes cholesterol concentrations per gram of tissue [35]. Because pasture raised beefiness is lower in overall fat [24-27,30], particularly with respect to marbling or IMF [26,36], it would seem to follow that grass-finished beef would be lower in overall cholesterol content although the data is very limited. Garcia et al (2008) report 40.iii and 45.eight grams of cholesterol/100 grams of tissue in pastured and grain-fed steers, respectively (P < 0.001) [24].

Interestingly, grain-fed beef consistently produces higher concentrations of MUFAs as compared to grass-fed beefiness, which include FAs such as oleic acid (C18:i cis-9), the primary MUFA in beefiness. A number of epidemiological studies comparing illness rates in different countries have suggested an inverse clan between MUFA intake and mortality rates to CVD [iii,21]. All the same, grass-fed beef provides a higher concentration of TVA (C18:1 t11), an of import MUFA for de novo synthesis of conjugated linoleic acrid (CLA: C18:2 c-9, t-11), a potent anti-carcinogen that is synthesized inside the body tissues [37]. Specific data relative to the wellness benefits of CLA and its biochemistry will be detailed after.

The important polyunsaturated fat acids (PUFAs) in conventional beef are linoleic acid (C18:2), alpha-linolenic acid (C18:3), described as the essential FAs, and the long-chain fatty acids including arachidonic acid (C20:4), eicosapentaenoic acid (C20:v), docosanpetaenoic acid (C22:five) and docosahexaenoic acid (C22:6) [38]. The significance of nutrition on fatty acid composition is clearly demonstrated when profiles are examined by omega 6 (due north-6) and omega 3 (due north-3) families. Table 2 shows no significant change to the overall concentration of north-half-dozen FAs between feeding regimens, although grass-fed beef consistently shows a higher concentrations of n-3 FAs equally compared to grain-fed contemporaries, creating a more than favorable north-6:n-3 ratio. In that location are a number of studies that study positive furnishings of improved northward-3 intake on CVD and other health related issues discussed in more detail in the next section.

Tabular array ii

Comparing of hateful polyunsatured fatty acrid composition (expressed as mg/g of fat acid or as a % of full lipid) between grass-fed and grain-fed cattle.

	Fat Acid

Writer, publication yr, breed, treatment	C18:one t11 Vaccenic Acid	C18:2 northward-6 Linoleic	Total CLA	C18:iii n-three Linolenic	C20:5n-3 EPA	C22:5n-3 DPA	C22:6n-3 DHA	Full PUFA	Total MUFA	Total n-vi	Total n-3	northward-6/n-3 ratio
Alfaia, et al., 2009, Crossbred steers	g/100 g lipid
Grass	1.35	12.55	v.14*	five.53*	2.13*	2.56*	0.20*	28.99*	24.69*	17.97*	10.41*	ane.77*
Grain	0.92	11.95	two.65*	0.48*	0.47*	0.91*	0.11*	19.06*	34.99*	17.08	i.97*	8.99*
Leheska, et al., 2008, Mixed cattle	thousand/100 g lipid
Grass	ii.95*	2.01	0.85*	0.71*	0.31	0.24*	na	3.41	42.5*	2.thirty	ane.07*	2.78*
Grain	0.51*	ii.38	0.48*	0.13*	0.nineteen	0.06*	na	2.77	46.two*	ii.58	0.19*	13.half-dozen*
Garcia, et al., 2008, Angus steers	% of total FAs
Grass	three.22*	3.41	0.72*	1.30*	0.52*	0.70*	0.43*	7.95	37.seven*	5.00*	ii.95*	1.72*
Grain	ii.25*	3.93	0.58*	0.74*	0.12*	0.30*	0.14*	9.31	40.8*	8.05*	0.86*	10.38*
Ponnampalam, et al., 2006, Angus steers	mg/100 g musculus tissue
Grass	na	108.viii*	fourteen.three	32.iv*	24.5*	36.5*	4.2	na	930*	191.6	97.6*	1.96*
Grain	na	167.4*	16.one	14.9*	thirteen.i*	31.6*	3.7	na	1729*	253.8	63.3*	3.57*
Nuernberg, et al., 2005, Simmental bulls	% of total fatty acids
Grass	na	6.56	0.87*	ii.22*	0.94*	1.32*	0.17*	14.29*	56.09	nine.80	4.70*	two.04*
Grain	na	five.22	0.72*	0.46*	0.08*	0.29*	0.05*	9.07*	55.51	7.73	0.90*	eight.34*
Descalzo, et al., 2005, Crossbred steers	% of full FAs
Grass	4.two*	5.4	na	one.4*	tr	0.vi	tr	10.31*	34.17*	seven.4	2.0	3.72*
Grain	2.8*	iv.7	na	0.7*	tr	0.four	tr	vii.29*	37.83*	6.three	one.one	5.73*
Realini, et al., 2004, Hereford steers	% fatty acrid within intramuscular fat
Grass	na	3.29*	0.53*	i.34*	0.69*	1.04*	0.09	nine.96*	40.96*	na	na	one.44*
Grain	na	2.84*	0.25*	0.35*	0.xxx*	0.56*	0.09	6.02*	46.36*	na	na	3.00*

