Carbohydrates in Metabolism
Eating Carbohydrate Produces Energy
Eating 1 cup of mashed potatoes or rice, converts very quickly to glucose in the blood.
That adds about 200kcal to your system over the next hour, creating excess blood glucose.
Only about 50kcal are burnt in normal activity, so at least 150kcal needs to be rapidly removed from the blood stream.
That pancreas produces insulin (The master hormone) to store the excess glucose.
Actions of Insulin
Insulin in the blood turns off fat burning, and forces glucose burning.
Insulin acts as a transporter, moving glucose across the cell membrane into cells.
Insulin helps the storage of glucose as glycogen in muscle tissues. (Limit about 2000kcal.)
Insulin over-rides the leptin signal to the appestat; saying "fat storage has begun." The restoration of the proper glucose level in the blood is more important.
Insulin instructs the liver to turn excess glucose into fatty acids (Lipogenesis).
These fatty acids are stored in your adipose tissue. (Mostly the fat around the belly)
The adipose tissue sends a leptin signal to the appestat, but it's ignored until the glucose storage crisis is resolved.
Carbohydrate Intolerance / Insulin Resistance
The Dietary Guidelines Advisory Committee Recommendations (2010) strongly state: "There are no detrimental effects of carbohydrates as a source of calories on these or other health outcomes." That doesn't tally well with recent research. For instance Prof Tim Noakes says, "I believe insulin resistance (carbohydrate intolerance) is the most important medical disorder in the population today."
The alternative term, carbohydrate intolerance, better describes what the problem is. Over a long period, many years of eating a diet where sugars and carbohydrates are always plentiful, your system adapts to a constant excess of carbohydrates. The homeostatic setting of your body is altered, and ceases to protect you.
In response to your diet, carbohydrate intolerance develops. Excess carbohydrate begins to make you sick. You lose control of your diet because the appestat no longer works efficiently.
After some time the symptoms of metabolic syndrome become evident, obesity, high blood pressure, high fasting glucose, high triglycerides, low HDL-Cholesterol, and perhaps gout.