The implications of recent research on trans fatty acids

The link between the intake of industrially produced trans fatty acids and risk of coronary heart disease (CHD) has been reviewed recently. The authors concluded that elimination of industrially produced trans fatty acids from the USA diet might avert 22% of the 1.2 million CHD events in the USA every year. Denmark has introduced legislation which limits the trans fatty acid content of oils and fats destined for human consumption to 2% of total fatty acids. This has reduced trans fatty acid intake in Denmark to insignificant levels and it will be interesting to see what effects this has on risk of CHD. By contrast in the USA the FDA has chosen the labelling option which puts the onus on the consumer to make the right food choices although New York City has adopted a more interventionist approach in its restaurants and food outlets. The Danish approach is far more effective as can be seen from the amounts of trans fatty acids present in French fries and chicken nuggets purchased from McDonalds and KFC in the two countries.     

The role of trans fatty acids in human nutrition

The role of dietary fats and oils in human nutrition is currently one of the key issues related to diet and health. Nutritional fats and oils contain both saturated and unsaturated fatty acids, mostly of cis‐configuration. Physiological functions of trans fatty acids in foods, especially their possible role in atherosclerosis, the level of blood cholesterol, and coronary heart disease is of concern, but still subject to controversy. Furthermore, the cancer prevention properties of conjugated linoleic acid isomers, present in small quantities in typical diets, remain to be confirmed. An overview on the occurrence and physiological considerations of trans fatty acids is given.     

Dietary C18:1 trans fatty acids increase conjugated linoleic acid in adipose tissue of pigs

The effect of dietary C18:1 trans fatty acids on back fat composition in pigs was investigated with special emphasis on conjugated linoleic acids (CLA). A total of 12 × 4 siblings of Large White and Swiss Landrace breed were housed in groups and fattened from 22 to 103 kg live weight. Pigs were fed a control diet (barley, wheat, soybean meal) or experimental diets which consisted of the control diet with a 5% replacement of olein or stearin fractions of pork fat, or partially hydrogenated fat. The hydrogenated fat was rich in C18:1 trans fatty acids but contained only negligible amounts of CLA. In contrast olein and stearin fractions contained far less C18:1 trans fatty acids but some CLA. In the control diet no C18:1 trans fatty acids and only traces of CLA were detected. The partially hydrogenated fat led to the highest CLA content in back fat (0.44%). Intermediate amounts of CLA were measured in pigs fed the fractionated pork fat (0.22/0.23%). In pigs fed the control diet, also small amounts of CLA were detected. The results indicate that CLA may be produced by endogenous Δ9‐desaturation out of dietary trans vaccenic acid in pigs.     

反式脂肪酸测定方法的研究

简要介绍了反式脂肪酸(TFA)的生成途径及主要的食物来源,反式脂肪酸对人体健康的主要危害和影响,综述了反式脂肪酸的分析检测方法如气相色谱法、红外光谱法、Ag离子色谱技术、毛细管电泳法等,并比较了各种方法的优缺点。     

Metabolism of trans fatty acids by hepatocytes

The present work was undertaken to study the metabolism of fatty acids with trans double bonds by rat hepatocytes. In liver mitochondria, elaidoyl-CoA was a poorer substrate for carnitine palmitoyltransferase I (CPT-I) than oleoyl-CoA. Likewise, incubation, of hepatocytes with oleic acid produced a more pronounced stimulation of CPT-I than incubation with trans fatty acids. This was not due to a differential effect of cis and trans fatty acids on acetyl-CoA carboxylase (ACC) activity and malonyl-CoA levels. Elaidic acid was metabolized by hepatocytes at a higher rate than oleic acid. Surprisingly, compared to oleic acid, elaidic acid was a better substrate for mitochondrial and, especially, peroxisomal oxidation, but a poorer substrate for cellular and very low density lipoprotein triacylglycerol synthesis. Results thus show that trans fatty acids are preferentially oxidized by hepatic peroxisomes, and that the ACC/malonyl-CoA/CPT-I system for coordinate control of fatty acid metabolism is not responsible for the distinct hepatic utilization of cis and trans fatty acids.     

