Trans- and postional isomers of common fatty acids

Oleic Acid Rich Tree-borne Oilseeds from Forests of Assam, India

North East India is a home of tremendous and versatile vegetative oil bearing materials because of the subtropical climatic conditions. Screening, characterization, and domestication of high yielding treeborne oilseeds rich in oleic acid and tocopherol are highly demandable from industrial aspects. As very few studies have been carried out in this regard from this region, our investigation aims to exploit new sources of tree-borne oilseeds rich in omega fatty acids for edible and non-edible purposes from both known and unknown plants. Six lesser-known tree-borne oilseeds were characterized based on oil content, tocopherol composition and metal content. The fatty oil was found more in Dysoxylum procerum (50%). The dominating fatty acid was oleic acid ranged between 38.4 to 64%. The oil of Terminalia bellirica showed high content of tocopherol (0.05%). Among eleven metals (Ca, Cu, Zn, Mg, Mn, Fe, Pb, Cd, As, Na, K) in all the six fatty oil contents, Pb and Cu showed high concentrations as compared to the codex standard while Fe values of all the oil contents were below the permissible concentrations.

Mandatory trans fat labeling regulations and nationwide product reformulations to reduce trans fatty acid content in foods contributed to lowered concentrations of trans fat in Canadian women's breast milk samples collected in 2009-2011

BACKGROUND

Recent efforts in Canada to reduce industrial trans fatty acids (TFAs) in foods include mandated inclusion of TFA content on food labels and recommendations by Health Canada that encourage the food industry to voluntarily limit TFA content in all vegetable oils and soft margarines and in all other prepackaged foods to <2% and <5% of total fat, respectively.

OBJECTIVE

To assess the impact of these efforts, we measured the concentration of TFAs in human breast milk samples.

DESIGN

The TFA content in 639 breast milk samples collected in 2009, 2010, and 2011 from breastfeeding mothers in 10 major cities across Canada was analyzed by gas chromatography.

RESULTS

The mean (±SD) TFA contents were 2.7 ± 0.9% (n = 153, range: 1.4-7.2%), 2.2 ± 0.7% (n = 309, range: 1.0-6.8%), and 1.9 ± 0.5% (n = 177, range: 0.9-3.4%) of total milk fat for samples collected in 2009, 2010, and 2011, respectively. These values are considerably lower than the value of 7.2 ± 3.0% (range: 0.1-17.2%) found previously for Canadian human milk in 1992. On the basis of a linear correlation between the percentage of TFAs in the diet and human milk fat established by Craig-Schmidt et al, and assuming that 30% of energy of a lactating mother's diet is derived from fat, we estimated from the TFA human milk fat data that TFA intake of Canadian breastfeeding mothers was 0.9%, 0.5%, and 0.3% of total energy in 2009, 2010, and 2011, respectively. These estimated values are lower than the WHO's maximum recommended intake of 1% of total energy for a healthy diet.

CONCLUSIONS

The results suggest that the trans fat labeling regulations introduced in 2003 and recommendations by Health Canada in 2007 instructing the food manufacturers and restaurants to limit TFAs in foods have resulted in significant reductions in TFAs in the diets of Canadian breastfeeding mothers and their breast milk.

Dietary trans fatty acids: Review of recent human studies and food industry responses

Dietary trans FA at sufficiently high levels have been found to increase low density lipoprotein (LDL)-cholesterol and decrease high density lipoprotein (HDL)-cholesterol (and thus to increase the ratio of LDL-cholesterol/HDL-cholesterol) compared with diets high in cis monounsaturated FA or PUFA. The dietary levels of trans FA at which these effects are easily measured are around 4% of energy or higher to increase LDL-cholesterol and around 5 to 6% of energy or higher to decrease HDL-cholesterol, compared with essentially trans-free control diets. Very limited data at lower levels of intake (less than 4% of energy) are available. Most health professional organizations and some governments now recommend reduced consumption of foods containing trans FA, and effective January 1, 2006, the U.S. Food and Drug Administration requires the labeling of the amounts of trans FA per serving in packaged foods. In response, the food industry is working on ways to eliminate or greatly reduce trans FA in food products. Current efforts focus on four technological options: (i) modification of the hydrogenation process, (ii) use of interesterification, (iii) use of fractions high in solids from natural oils, and (iv) use of trait-enhanced oils. Challenges to the food industry in replacing trans FA in foods are to develop formulation options that provide equivalent functionality, are economically feasible, and do not greatly increase saturated FA content.

