Exercise, white fat cells and brown fat cells
Previously, we have written about how how lack of exercise can turn actual muscle tissue into fat, creating that "lovely" marbled meat effect inside our muscles.
Now recent research has shown how exercise can do quite the opposite, i.e. how to make fat tissue behave like fat-burning organs, not fat accumulating organ, similar to muscles and the liver, via a newly discovered hormone, called irisin.
Our body has two types of fat cells: white and brown. White adipocytes (fat cells) are lighter in color and accumulate fat while brown adipocytes (fat cells) are much darker in colour and burn fat.
We always knew that exercise stimulates fat cells to release fat which is then used by the muscles, and other organs, for energy. However, now we know that with intensive exercise irisin is secreted by muscle cells, taken up by the circulation and ends up in white fat cells. Once inside fat cells, irisin stimulates them to start behaving like brown fat cells and burn fat to produce heat, instead of accumulating fat.
Because they are physically and functional somewhere between white and brown adipocytes, these altered fat cells are called beige adipocytes - and sometimes, brite (i.e. brown-white) adipocytes.
Irisin, UCP1 and betatrophin
Irisin "convinces" the white fat cells to burn fat for heat (thermogenesis) by boosting the production of UCP1, the main thermogenic protein. UCP1 can also be stimulated by various herbal extracts, including fucoxanthin, found in in the Wakame seaweed (Undaria pinnatifida).
In addition to stimulating UCP2, it has now been found that irisin also boosts the production of betatrophin, another newly identified hormone that increases the number of beta cells in the pancreas. Since beta-cells are responsible for insulin production, this explains the anti-diabetic, blood sugar-regulating effect of irisin.
The holy grail of fat loss (and cellulite reduction)
These new amazing discoveries do not only shed light to the different ways in which exercise stimulates fat reduction but are also bringing us closer to the goal of helping reduce obesity and metabolic disease and reducing local adiposity and cellulite via the local application of irisin-boosting or UCP1-boosting natural ingredients.
- Journal: Diabetes
- Irisin stimulates browning of white adipocytes through mitogen-activated protein kinase p38 MAP kinase and ERK MAP kinase signaling.
- Link: http://www.ncbi.nlm.nih.gov/pubmed/25353662
- Excerpt: "The number and activity of brown adipocytes are linked to the ability of mammals to resist body fat accumulation. In some conditions, certain white adipose tissue (WAT) depots are readily convertible to a ''brown-like'' state, which is associated with weight loss. Irisin, a newly identified hormone, is secreted by skeletal muscles into circulation and promotes WAT "browning" with unknown mechanisms. In the current study, we demonstrated in mice that recombinant irisin decreased the body weight and improved glucose homeostasis. We further showed that irisin upregulated uncoupling protein-1 (UCP-1; a regulator of thermogenic capability of brown fat) expression. This effect was possibly mediated by irisin-induced phosphorylation of the p38 mitogen-activated protein kinase (p38 MAPK) and extracellular signal-related kinase (ERK) signaling pathways. In addition, irisin also promoted the expression of betatrophin, another newly identified hormone that promotes pancreatic β-cell proliferation and improves glucose tolerance. In summary, our data suggest that irisin can potentially prevent obesity and associated type 2 diabetes by stimulating expression of WAT browning-specific genes via the p38 MAPK and ERK pathways."
- Journal : Diabetes
- Paper: Irisin ERKs the Fat
- Link: http://diabetes.diabetesjournals.org/content/63/2/381.long
- Excerpt: "Recent data has shown that exercise, besides using calories to do physical work, also causes an increase in energy expenditure through augmentation in brown fat and the browning of white fat. Indeed, these effects on brown fat could represent part of the longer-lasting benefits of exercise... Irisin regulates the thermogenic program in fat through ERK and p38 pathways. Irisin induces the thermogenic gene program in 3T3-L1 cells and primary subcutaneous adipocytes. In vivo treatments of this recombinant protein in mice show strong anti-obesity effects and improve systematic glucose homeostasis... Last and of import, Zhang et al. gave irisin by injection daily for 2 weeks and saw strong changes in body weight, browning of the adipose tissues, and improvements in glucose tolerance. While these data are consistent with our earlier studies using viral vectors, showing these effects with a stable version of the protein is a very substantial step in the direction of human therapeutics. Scale up and production of recombinant proteins in yeast is well established, so this new irisin reagent will be of great interest to the fields of diabetes, metabolism, and exercise science. Exercise, of course, benefits other disorders of the liver, heart, muscle, and brain. It will be of great interest to apply these and other irisin preparations to models of other disease states. Identification of the irisin receptor will also open new possibilities for activation of these areas."