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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