A second look at the relation between colorectal adenomas and consumption of foods containing partially hydrogenated oils

The trans fatty acids in partially hydrogenated vegetable oil may cause colorectal neoplasia by interfering with cell membrane function or eicosanoid metabolism. This possibility provided a rationale for looking at the relation between colorectal adenomas and consumption of foods containing partially hydrogenated vegetable oils in 234 cases and 407 controls recruited from referrals for colonoscopy at University of North Carolina Hospitals in Chapel Hill, between 1988 and 1990. Foods containing partially hydrogenated vegetable oils were divided into four groups: sweetened baked goods, chocolate candy, oils and condiments, and french fries and chips. We observed no evidence of increased adenoma prevalence associated with consumption of fries and chips (200+ vs 0 kcals/day: odds ratio (OR) = 0.70; 95% confidence limits (CL) = 0.27, 1.8) or chocolate candy (50+ vs 0 kcals/day: OR = 0.49; 95% CL = 0.23, 1.1). We did, however, find evidence of increased adenoma prevalence associated with consumption of sweetened baked goods (400+ vs < 100 kcals/day: OR = 1.9; 95% CL = 0.95, 3.8) and oils and condiments (200+ vs < 100 kcals/day: OR = 2.4; 95% CL = 1.3, 4.2).

Specific versus non-specific effects of dietary fat on carcinogenesis

It will be apparent from this review that dietary fat can exert both specific and non-specific effects on carcinogenesis, at least in experimental animals. The non-specific effects appear to be related primarily to effects of dietary fat on energy balance. Although a positive energy balance can be achieved on a high-carbohydrate low-fat diet, it is much more likely to occur on a high-fat diet because of the high energy density of fat [101] and the fact that dietary fat is less capable of imparting a sense of satiety [102]. A continuing state of positive energy balance leads to obesity which has been associated with increased risk of cancer at a number of sites, including endometrium [103-106], postmenopausal breast cancer [107-113], renal cancer [114,115] and possibly cancers of the colorectum [116-122], pancreas [103,123] and prostate [124]. Whereas the non-specific effects of dietary fat appear to be deleterious for cancer, the specific effects in some cases can be beneficial. Examples are long-chain n-3 polyunsaturated fatty acids. CLA and tocotrienols. It is still too early to predict whether these may be of value in the prevention and/or treatment of human cancer but they seem worthy of further investigation. Knowledge of their mechanism of action may suggest novel approaches to the cancer problem and, as in the case of vitamins A and D, it may be possible to find analogues with more potent anti-cancer activity.

Occurrence of 5c,8c,11c,15t-eicosatetraenoic acid and other unusual polyunsaturated fatty acids in rats fed partially hydrogenated canola oil

Uncommon cis and trans fatty acids can be desaturated and elongated to produce unusual C18 and C20 polyunsaturated fatty acids in animal tissues. In the present study we examined the formation of such metabolites derived from cis and trans isomers of oleic and linoleic acids of partially hydrogenated vegetable oil origin in rats. For two months, adult male rats were fed a partially hydrogenated canola oil diet containing moderately high levels of trans fatty acids (9.6 energy%) and an adequate level of linoleic acid (1.46 energy%). Analysis of the phospholipid (PL) fatty acids of liver, heart, serum and brain showed no new C18 polyunsaturated fatty acids, except for those uncommon 18:2 isomers originating from the diet. However, minor levels (each < 0.3% PL fatty acids) of six unusual C20 polyunsaturated fatty acids were detected in the tissues examined, except in brain PL. Identification of their structures indicated that the dietary 9c,13t-18:2 isomer, which is the major trans polyunsaturated fatty acid in partially hydrogenated vegetable oils, was desaturated and elongated to 5c,8c,11c,15t-20:4, possibly by the same pathway that is operative for linoleic acid. Furthermore, dietary 12c-18:1 was converted to 8c,14c-20:2 and 5c,8c,14c-20:3; dietary 9c,12t-18:2 metabolized to 11c,14t-20:2 and 5c,8c,11c14t-20:4, and dietary 9t,12c to 11t,14c-20:2. These results suggested that of all the possible isomers of oleic and linoleic acids in partially hydrogenated vegetable oils, 12c-18:1, 9c,13t-18:2, 9c,12t-18:2 and 9t,12c-18:2 are the preferred substrates for desaturation and elongation in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acids in some common food items in Canada

