Abstract
Background: The link between meat and various chronic diseases has been qualified recently, and is now accepted as being related to the amount of saturated fat present. Other work has shown differences in total lipid profiles between meat from ‘wild’ and ‘domesticated’ animals, with the ‘wild’ reflecting higher levels of polyunsaturated and lower saturated fat. This study assessed both meat types from South African sources. Materials and Methods: All ‘wild’ meat samples were obtained fresh from a specialist restaurant. All ‘domestic’ samples were purchased from commercial outlets. Lipids were quantified using thin layer and gas chromatography. Results: All of the domestic meats had higher saturated and lower polyunsaturated lipid levels than the wild meats. There was little difference between the phosphoglyceride, but large differences between the triacylcglycerol, fractions. Conclusion: Meat from animals raised under intensive agricultural methods in Africa is similar to those from the rest of the world, while wild meats are markedly different.
For a large part of its evolutionary history, humanity has followed a hunter-gatherer diet, with only a comparatively recent transition to a Westernised diet. While both diets contain significant proportions of meat, the hunter-gatherer diet is associated with ‘wild’ meat and the Westernised with ‘domestic’ meat. In lean meat, the major lipids are largely structural, i.e. phosphoglycerides (PG), while the adjacent adipose tissue lipid is largely storage, i.e. triacylglycerols (TG). Evidence has accumulated that lean meat itself is not a risk factor for chronic disease, but rather risk stems from the excessive fat, particularly saturated fat, associated with the meat of domesticated animals raised using intensive agricultural practices (1-5). The high saturated fat content of ‘domestic’ meat is a result not only of the adipose tissue adjacent to the lean meat, but also the occurrence of marbling – the deposition of TGs amongst the muscle fibres (6). In parallel, ‘domestic’ meat has also been found to be low in polyunsaturated fatty acids (PUFAs) (7-10).
Until recently, dietary guidelines recommended a diet providing low total fat and increased carbohydrate. Lately, the role of total fat as a major risk factor for chronic disease has been de-emphasized, and the influence of saturated and polyunsaturated fatty acids have been the focus of attention, with saturated fatty acids shown to increase and PUFAs to decrease the risk of chronic conditions (11-12).
Dietary fat is the source of the two essential PUFAs (EFAs) – linoleic (LA, cis-C18:2n6) and α-linolenic (ALA, cis-C18:3n3) acids. The EFAs, via their longer chain n6 and n3 derivatives, and their eicosanoid metabolites play important roles in structural and regulatory functions in the body (13, 14). In contrast, saturated fat has been shown to reduce the activity of Δ-6-desaturase, the first enzyme in the cascade that converts the EFAs to the longer chain, more polyunsaturated moieties of both the n6 and n3 series (15).
The Inuit, a community with a high fish consumption, show decreased incidence of chronic diseases, and whilst their diet is high in fat, much of that fat is n3 PUFAs, particularly eicosapentaenoic acid (EPA, cis-C20:5n3) and docosahexaenoic acid (DHA, cis-C22:6n3), both of which originate from marine phytoplankton (16-17).
At the same time, it has also been shown that reduction in dietary saturates, and a parallel increase in monounsaturates, is associated with a decreased risk of chronic conditions (18). The Mediterranean diet, which is rich in monounsaturated and low in saturated and trans-unsaturated fats, correlates with the low rates of cardiovascular disease seen in people of the peri-Mediterranean region (19, 20). In parallel, many studies have indicated the potency of PUFAs in inhibiting transformed cell growth, while not affecting normal cells (22, 23). In most studies, the n6 and n3 PUFAs were of comparable potency, often completely inhibiting net cell division (24-25). However, studies using human breast carcinoma cells showed a potentiation of cell division when n6, but not n3, PUFAs were used (26). Thus, increased availability of both n6 and n3, but especially of n3, may be of benefit in many chronic disease conditions (27-34).
