Does IF fat burning = Ketosis?

by 10 · April 17, 2012 7:41 PM

I am NOT on a low carb diet. I eat around 125 to 175 grams of carbs per day. I also IF 16 to 18 hours, eat in a small window. If I am in a fasted state, am I burning fat or carbs? If I am burning fat, is that the same as being in Ketosis?

I understand:

Low carbs- burn Ketones / Intermittent fasting - burn fat

I am not trying to enter in to Ketosis, but I am IF, sometimes 20hrs on the weekends. Just wondering if switching to fat burning mode is the same as burning Ketones on a higher carb paleo diet.


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2 Replies

20762 · April 17, 2012 6:50 PM

From the wikipedia page (http://en.wikipedia.org/wiki/Ketosis)

When glycogen stores are not available in the cells, fat (triacylglycerol) is cleaved to provide 3 fatty acid chains and 1 glycerol molecule in a process called lipolysis. Most of the body is able to use fatty acids as an alternative source of energy in a process called beta-oxidation. One of the products of beta-oxidation is acetyl-CoA, which can be further used in the Krebs cycle. During prolonged fasting or starvation, acetyl-CoA in the liver is used to produce ketone bodies instead, leading to a state of ketosis.

During starvation or a long physical training session, the body starts using fatty acids instead of glucose. The brain cannot use long-chain fatty acids for energy because they are completely albumin-bound and cannot cross the blood-brain barrier. Not all medium-chain fatty acids are bound to albumin. The unbound medium-chain fatty acids are soluble in the blood and can cross the blood-brain barrier.[2] The ketone bodies produced in the liver can also cross the blood-brain barrier. In the brain, these ketone bodies are then incorporated into acetyl-CoA and used in the citric acid cycle.

I interpret that as, you burn sugar first, then fat second, after sufficient time buring fat you start burning the actyl-CoA as ketones. How long that "sufficient time" is probably varies greatly from individual to individual, so the only want to know for sure is to test it. I'm pretty sure that if I skip lunch, by the time I get home from work I'm in ketosis.

272 · April 17, 2012 7:41 PM

I can always tell when I'm at that "boundary zone" of slipping into ketosis because I become hyper-sensitive to food. I'm actually in the state right now. I fasted yesterday (after a big weekend with lots of extra food). I had a lot of food in my system, still--so I don't think I was in ketosis yesterday. Today, however, I'm hyper-sensitive to food smells, visualizations, etc. My body is transitioning and my brain is encouraging me to eat so that it doesn't have to shift my body to burning ketones.

What my brain doesn't realize is that I'm going to fast all week and it won't have any food at all till Saturday... ;)

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