* Indicates a significant departure (at least P < 0.05) between feeding regimens within each respective report reported. "na" indicates that the value was not reported in the original report. "tr" indicates trace amounts detected.

Review of Omega-3: Omega-6 fatty acid content in grass-fed beefiness

There are two essential fatty acids (EFAs) in human being nutrition: α-linolenic acid (αLA), an omega-3 fatty acid; and linoleic acid (LA), an omega-6 fatty acid. The human body cannot synthesize essential fat acids, all the same they are critical to human wellness; for this reason, EFAs must be obtained from food. Both αLA and LA are polyunsaturated and serve as precursors of other important compounds. For instance, αLA is the precursor for the omega-3 pathway. Likewise, LA is the parent fat acrid in the omega-6 pathway. Omega-3 (n-iii) and omega-half-dozen (northward-vi) fat acids are two separate singled-out families, yet they are synthesized by some of the aforementioned enzymes; specifically, delta-5-desaturase and delta-6-desaturase. Excess of i family of FAs tin can interfere with the metabolism of the other, reducing its incorporation into tissue lipids and altering their overall biological effects [39]. Figure 1 depicts a schematic of north-vi and due north-3 metabolism and elongation within the trunk [xl].

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Linoleic (C18:2n-half-dozen) and α-Linolenic (C18:3n-iii) Acrid metabolism and elongation. (Adapted from Simopoulos et al., 1991)

A healthy diet should consist of roughly one to 4 times more omega-half dozen fat acids than omega-3 fat acids. The typical American diet tends to contain 11 to 30 times more omega -half-dozen fatty acids than omega -iii, a phenomenon that has been hypothesized equally a significant factor in the ascension charge per unit of inflammatory disorders in the U.s.[40]. Tabular array 2 shows pregnant differences in n-6:n-3 ratios between grass-fed and grain-fed beef, with and overall boilerplate of one.53 and 7.65 for grass-fed and grain-fed, respectively, for all studies reported in this review.

The major types of omega-3 fatty acids used past the body include: α-linolenic acid (C18:3n-3, αLA), eicosapentaenoic acid (C20:5n-iii, EPA), docosapentaenoic acid (C22:5n-three, DPA), and docosahexaenoic acid (C22:6n-three, DHA). In one case eaten, the body converts αLA to EPA, DPA and DHA, albeit at low efficiency. Studies more often than not agree that whole body conversion of αLA to DHA is below 5% in humans, the majority of these long-concatenation FAs are consumed in the nutrition [41].

The omega-3 fatty acids were first discovered in the early 1970's when Danish physicians observed that Greenland Eskimos had an exceptionally depression incidence of middle disease and arthritis despite the fact that they consumed a diet high in fat. These early on studies established fish equally a rich source of n-3 fatty acids. More recent inquiry has established that EPA and DHA play a crucial role in the prevention of atherosclerosis, heart assail, low and cancer [twoscore,42]. In add-on, omega-3 consumption reduced the inflammation caused past rheumatoid arthritis [43,44].

