Nutritional Aspects of Trans Unsaturated Fatty Acids

Dietary trans unsaturated fatty acids from hydrogenated vegetable and fish oils have been shown to raise plasma low density lipoprotein cholesterol and lower high density lipoprotein cholesterol levels at 10%, 6% and 3% of energy intake. As trans fatty acid intake has not been previously assessed in Ireland a food frequency questionnaire (FFQ) was developed to assess fat intake with particular focus on trans fatty acids. A nutrient database was developed which included the fatty acid and total trans fatty acid composition of foods (measured by gas chromatography and infra-red spectroscopy) which are sources of fat in the Irish diet. The FFQ was used to assess fat intake in 105 healthy volunteers and was validated by comparison with results obtained in the same population using the diet history method. In addition the linoleic acid and total trans fatty acid intake was assessed by gas chromatographic analysis of adipose tissue biopsies taken from the study group and this provided additional validation of the mean TUFA intake assess by the FFQ. Mean TUFA intake assessed by the FFQ was 5.4g/day (2% energy) although intakes ranged from 0.3-26 g/day. Although the chronic postprandial effects of TUFA from hydrogenated vegetable and marine oils have been studied extensively, the acute postprandial effects remain unknown. High melting point fats such as lard and palm oil have been used extensively in the food industry as replacements for hydrogenated fats. Therefore the acute postprandial effects of lard, palm oil and hydrogenated fish oil were examined in eight healthy male volunteers. Forty grams of each fat were given to each volunteer as a milkshake using a latin square design. Blood samples were drawn before ingestion of the test mean and 2,4,5, and 8 hours postprandially. Plasma triacyglycerol (TAG), cholesterol and non-esterified fatty acid (NEFA) concentrations were measured enxymatically. In addition the fatty acid composition of postprandial triachylglycerol-rich-lipoproteinTAG and NEFA samples were measured by gas chromatography. There was no significant difference in the postprandial response in plasma TAG, TRL-TAG, total cholesterol or plasma NEFA, measured as the area under the postprandial curve between test meals. Although mean TUFA intake in Ireland was only 5.4 g/day, the possibility of TUFA intakes as high as 26g/day in some men and 11.9 g/day in some women highlights the need for careful monitoring of the health risks at these high levels. In conclusion the effects of different forms of hydrogenated fat consumed in amounts reflective of current use in Ireland must be ascertained