Fat content and fatty acid (FA) composition of 100 common items in 17 food categories from the Canadian retail market were determined. Of these, 52 samples were made from partially hydrogenated fat. Their fat (in parentheses) and trans FA levels were as follows: breads (3.7% fat) 15.7%, hamburger buns (5.5% fat) 26.3%, cakes (8.7-36.7% fat) 10.1-25.7%, candies/chocolates (27.1% fat) 11.1%, cereals (1.3-12.9% fat) 9.2-33.7%, cookies (5.0-40.5% fat) 7.6-38.7%, crackers (9.2-33.0% fat) 13.8-35.4%, donuts (16.6-29.6% fat) 27.7-32.7%, french fries (pre-cooked) (4.3-4.5% fat) 32.8-42.8%, muffins (12.5-23.7% fat) 16.5-24.2%, pizza crusts (6.0-7.2% fat) 22.1-28.8%, shortenings (100% fat) 17.4-20.2%, potato chips (33.2-40.0% fat) 29.7-39.7%, and corn chips (25.0-34.2%) 29.9-33.9%. Generally the sum of saturated and trans FA in the food items made with partially hydrogenated fat was higher than that of the corresponding food items made with unhydrogenated oils. The higher levels of saturates plus trans were at the expense of the essential fatty acids (EFA). The high-fat foods, such as cakes, cookies, crackers, donuts and potato chips, made with partially hydrogenated fat, were substantially lower in EFA and contained relatively higher levels of trans polyunsaturated fatty acids (PUFA). In some samples of potato chips and french fries, the level of trans PUFA was almost the same or more than the sum of linoleic and linolenic acids.

A comparative study of micronucleus frequency in peripheral blood lymphocytes of human subjects given dietary cis, trans and saturated fat

The micronucleus test using peripheral blood lymphocytes has been used to study the clastogenic effects of saturated, cis or trans fatty acids in human volunteers. Consumption of diets rich in either saturated fats (palmitic acid), monounsaturated cis fats (oleic acid) or monounsaturated trans fats (elaidic acid) for 3 wk had no effect on either the number of micronuclei or the frequency of micronucleated cells in lymphocytes in culture. This study adds to the accumulating body of evidence to suggest that dietary intake of trans fatty acids is not especially linked to genetic damage.

Lack of effects of trans fatty acids on eicosanoid biosynthesis with adequate intakes of linoleic acid

The minimum requirement of linoleic acid to prevent effects of dietary C18 trans fatty acids on eicosanoid biosynthesis in rats was assessed. In a first experiment, six groups of animals were fed diets with a high content of trans fatty acids [20% of energy (en%)], and increasing amounts of linoleic acid (0.4 to 7.1 en%). In a second experiment, four groups of rats were fed diets designed to compare trans fatty acids with saturated and cis-monounsaturated fatty acids of the same chain length at the 2 en% linoleic acid level. After 9-14 weeks the biosynthesis of prostacyclin by pieces of aorta and the biosynthesis of hydroxy-heptadecatrienoic acid and 12-hydroxy-eicosatetraenoic acid by platelets were measured. The fatty acid compositions of aorta phospholipid and platelet lipid were also determined. Both the prostacyclin-production by aorta pieces and the production of hydroxy-heptadecatrienoic acid and 12-hydroxy-eicosatetraenoic acid by platelets appeared to be a linear function of the arachidonic acid level in aorta phospholipid and platelet lipid, irrespective of the trans fatty acid content in the diet. This indicates that trans fatty acids do not directly influence enzymes involved in eicosanoid biosynthesis. In a direct comparison with cis-monounsaturated or saturated fatty acids with 2 en% linoleic acid in the diet, only a moderate reduction in arachidonic acid level in aorta phospholipids in the group fed trans fatty acids was observed. The geometry of the double bond did not influence the arachidonic acid level in platelet lipid, although the diet rich in saturated fatty acids increased arachidonic acid levels significantly compared with all other diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Linoleic acid requirement of rats fed trans fatty acids

