Of the 200 different cells in the human body, the adipocyte -- the humble fat cell -- is by far the most maligned. Vilified even more maliciously is the adipose tissue it forms, otherwise known as fat. All we seem to want to do is "shed," "cut," or "burn" it. Until the 1940s, scientists were indifferent to fat, simply characterizing it as a form of connective tissue. But in the past four decades, that view has evolved considerably.

Nearly 100,000 papers have been published on fat during that time. From these learned exploits, researchers have learned that fat, far from being dead weight, is an "endocrine organ at the center of energy homeostasis." Without it, the human body could not function properly.

Harvard biologists Evan Rosen and Bruce Spiegelman paid homage to fat in the January 16th issue of the journal Cell, revealing an array of incredible facts about the tissue and offering insight into the future of fat research.

"Adipose tissue is a remarkably complex organ with profound effects on physiology and pathophysiology..." they wrote. "It seems certain that we will discover much more about this highly complex and relatively unloved cell in the very near future."

Here are eight fascinating facts about fat:



1. Only vertebrates are known to have specialized fat cells. All eukaryotes -- organisms whose cells contain a nucleus -- can store fat in the form of lipid droplets, but only those organisms with a backbone -- vertebrates -- have adipocytes. Consider yourself special!

2. There are three, count em', three types of fat: white, brown, and beige! White adipocytes contain a single lipid droplet and are used to store excess energy. Brown adipocytes contain numerous droplets and a great many mitochondria, the cellular power plants. More related to muscle cells than white adipocytes, brown adipocytes' primary purpose is to generate heat. They are primarily found around the back and shoulders. Beige adipocytes are very similar to brown adipocytes, except they are found scattered amongst white adipocytes and contain lower levels of a protein called UCP1.

3. You have a fixed number of fat cells as an adult. New fat cells are constantly created and destroyed, but the body always remains below a fixed limit, which is set during adolescence. This is a key reason why it's so important to prevent childhood obesity.

4. Fat cells are microscope balloons. If the body has a fixed amount of fat cells, then how have 1.7 billion across the globe come to be obese? The answer is that fat cells are endowed with the incredible ability to grow well beyond their original size, soaking up extra energy -- in the form of lipids -- like a sponge. Under prolonged overeating, progenitor fat cells called preadipocytes can become full adipocytes. But once these are gained, they're almost impossible to lose. Weight loss reduces the volume of fat cells, but not their number.

5. Liposuction doesn't work. It's the most common cosmetic surgery in the world. And in the long-term, it's completely pointless. Removing a hefty 20% of total body fat may make you superficially slimmer, but it doesn't improve insulin sensitivity or reduce risk factors for cardiovascular disease. Moreover, studies have clearly demonstrated that unless patients take steps to live healthier, the excised fat mass will regrow in about a year.

6. You might joke that fat is great padding, but it really is. Fat protects delicate organs. "The eye, for example is surrounded by fat in a manner analogous to the way one might pack a teacup in bubble wrap," Rosen and Spiegelman say. It also cushions body parts exposed to high amounts of stress. Your toe- and heelpads are composed of fat, and your buttocks is brimming with it.

7. Fat may boost your metabolism. Research has shown that transplanting fat taken from beneath the skin (subcutaneous) and placing it around internal organs can actually reduce the overall amount of fat in the body and balance glucose levels.

8. Seven out of every ten cells in fat tissue aren't fat cells. According to Rosen and Spiegelman, "every gram of adipose tissue contains 1–2 million adipocytes but 4–6 million stromal-vascular cells." Half of the latter cells are white blood cells. Under obese conditions, other types of immune cells latch on to the expanding adipocytes, contributing to insulin resistance and chronic low-level inflammation. Why they heap on is not entirely clear.

(Images: Wikimedia Commons, Spiegelman)

Source: Evan Rosen & Bruce Spiegelman. "What We Talk About When We Talk About Fat." Cell 156, January 16, 2014