This might help what JohnP was saying:
Quote:
Fat Storage
In the last section, we learned how fat in the body is broken down and rebuilt into chylomicrons, which enter the bloodstream by way of the lymphatic system.
Chylomicrons do not last long in the bloodstream -- only about eight minutes -- because enzymes called lipoprotein lipases break the fats into fatty acids. Lipoprotein lipases are found in the walls of blood vessels in fat tissue, muscle tissue and heart muscle.
Insulin
When you eat a candy bar or a meal, the presence of glucose, amino acids or fatty acids in the intestine stimulates the pancreas to secrete a hormone called insulin. Insulin acts on many cells in your body, especially those in the liver, muscle and fat tissue. Insulin tells the cells to do the following:
Absorb glucose, fatty acids and amino acids
Stop breaking down glucose, fatty acids and amino acids; glycogen into glucose; fats into fatty acids and glycerol; and proteins into amino acids
Start building glycogen from glucose; fats (triglycerides) from glycerol and fatty acids; and proteins from amino acids
The activity of lipoprotein lipases depends upon the levels of insulin in the body. If insulin is high, then the lipases are highly active; if insulin is low, the lipases are inactive.
The fatty acids are then absorbed from the blood into fat cells, muscle cells and liver cells. In these cells, under stimulation by insulin, fatty acids are made into fat molecules and stored as fat droplets.
It is also possible for fat cells to take up glucose and amino acids, which have been absorbed into the bloodstream after a meal, and convert those into fat molecules. The conversion of carbohydrates or protein into fat is 10 times less efficient than simply storing fat in a fat cell, but the body can do it. If you have 100 extra calories in fat (about 11 grams) floating in your bloodstream, fat cells can store it using only 2.5 calories of energy. On the other hand, if you have 100 extra calories in glucose (about 25 grams) floating in your bloodstream, it takes 23 calories of energy to convert the glucose into fat and then store it. Given a choice, a fat cell will grab the fat and store it rather than the carbohydrates because fat is so much easier to store.
http://science.howstuffworks.com/lif.../fat-cell2.htm
This is why you can say that fat turns into fat, because it can be absorbed into a fat cell much easier.
In order to break down a carbohydrate into a sugar to then convert into a fatty acid so it can get absorbed by a fat cell takes much more energy and the body likes to be efficient.
So, your body will take the carbohydrates and store them in your muscles as glycogen because it's easier.
The issue with insulin resistance and really, why the low-carb craze has taken off, is because there are studies that show that sugary foods can be blamed for the cause of weight gain in the body.
Studies have shown that fructose switches off the body's ability to produce insulin, resulting in excess glucose floating around in the blood stream, which then means it has to create more insulin in order to stuff the excess glucose into the cells.
But this affects your appetite regulators, which makes you feel hungry even though you just had a massive piece of cake, so you end up eating even more because your hunger cues are all off.
And now, you've consumed more calories that are probably fat, carb, and protein which will then be converted again in your body. If you are not exercising to burn the glycogen stored in your muscles and organs, it will not have any room for the other glucose that the insulin is trying to store in your fat cells. And if you develop insulin resistance, a whole other host of problems appear, like NFLAD (fatty liver disease), weight gain, high cholesterol, hormonal changes, and so on.
Some of this is simplified, because the science is more complicated than this and there is still much that has to be discovered.
Please feel free to correct me if I'm wrong in my understanding.
But this is pretty interesting, and not something I'd given much thought to recently.
The only thing I see as even remotely evil these days is added sugar, but only because I know how it messes with my system (blood sugar spiking, added cravings, lack of satisfaction over smaller portions). It almost feels like eating sugar (well, too much of it anyway) is having high-octane fuel but my body doesn't know what to do with it all.
The package says "fat free," so it's ok to eat as much as I want, right? 
I had to do something at that point since I was at my highest weight ever! 