The amount of linoleic acid required to prevent undesirable effects of C18 trans fatty acids was investigated. In a first experiment, six groups of rats were fed diets with a high content of trans fatty acids (20% of energy [en%]), and increasing amounts of linoleic acid (0.4 to 7.1 en%). In a second experiment, four groups of rats were fed diets designed to compare trans fatty acids with saturated and cis-monounsaturated fatty acids of the same chain length at the 2 en% linoleic acid level. After 9-14 weeks, the oxygen uptake, lipid composition and ATP synthesis of heart and liver mitochondria were determined. The phospholipid composition of the mitochondria did not change, but the fatty acid compositions of the two main mitochondrial phospholipids were influenced by the dietary fats. Trans fatty acids were incorporated in all phospholipids investigated. The linoleic acid level in the phospholipids, irrespective of the dietary content of linoleic acid, increased on incorporation of trans fatty acids. The arachidonic acid level had decreased in most phospholipids in animals fed diets containing 2 en% linoleic acid. At higher linoleic acid intakes, the effect of trans fatty acids on the phospholipid arachidonic acid level diminished. However, in heart mitochondrial phosphatidylethanolamine, trans fatty acids significantly increased the arachidonic acid level. Despite these changes in composition, neither the amount of dietary linoleic acid nor the addition of trans fatty acids influenced the mitochondrial function. For rats, a level of 2 en% of linoleic acid is sufficient to prevent undesirable effects of high amounts of dietary C18 trans fatty acids on the mitochondrial function.

Polyunsaturated fatty acids in tissues of rats fed trielaidin and high or low levels of linolenic acid

Male and female weanling rats that were born to dams fed a diet low in linolenic acid received diets of 15% lipids by weight containing 45% elaidic acid (as trielaidin) and 8.5% or 0.1% linolenic acid for 10 weeks. Four other groups, in which palmitic or oleic acid replaced elaidic acid in the diet, served as controls. The fatty acid profiles of several lipid classes were determined in adipose tissue, adrenals, testes, heart and brain. Elaidic acid was incorporated into tissue lipids in varying degrees, depending on the organ and on the lipid class. Feeding elaidic acid induced no changes in the polyunsaturated fatty acid (PUFA) profiles of testes lipids but resulted in definite modifications of the PUFA patterns of heart phosphatidylcholine (PC) and phosphatidylethanolamine (PE). In linolenic acid-deprived rats, arachidonic acid was decreased in PC and linoleic acid was increased in both PC and PE; 22:5n-6 was strongly depressed in both PC and PE. In linolenic acid-fed rats, 22:6n-3 was decreased in PC and PE. These changes, on the whole, were more evident in females, and some also were observed in adrenal cholesteryl esters but only slightly in brain phospholipids. The apparent inhibition of the biosynthesis of PUFA induced by dietary elaidic acid appeared to be complex and of greater intensity in the n-6 fatty acid series than in their n-3 homologues.

Summation: which fat/how much fat--animals

Promotion of carcinogenesis in rats by dietary fat depends on the amount and type of fatty acids ingested, mainly as triglycerides. A certain amount of essential fatty acid of the linoleate type (n-6) is required for promotion of mammary cancer and pancreatic cancer and probably also for colon cancer. Promotion is also enhanced by a high level of dietary fat, and this additional effect seems to be relatively independent of the type of fat. Saturated fatty acids, either medium or long chain, and cis and trans monoenoic fatty acids appear to have no specific promoting effects. Fish oils containing long-chain polyunsaturated fatty acids of the linolenate type (n-3) are inhibitory, and this may also be true for rapeseed oil high in erucic acid, a long-chain monoenoic fatty acid. The promoting action of dietary fat can be modified by other components of the diet, such as starch, sugar, and fiber. Promotion is also dependent on the length of time animals are exposed to the high-fat diet. The overall tumor yield can be decreased by reducing the level and degree of unsaturation of the dietary fat after a period of feeding a high polyunsaturated-fat diet.

