Ashley Moran wrote:

> I'm still confused about ketosis.  I  hear a lot of contradictory  
> explanations.  Maybe someone can explain this to me once and for all.
> Here is how I understand it:
>
> - most of the body's cells can run on fat (ketones) and do not need  
> carbohydrates


Yes and no.  Fat and ketones are not the same thing.  Fat is composed of 
fatty acids, and are burned as such.  When the fatty acids are bound 
together with a molecule of glycerol, it's called triglyceride, and most 
stored fat is in that form.  Fat circulating in the blood is in the form 
of both free fatty acids and trigylceride.  Ketones are molecules 
produced in the liver, from fatty acid molecules, but the liver only 
does this when stored glycogen is very low.  Some, but not all, of the 
cells that burn glucose can also use ketones.

> - the cells that do need carbohydrates can obtain them from  
> carbohydrates in food or protein (through glucogenesis)  (I also read  
> in one place that carbohydrates can be produced from fat, but I'm not  
> sure about that)


This is correct.  Carbohydrate isn't really "produced" from fat, but the 
glycerol molecule that binds three fatty acid molecules into a 
triglyceride can be converted into glucose, so in a sense a small amount 
of glucose can be culled from the fat you eat, most of which is in the 
form of triglyceride.

> - stored carbohydrates (glycogen) are used rapidly during strenuous  
> exercise and must be replenished later


Yes, because strenuous (anaerobic) exercise uses fast-twitch muscle 
fibers, which require glucose.  Some glucose is stored in the muscle 
tissue itself, in the form of muscle glycogen, and this is what is 
immediately used during strenuous exercise.  When we use that, the liver 
immediately attempts to release glucose to replace it, since stored 
muscle glycogen is "fight or flight" fuel.  This is why, if you check 
your BG *immediately* after strenuous exercise, it might be higher than 
normal.  The liver has dumped glucose into circulation to replace what 
the muscles just used, but this takes a little time.

> - if I eat once a day in the evening, am I in ketosis at 3pm the next  
> day, or not?


It depends on what you ate.  If you ate a reasonable amount of 
carbohydrate, then probably not.

> - if I'm not, why is my body burning glycogen if it is needed in an  
> emergency?


Your cells will not make much use of ketones until no more glucose is 
available (some ketones are used all the time, but not a lot).  Your 
*hepatic* glycogen reserves function as a reservoir of glucose, from 
which your tissues can draw, so that your availability of glucose 
doesn't depend on what you ate a few hours ago.  This is necessary 
because your blood glucose needs to be kept within narrow bounds.  So as 
soon as you eat any quantity of carbohydrate, the first thing that 
happens is it's dumped directly into the blood as glucose (and other 
simple sugars).  If glycogen storage is not full, it gets topped up.  If 
muscle glycogen is not full, it gets topped up.  Any cells that can use 
glucose will attempt to do so.  If BG still needs to be lowered, the 
rest will be pulled out of circulation, converted to triglyceride and 
stored that way.

> - I've gone for several days before eating very few carbs (10-20g)  
> and not noticed any difference in how I feed.  No metallic taste in  
> my mouth (like Atkins promises) and no noticeable difference in  
> stamina.  In fact I dont feel much different if I miss a whole day's  
> food (except more hungry).  Am I missing something?


After a couple of days you should be in ketosis.  When you start 
producing ketones, you produce various kinds.  Not all of them can be 
used as fuel; in fact one sort is toxic and must be dumped.  I believe 
that's acetaldehyde, but I could be wrong.  This is from memory.  So 
your body will excrete the ketones it doesn't or can't use.  They will 
be present in urine, sweat, and breath, since your breath contains water 
droplets.  If in your breath or sweat, there will be that distinctive 
"ketoney" odor.  But if you are drinking a lot of water and peeing a 
lot, most of the ketones will exit that way, so there might not be many 
going out through your breath--not enough to cause the taste and odor. 

A couple of days would probably only just induce a mild ketosis anyway.

Todd Moody
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