Oxidised fats can interfere with insulin resistance because they initiate free radical chain reactions that can lead to oxidative stress. This oxidative stress then interferes with the insulin signal cascade decreasing the strength of the insulin signal reaching the interior of the cell. This then leads to a decrease in the uptake of glucose from the blood to the cells. Trans fats are another group of modified fats that may decrease insulin sensitivity. Like oxidised fats, trans fats may decrease insulin sensitivity through the generation of oxidative stress. However, unlike oxidised fats, trans fats are not thought to decrease insulin sensitivity through the direct initiation of free radical chain reactions, but through an indirect immune related mechanism. The ability of trans fats to initiate oxidative stress likely relates to their ability to interfere with the metabolism of the essential fatty acids alpha linolenic acid and linoleic acid that belong to the omega-3 and omega-6 families of fat, respectively.
The essential fatty acids alpha linolenic acid and linoleic acid are natural cis-structured fats which are essential to the health. When ingested in the correct ratios they form a number of short lived hormones called eicosanoids that can regulate cell function. One of the main functions they regulate in the cell is that of inflammation. For health to be maintained and for inflammation to be controlled the diet must contain roughly 1 gram of linolenic acid for every 3 grams of linoleic acid. By interfering with the metabolism of the essential fatty acids, trans fats negatively affect the delicate balance between the omega-3 and omega-6 fatty acids and this modifies production of the antiinflammatory eicosanoids. Ingestion of trans fats may therefore result in the generation of inflammation. Inflammation is detrimental to insulin sensitivity, because the inflammatory immune response is a sources of oxidative stress. Indirectly therefore trans fats lead to oxidative stress and this interferes with the insulin signal cascade.
Another possible mechanisms by which trans fats interfere with insulin sensitivity is though changes to the fluidity of membranes. The cell membrane fluidity is regulated by incorporation of different types of lipid into the cell membrane. Increasing the amount of long chain polyunsaturated fatty acids such as the omega-3 and omega 6-fatty acids derived from alpha linolenic acid and linoleic acid into the membranes increases their fluidity because these molecules have many double bonds that gives the carbon tails a pronounced kink. This means that packaging the fats together closely is more difficult, and the extra space within the membrane causes increase fluidity. High fluidity in the beta cells of the pancreas that release insulin as well as the target cells of insulin may increase insulin sensitivity. Trans fats have straight carbon tails, and ingesting trans fats increases their concentration in the cell membranes in place of the polyunsaturated fats, decreasing membrane fluidity and insulin sensitivity.