"Trans Fatty Acid Update"

Transcription

1 "Trans Fatty Acid Update" Trans Fatty Acids (Prepared by University Professor Emeritus Bruce Holub, Department of Human Biology & Nutritional Sciences, University of Guelph) Introduction Trans fatty acids (TFA) have become of increasing health concern to the public and health professionals alike as their levels in typical diets in North America and elsewhere have increased markedly during the past decade. Unlike naturallyoccurring monounsaturated (monounsaturates) and polyunsaturated fatty acids (polyunsaturates) as found in many liquid non-hydrogenated vegetable oils, which have cis double bonds at their unsaturation sites, TFA have trans double bonds at the unsaturation sites within the fatty acid structure. Whereas natural monounsaturates and polyunsaturates have curvilinear structures and are highly liquid at room temperatures, the industrial TFA are typically linear structures that are solid fats at room temperatures due to their much higher melting points. Thus, TFA approach saturated fats in many of their physical-chemical properties. The industrial process known as partial hydrogenation as performed on highly unsaturated liquid oils (such as soybean oil or canola oil) containing natural or cis double bonds free of TFA results in the chemical transformation of these liquid oils into solid partially-hydrogenated oils and vegetable shortenings. These latter commercially-processed oil products as used extensively in assorted processed and fast foods which impart the desired solidity, greater resilience to oxidation and rancidity including longer shelf-lives, while allowing for labeling/marketing terms including cholesterol-free, low in saturated fat, and free of animal fat, etc. which are of receptive appeal to consumers. Consequently, a considerable portion of the so-called monounsaturates in a typical diet in North America and elsewhere is now represented by TFA ( trans monounsaturates) in addition to the naturally-occurring cis monounsaturates. It is also noteworthy that partial hydrogenation of vegetable oils gives rise to a diverse mixture of several TFA isomers (types) which are included in the collective TFA designation. Edible oil refining (including deodorization), heating and conventional frying with oils generates very small amounts of TFA (usually <1% of total fat) in contrast to partial hydrogenation in the presence of hydrogen, pressure, as typical nickel as a metal catalyst. Origins, Food Sources, and Intake Levels Approximately 90% of the total TFA consumed per person daily in North America and many countries is derived from processed and fast-food products. Unlike the industrial TFA, animal sources/fats contribute approximately 10% to the total dietary intake of TFA in the form of milk, butter, and beef where TFA represents approximately 2-4% of the total fat. The natural bio-hydrogenation process as performed by microorganisms in the stomach of ruminant animals (dairy cows, beef cattle) produces some TFA from the unsaturated dietary fat as consumed. The pattern of TFA isomers (rich in vaccenic acid) in such natural TFA is rather different from the types of TFA (rich in elaidic acid plus others) that predominate in partially-hydrogenated vegetable oils ( industrial TFA). Margarines represent approximately 20% of the total TFA intake in the North American diet with fried plus processed foods combined being major contributors (approximately 70%). Various snack foods including crackers, croissants, cookies, potato chips, etc. often contain up to 25-45% of the total fat as TFA although such levels are now decreasing in many commercial products due to the current and pending labeling/regulatory requirements on TFA in such foods. Other rich TFA sources in many but not all brand-name products including cake/pancake mixes, frozen breakfast waffles, and fast-foods include doughnuts, French fries, breaded meats including fish fillets, breaded chicken produce, etc. Some processed foods have up to 5-6 grams of TFA per serving