The homo brain has a high requirement for DHA; low DHA levels have been linked to depression brain serotonin levels, which are connected to an increased tendency for depression and suicide. Several studies have established a correlation between low levels of omega -iii fatty acids and depression. Loftier consumption of omega-3 FAs is typically associated with a lower incidence of depression, a decreased prevalence of historic period-related memory loss and a lower risk of developing Alzheimer's illness [45-51].

The National Institutes of Health has published recommended daily intakes of FAs; specific recommendations include 650 mg of EPA and DHA, 2.22 g/day of αLA and 4.44 m/day of LA. Nevertheless, the Establish of Medicine has recommended DRI (dietary reference intake) for LA (omega-6) at 12 to 17 chiliad and αLA (omega-3) at 1.1 to 1.6 one thousand for adult women and men, respectively. Although seafood is the major dietary source of n-iii fat acids, a recent fatty acid intake survey indicated that crimson meat also serves as a significant source of northward-3 fat acids for some populations [52].

Sinclair and co-workers were the offset to show that beef consumption increased serum concentrations of a number of n-3 fatty acids including, EPA, DPA and DHA in humans [twoscore]. Likewise, there are a number of studies that have been conducted with livestock which report similar findings, i.e., animals that consume rations high in precursor lipids produce a meat product higher in the essential fat acids [53,54]. For instance, cattle fed primarily grass significantly increased the omega-3 content of the meat and besides produced a more favorable omega-vi to omega-three ratio than grain-fed beef [46,55-57].

Tabular array two shows the effect of ration on polyunsaturated fatty acid limerick from a number of recent studies that contrast grass-based rations to conventional grain feeding regimens [24-28,30,31]. Grass-based diets resulted in significantly college levels of omega-3 within the lipid fraction of the meat, while omega-6 levels were left unchanged. In fact, equally the concentration of grain is increased in the grass-based nutrition, the concentration of n-3 FAs decreases in a linear way. Grass-finished beef consistently produces a college concentration of northward-3 FAs (without effecting n-6 FA content), resulting in a more than favorable n-6:northward-3 ratio.

The corporeality of total lipid (fat) found in a serving of meat is highly dependent upon the feeding regimen equally demonstrated in Tables 1 and 2. Fat volition also vary by cutting, as not all locations of the carcass will deposit fat to the same degree. Genetics as well play a office in lipid metabolism creating significant breed furnishings. Nevertheless, the result of feeding regimen is a very powerful determinant of fat acrid limerick.

Review of conjugated linoleic acid (CLA) and trans vaccenic acid (TVA) in grass-fed beef

Conjugated linoleic acids brand upwardly a group of polyunsaturated FAs plant in meat and milk from ruminant animals and exist as a general mixture of conjugated isomers of LA. Of the many isomers identified, the cis-9, trans-11 CLA isomer (as well referred to every bit rumenic acid or RA) accounts for upward to 80-ninety% of the total CLA in ruminant products [58]. Naturally occurring CLAs originate from two sources: bacterial isomerization and/or biohydrogenation of polyunsaturated fatty acids (PUFA) in the rumen and the desaturation of trans-fatty acids in the adipose tissue and mammary gland [59,threescore].

Microbial biohydrogenation of LA and αLA by an anaerobic rumen bacterium Butyrivibrio fibrisolvens is highly dependent on rumen pH [61]. Grain consumption decreases rumen pH, reducing B. fibrisolven activity, conversely grass-based diets provide for a more favorable rumen environment for subsequent bacterial synthesis [62]. Rumen pH may assist to explain the apparent differences in CLA content between grain and grass-finished meat products (encounter Table 2). De novo synthesis of CLA from 11t-C18:one TVA has been documented in rodents, dairy cows and humans. Studies advise a linear increase in CLA synthesis as the TVA content of the diet increased in human subjects [63]. The rate of conversion of TVA to CLA has been estimated to range from 5 to 12% in rodents to 19 to thirty% in humans[64]. Truthful dietary intake of CLA should therefore consider native 9c11t-C18:2 (actual CLA) equally well equally the 11t-C18:1 (potential CLA) content of foods [65,66]. Figure ii portrays de novo synthesis pathways of CLA from TVA [37].

