Fat and Cancer

Abstract

Fat has been the subject of much epidemiologic research on the role of nutritional factors in the etiology of cancer. 1,2 Some studies reported only on fat as a single entity, whereas others distinguished among different types of fat in an effort to refine the analyses. Fat (i.e., fatty acids) can be categorized in many ways, e.g., by their chemical structure, by sources in the diet, or by human nutritional requirements. Chemically, fatty acids may be classified as unsaturated or saturated, depending on whether or not they contain any double bonds between adjacent carbon atoms. Unsaturated fats may be monounsaturated (only a single double bond, as in oleic acid) or polyunsaturated (multiple double bonds, as in linoleic acid). Polyunsaturated fatty acids can be further broken down into the omega-6 or omega-3 series, determined by the location of the first double bond from the methyl end of the molecule (e.g., arachidonic vs. docosapentaenoic acid, respectively) (Figure 1). Unsaturated fatty acids can occur as cis or trans isomers, which are different geometric configurations of the same molecule (e.g., oleic vs. elaidic acid, respectively) (Figure 2). Most naturally-occurring fatty acids are in the cis form. Trans fatty acids are largely a result of the industrial hydrogenation of liquid oils, as occurs in the production of margarine. Because the biological effects of dietary constituents depend on their chemical structures, these different forms of fat may have independent relationships to disease. Most of the epidemiologic studies that have examined different chemical forms of fat have distinguished between saturated and polyunsaturated fats, probably reflecting the earlier experience in cardiovascular disease research. More recently, studies have also been reporting on monounsaturated fats. There are few epidemiologic data on cis and trans isomers of fatty acids in relation to cancer risk.