When you eat food, the body digests the carbohydrates, proteins and fats. (Anything it can't digest, like alcohol or fiber or toxins, either passes right on through or, if it makes it into the bloodstream, gets filtered by your liver). We measure these foods in grams and calories, but your body operates in terms of fuel. If you eat more food than your body needs - which most people do - the body is forced to store this excess.
Bear in mind that every type of carbohydrate you eat is eventually converted to a simple form of sugar known as glucose, either directly in the gut or after a brief visit to the liver. The truth is, all the bread, pasta, cereal, potatoes, rice (stop me when you've had enough), fruit, dessert, candy, and sodas you eat and drink eventually wind up as glucose. While glucose is a fuel, it is actually quite toxic in excess amounts unless it is being burned inside your cells, so the body has evolved a way of getting it out of the bloodstream quickly and storing it in those cells.
It does this by having the liver and the muscles store some of the excess glucose as glycogen. But here's the catch: once those cells are full, as they are almost all the time, the rest of the glucose is converted to fat. Saturated fat.
Insulin was one of the first hormones to evolve in living things. It helps the body store extra nutrients for a bad day. Today when we eat too many carbohydrates, the pancreas pumps out insulin exactly as the genes tell it to (hooray pancreas!), but if the liver and muscle cells are already filled with glycogen, those cells start to become resistant to the call of insulin. Since the glucose can't get into the muscle or liver cells, it remains in the bloodstream. Now the pancreas senses there's still too much toxic glucose in the blood, so it frantically pumps out even more insulin, which causes the insulin receptors on the surface of those cells to become even more resistant, because excess insulin is also toxic! Eventually, the insulin helps the glucose finds it way into your fat cells, where it is stored as fat. Again - because it bears repeating - it's not fat that gets stored in your fat cells - it's sugar.
Over time, as we continue to eat high carbohydrate diets and exercise less, the degree of insulin insensitivity increases. Unless we take dramatic steps to reduce carbohydrate intake and increase exercise, we develop several problems that only get worse over time.
When your liver becomes insulin resistant, it can't convert thyroid hormone T4 into the T3, so you get those mysterious and stubborn "thyroid problems".
But the good news is that there is a way to avoid all this. It's all right there in your genes. First off, exercise does have a major impact on improving insulin sensitivity since muscles burn your stored glycogen as fuel during and after your workout. Muscles that have been exercised desperately want that glucose inside. That's one reason exercise is so critical for type 2 diabetics in regaining insulin sensitivity. It's also the reason why endurance athletes can eat 400 or 600 grams of carbs a day and stay lean – they burn it all off and make room for more.
Second, cutting back on carbohydrates, especially the obvious sugars and refined stuff is absolutely essential. Make fresh vegetables the main part of your meal. Not only should diabetics limit carbohydrate intake – everyone should. We are after all, in an evolutionary sense, predisposed to becoming diabetic.