In 1968, Crawford showed differences in tissue fatty acids between ‘wild’ and ‘domestic’ meats (8). ‘Domestic’ meat had a high percentage of saturated fat, due both to the nature of the meat and marbling effects, whilst ‘wild’ meat was low in saturated fat. ‘Domestic’ meat was also low in PUFAs, at only 2%, whilst ‘wild’ meat was relatively high in PUFAs (30%), although with a low concentration of long-chain PUFA. In 1970, Crawford et al. reported on further studies where they found high levels of both LA and ALA present in ‘wild’ meat. Since then, other comparative studies have been performed elsewhere with similar results (12, 35, 36). These paralleled the earlier research and demonstrated that ‘wild’ meats had lower saturated fat and higher PUFA levels, when compared to ‘domestic’ meats. A possible explanation for the differences in fat content of ‘domestic’ meat versus ‘wild’ meat is a combination of selective breeding, management practices and readily available food, resulting in domesticated animals having the large amount of visible fat reported (37-40).
This study reports on similar work carried out on species endemic to Africa, as well as exotic domesticated species, and characterizes both the profile of total lipid fatty acids and those of two major classes within the total lipid (PG and TG).
Materials and Methods
Meat samples were obtained from two sources: a restaurant specialising in ‘wild’ meats (the ‘Carnivore’ in Johannesburg), while a commercial retail outlet provided the ‘domestic’ samples. ‘Wild’ meats included eland, gemsbok, giraffe, hartebeest, kudu, sable, warthog, zebra, ostrich and crocodile. All mammalian samples, except warthog which was a loin chop, were taken from the rump region of the carcass, the cut most used by the restaurant, while ostrich was from breast and crocodile from thigh. ‘Domestic’ meats were beef (rump), lamb (chop), pork (chop) and chicken (breast). A minimum of 20 g of each sample was weighed, and the lipids extracted using standard techniques (41). Lipid dry weights were determined, and methyl esters of the fatty acids prepared (42). These were then separated using a Varian 3400 gas chromatograph with 4270 integrator and a 10% SP2330 on Chromosorb WAW 6’ × 1/8’’ packed column run isothermally at 195°C with flame ionization detector. Fatty acyl methyl esters (FAME) were identified by comparison with authentic standards.
Further lipid aliquots were separated into PG and TG fractions by thin layer chromatography, with development using petroleum ether:diethyl ether:acetic acid (65:15:2.5). The lipids were eluted with chloroform: methanol (49:1) (43). The resultant PG and TG fractions were weighed and the FAME prepared and analysed as described above. Means and standard deviations were calculated and tabulated. Data were compared using Student's t-test (Statistica 9 software package).
The amounts and proportions of the lipids of the meat samples (mg/g wet mass).
Results
This study compared the fatty acid profiles of South African ‘wild’ meats with ‘domestic’ meats. The results are shown in Tables I, II and III. The results of the mammalian species (red meat) have been tabulated individually and as the mean±SD. The non-mammalian species (avian and reptilian) are shown for comparison, but not included in the group data with the mammals.
Table I shows the amount of total lipid as mg/g wet weight original muscle tissue sample and the proportions of PG and TG as determined using thin layer chromatography and gravimetry. The total lipids were greater in the domestic species (p=0.03). This compared with the earlier studies from elsewhere (10-11). Generally the PG amounts were comparable between the wild and domestic species (p=0.24), although the wild species tended to be greater. In contrast the TG fractions were greater in the domestic species (p=0.01). Interestingly, meat from the two avian species (chicken and ostrich) both had low proportions of TG, compared to the domestic mammal species.
Tables II and III show the results of the fatty acid analyses of the muscle tissue samples, for both the total lipids and the PG and TG fractions, for the domestic and wild species, respectively.