2 with many high TFA sources being somewhat unexpected such as microwaveable popcorn products. Some food products directed towards young children (eg., baby biscuits) have a considerable portion of the total fat represented by industrial TFA (up to 35%) due to the inclusion of vegetable shortening and partially-hydrogenated vegetable oil in these formulated products. Table 1 gives the estimated intakes of the different types of fats/fatty acids and sources in a typical North American diet. Estimates during the past decade on the per capita (adult) intakes of total TFA in the North American diet have ranged from an average of 5 up to 10 grams/person/day. Estimates of average TFA intakes across numerous countries (grams/person/day) have indicated much higher intakes in Canada (at 8) and the United States (at 6) as compared to Japan and China (at 1). With the aggressive regulatory approach on industrial TFA contents and restrictions in Denmark, the average intake of TFA there has now dropped to approximately one gram/person/day. Almost all of this very low intake is natural TFA mostly from dairy and beef produce. The higher intakes of TFA in the North American population appear to be in the younger sectors (eg., up to ages years). Unfortunately, one of the highest dietary sources of industrial TFA in the North American food supply is mothers breast milk; these high levels relate directly to their high dietary intake of TFA during pregnancy and lactation. A Canadian report in 1995 revealed that the average total TFA content was found to be 7.2% of the total milk fat with the TFA ranging up to 17.2% (corresponding to average intakes in lactating women of 10.6 grams/person/day with intakes as high as 20.3 grams/person/day in some women). Elevations of TFA levels in the breast milk and elsewhere in the human body are very closely related to the intake of industrial TFA in the diet since the body itself generates no significant amount of TFA. Restriction or elimination of industrial TFA in the diet results in the corresponding depletion of TFA from these various sites within the body. TFA can undergo metabolic oxidation (betaoxidation) in the body and be used as an energy source as for natural monounsaturates. Effects on Cardiovascular/Diabetes Disease Risk Epidemiological/population studies have indicated that dietary TFA, as consumed mostly in processed and fast foods, represent major dietary risk factors for coronary heart disease (CHD) in the population. A perspective study on 80,082 women from the United States followed for fourteen years indicated that the relative risk for developing CHD was almost doubled for every two percent increase in energy intake from TFA (i.e., approximately 4-5 grams daily). These findings are rather disturbing when considered in the context of the aforementioned high intakes of TFA in the North American population. Furthermore, when compared on an equal intake basis (by weight), dietary TFA was found to be a significantly greater dietary risk for CHD when compared with saturated fats (up to five- to ten-fold). Controlled intervention trials in humans have indicated that both saturated fatty acids and TFA increase total and LDLcholesterol levels in the circulation thereby increasing the risk of cardiovascular disease (CVD). However, TFA also lowered protective HDL-cholesterol levels whereas saturated fats did not; lowering of HDL-cholesterol levels has been associated with a substantially increased risk of CVD. In addition, TFA but not saturates tend to increase the levels of a highly atherogenic blood lipoprotein known as lipoprotein (a) which further increases the risk for CVD. The more profound increase in the ratio of circulating LDL-cholesterol: HDL-cholesterol ratio with TFA intakes as compared to equivalent amounts of saturated fats further supports population data indicating TFA to be a much great risk for CVD than saturated fats. The impact, if any, of natural monounsaturated TFA as found in ruminant fats (approximately 10% of the industrial TFA intake) on the risk of CVD is still under investigation. The very small amount of unique polyunsaturated trans fat known as CLA (conjugated linoleic acid) in the diet (including ruminant fats) is also under investigation with respect to any health implications although such is unlikely based on the very low levels in our food supply. High TFA intakes have also been implicated in other health affects such as the risk of type 2 diabetes. A major population study suggested that increased intakes of saturated fats were not significantly associated with the fourteen-year risk of type 2 diabetes risk in women whereas a two percent increase in energy consumed as TFA (approximately 4-5 grams per day) appeared to increase the risk of type 2 diabetes by 39%. There is also some evidence that high TFA intakes during pregnancy may interfere with the metabolism and deposition of important omega-3 fatty acids as are needed for the growth and development of infants during their neonatal period.

