Yeah and people try to tell nonsense like "ketones are the body's preferred energy source" okay so why does the body only use it when all carbs have been exhausted?

Because the body cannot tolerate high levels of blood sugar.

The sugar must be dealt with, which is done by (a) transporting to the cells to "burn" as fuel, and if there is too much, then next (b) storing some as glycogen in the liver and muscles, and finally, if still too much (c) converting excess to bodyfat and storing in the fat cells.

Regardless, the body wants that sugar OUT of the blood.

Excess amino acids from protein consumption are simply excreted in the urine.

Excess fatty acids from fat consumption are converted to ketones to either be used as fuel for the body, or excreted in the urine or breathed out through the lungs.

Extra protein and fat are "free" in that they cause no harm to the body and are simply discarded.

But extra carbs are stored as bodyfat.

Carbs also cause a jacking up of insulin, which is the cause of inflammaion.

This combination of excess bodyfat and inflammation are the primary causes of poor health and death today.

So, carbs are damaging to the body.

Carbs also produce "Advanced Glycation End-Products" (AGE's) which age the body by "gluing together" proteins of the body. This comes mostly from fruit, but all carbs contribute to advanced body deterioration as we age.