How do you / I know what your / my cells choose first for their energy source if available?
I don't know, however, your description of how you feel when you exclude carbs from your diet is a major clue. I've also been there, done that, and know that reducing carbs low enough in your diet to switch to a fat based metabolism is difficult at best and few are able to do it. Most have the same experience as you and give up, insisting that their body requirements are different than others that are successful and they NEED carbs. 100g of carbs per day is huge, and my experience and that of many others as well, show that your body just won't switch to using fatty acids as its primary fuel without severely reduce carb intake for an extended period of time.
Kata Strong and Mary Massung did much work in this area. They found that carbs had to be reduced below 30g per day for an extended period (weeks or months depending on how many carbs were included in the diet) to cause the body to switch from a glucose based metabolism to a fat based metabolism. During the transition there is a massive craving for carbs, and in my case, lab tests and houly BG measurements showed my body was still adapting to a fat based diet with zero plant based carbs after a year or 18 months. I could be very wrong, but what you've said in your posts tells me that your metabolism is still glucose based and not fat based.
Another interesting tidbit is that those of us that have transitioned to a fat based metabolism tend to appear to be insulin resistant as our pancreas is no longer poised to produce massive amounts of insulin after a meal heavy in carbs. Our blood sugars also tend to be very steady, right around 100, regardless of when we take the measurement, before eating, after eating, or overnight fasting. I have detailed records of how my BG curve has changed over the last 5 years of eating ZC. Others that have committed to ZC for extended periods find that their experience is the same. One of your posts indicates that your BG is in the mid 70s. This would not be the case if your metabolism was fat based. BG would rise into the 90s and stay in the upper range as your body would not be using it. Little BG would be produced and very slowly. Small amounts of insulin would be released to keep it stable, but since the BG rise is very gentle when no carbs are eaten, insulin doesn’t over shoot. A low fasting BG indicates that high carb intake at meals creates a rapid rise in BG causing insulin to overshoot and then BG plummets to the low end and stays there until your next meal.
Lex, my definition of veganism seems to be different from yours. If you are really interested in my former or current diet (which I don´t believe is the case 
), would you please look into my previous posts. Here they are:
http://www.rawpaleoforum.com/?action=profile;u=1130;sa=showPosts
Veganism to me is a plant based diet. If you are primarily eating foods that come from plants then you are eating far more carbs than would allow your body to transition to a fat based metabolism. It has nothing to do with how much fat you eat, but only how many carbs. From the various foods you mention in your posts you eat loads of carbs. You could add a gallon of fat to what you are currently eating every day and your body still wouldn’t transition to a fat based metabolism.
Why? Because the carbs you eat cause BG to rise rapidly. The body senses this rapid rise and detects danger as high BG will harm us. It reacts in various ways and by various hormones such as insulin, to cause the body and its cells to quickly sweep the excess glucose from the blood. As much as possible is forced into the cells to be used as fuel and the rest is converted to fat and stored.
What happened to that gallon of fat you ate with the carbs? Well, high levels of fatty acids are not dangerous to the body so they are allowed to float around until they can be stored or eliminated. There is also evidence that much of it won’t even be digested as it is rejected when blood levels of fatty acids are high. The body’s cells will reject the fatty acids as fuel because their priority is to get rid of the dangerous levels of BG and are overloaded with glucose from the carbs you ate. Dealing with the glucose has to be the body’s first priority or we will go into a coma and die.
I mean no disrespect. Each of us is on our own path and must find our own way. I always tell people what I believe based on many years of experience and much failure. Over the years I’ve fooled myself into believing as much nonsense as everyone else and probably more. I’d even venture to say that most of what I think I know and understand now is so much nonsense as well. I certainly don’t have all the answers, and many of the answers I have are probably wrong. Therefore, I do my best to tell you exactly what I’m doing, show you the lab tests, hazard a guess or two about what I THINK is going on, and then let you make up your own mind on the subject.
Hope this helps,
Lex
