Trans fatty acids are monosaturated fatty acids or polyunsaturated fatty acids that contain at least one double bond in the trans configuration, rather than the usual cis configuration found in most lipids. This configuration may occur either as s result of microbial fermentation in the rumen or through the process of hydrogenation. The consumption of trans fatty acids has been associated with increased cornonary heart disease since reports from the 1990s.
In human studies, consumption of trans fatty acids was most commonly determined by assessing dietary intakes through food frequency questionnaires or diet diaries. Care must be taken when estimating trans fatty acids intake based n reported food intake as it has been shown that different brands of food products can result in considerable varitation in trans fatty acid content for the same diet. The study showed that the waist-hip ration as a measurement of abdominal obesity found no correlation with trans fatty acid intake in 600 UK volunteers of mixed ethnic origin. Studies provide limited but consistent evidence to support a weak association between trans fatty acid consumption and a small increase in weight gain.