Health and nutrition update on trans fatty acids

This article covers four topics related to current health and nutrition aspects of dietary trans fatty acids (TFA): (1) current dietary guidelines for TFA; (2) an updated exposure estimate to industrially‐produced TFA; (3) a consideration of effects of TFA from ruminant sources; and (4) a discussion of effects of substituting stearic acid (STA) for TFA. Health professional organizations recommend that intake of TFA from industrial sources be as low as possible. Doell and coworkers 2 have reported a substantial reduction in exposure to industrially‐produced TFA in the US from 4.6 g/person/day in 2003 to 1.0 g/person/day currently. Brouwer et al. 5 have concluded that all TFA, whether from animal or industrial sources, raise the ratio of plasma LDL‐ to HDL‐cholesterol. Studies involving one‐to‐one substitution of STA for TFAs have shown a decrease or no effect on LDL‐cholesterol concentration and an increase or no effect on HDL‐cholesterol concentration. Overall, during the last 10 or more years, there has been a major reduction in TFA levels in the U.S. food supply, and efforts continue to reduce these levels further.     

Dietary intakes and food sources of omega-6 and omega-3 polyunsaturated fatty acids

Both n−6 and n−3 polyunsaturated fatty acids (PUFA) are recognized as essential nutrients in the human diet, yet reliable data on population intakes are limited. The aim of the present study was to ascertain the dietary intakes and food sources of individual n−6 and n−3 PUFA in the Australian population. An existing database with fatty acid composition data on 1690 foods was updated with newly validated data on 150 foods to estimate the fatty acid content of foods recorded as eaten by 10,851 adults in the 1995 Australian National Nutrition Survey. Average daily intakes of linoleic (LA), arachidonic (AA), α-linolenic (LNA), eicosapentaenoic (EPA), docosapentaenoic (DPA), and docosahexaenoic (DHA) acids were 10.8, 0.052, 1.17, 0.056, 0.026, and 0.106 g, respectively, with longchain (LC) n−3 PUFA (addition of FPA, DPA, and DHA) totaling 0.189 g; median intakes were considerably lower (9.0 g LA, 0.024 g AA, 0.95 g LNA, 0.008 g EPA, 0.006 g DPA, 0.015 g DHA, and 0.029 g LC n−3 PUFA). Fats and oils, meat and poultry, cereal-based products and cereals, vegetables, and nuts and seeds were important sources of n−6 PUFA, while cereal-based products, fats and oils, meat and poultry, cereals, milk products, and vegetable products were sources of LNA. As expected, seafood was the main source of LC n−3 PUFA, contributing 71%, while meat and eggs contributed 20 and 6%, respectively. The results indicate that the majority of Australians are failing to meet intake recommendations for LC n−3 PUFA (>0.2 g per day) and emphasize the need for strategies, to increase the availability and consumption of n−3-containing foods.     

Dietary intakes and food sources of fat and fatty acids in Guatemalan schoolchildren: A cross-sectional study

Background  

Consumption of healthy diets that contribute with adequate amounts of fat and fatty acids is needed for children. Among Guatemalan children, there is little information about fat intakes. Therefore, the present study sought to assess intakes of dietary fats and examine food sources of those fats in Guatemalan children.     

Dietary intakes and food sources of fatty acids for Belgian women, focused on n-6 and n-3 polyunsaturated fatty acids