The PG showed little difference in the total saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and PUFA, while in the TG fraction, the SFA and MUFA were higher and the PUFA were lower in the domestic species. When the SFA:PUFA (S:P) ratios were calculated, the domestic species total lipid and TG fractions showed increased ratios, while the PG ratios were similar for the two groups. There were some significant differences between species within the wild and domestic groups, however, there was no consistent pattern. For beef, PG cis-C18:2n6 (p=0.04) and PG cis-C20:5n3 (p=0.04) were lower; and for pork, TG SFA (p=0.03) and S:P (p=0.04) were also lower. For hartebeest, total lipid cis-C18:2n6 (p=0.04) was higher. The same was true for kudu (p=0.03), which also had higher PG cis-C20:4n6 (p=0.04) and total lipid cis-C18:3n3 (p=0.03). Sable PG total n3 was higher (p=0.03), as were total lipid cis-C22:5n3 (p=0.04) and total n3 (p=0.04) for zebra.
Fatty acid profiles of the lipids in meat from domestic species.
Discussion
When comparing the means of the two groups, most of the total lipid and TG fatty acids were significantly different. Total lipid PUFA (p=0.01), cis-C18:2n6 (p=0.02), cis-C20:4n6 (p=0.01), cis-C22:4n6 (p=0.03), total n6 (p=0.01), cis-C18:3n3 (p=0.04), cis-C20:5n3 (p=0.02), cis-C22:5n3 (p=0.02) and total n3 (p=0.02) were all higher, while the SFA (p=0.01) and S:P (p=0.01) were lower. Cis-C22:5n6 and cis-C22:6n3 were borderline higher (p=0.05 for both). TG PUFA (p=0.02), cis-C18:2n6 (p=0.01), cis-C20:4n6 (p=0.02), cis-C22:4n6 (p=0.04), total n6 (p=0.02), cis-C20:5n3 (p=0.01) and total n3 (p=0.03) were all higher, while the S:P (p=0.01) was lower. Cis-C22:5n6 and cis-C18:3n3 were borderline higher (p=0.05 for both). In contrast, the PG fatty acids only showed significant differences in cis-C22:6n3 (p=0.03). The differences in total lipid fatty acid profiles were comparable to those shown by others (3-6, 8-9).
The overall trend was for the structural lipids, the PG, to be conserved, both in amount and composition, while the storage lipids, the TG, increased in ‘domestic’ meat samples compared to ‘wild’ samples. Since TG tends to have higher levels of SFA, with concomitantly lower PUFA, this will predispose domestic species to having increased SFA, and explains the increased S:P ratios. The wild species may thus be preferable as sources of lean meat for human consumption. This was a consistent pattern, irrespective of species, but the degree of difference did vary between species. Thus it might be important to be selective in the choice of wild species to recommend as replacements for domestic meats.
Whilst it is probable that lipid profiles may vary between muscle types, the lack of variability within the wild and the domestic species suggests that any such differences would be unlikely to be significant enough to outweigh the differences seen between the two groups. Thus the ‘wild’ samples used (rump) were probably a reasonable reflection of the profiles expected in other muscles.
Fatty acid profiles of the lipids in meat from wild species.
The population at large is unlikely ever to completely stop eating red meat, as habits are difficult to change, and the most likely possibility is to try change the red meat content of people's diets from current ‘domestic’ to specific ‘wild’ meats. Any such shift in dietary lipid intake might be beneficial, by decreasing both the incidence and progression of the chronic diseases associated with a high SFA and low PUFA intake.
However, it would not be effective for agriculture to merely change the species being farmed. It has previously been shown that it is the agricultural practice, not the species, which is a major factor in the amount and type of fatty acids in the meat of porcine species, with laboratory pigs and warthogs showing very similar profiles when compared to those of intensively raised pigs (37).
Acknowledgements
The Authors would like to thank the National Research Foundation of South Africa for funding support, and the Carnivore restaurant for the provision of the ‘wild’ meat samples.
- Received November 17, 2010.
- Revision received December 13, 2010.
- Accepted December 15, 2010.
- Copyright © 2011 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved
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