The term fat evokes a multitude of ideas, images, and prejudices. It encompasses the
different types of adipose tissue (AT) and cellular components as well as the myriad
of lipid molecules. The AT and lipid molecules throughout the body carry out scores
of vital functions ranging from thermal insulation to energy homeostasis to signal
transduction. A fact that is not generally appreciated is that in addition to its
roles in energy balance and thermoregulation, the AT is also an integral part of both
the endocrine and immune systems. Fatty acids (FAs) are the primary building blocks
of most lipids. They serve as fuel, structural components, and regulatory molecules
(mediators). Most of the free FAs in the body are either obtained from the diet or
released by the AT (lipolysis). However, most of the short-chain FAs such as propionate
and butyrate are generated in the colon by the fermentation of dietary fiber by the
gut microbiota. In addition to providing fuel for the colon enterocytes, these molecules
act on specific G protein-coupled receptors in the gut cells stimulating the release
of glucagon-like peptide-1 and peptide YY simultaneously improving insulin sensitivity
and curbing appetite. The essential FAs linoleic and α-linolenic give rise to two
distinct classes of omega FAs, n-6 and n-3, respectively, and hence to more complex
lipid derivatives (eicosanoids) which are involved in virtually all aspects of cellular
function including immunomodulation and inflammation. These include prostacyclins,
thromboxanes, leukotrienes, and epoxyeicosatrienoic acids.
Key-words:
Adipokines - adipose - free fatty acids - lipids
