There are a number of minor lipid or fat constituents of the normal human diet that are worthy of any discussion involving fat loss. In particular conjugated linoleic acid and lecithin are minor dietary components that have useful fat loss properties. While conjugated linoleic acid (CLA) and lecithin are available as supplements, they are present in foods, and under such circumstances, it may be correct to refer to them as health foods. Conjugated linoleic acid is a minor fat component of dairy foods, produced in the ruminant digestive tract by bacteria. Conjugated linoleic acid is not a single substance, but instead a family of isomers of the essential fatty acid linoleic acid. Conjugated linoleic acid is a polyunsaturated fatty acid, with two double bonds that are conjugated (on adjacent carbons) and these double bonds can be either cis- or trans- in their configuration. Although many isomers exist in the CLA family, the most common dietary CLA isomers used in studies are the cis-9, trans-12- and trans-10, cis-12 isomers.
Conjugated linoleic acid is of interest nutritionally because studies show that it has fat loss effects. In particular conjugated linoleic acid isomers appear to be able to decrease body fat and increase the lean muscle mass of both experimental mammals and humans. It is not fully understood how conjugated linoleic acid causes such changes, but it is thought that an improvement in insulin sensitivity may be involved. However, it is not entirely clear if the improved insulin sensitivity is caused directly by the conjugated linoleic acid, or is a consequence of some other action. Other studies show that the trans-10, cis-12 isomers may decrease the uptake of fatty acids into adipocytes by inhibition of lipoprotein lipase. Either way, supplementation of conjugated linoleic acid to humans has resulted in increased fat loss, when compared to placebo treatments. The presence of some conjugated linoleic acid in dairy foods may explain the small but consistent association between the two in epidemiological studies.
Another interesting lipid substance in the human diet with possible fat loss implications is lecithin. Lecithin is a choline containing phospholipid (choline joined to two fatty acids and a phosphate group), and forms a natural part of the membranes of all of our cells. Dietary sources of lecithin include all plant and animal products as it is a constituent of all living things, but rich sources include egg yolks, chicken, fish and liver. However, lecithin is available as a dietary supplement, usually synthesised from soybeans. The fat loss properties of lecithin centre on its content of choline, that may be a conditionally essential element required for the export of fats from the liver. When choline intake drops below a threshold level, or when fatty acid synthesis is excessive, as might occur from a poor quality diet, a breakdown in the process of exporting fats from the liver may occur. This can cause an accumulation of fatty acids in the liver, and this may be a contributory cause to the development of nonalcoholic fatty liver and insulin resistance.
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