Quote:
Originally Posted by Jamackarch
Is it true that once you are fully "keto adapted" (aaand, I don't actually know wha that means...) that the stx are no longer useful becasue you can be efficiently and exclusively burning body fat for energy, but the ketones no longer show in your urine?
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That sort of depends. Early on, brain and muscle both will use fair amounts of ketone for energy. With fasting, ketoadaptation actually involves muscle adapting to free fatty acids to a greater extent for energy, this spares ketones and glucose for the brain. With nutritional ketosis, this switch away from glucose/ketone metabolism for muscle could spare both--with less competition for the bit of glucose the body produces even on a ketogenic diet, this could make for a decreased demand for ketone production.
If you look at it, actual brain demand for energy is about what you'd get from 100 grams of glucose.
For a person eating a moderate 100 grams of protein, in theory you could get two thirds as much glucose through gluconeogenesis, but call it fifty, expecting things to be that efficient is probably a bit much.
Add 20 grams of glucose from a fairly strict level of carbohydrate restriction. We're up to 70 grams of glucose.
Call daily metabolism 2000 calories per day, whether the rest of the calories are made up from body or dietary fat, and assuming protein is in balance. That's about 169 grams of fat as triglyceride. About ten percent of that triglyceride is glycerol, so there's 17 grams or so of glycerol available to produce a similar mass of glucose. We're up to 87 grams of glucose, at least potentially, so you can see that depending on just how efficient the body can become at sparing glucose for the brain, it's not entirely surprising if not everybody is throwing off much in the way of ketones even if they're on what looks like a fairly ketogenic diet. Two people could be eating the same exact diet, burning the same calories, on in ketosis, the other not--but both burning just as much fat.