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De novo synthesis of CLA from 11t-C18:1 vaccenic acid. (Adapted from Bauman et al., 1999)

Natural augmentation of CLA cixteleven and TVA within the lipid fraction of beef products can be accomplished through diets rich in grass and lush green forages. While precursors can be found in both grains and lush green forages, grass-fed ruminant species take been shown to produce 2 to 3 times more CLA than ruminants fed in confinement on high grain diets, largely due to a more than favorable rumen pH [34,56,57,67] (see Table 2).

The impact of feeding practices becomes even more evident in light of recent reports from Canada which suggests a shift in the predominate trans C18:1 isomer in grain-fed beef. Dugan et al (2007) reported that the major trans isomer in beef produced from a 73% barley grain diet is xt-18:one (2.13% of total lipid) rather than 11t-18:1 (TVA) (0.77% of total lipid), a finding that is not particularly favorable because the data that would support a negative impact of tent-eighteen:one on LDL cholesterol and CVD [68,69].

Over the by two decades numerous studies have shown pregnant health benefits owing to the actions of CLA, as demonstrated by experimental animal models, including actions to reduce carcinogenesis, atherosclerosis, and onset of diabetes [lxx-72]. Conjugated linoleic acid has too been reported to modulate body composition by reducing the accumulation of adipose tissue in a diversity of species including mice, rats, pigs, and now humans [73-76]. These changes in trunk composition occur at ultra loftier doses of CLA, dosages that can merely be attained through synthetic supplementation that may too produce ill side-effects, such equally gastrointestinal upset, adverse changes to glucose/insulin metabolism and compromised liver function [77-81]. A number of splendid reviews on CLA and homo health tin can exist found in the literature [61,82-84].

Optimal dietary intake remains to be established for CLA. Information technology has been hypothesized that 95 mg CLA/day is enough to show positive effects in the reduction of breast cancer in women utilizing epidemiological data linking increased milk consumption with reduced breast cancer[85]. Ha et al. (1989) published a much more conservative estimate stating that 3 g/twenty-four hours CLA is required to promote human health benefits[86]. Ritzenthaler et al. (2001) estimated CLA intakes of 620 mg/day for men and 441 mg/day for women are necessary for cancer prevention[87]. Patently, all these values stand for rough estimates and are mainly based on extrapolated fauna data. What is clear is that we as a population do not consume enough CLA in our diets to have a significant impact on cancer prevention or suppression. Reports bespeak that Americans swallow betwixt 150 to 200 mg/day, Germans consumer slightly more than between 300 to 400 mg/day[87], and the Australians seem to be closer to the optimum concentration at 500 to g mg/24-hour interval co-ordinate to Parodi (1994) [88].

Review of pro-Vitamin A/β-carotene in grass-fed meat

Carotenoids are a family of compounds that are synthesized past higher plants every bit natural constitute pigments. Xanthophylls, carotene and lycopene are responsible for yellow, orangish and red coloring, respectively. Ruminants on high forage rations pass a portion of the ingested carotenoids into the milk and body fat in a fashion that has however to be fully elucidated. Cattle produced under extensive grass-based production systems generally accept carcass fat which is more yellow than their concentrate-fed counterparts caused past carotenoids from the lush green forages. Although xanthous carcass fat is negatively regarded in many countries around the globe, it is also associated with a healthier fatty acid profile and a higher antioxidant content [89].

Establish species, harvest methods, and season, all have pregnant impacts on the carotenoid content of forage. In the process of making silage, haylage or hay, as much as lxxx% of the carotenoid content is destroyed [xc]. Further, significant seasonal shifts occur in carotenoid content attributable to the seasonal nature of plant growth.

