The need for dietary fat is not necessarily for energy purposes. Fat is needed in our diet as a means of providing two essential fatty acids, linoleic acid, an ra-6 PUFA, and a-linolenic acid, an ra-3 PUFA. Since the amount of these fatty acids in fat storage (adipose tissue) is limited, this suggests that their role in our body isn't really to provide calories, although they will be used for energy. Linoleic and a-linolenic acid are used to make longer, more complex fatty acids that have special functions.
Linoleic acid is used to make a longer ra-6 fatty acid called arachidonic acid (ARA) while a-linolenic acid is used to produce longer ra-3 fatty acids, namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Both ARA and DHA are found in higher concentration in the brain and are vital for the development of the central nervous system and eyes. Meanwhile, EPA and ARA can be used to make factors called eicosanoids (for example, prostaglandins, thromboxanes, and leukot-rienes) that help regulate many bodily functions as discussed below and in later chapters.
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