Ketosis and glucose synthesis

I was reading over the Wikipedia page on ketosis.

From it:

“Glucose must be conserved in the fasting state because parts of the brain, retina, kidney and red blood cells depend exclusively on it for energy, and in order to conserve muscle protein which must be catabolized to provide the glucogenic amino acid substrate for synthesis of glucose.”

First, the easy question - if ketosis is maintained without fasting (that is, with an extremely restricted carb diet), the protein required to synthesize glucose can come from dietary protein, and not from muscle protein, right? That is…does breaking down muscle protein only occur during starvation?

“But after several days of starvation, the brain transitions to burning ketones in order to more directly utilize the energy from the fat stores that are being depended upon, and to reserve the glucose only for its absolute needs, thus slowing the depletion of the body’s protein store in the muscles.”

Secondly, are there negative health implications for the retina, brain, kidneys, etc. to operate on synthesized glucose for extended periods, either due to availability of glucose or other reasons?

And does the brain suffer any deficiencies by transitioning to burning ketones in order to save glucose?
The article also mentions a side effect of prolonged ketosis is “depleted glycogen stores”. Does that make sense? Ketosis only happens after glycogen stores are depleted - it’s a cause, rather than a side effect… or do I not understand?

Ok, These are WAGS based on what i’ve learned in Biochemistry.

Metabolism is very complex, but it generally follows Le Chatelier’s Principle

When you starve the body of glucose all reactions/reaction chains that produce glucose will shift toward glucose production. If you switch to glucogenesis from amino acids then in order to stop muscle catabolism you must have a glucogenesis rate fast enough to match normal intake of glucose. whether or not that is possible I don’t know. My gut feeling is you probably don’t (because you’re not always eating, you can’t always have high levels of amino acids and theres a maximum rate at how fast glucogenesis can happen) and you will strip more muscle on atkins then otherwise.

Synthesized glucose is identical to ingested glucose. Availability is the only issue, and that depends on whether or not your body is capable of glucogenesis to match the need.

I seem to recall Ketosis raises blood acid level. That would have system-wide problems.

Theres a reason why a large portion of your blood supply goes directly to the brain first. Since your brain is pretty much priority #1 to your body it will activate any and all Homeostatic mechanisms to supply the brain. This of course means the rest of your tissues will starve.

I suspect a side effect of maintained ketosis is that not enough glucose can be made to fill the glycogen stores, as Glycogen(and later fat) is only made when there is excess glucose. This would also seem to support my gut feeling that your body is generally not capable of fast enough glucogenesis to supply the body.

The body is a finely tuned machine and is so because of self-adjusting A la Le chatlier’s principle and on a higher level Feedback mechanisms(both positive and negative). Feedback mechanisms are located at both global and local levels and they may compound or compete or complement. Low Glucose will globally shut down your mebolism, and I suspect burning fat also signals to locally lowering one’s metabolism, thus compounding. However Once glucose levels are restored, but fat is still being burned I can see competition between the feedback mechanisms.

Just to reinforce the WAGness of this. Take the last paragaph with a grain of salt. It’s based entirely off suspicions and assumptions.

Yes. After you have used up all the glycogen in your liver, if blood glucose remains low, your body begins breaking down protein. It’s the equivalent of chopping up your furniture to keep your house warm when you run out of oil.
This is why people eat lots of protein during Atkins. Their body “thinks” they are starving/fasting because there is no ready source of glucose. FLooding yourself with proteins prevents you from basically digesting yourself.

Glycogen is a short-term, readily-available storage form of glucose. You store a limited supply to keep blood levels normal during short fasting periods (such as the 8-10 hours when you are sleeping). Once this is used up (1-2 days?), your body starts “burning” protein. In cases of actual starvation, your own body supplies the protein. After a couple of days of this, THEN you start “burning” fat reserves and generating the ketone bodies that define “ketosis.”

