Update on food sources and biological activity of odd-chain, branched and cyclic fatty acids –– A review

Odd-, branched-chain and cyclic fatty acids are rare food components. Recently, these compounds have generated great scientific interest, since they interact on the cellular level in many diseases, at least partly by modulation of the fluidity and oxidative stability of lipid bilayers. This review aims to synthesise recent data on food sources and physiological properties of these fatty acids. Manuscript focuses on references from the last five years. For each group of studied fatty acids, their basic physicochemical properties, dietary sources, estimated dietary intake, biosynthetic pathways and concentrations in selected tissues and cells, as well as their impact on human health are presented. As large discrepancies in the results were noticed, only papers using mass spectrometry or authentic fatty acid standards for identification and quantification are presented. Estimated daily intake of these fatty acids from typical diet in Western countries is approximately 1.5 g, including approximately 1.0 g odd-, 0.5 g branched-, and 12 mg of cyclic fatty acids, mostly from ruminant fat (beef and dairy). In Asian countries, significant sources are mostly nātto and fish (especially fermented). For vegans and vegetarians, the best sources are algae, selected plants, mushrooms and fermented plants. These data can be used to incorporate less known food sources into the diet and thus improve its nutritional properties. Unfortunately, some sources of specific fatty acid data are still inconsistent, for example, odd-chain fatty acids share in turkey fat varies from below 1% to ca 10%.