What happens if a large percentage of your diet consists of bread, potatoes, gravy, corn, sugary soft drinks and desserts? How could that contribute to obesity and type II diabetes?
The key to this question comes from understanding the Glycemic Index or GI.
The glycemic index of a food is measured by having a person eat a certain amount of that food and measuring how much of the carbohydrate in the food is converted into glucose in the blood within two hours. If a food has a high glycemic index, it will raise blood glucose very rapidly. If it has a low glycemic index, it will raise it slowly. In general, the higher the glycemic index, the more insulin your pancreas will have to secrete in order to bring your blood glucose reading back into the safe and normal range.
If pure glucose has a glycemic index of 100, a baked potato has a glycemic index of 111. Kellogg's Corn Flakes have a glycemic index of 92. Wonder Bread has a glycemic index of 73. Coca Cola has a glycemic index of 58. Beef, chicken and fish have a glycemic index close to zero.
It used to be thought that simple carbohydrates (like the high fructose corn syrup in Coca Cola) raised blood sugar quickly and complex carbohydrates (like the starch in potatoes) raised it slowly. From studying the glycemic index of various foods, we now know this isn't true. If you want to raise your blood sugar rapidly and release a large amount of insulin in response, eating significant quantities of any carbohydrate will do it for you. That's fine as long as your muscles and liver remain insulin responsive. But when they start to become insulin resistant, your blood sugar will go higher than it should and will stay elevated for longer than it should. Your pancreas will have to secrete more insulin to keep your blood sugar levels under good control. As we have seen, hyperinsulinemia is hard on our bodies. Hyperglycemia is hard on our bodies, too. Unfortunately, it's a Catch-22.