INTRODUCTION TO ESSENTIAL FATTY ACIDS

I. INTRODUCTION TO ESSENTIAL FATTY ACIDS

Lipids (oils and fats) are water insoluble macronutrients that provide the most concentrated form of food energy to the body. The major portion of the fat in our diet is in the form of triglyceride, which provides 9.0 kCal/g compared to the 4.0 kCal/g provided by protein or carbohydrate. These lipids are absorbed by the gut and transported to various parts of the body to be oxidized to provide energy in times of need, or to be stored in adipose tissue in times of plenty. Certain lipids, the phospholipids, make up the bilayer membranes surrounding all cells of the body. Lipids are not only structural elements, but they can also be primary and secondary messengers within and between cells and tissues. As a consequence, there are complex biochemical mechanisms controlling synthesis, oxidation, and interconversion of the multitude of different lipids that are obtained from our diet.

It was first suggested that certain fats are essential for life as early as 1929 (Mead, 1982). That is, although the body could synthesise most fats de novo, certain fatty acids were required as dietary precursors to the more important functional fatty acids. It was later recognized that two specific fatty acids, linoleic acid (LA) and alpha-linolenic acid (ALA), could not be synthesised de novo because of the position of certain double bonds close to the methyl end of the molecule (described in detail in the next section). Thus, these two fatty acids were considered essential for growth. Without them in the diet, animals developed a series of symptoms such as dry, scaly skin, excessive water consump- tion, reduced growth, infertility, etc., which are now known as classic symptoms of essen- tial fatty acid (EFA) deficiency. We now understand that the symptoms associated with the deficiency are not necessarily due to the absence of LA or ALA, but rather to the resulting absence of the products of LA and ALA metabolism—the long-chain polyunsat-

Similar to classic vitamin deficiencies, essential fatty acid deficiency can be over- come by only a small amount of dietary LA and ALA, and there are not many cases of essential fatty acid deficiency reported in humans. However, once we go beyond the pathologies of EFA deficiency, we recognize that optimum function of our bodies (not absolute function) is very dependent on the amount, and ratio, of these EFAs and their metabolites. Such a ratio can be, and has been, drastically affected by changes in our diet over the last 100 years (Simopoulos, 1998). It is, therefore, quite appropriate to consider the fortification of foodstuffs with certain dietary fats, as if they were food additives, in order to provide an optimal ratio of these EFAs to maximize health and longevity. Such

a rationale has been used for the development of new types of food products referred to as ‘‘functional foods.’’ Since this is of growing interest in the food industry, this chapter will discuss the biochemical rationale and functional consequences of the inclusion of EFAs into our diet.