White flour is in the form of sugar by the time it reaches the blood. Carbohydrate intake causes a rise in blood sugar. A rise in blood sugar causes a rise in insulin. The pancreas has to put out insulin to enable blood sugar to enter cells for energy production, and to keep the blood sugar level normal. In children, the insulin receptors on the cells usually respond to insulin normally, and a fairly small amount of insulin is able to keep blood sugar in the normal range in spite of large sugar and starch consumption.
Some people can eat lots of starch and sugar all their lives and stay thin.
Their health is not as good as it could have been, but they do not develop obesity, high blood pressure, heart disease, or diabetes. Many people do not inherit such good genes. The high intake of carbohydrates and resulting insulin production results in the cells becoming less and less responsive to insulin. It takes larger and larger amounts of insulin to enable cells to take in blood sugar and to keep the blood sugar level normal. This is insulin resistance.