Almost.
When your body runs out of carbs, fat gets broken down into acetyl-CoA to get energy. aCoA is not being recycled by the Krebs cycle because the intermediates in the cycle have been depleted to be used for the gluconeogenesis process. As such an accumulation of aCoA triggers ketogenesis.
When your body has lots of carbs to use as energy, glucose becomes oxidized and aCoA is formed as an intermediate, and then enters the Krebs cycle first which
then goes to a conversion of ATP (energy).
If your body has excess carbs,
some of the glucose is completely metabolised, however, some of it is also stored by using aCoA to create fatty acids (which insulin then shuffles away and stores as what we call - "fat").
If your diet is changed from one which has lots or excess carbs to a ketogenic diet, i.e. meaning your body isn't provided with sufficient carbs to replen glycogen stores, it's the stages that your body goes through to enter ketosis that you must remember. The first stage is that the levels of glucose in your blood are maintained, as you correctly stated, through gluconeogenesis (sp? I always spell it wrong!
).
However, our brains do not "burn" ketones in the initial stages, instead, it uses them for fat (lipid) synthesis within it. When you get to about 40-48hrs or so in that state, your brain start to "burn" ketones to use up your fat stores, also it reserves glucose specifically for it's use (so your other muscles have to rely on the fat stores). This avoids your body depleting it's protein stores in the muscles.
Also remember that when your body is in Keto it becomes very acidic (i.e. your pH levels drop) - your body should NOT be in this state for prolonged periods of time. You should strive to be as Alakline as possible! Furthermore, cancers thrive on acidic environments - something else to think about.