The intake of fat, saturated and monounsaturated FA (SFA and MUFA), and omega-6 and omega-3 PUFA has been estimated in 641 Belgian women (age 18-39 y). Their food intake was recorded using a 2-d food diary. The PUFA included were linoleic (LA), alpha-linolenic (LNA), arachidonic (AA), eicosapentaeonoic (EPA), docosapentaenoic (DPA) and docosahexaenoic (DHA) acids. The mean total fat intake corresponded to 34.3% of total energy intake (E). The mean intake of the FA groups corresponded to 13.7%, 13.1%, and 6.0% of E, for SFA, MUFA, and PUFA, respectively. The mean intake of LA was 5.3% of E and of LNA was 0.6% of E, with a mean LA/LNA ratio of 8.7. The mean intake of AA was 0.03% of E. The mean intake of EPA, DPA, and DHA was 0.4%, 0.01%, and 0.06% of E, respectively. According to the Belgian recommendations, the total fat and SFA intake was too high for about three-quarters of the population. The mean LA and overall n-6 PUFA intake corresponded with the recommendation, with part of the population exceeding the upper level. Conversely, the population showed a large deficit for LNA and n-3 PUFA. The major food source for LA and LNA was fats and oils, followed by cereal products. The main sources of long-chain PUFA were fish and seafood, and meat, poultry, and eggs. From a public health perspective, it seems desirable to tackle the problem of low n-3 PUFA intake.     

Influence of moderate amounts of trans fatty acids on the formation of polyunsaturated fatty acids

The effect of trans fatty acids from partially hydrogenated soybean oil and butterfat on the formation of polyunsaturated fatty acids was investigated. Five groups of rats were fed diets that contained 20 wt% fat. The content of linoleic acid was adjusted to 10 wt% of the dietary fats in all diets, whereas the amount of trans fatty acids from partially hydrogenated soybean oil (PHSBO) was varied from 4.5 to 15 wt% in three of the five diets. The fourth group received trans fatty acids from butterfat (BF), while the control group was fed palm oil without trans fatty acids. Trans fatty acids in the diet were portionally reflected in rat liver and heart phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylinositol, and phosphatidylserine. Incorporation in the sn-1 position was compensated by a decrease in saturated fatty acids. Trans fatty acids were not detected in diphosphatidylglycerol. Compared to the presence in the dietary fats, 8t- and 10t-18:1 were discriminated against in the incorporation in PE and PC from liver and heart, whereas 9t- and 12t-18:1 were preferred. The formation of 20:4n-6 was not influenced by 4.5 wt% trans fatty acids (from PHSBO) but apparently was by 10 wt% in liver. In contrast, even a content of 2.5 wt% trans fatty acids from BF reduced the formation of 20:4n-6. The inhibitory effect of trans isomers on linoleic acid conversion was reflected less in heart than in liver and less for PE than for PC. Groups with trans fatty acids showed increased 22:6n-3 and 22:5n-3 deposition in liver and heart PE and PC.     

Dietary fatty acids and coronary heart disease

The effects of dietary fats have been established in epidemiological and intervention studies and through relationship to risk factors for development of coronary heart disease (CHD). During a period where the impressive effects of hydroxymethylglutaryl-CoA reductase inhibitors on the mortality of CHD dominate the medical journals, it is important to realize the major effects of dietary fatty acids on a series of events included in the multifactorial disorder of CHD.     

Dietary fatty acids: Their metabolic fate and influence on fatty acid biosynthesis

Adult rats fed a low-fat diet or diets containing 15% of either tripalmitin, triolein or trilinolein were injected intraperitoneally with H³-labeled acetate. Those which received fat were also given by mouth, simultaneously with acetate, the 1-C¹⁴-labeled sodium salt of the respective dietary fatty acid. The fate of the tagged material was followed by time-spaced biopsies of subcutaneous adipose tissue and by collection of the expired C¹⁴O₂. After 72 hr, 51, 64, and 52% of the dietary palmitate, oleate, and linoleate, respectively, were catabolized, as indicated by the corresponding percentages of the label having been excreted as C¹⁴O₂. Dietary linoleate was relatively less incorporated into body triglycerides than palmitate and oleate. Animals ingesting diets of 15% triolein had only about one-half the amount of phospholipids in their tissues as had the other groups. The distribution of both the C¹⁴ and H³ labels in the tissue triglycerides showed that all diets containing fats decreased fatty acid synthesis but did not inhibit conversion of palmitate to oleate. Conversions of oleate or linoleate appeared to be through acetate. As a result of these factors, the fatty acid composition of the tissue triglycerides after 3 months’ ingestion of tripalmitin was essentially the same as that of the low-fat group, whereas the ingestion of triolein produced triglycerides with a very high content of oleic acid. Trilinolein ingestion produced effects similar to triolein but to a less pronounced degree. Both the respiratory C¹⁴O₂ and the C¹⁴- and H³-labeled fatty acids in subcutaneous adipose tissue exhibited a second rise in specific activity 12 to 24 hours after the administration of the label. Presented at the AOCS meeting, Chicago, 1964.     

