Where fat cells come from

All fat is not the same, according to a report in the latest edition of the journal Cell.

Researchers at Harvard School of Public Health have discovered that a hormone produced by "home-grown" fat has big benefits for the metabolism. What's more, this is the first known example of a fat-based hormone - hormones are usually made of proteins. The hormone in question is a fatty acid known as palmitoleate.

The researchers studied mice whose fat tissue lacked two fatty acid binding proteins, and found that they were extremely healthy, resisting obesity, diabetes and other metabolic problems.  But instead of finding that these animals had lower levels of fatty acids in their blood, they actually found high levels.

Further studies showed that these changes in the fat cells were having effects elsewhere in the body, including the liver and muscles, implicating that a hormone of some sort was involved. Eventually, the team discovered that the fatty acid palmitoleate was acting as a hormone.  In normal mice, levels of palmitoleate drop by around half when the animal are on a high fat diet.  But in the genetically engineered mice, they only have a palmitoleate drop of around 10%, which explains their resistance to the effects of a fatty diet.

The team found that palmitoleate can stimulate the effects of insulin on muscles, pushing sugar out of the bloodstream and into the muscles where it's needed, and it also prevents fat building up in the liver. It's produced when the body creates its own fat, rather than storing it from high-energy foods. So we have the unusual situation that a fatty molecule may help to prevent the buildup of fat in the body - effectively fat fighting fat.

The next step will be to see if this holds true in humans as well as mice, by measuring palmitoleate levels in healthy people and comparing them with the levels in people with metabolic problems.