Dietary fatty acids are a complex group of chemicals containing a number of different classes including saturated, monounsaturated and polyunsaturated variants. Within the saturated fatty acid group, there are a number of fatty acids that are consumed in the human diet and these range in chain length from 2 to 20 or more carbons in length. The most common dietary saturated fatty acids are palmitic (C16:) and stearic acid (C18:0), 16 and 18 carbon length saturated fatty acids, respectively, mainly from animal fats. Animals have the ability to synthesise their own fatty acids and humans are no exception. The process of de novo lipogenesis results in the production of palmitic acid, that can then stored in adipose tissue, and subsequently be used as a source of energy. The conversion of carbohydrates to saturated fatty acids occurs in the live and this pathway is particularly stimulated by fructose and other refined carbohydrates. High consumption of refined carbohydrates and sugar therefore stimulate fatty acid synthesis.
One of the problems associated with elevated circulating levels of saturated fatty acids is the development of insulin resistance. In fact, circulating levels of certain saturated fatty acid and the presence of very low density lipoprotein (VLDL) particles carrying triglycerides can be used as a marker for insulin resistance. The exact reason for this is not clear, but some evidence suggests that high levels of certain saturated fatty acids interfere with the insulin signal cascade and this decreases insulin sensitivity, and may also increase β-cell toxicity. Both palmitic and stearic acid have been shown to have these effects, but a monounsaturated fatty acid palmitoleic acid is particularly strongly associated with these effects and is a highly useful biomarker for the identification of underlying insulin resistance and its associated pathology. However, not all saturated fatty acids appear to be detrimental, and very long chain fatty acids (>20 carbons) may have a protective effect, possibly through a substitution for the shorter fatty acids.
For example, in one study1, researchers investigated the effects of very long chain saturated fatty acids, containing 20 carbons or more, on the association with diabetes using epidemiological data from previous studies. The results showed that baseline levels of very long chain saturated fatty acids were associated with lower triglyceride (VLDL) levels as well as lower levels of circulating palmitic acid. Those with the highest levels of arachidic acid (C20:0), a 20 carbon saturated fatty acid, had a 47 % lower risk of diabetes compared to those with the lowest levels. Levels of behenic (C22:0) and lignoceric (C24:0) acid were associated with a 33 and 37 % reduction in diabetes risk, from the highest intakes compared to the lowest intakes. Using regression analysis, the authors determined that the protective effects of very long chain saturated fatty acids may be due to the reductions in palmitic acid and triglycerides. Saturated fat is therefore not all the same and health differences exist based on chain length.
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