Activities of liver mitochondrial and peroxisomal fatty acid oxidation enzymes in rats fed trans fat

The effect of trans fat on the activities of liver mitochondrial and peroxisomal fatty acid oxidation enzymes was examined in various strains of rats. When Wistar and Sprague-Dawley rats were fed for 30 days diets containing either olive oil or partially hydrogenated corn oil as a source of cis- or trans-octadecenoate, respectively, the activities of various enzymes of mitochondrial and peroxisomal beta-oxidation measured with cis- and trans-9-octadecenoic acid as substrates showed little dietary fat-dependent change. In Fischer 344 rats, feeding trans fat for 15 mo increased only moderately various enzymes of beta-oxidation except for carnitine acyltransferase. The rate of mitochondrial ketogenesis and the activity of carnitine acyltransferase measured with trans-9-octadecenoic acid as a substrate were about half those with the cis-counterpart. Peroxisomes oxidized trans-9-octadecenoyl-CoA at a rate comparable to the cis-counterpart. It was concluded from this study and previous ones that the difference in the geometry of dietary fatty acid had only a marginal effect in modulating the hepatic fatty acid oxidation system, in spite of marked differences in the metabolic behavior of cis- and trans fatty acid in cell-free preparations and perfused liver.

Modification of alkenyl chain profile in plasmalogens of rat heart mitochondria by dietary trielaidin

Effects of dietary trielaidin upon the alkenyl chain profile of plasmalogens were studied using heart mitochondria of rats fed a semi-purified diet containing 10% of fat supplement in which elaidic acid accounted for 69% of total fatty acids. Alkyl substituted dioxane (ASD) derivatives of the alkenyl groups of plasmalogens were prepared and analyzed by silver nitrate TLC and by GLC on different phases (BDS and OV-275). After two months of feeding the experimental diet, 40% of the ASD contained a trans-octadecenyl chain, suggesting that dietary elaidic acid was reduced in vivo to the corresponding alcohol and incorporated into plasmalogens. There was a simultaneous decrease in the percentage of ASD containing saturated chains, but the percentage of ASD substituted with cis-octadecenyl chains was not significantly affected. These observations suggested that elaidic acid may compete with saturated fatty acids, but not with cis-octadecenoic acids during the plasmalogen biosynthesis. Feeding trielaidin did not seem to have any significant influence on the relative proportions of plasmalogens, which accounted for 11-12%, on a phosphorus basis, of total heart mitochondria phospholipids.

Activities of liver mixed function oxidase system in rats fed trans fat

Rats were fed diets containing either camellia oil or partially hydrogenated corn oil as a source of cis or trans octadecenoate, respectively, in the presence of adequate linoleic acid. After 35 days of feeding the diets, activities of several hepatic drug metabolizing enzymes as well as the content of hepatic microsomal cytochrome P-450 were determined. Geometrical difference in the dietary fat did not affect the amount of microsomal protein nor the content of cytochrome P-450. Also, activities of NADPH cytochrome C reductase, aminopyrine N-demethylase and biphenyl hydroxylase were approximately the same between two groups of rats. Aniline hydroxylase was slightly elevated in the rats fed trans fat. It was concluded that the difference in the geometry of dietary fatty acids had little effect in modulating the hepatic mixed function oxidase system.

Isomeric fatty acids and tumorigenesis: a commentary on recent work

This article critically reviews the existing, although limited, literature concerning trans fatty acids and tumorigenesis. Neither epidemiological nor experimental studies published to date have demonstrated any valid association between trans fatty acid ingestion and tumorigenesis. A recent study showed that under controlled conditions, a fat with a high content of trans fatty acids did not promote the development of mammary tumors induced in rats by 7,12-dimethylbenz[a]anthracene to any greater extent than did a comparable fat with a high content of cis fatty acids. In addition, in this study a high trans fat was less tumor promoting than was a blend of fats that simulated the dietary fat composition of the United States and had a lower level of trans fatty acids. Another study using comparable cis and trans fats demonstrated that the high trans fat did not affect the growth and metastasis of implanted mammary tumors in mice relative to the high cis fat. Also, two recent studies reported no significant difference in the development of induced colon tumors in rats fed diets high in cis or trans fatty acids. The results of these and other studies are consistent with the conclusion that trans fatty acids are not uniquely related to tumor development.