Carotenes (mainly β-carotene) are precursors of retinol (Vitamin A), a critical fatty-soluble vitamin that is important for normal vision, bone growth, reproduction, cell division, and cell differentiation [91]. Specifically, information technology is responsible for maintaining the surface lining of the eyes and also the lining of the respiratory, urinary, and abdominal tracts. The overall integrity of skin and mucous membranes is maintained past vitamin A, creating a barrier to bacterial and viral infection [xv,92]. In addition, vitamin A is involved in the regulation of allowed role by supporting the product and role of white blood cells [12,13].

The current recommended intake of vitamin A is 3,000 to 5,000 IU for men and 2,300 to 4,000 IU for women [93], respectively, which is equivalent to 900 to 1500 μg (micrograms) (Note: DRI equally reported by the Institute of Medicine for non-pregnant/non-lactating developed females is 700 μg/twenty-four hour period and males is 900 μg/24-hour interval or two,300 - 3,000 I U (assuming conversion of 3.33 IU/μg). While there is no RDA (Required Daily Assart) for β-carotene or other pro-vitamin A carotenoids, the Institute of Medicine suggests consuming three mg of β-carotene daily to maintain plasma β-carotene in the range associated with normal function and a lowered risk of chronic diseases (NIH: Office of Dietary Supplements).

The effects of grass feeding on beta-carotene content of beef was described past Descalzo et al. (2005) who constitute pasture-fed steers incorporated significantly higher amounts of beta-carotene into muscle tissues as compared to grain-fed animals [94]. Concentrations were 0.45 μg/m and 0.06 μg/g for beef from pasture and grain-fed cattle respectively, demonstrating a seven fold increment in β-carotene levels for grass-fed beefiness over the grain-fed contemporaries. Similar data has been reported previously, presumably due to the loftier β-carotene content of fresh grasses every bit compared to cereal grains[38,55,95-97]. (see Table 3)

Table iii

Comparison of hateful β-carotene vitamin content in fresh beef from grass-fed and grain-fed cattle.

	β-carotene

Author, yr, creature course	Grass-fed (ug/grand tissue)	Grain-fed (ug/g tissue)
Insani et al., 2007, Crossbred steers	0.74*	0.17*
Descalzo et al., 2005 Crossbred steers	0.45*	0.06*
Yang et al., 2002, Crossbred steers	0.xvi*	0.01*

* Indicates a significant deviation (at least P < 0.05) between feeding regimens was reported within each corresponding study.

Review of Vitamin E/α-tocopherol in grass-fed beef

Vitamin E is besides a fat-soluble vitamin that exists in eight different isoforms with powerful antioxidant activity, the most active beingness α-tocopherol [98]. Numerous studies have shown that cattle finished on pasture produce college levels of α-tocopherol in the final meat product than cattle fed high concentrate diets[23,28,94,97,99-101] (run across Table 4).

Table 4

Comparing of mean α-tocopherol vitamin content in fresh beef from grass-fed and grain-fed cattle.

	α-tocopherol

Author, year, animal class	Grass-fed (ug/g tissue)	Grain-fed (ug/thousand tissue)
De la Fuente et al., 2009, Mixed cattle	4.07*	0.75*
Descalzo, et al., 2008, Crossbred steers	three.08*	1.50*
Insani et al., 2007, Crossbred steers	2.1*	0.viii*
Descalzo, et al., 2005, Crosbred steers	four.6*	2.2*
Realini et al., 2004, Hereford steers	three.91*	2.92*
Yang et al., 2002, Crossbred steers	4.v*	1.8*

* Indicates a significant difference (at least P < 0.05) between feeding regimens was reported within each corresponding study.

Antioxidants such equally vitamin Due east protect cells against the effects of free radicals. Gratuitous radicals are potentially dissentious by-products of metabolism that may contribute to the development of chronic diseases such equally cancer and cardiovascular disease.

Preliminary inquiry shows vitamin E supplementation may aid prevent or delay coronary eye affliction [102-105]. Vitamin East may also cake the formation of nitrosamines, which are carcinogens formed in the stomach from nitrates consumed in the nutrition. It may also protect against the evolution of cancers by enhancing immune part [106]. In improver to the cancer fighting effects, there are some observational studies that constitute lens clarity (a diagnostic tool for cataracts) was better in patients who regularly used vitamin E [107,108]. The current recommended intake of vitamin East is 22 IU (natural source) or 33 IU (synthetic source) for men and women [93,109], respectively, which is equivalent to 15 milligrams by weight.