Why is there an obligation to match the normal intake of glucose? Given that most parts of the body can run directly on fat for energy, wouldn’t the rate of glucogenesis only need to be sufficient for those organs that require glucose?

I’m curious, with all this talk about low carb being bad or good for you, are you telling me there are no cultures/people that naturally eat mostly protein diet?

Claims that Atkins will kill you, or damage your kidneys make me annoyed because I can’t fathom that after millions of years of meat eating(or am I wrong here), the few thousands of years of agriculture that we had ruined our ability to eat meat?

I can understand how an all-grain diet can be harmful, but claims that an all meat diet is anything but healthy seem rather dubious.

I’m with you, generally, but I wanted to know some specific aspects about the metabolic processes involved.

Again, Wag.

There will be some base-line level that your body WANTS your glucose level to be at. This is intrinsic, but there is likely a range your metabolism can adapt to. It will do anything it can to reach that level. When glucose levels are lower then optimal then Fat and free amino acids will probably be preferentially used for gluconeogenesis, barring the availiability of those, muscle catabolism will be next.

But you are probably right that the minimum acceptable level is sufficient production to feed anaerobic tissues, as they will likely preferentially get the glucose.

(bolding mine)

No. The brain is not able to use anything as fuel except glucose. Without adequate glucose, irreversible damage and brain death are only minutes away. The body’s catabolic processes work to turn the ketones into glucose for just that reason.

Well a hunter gatherer’s diet was not all meat, but the ratio of meat to carbohydrates was higher than modern western diet. Here is a nice (warning PDF) paper on the eating habits of modern hunter gatherer societies.

The article in the OP mentioned that certain nerve fibers required the glucose for anerobic respiration, but that the rest of the brain switched over to working directly off of ketones.

Checkin’ back in. I looked up some references yesterday on the office computer, and I was mistaken. Most nerve cells, including the brain cells essential for continued life, can synthesize significant amounts of 3-hydroxybutyrate dehydrogenase under terms of starvation, and that does allow them to use of small-chain ketones. I apologize for the error. Also I promise humbly to update my knowledge any time I’m tempted to speak out on the basis of 20-year-old medical education.

From the Atkins Frequently Asked Questions:

Senior Beef, given that the diet you are proposing to follow is a combination of both Atkins (very low-carb) and very low calorie (around 900/day) the comment above would indicate that you are likely to lose muscle loss. Totally support your right to choose a diet that suits you and commend you for trying, but I do think you are playing on dangerous ground taking the most extreme elements of a number of diets and cobbling them into your own version, of which you don’t clearly know the side-effects. Why don’t you just follow Atkins, and forget the calorie restriction, or restrict calories to around 2,500 and eat what you want?

Wha? where does seniorbeef say he has low calorie diet?

Another sidetrack:

I find it rather odd that the body would burn any muscle while there are fat reserves available. That would seem to be a serious evolutionary disadvantage for anybody living in a northern climate, since you’d be too weak by the end of winter. Have there been conclusive studies that show that in overweight individuals, there’s muscle loss due to catabolism(not just atrophy from non-use, or whatever)?

IIRC this has been proven false, and the brain functions better on ketones than glucose. I’ll try to find the cite.

First off, evolution isn’t directed. It only selects among what is available.

Second, protein is broken down, rebuilt and recycled all the time. Those enzymes are ALREADY there and in number. It makes sense that metabolism would initially shift to protein based gluconeogenesis then switch to fat reserves after a few days(because enzymes take time to make and it’s wasteful to maintain enzymes which aren’t being used).

I find this hard to believe.

Better? As good maybe, but better?

looking forward to cite

Sorry, that was from his thread about his planned diet in MPSIMS, apologies Senior Beef, don’t want you to think I am stalking you! The GQ question just caught my eye as I had read your other thread.

I found this. From Girl from mar’s link what you are proposing sounds alot like their “starvation diet”

It says theres going to be muscle catabolism.

900 calories a day? How much protein can that possible be? At the very least I hope you’re taking your vitamens.