There are currently three types of fat known: white, brown, and beige. If you're interested in where fat tissue comes from and how it behaves, skip ahead to the section titled "The Developmental Origins of Adipose Tissue: A Bloody Mess", which means that it's actually bloody and that it's just bloody confusing to understand how all the genes involved relate to each other. There you'll find a handful of good factoids:
- The total number of fat cells humans carry as adults is set by adolescence.
- Humans turn over about 8% of their fat cells per year.
- Mice turn over about 0.6% of their fat cells every day.
- Fat cells can be derived from stem cells that can also create blood cells.
- Brown fat cells are derived from stem cells that actually reside in muscles, not fatty tissue. A single gene controls the switch between the two.
In this review, it's best shown in the first figure, where it's not until several fat related cytokines were identified in the mid-1990's that work in the fat field really took off. Though interest in the field slowly grew, it wasn't until reaching milestones like the discovery of leptin and adiponectin that both raw and relative numbers of papers (blue and red), respectively, shot up from a baseline that spanned more than two decades.