3 Food Labeling and Regulatory Policies Traditional approaches with respect to food regulation and labeling requirements and protection against premature CVD have focused upon labeling for cholesterol (in mg units) and saturated fats (in gram units). Consequently, labeling and marketing terms such a cholesterol-free and low in saturated fats, when allowed by regulatory agencies, have implied to many in the public sector that such products have been deemed to be of potential benefit with respect to the prevention and/or management of CVD. Unfortunately, many of these products contained substantial levels of industrial TFA which might potentially promote rather than prevent the development of CVD via their aforementioned deleterious effects on risk factors such as LDL-cholesterol, HDL-cholesterol, and lipoprotein (a). In the present era, numerous countries have instituted or are implementing mandatory labeling for TFA on various food products and/or restrictions on the amounts allowed per food product serving. In order to qualify for a potential trans-free claims on processed foods, Canadian labeling laws require <0.2gm of TFA per serving (plus restrictions on the amount of saturates present) while the corresponding cut-off is <0.5g per serving in the United States. It needs to be recognized that the actual intakes of certain foods (particularly snack foods) often surpass the official serving sizes as listed on food packages. Mandatory labeling for TFA amounts are often included next to saturated fat amounts on food labels while giving the amounts of each of these two fat types in gram units. While such labeling for TFA is an improvement over traditional labeling wherein TFA contents were not made available, such labeling might ideally provide TFA amounts per serving in mg amounts as now done for cholesterol or in gram quantities if both cholesterol and TFA were to be given in the same quantitative units. Many in the public sector cannot readily differentiate that one gram of TFA is five times greater than 200 mg of cholesterol. Population data from the Nurses Health Study indicated that the risk for CVD per unit of TFA approaches that for dietary cholesterol; furthermore, TFA intakes in North America are approximately times greater at 5-10 gram per day as compared to gram/day in the case of cholesterol (all consumed from animal food sources). Mandatory labeling for TFA on processed foods does not protect the consumer from prepared foods as purchased in restaurants and other outlets. Consequently, many jurisdictions (New York city, selected other cities in North America, selected US states, etc) are instituting or considering legal bans on industrial TFA in processed and restaurant/fast foods. The argument for such a ban often includes restricting the availability of industrial TFA at source (supply) prior to its entry into a wide range of processed and fast foods which would also reduce the costs of inspections and analytical monitoring of numerous food products. Consumer protection through a legislative ban on industrially-produced TFA in foods in Denmark has been found to be accomplished without noticeable effects on the availability, price, or quality of food previously containing high amounts of industrial TFA in that country. Alternatives to Trans Fats Numerous alternatives to the use of industrial TFA in processed and fast foods are available. Some of these will require a return to some increased usage of palm and palm kernel or other tropical oils (containing saturated fatty acids but free of TFA from partial hydrogenation) alone or mixed with unsaturated vegetable oils to produce the necessary properties for food applications. While a partial replacement of saturated fats for TFA may be of concern; it should be emphasized that saturated fats are generally considered to be a much lower dietary risk for CVD as compared to equivalent amounts of industrial TFA as discussed. Other alternatives to TFA include high-monounsaturated vegetable oils (some via genetic modification) with lowered susceptibility to oxidative deterioration as compared to highly polyunsaturated oils and blends (or inter-esterification ) of such with more saturated fats for appropriate textures. While butter fats typically contain approximately 62% of the total fat found as saturates, a 50:50 to 67:33 blend of butter fat with highly unsaturated liquid vegetable oils (low in saturates) can give rise to mixtures which often have desirable physical properties (including spreadability, taste, etc.) and levels of saturated fats which are below 42% of total fat (without industrial TFA) and which may not increase risk factors for CVD when consumed along with 58-66% of the total fat mixture as natural monounsaturates plus polyunsaturates. In some alternatives, unsaturated vegetable oils (eg., soybean oil and canola oil) can be subjected to complete hydrogenation as compared to partial hydrogenation thereby giving rise to a predominant fatty acid product (18-carbons in chain length) known as stearic acid (fully saturated) which, unlike other saturates, has been found not to increase blood cholesterol levels in controlled human trials. Thus, mixing the high stearic acid product from complete hydrogenation with non-hydrogenated vegetable oils by blending or inter-esterification techniques can result in a usable fat product which is TFA-free and which does not increase total blood cholesterol and LDL-cholesterol levels. Numerous other options are becoming available in the marketplace such that these technologies should help to accelerate the marked reduction or elimination of industrial TFA from the food supply if supported by the required legislation, consumer education, and reasonable pricing. It is anticipated that the established health concerns with industrial TFA will

4 continue to drive the impetus towards an industrial TFA-free global society. Table 1. Estimated Fatty Acid Intakes and Sources in a Typical North American Diet Fat Component Common Food Source Avg. Daily Consumption gm/day % of energy (avg.) Total fat (fatty acids) mixed (animal/plant) Saturated fatty acids Monounsaturated fatty acids (natural) Trans fatty acids (monounsaturated) Polyunsaturated fatty acids (mostly omega-6 as linoleic acid) dairy products, fatty meats palm/coconut oils canola oil, olive oil, animal fats hydrogenated vegetable oils, shortenings, processed and fast foods, ruminant fats (minor) Corn, safflower and sunflower oils, others Polyunsaturated fatty Canola oil, soybean oil, acids (mostly omega-3 asflaxseed, others alpha-linolenic) Polyunsaturated fatty acids (omega-3 as EPA/DHA) fish/fish oil Cholesterol animal foods/fats (Data compiled by B.J. Holub) Selected Publications Ascherio, A. Trans fatty acids and blood lipids. Atheroscler. Suppl. 7:25-27, Holub, B. J. Hydrogenated fats and serum cholesterol levels. N. Engl. J. Med. 341: , Mozaffarian. D., et al. Trans fatty acids and cardiovascular disease. N. Engl. J. Med. 354: , Moss, J. Labeling of trans fatty acid content in food, regulations and limits-the FDA view. Atheroscler. Suppl. 7:57-59, Stender, S., et al. High levels of industrially produced trans fat in popular fast foods. N. Engl. J. Med. 354: , 2006.

5 Suggested Websites Institute of Medicine of the National Academics, U.S. Food and Drug Administration,