Flavonoids as inducers of white adipose tissue browning and thermogenesis: signalling pathways and molecular triggers

Background: Flavonoids are a class of plant and fungus secondary metabolites and are the most common group of polyphenolic compounds in the human diet. In recent studies, flavonoids have been shown to induce browning of white adipocytes, increase energy consumption, inhibit high-fat diet (HFD)-induced obesity and improve metabolic status. Promoting the activity of brown adipose tissue (BAT) and inducing white adipose tissue (WAT) browning are promising means to increase energy expenditure and improve glucose and lipid metabolism. This review summarizes recent advances in the knowledge of flavonoid compounds and their metabolites. Methods: We searched the following databases for all research related to flavonoids and WAT browning published through March 2019: PubMed, MEDLINE, EMBASE, and the Web of Science. All included studies are summarized and listed in Table 1. Result: We summarized the effects of flavonoids on fat metabolism and the specific underlying mechanisms in sub-categories. Flavonoids activated the sympathetic nervous system (SNS), promoted the release of adrenaline and thyroid hormones to increase thermogenesis and induced WAT browning through the AMPK-PGC-1 alpha/Sirt1 and PPAR signalling pathways. Flavonoids may also promote brown preadipocyte differentiation, inhibit apoptosis and produce inflammatory factors in BAT. Conclusion: Flavonoids induced WAT browning and activated BAT to increase energy consumption and non-shivering thermogenesis, thus inhibiting weight gain and preventing metabolic diseases.