The concentration of natural α-tocopherol (vitamin Due east) found in grain-fed beef ranged betwixt 0.75 to 2.92 μg/g of muscle whereas pasture-fed beef ranges from ii.one to vii.73 μg/g of tissue depending on the type of forage made available to the animals (Tabular array 4). Grass finishing increases α-tocopherol levels iii-fold over grain-fed beef and places grass-fed beef well inside range of the muscle α-tocopherol levels needed to extend the shelf-life of retail beefiness (three to 4 μg α-tocopherol/gram tissue) [110]. Vitamin Due east (α-tocopherol) acts postal service-mortem to filibuster oxidative deterioration of the meat; a process past which myoglobin is converted into brown metmyoglobin, producing a darkened, brown advent to the meat. In a study where grass-fed and grain-fed beef were directly compared, the bright red colour associated with oxymyoglobin was retained longer in the retail brandish in the grass-fed group, even thought the grass-fed meat contains a college concentration of more oxidizable n-3 PUFA. The authors ended that the antioxidants in grass probably caused higher tissue levels of vitamin Due east in grazed animals with benefits of lower lipid oxidation and better color retention despite the greater potential for lipid oxidation[111].

Review of antioxidant enzyme content in grass-fed beef

Glutathione (GT), is a relatively new protein identified in foods. It is a tripeptide composed of cysteine, glutamic acid and glycine and functions as an antioxidant primarily as a component of the enzyme system containing GT oxidase and reductase. Within the prison cell, GT has the capability of quenching costless radicals (similar hydrogen peroxide), thus protecting the cell from oxidized lipids or proteins and prevent damage to Dna. GT and its associated enzymes are found in about all found and animal tissue and is readily absorbed in the small intestine[112].

Although our knowledge of GT content in foods is notwithstanding somewhat limited, dairy products, eggs, apples, beans, and rice incorporate very niggling GT (< iii.3 mg/100 g). In contrast, fresh vegetables (e.g., asparagus 28.3 mg/100 g) and freshly cooked meats, such as ham and beef (23.iii mg/100 grand and 17.5 mg/100 thou, respectively), are high in GT [113].

Because GT compounds are elevated in lush dark-green forages, grass-fed beef is particularly high in GT as compared to grain-fed contemporaries. Descalzo et al. (2007) reported a significant increment in GT molar concentrations in grass-fed beef [114]. In addition, grass-fed samples were too higher in superoxide dismutase (SOD) and catalase (CAT) action than beef from grain-fed animals[115]. Superoxide dismutase and catalase are coupled enzymes that work together equally powerful antioxidants, SOD scavenges superoxide anions by forming hydrogen peroxide and True cat then decomposes the hydrogen peroxide to H_twoO and O₂. Grass only diets improve the oxidative enzyme concentration in beef, protecting the muscle lipids against oxidation as well as providing the beef consumer with an additional source of antioxidant compounds.

Problems related to flavor and palatability of grass-fed beef

Maintaining the more favorable lipid profile in grass-fed beef requires a high percentage of lush fresh fodder or grass in the ration. The higher the concentration of fresh green forages, the higher the αLA precursor that volition be bachelor for CLA and n-iii synthesis [53,54]. Fresh pasture forages have 10 to 12 times more than C18:iii than cereal grains [116]. Dried or cured forages, such equally hay, will have a slightly lower amount of precursor for CLA and n-iii synthesis. Shifting diets to cereal grains will cause a significant modify in the FA profile and antioxidant content within 30 days of transition [57].