Determination of trans fatty acids and fatty acid profiles in margarines marketed in spain

Two gas chromatography (GC) procedures were compared for routine analysis of trans fatty acids (TFA) of vegetable margarines, one direct with a 100-m high-polarity column and the other using argentation thin-layer chromatography and GC. There was no difference (P>0.05) in the total trans 18∶1 percentage of margarines with a medium level of TFA (∼18%) made using either of the procedures. Both methods offer good repeatability for determination of total trans 18∶1 percentage. The recoveries of total trans isomers of 18∶1 were not influenced (P>0.1) by the method used. Fatty acid composition of 12 Spanish margarines was determined by the direct GC method. The total contents of trans isomers of oleic, linoleic, and linolenic acids ranged from 0.15 to 20.21, from 0.24 to 0.99, and from 0 to 0.47%, respectively, and the mean values were 8.18, 0.49, and 0.21%. The mean values for the ratios [cis-polyunsaturated/(saturated +TFA)] and [(cis-polyunsaturated + cis-monounsaturated)/(saturated +TFA)] were 1.25±0.39 and 1.92±0.43, respectively. Taking into account the annual per capita consumption of vegetable margarine, the mean fat content of the margarines (63.5%), and the mean total TFA content (8.87%), the daily per capita consumption of TFA from vegetable margarines by Spaniards was estimated at about 0.2 g/person/d.     

Dietary fatty acids,membrane transport,and oxidative sensitivity in human erythrocytes

This study examined effects of dietary n−3 fatty acids on age-related changes in erythrocyte anion transport and susceptibility to oxidation. Blood was drawn from healthy adult volunteers before and after six weeks' supplementation (nine/group) with 4.0 g/day of safflower oil (containing 2.9 g n−6 fatty acids) or fish oil (containing 1.2 g long-chain n−3 fatty acids). Following density separation of young and old erythrocytes, membrane anion transport and cell membrane lipid composition were measured. Oxidative damage was measured in erythrocyte ghosts exposed to a free radical generator. Fish oil significantly increased 16∶0 and 20∶5n−3 in ghosts of both young and old cells, and 22∶5n−3 and 22∶6n−3 in old cells alone. Safflower oil increased 16∶0, 18∶0, 18∶1n−9, and 22∶5n−6 in ghosts of young cells only. The age-dependent increase in membrane anion transport (P<0.01) was decreased by dietary fish oil supplementation, but not by safflower oil supplementation. Safflower oil and fish oil increased the susceptibility of both young and old erythrocytes to oxidative damage by free radical generation (P<0.001).     

The metabolism of triglycerides containing cis and trans octadecenoic fatty acids

Summary Weanling rats were fed diets containing triglycerides composed of bothcis andtrans fatty acids for 16 days. The animals were sacrificed, and the lipides were extracted quantitatively from the heart, liver, feces, and the rest of the carcass. Infrared analyses were carried out to determine the fate of thetrans acids.Trans acids with the double bond either in the 8 or 9 position are metabolized efficiently by the rat organism. Armour Fellow, University of Illinois, 1955–56.     

Use of dried blood for measurement of trans fatty acids

Background  

Fatty acid measurements especially trans fatty acid has gained interest in recent times. Among the various available biomarkers, adipose tissue is considered to be the best for the long term dietary intake but the invasive nature of tissue aspiration reduces its utility. Phlebotomy is a much less invasive method of sample collection when a large number of participants are involved in the study and therefore is an alternative, most suitable for large population based studies. In the present study fatty acid (with special emphasis on trans fatty acid) extraction from blood spotted and dried on filter paper was carried out to simplify the sample collection procedure and transportation.