Conjugated linoleic acids CLAs and white adipose tissue: how both in vitro and in vivo studies tell the story of a relationship

Abstract

The distribution of adipose tissue in mammals is dependent on genetic and environmental factors, and in health the fundamental role of adipocytes is to store triacylglycerol during energetic excess and to mobilize this reserve during energy expenditure or reduced food intake. This requires an accurate balance, which is maintained through the interactions of several regulatory factors, as well as dietary manipulations. Dietary supplementation with CLAs (conjugated linoleic acids) is regarded as promising in many mammalian species for obtaining good body mass repartition and diminution of fat depots. CLAs are a group of positional and geometric isomers of conjugated dienoic derivatives of linoleic acid, naturally present in foods originating from ruminant species, and normally present in human adipose tissue. CLAs can, however, also be obtained as commercial supplements, usually containing synthetically prepared isomeric mixtures, and as dietary supplements CLAs are widely used by obese people, above all in the USA and Europe. CLAs are claimed to have protective effects against human degenerative pathologies, such as cancer, atherosclerosis, and diabetes, as well as showing beneficial effects on immune functions and food and energy intakes. The mechanisms of action of CLAs are not fully clarified at present, because in vitro and in vivo studies are not always in agreement, and possibly because CLAs act in different ways and with different consequences when administered in the diet to different species. The present review summarizes the ascertained mechanisms of action of CLAs, the mammalian species of major interest in which important studies have been conducted, and the future prospects for the use of CLAs in both humans and food animal species.