Hi there. Does anyone have any scientific evidence showing how long it takes before the body becomes catabolic (starvation mode) - is it 16 hours or more like 40? Also many people insist on eating caloric sources while fasting like coconut oil. What do you think of this? Is it necessary? If so, what other caloric sources could be acceptable while fasting? Any scientific articles would be much appreciated!
asked byYoungPaleoLover (1670)
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on June 11, 2012
at 07:46 PM
There isn't a specific "starvation mode" biomarker - different body systems have different type scales. And for each, there is a graph of response over time, and usually there isn't a predefined level that's "starvation mode". So you have to look at the graph and pick a "corner" point. The best data I've seen is from Brad Pilon's book "Eat Stop Eat". To summarize:
- For plasma insulin levels, there isn't a clear corner, but 70% of reduction occurs in the first 24 hours. IT drops rapidly for about 20 hours, then slows down (though continues dropping) through 48 hours.
- For increase is plasma free fatty acids (indicating the body has switched to fat burning), the big jump is between 16 and 24 hours. Then it levels off. (Though Brad's graph doesn't have data from 3 to 12 hours).
- Expression of UCP3 (a marker of fat burning) goes up by 5x from 3 to 15 hours, and by another 2-3x from 15 to 40 hours.
Another good source of data is Dr. Johnson's Up Day Down Day diet book, about alternate-day calorie restriction. His data is about duration of doing IF, not per-fast duration, but it's still interesting. To summarize:
- Peak expiratory flow for asthma patients (a measure of inflammation) improved steadily for the first 3 weeks, then was flat.
- Mood and energy showed the same pattern.
- Nitrotyrosine levels, a measure of oxidative stress, dropped by 50% after 2 weeks, dropped by another 75% (so about 1/8th of original) after 4 weeks, and dropped a little more by 8 weeks, down to 1/10th of original.
- Concentrations of TNF (Tumor Necrosis Factor alpha), one of the most commonly used measures of activation, dropped slightly after 2 weeks, moderately after 4 weeks (way down on fast days, only moderately down on up days), and dropped to about 1/4 of original levels on both up & down days by 8 weeks.
- Concentrations of BDNF (another inflammation marker) dropped steadily over the first 4 weeks, then were flat.
Hope this helps.
on June 10, 2012
at 06:10 PM
Even if you remain sedentary during a fast your glycogen stores will be depleted within about 14 hours. After that your liver and kidneys will have to synthesize glucose from catabolized muscle tissue.
on June 10, 2012
at 12:53 PM
Fasting is a catobolic state. How long you can fast before you start eating into muscle tissue depends on macronutrient intake, caloric intake, how adapted your body is to burning fat and fasting, hormones like Growth Hormone, etc. By this I mean, best case scenario: Your glycogen stores are full, you've got a healthy amount of bodyfat, you're fully adapted to fat burning and a fasted state, and you've got awesome hormones. In my opinion you'd be able to fast quite a while before breaking down large amounts of muscle.
I saw calories as necessary for comfort during the initial adaptation phase. Once I was adapted, eating became counterproductive, especially carbs since they inhibit fat burning to at least some degree.
Brad Pilon has some good information about the things you asked. His videos can be found on youtube.
on July 05, 2012
at 01:56 PM
Leangains.com has an article that cited 36 hours & up will result in loss of muscle. Sorry I dont have a link (I'm on my cellphone) but I believe it's in the FASTING MYTHS article.