Considering grass-finishing alters the biochemistry of the beef, aroma and flavor volition likewise be afflicted. These attributes are directly linked to the chemical makeup of the final product. In a written report comparison the flavour compounds between cooked grass-fed and grain-fed beefiness, the grass-fed beef independent higher concentrations of diterpenoids, derivatives of chlorophyll call phyt-1-ene and phyt-2-ene, that changed both the flavor and olfactory property of the cooked production [117]. Others accept identified a "green" odor from cooked grass-fed meat associated with hexanals derived from oleic and αLA FAs. In contrast to the "greenish" odor, grain-fed beef was described every bit possessing a "soapy" aroma, presumably from the octanals formed from LA that is establish in high concentration in grains [118]. Grass-fed beef consumers can expect a different flavor and aroma to their steaks as they cook on the grill. Likewise, because of the lower lipid content and high concentration of PUFAs, cooking time will exist reduced. For an exhaustive look at the effect of meat compounds on season, come across Calkins and Hodgen (2007) [119].

With respect to palatability, grass-fed beef has historically been less well accustomed in markets where grain-fed products predominant. For case, in a written report where British lambs fed grass and Spanish lambs fed milk and concentrates were assessed by British and Spanish taste panels, both found the British lamb to accept a higher odor and flavor intensity. Nevertheless, the British console preferred the season and overall eating quality of the grass-fed lamb, the Spanish panel much preferred the Spanish fed lamb [120]. Likewise, the U.Due south. is well known for producing corn-fed beefiness, gustatory modality panels and consumers who are more familiar with the taste of corn-fed beefiness seem to adopt information technology as well [16]. An private usually comes to adopt the foods they grew up eating, making consumer sensory panels more than of an art than science [36]. Trained taste panels, i.due east., persons specifically trained to evaluate sensory characteristics in beefiness, found grass-fed beefiness less palatable than grain-fed beef in flavor and tenderness [119,121].

Conclusion

Research spanning three decades supports the argument that grass-fed beefiness (on a g/grand fatty basis), has a more desirable SFA lipid contour (more C18:0 cholesterol neutral SFA and less C14:0 & C16:0 cholesterol elevating SFAs) equally compared to grain-fed beef. Grass-finished beef is also college in total CLA (C18:2) isomers, TVA (C18:1 t11) and n-3 FAs on a k/g fat basis. This results in a improve n-half dozen:n-iii ratio that is preferred past the nutritional customs. Grass-fed beefiness is also higher in precursors for Vitamin A and E and cancer fighting antioxidants such every bit GT and SOD activity as compared to grain-fed contemporaries.

Grass-fed beef tends to be lower in overall fat content, an important consideration for those consumers interested in decreasing overall fat consumption. Because of these differences in FA content, grass-fed beef also possesses a distinct grass flavor and unique cooking qualities that should be considered when making the transition from grain-fed beef. To maximize the favorable lipid profile and to guarantee the elevated antioxidant content, animals should exist finished on 100% grass or pasture-based diets.

Grain-fed beef consumers may achieve similar intakes of both north-3 and CLA through consumption of higher fat portions with higher overall palatability scores. A number of clinical studies accept shown that today's lean beef, regardless of feeding strategy, tin be used interchangeably with fish or skinless craven to reduce serum cholesterol levels in hypercholesterolemic patients.

Abbreviations

c: cis; t: trans; FA: fatty acid; SFA: saturated fat acrid; PUFA: polyunsaturated fatty acid; MUFA: monounsaturated fatty acid; CLA: conjugated linoleic acrid; TVA: trans-vaccenic acid; EPA: eicosapentaenoic acrid; DPA: docosapentaenoic acid; DHA: docosahexaenoic acid; GT: glutathione; SOD: superoxide dismutase; Cat: catalase.

Competing interests

The authors declare that they take no competing interests.

Authors' contributions

CAD was responsible for the literature review, completed well-nigh of the principal writing, created the manuscript and worked through the submission process; AA conducted the literature search, organized the articles according to category, completed some of the principal writing and served as editor; SPD conducted a portion of the literature review and served equally editor for the manuscript; GAN conducted a portion of the literature review and served equally editor for the manuscript; SL conducted a portion o the literature review and served as editor for the manuscript. All authors read and canonical the concluding manuscript.

Acknowledgements

The authors would similar to acknowledge Grace Berryhill for her assistance with the figures, tables and editorial contributions to this manuscript.

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