The pain of discipline or the pain of regret? You choose.
Oh look - I made a Journal.
To Mr Mom,
I can't tell you Robyn Landis' workout regimen or exactly how she ate prior to her nutritional education. What I can tell you is that she had been in the habit of working out first thing in the morning, on an empty stomach. But no matter how hard she worked, she could not lose her last 10-15 lbs (I am paraphrasing based on my recollection of the book). Then she spent a year doing nutritional research from biochemistry textbooks because she was sick of the shallow and conflicting info. that the mainstream 'authorities' were publishing. The result of the research was the book, and of course her own experiment of eating more than before (not less), and making sure to "fuel up" before exercise. Fuel always contained carbs for her. IIRC, she kept her fat % to an average of 10% of total calories so it must have been ~25% protein, 10% fat, and 65% carbs. Not primal but it worked well for her as I posted before.
Here is something else I just ran across, in response to the OP's question, when do we burn only fat? I posted an excerpt that says the same thing Robyn Landis did about how fat burns in the presense of carbohydrate:
As the researchers explained in the “discussion” portion of the report, “fatty acids and lipids are preferred substrates for exercising muscle.” There’s a catch, however. Glucose must be present.
“In order for your muscles to burn fat…, carbohydrate [glucose] has to be present,” Chris Carmichael explained in Food for Fitness. “In conditions where your body is depleted of carbohydrates [glucose], the rate at which you burn fat decreases, and your capacity for high-intensity disappears.” Marathon runners and other endurance athletes call this “hitting the wall” or “bonking.”
I don't think your body is ever only burning one type of fuel.
Basic biochemistry says we do need some carbohydrate to burn fat. There are two biochemical cycles involved. First Glucose is oxidized to pyruvate where ATP (the enegry currency of the cell) is made. We need ATP (Remember ultra-low carbers that gluconeogensis may occur from amino acids and protein-you can make glucose from protein). Fatty Acids are broken down to Acetyl-CoA. Both the endproducts of glycolysis and fatty acid metabolism are used in the citric acid cycle. This happens in normal fatty acid breakdown in the mitochondria. The citric acid cycle is imporatant because in the citric acid cycle NAD is returned to NADH. Since this is the thumbnail version of this, rather than a biochem course, NADH is required for a number of other biochemical reactions in the body, one place it is used is in the mitochondria to produce more ATP. If there is no carbohydrate, we will not make the ATP we need to provide energy for things like muscle contraction. A lack of ATP makes muscle contraction impossible. Ketosis is fatty acid breakdown in the liver in the absence of carbohyrate and CW also infers starvation or reduced caloric intake and is an alternate pathway. Ketone bodies can be broken back down to acetyl Co A and used in the citric acid cycle. But ...here is the kicker...if there is no pyruvate from glucose (carbohydrate metabolism) we can't use this ketogenic acetyl-Co A to make energy in the citric acid cycle. There are more branches and sub-branches to all these pathways...so this ..is not complete... but...I hope this helps. But it is very complex and hard to just find one switch that turns everything from the use of one type of metabolic fuel to the other.