Occurrence and Characteristics of Oils and Fats

INTRODUCTION 340 DIETARY SOURCES OF ISOMERIC FATTY ACIDS ... ... 340 DIETARY INTAKE OF HYDROGENATED FATS AND FATTY ACID ISOMERS... 341 PHYSIOLOGICAL AND METABOLIC STUDIES 342 Absorption 342 Growth. Organ Size.and Longevity . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . 343 Cell Function . . . ..... . . . . . . . . . . . . 344 EFFECT OF ISOMERIC FATS ON LIPID-METABOLIZING ENZYMES 345 Desaturases and Elongases 345 Lecithin:Cholesterol Acyltransferase ..... . 346 Oxygenases . . ,., 346 Prostaglandin Synthetase ...... ,., . . . ,., .. . . , . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . , . . , . . . . . . . . . . . . 347 EFFECT OF ISOMERIC FATS ON LIPOPROTEINS. TISSUE LIPIDS. AND FATTY ACID COMPOSITION "."" . . . . . . . . . . . . . . . . . " . . . . . . . . . . . " . . . . . . . ".". . . 347 Serum Lipid and Lipoprotein Concentrations ... " ... . . .. . . . . . . . . . . .. " . . . . . " . . . . . . . .. "". . 347 Tissue Lipid Class Concentrations ........ ". . . . . 348 Fatty Acid Composition ... , '"'' " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "",,. . . . . . . . . . . . . 349 HEALTH·RELATED NUTRITION STUDIES ..... "" . . . . . . . . . . . . . " .. . . . . . . . " . . . . . . . . . "". . 350 Atherosclerosis " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " " 350 Cancer , . . . . . . . , . . . . . . . . . , . . . . . . . . ......... . . . . . . . . ..... . . . . . . . . . . ... . . . . . . ," 351 Prostaglandins and Related Studies ...... , . . . . . . . . . . . ..... . . . . . . . . . .... , . . . . . . . . . . . . . . . . . . . . . . 352

Nutrition and biochemistry of trans and positional fatty acid isomers in hydrogenated oils.

Trans unsaturated fatty acids in natural products and processed foods.

The decisions to limit (Europe) or declare (USA) the trans isomer content of certain fatty foodstuffs have caused a demand for hardstocks with a reduced trans isomer content. One way to produce such hardstocks is by interesterifying high-melting components such as palm stearin or fully hydrogenated vegetable oils with lauric or liquid oils. Another way is to modify the hydrogenation process. Possible modifications are reviewed. A moderate reduction in trans isomer content results from operating the hydrogenation process at much reduced temperature, but this also leads to an increase in saturates. Larger reductions in trans isomers may well be made possible by the recent development of new catalysts. One development involves the use of zeolites that allow the rather straight trans isomer to enter the pores while keeping the more curved cis isomers outside. The other development involves a precious metal catalyst that may have been modified in such a way that it has a reduced affinity for mono-unsaturated fatty acid moieties.

Revisiting the formation of trans isomers during partial hydrogenation of triacylglycerol oils

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 govemments 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 fer 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.

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

Soybean oil is the leading edible vegetable oil in the world in terms of volume, and considerable amounts are consumed in partially hydrogenated forms. Early recognition that commercial hydrogenation of vegetable fats produces isomeric forms of monoenes and polyunsaturates has prompted much research and speculation on the nutritional properties of hydrogenated fats, including soya oil. Past results of studies with animals and humans will be reviewed and key findings will be summarized and discussed. Particular attention will be devoted to questions recently raised concerning the relationships of health and hydrogenated fats and an attempt will be made to put these matters into factual perspective in light of current knowledge.

T. H. Applewhite

Papers

Nutritional effects of hydrogenated soya oil