Why Are Thin People Not Fat?

Some people remain overweight despite working very hard to lose weight, while some people remain underweight despite trying hard to put on weight.

Here's a fat cell under the microscope

Is there a scientific explanation for this?

This interesting documentary explains it all, backed by findings from a very controversial "over-eating" experiment.

BBC Horizon: Why Are Thin People Not Fat

Here are some important points taken from this documentary:

• Fat is stored in our body as a emergency source of energy during times of famine, when food is scarce.
• People whose body is genetically better at storing fat have a higher chance of surviving a famine. Therefore these genes have a higher chance of being passed on to the next generation. This explains why there are more people who easily put on fat than people who don't.
• Putting on fat easy might be an advantage for people living in the past, but in today's environment the opposite is true.
• All of us have a natural body weight which our brain remembers, and our brain will always work very hard to keep us at our natural body weight. Some people can easily resist the urge of over-eating because their brain wants to stop them from gaining weight, and vice versa.
• Scientists have also found that a common human virus called "adenovirus-36" is strongly linked to human obesity. Those infected with the virus are significantly heavier than the average. But this viral infection is NOT the only cause for obesity, as obviously there are other reasons causing people to become obese.
• When a normal healthy cell becomes a fat cell, it will grow bigger having the ability to accumulate more fat in the cell. At the same time, our body will also grow more and more fat cells to accumulate more fat when it finds that the existing cells have achieved their maximum fat storage.
• Once these fat cells have grown in our body, it is almost impossible to remove them.
• It's easier for our body to produce fat cells during childhood or adolescence. Overweight children have a higher tendency to grow up as overweight adults.
• For some people, over-eating will result in more muscle mass being produced, instead of fat. This also contributes to weight gain.
• Once stopping ourselves from over-eating, our brain will act to bring us back to our natural body weight which it remembers.

Here are some information regarding the findings on "adenovirus-36" obtained from WebMD.

Title: Obesity Virus: More, Bigger Fat Cells 

Link: http://www.webmd.com/diet/news/20070820/obesity-virus-more-bigger-fat-cells

"Dhurandhar's team finds evidence that Ad-36 has a direct effect on human fat cells. Infection of adult stem cells from human fat triggers their transition into pre-fat cells. And these virus-infected cells hold much more fat than normal pre-fat cells. The end result: more, fatter fat cells." ~ WebMD

To me, these findings from the documentary sound more like good news than bad news for me. Why? Because it says that our brain remember the body's natural weight and will do all it can to prevent us from gaining weight. So, the catch here is that, in order to gain or lose weight, apart from going through the weight gain or weight loss process, we must make our brain "reset" the natural body weight which it remembers and to create a new reference point.