Fat-lovers advise us to fast at least occasionally. Depleting readily available glucose causes the body to burn fat, leading to fat-adaptation and all manner of good outcomes. Conventional-wisdom carb-lovers advise us to never fast. Depleting readily available glucose causes the body to devour its own muscle tissue, leading to weakness and wasting that can take months to repair.
Are there any signs that can tell you what macronutrient it's primarily relying on at a given moment? Are there good signs that you're oxidizing glucose vs. fat? (not ketosis, just good old beta oxidation)
If you're oxidizing glucose, is there a way to tell whether you're burning glycogen vs. muscle? (let's assume you're fasted enough that directly ingested macronutrients aren't in the picture.)
Knowing this seems like it would be highly valuable in the quest for fat-adaptation, or for finding out whether you're at a point where intermittent fasting will do you more good than harm.
asked byAxialGentleman (2624)
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on July 15, 2013
at 10:11 AM
Generally, if your fast is under 16h, you'll first burn through your muscle glycogen stores, and then make ketones. After that you may or may not start catabolizing muscle. The question is at what point.
You can ignore ketone blood/urine tests for this as the mechanism needed to supply glycogen for red blood cells and long nerves cannot be used - these cells require glucose, and the only way to get it once your supply is exhausted is to make it from protein.
One way to tell is if you start feeling a bit anxious; the signal to do gluconeogenesis is cortisol. (Yes, we can make glycogen out of the glycerin backbone of used fats, but this is a very tiny amount). So if you've already depleted your supply of free protein, the only way to start gluconeogenesis is to catabolize muscle. On my own n=1, I only noticed this around 20h or so.
You'll also notice other somewhat detrimental effects such as failure to stay asleep or waking up in the middle of the night - this is also due to higher cortisol, but this happens if you over do it.
But there are things you can do to prevent that, which include having shorter fasts than that, and using BCAAs (which do raise your insulin a bit.)
You can also add in MCT oil or coconut oil to help give yourself some ketones - you'd want this in the day time/morning, not anywhere near night as they'll keep you awake - I usually do that by making bulletproof coffee. This won't stop gluconeogenesis, but it will help you avoid that lower energy transition period between burning glucose and burning ketones if you're not fully adapted yet.
That said a fast day a week or two of 20h+ fasts isn't going to cause very much of a problem, and has plenty of positive effects such as autophagy.
You might not always notice that anxiousness, or have an impact on sleep, so tread carefully, and be sure you don't do both VLC and long fasts.
One thing to note, avoid all sweeteners, even stevia if you're going to be doing this. i.e. don't sweeten your coffee or tea with it. The reason is that you'll taste sweet, which in turn will cause insulin to rise and that signals that your muscles, fat cells, and liver, should take whatever glucose is in your blood and store it. This will cause hypoglycemia, which in this state is a very bad thing.
on July 13, 2013
at 11:30 PM
If you can go long periods of time without getting cranky and needing to eat something, you are fairly fat adapted and an mix in some IF. If you feel lacking in energy after going a couple hours without carbs, you are still dependent on glucose and glycogen. There are tests for RQ to check your primary source of fuel, but they are expensive.
on July 13, 2013
at 03:00 PM
With regard to the fasting: I have lost a great deal of fat while gaining the most muscle I've had in my life over the past nine months. I've done this with 24 hour fasting every single day (not out of some guidance from the internet, this is actually how I've always eaten - I just prefer it). Have I lost some of my gains due to my daily fasting? It is entirely possible, and I may have been stronger if I ate more often, but I think it's fair enough evidence (at least to me) that this whole "muscle wasting" business is completely blown out of proportion and over dramatized. It may be occurring at some level but it has definitely not caused me to shrivel up and die.
Is there a way to tell what fuel your body is burning? Actual medical tests aside I think this is something that becomes more and more difficult to determine the more metabolically flexible you become. That, after all, is the whole point. Your engine keeps churning just the same with either diesel or gasoline without skipping a step. Without those little energy roadbumps throughout the day it may be difficult to determine when your body shifts gears. At this point I reckon you would just have to make an educated guess based on your previous intake and activity.
on July 14, 2013
at 09:46 PM
I don't really know the answer. I am trying to lose weight and upped the fat. I can go much longer between meals now. Yesterday after a very large protein breakfast I was not hungry until about 5 when I thought I had better eat something before swimming as dinner was a while away, ate a huge whole piece of brie cheese and then had to force down 2 sausages for dinner.
I tried those ketosis sticks in urine a while back but they never showed any ketosis.
I certainly took 21 days to get off sugar/refined carsb/chocolate, got "candida die off" and day 21 was the worst. Then I felt fine. I gave up fruit too as I abused it. I am very very sugar sensitive. I now have no cravings at all and no need for sugar which for me will always be the biggest achievement even if I do not lose 30 pounds.
I would like a test as described. As we are away on holiday it is easier as we're busy and active not to have my usual carby things like butternut squash, carrots, sweet potato. So I though okay will have lost a load of weight in the last few days as almost virtually on protein and fat and not even much veg and yet not a single loss at all. I don't think many people could eat just meat/fish/eggs/butter and a tiny bit of spinch and cucumber and still not lose weight. I only drink water. I don't cheat. Perhaps I'm too impatient. I would love to have a test to show what is going on inside. I must be kind of fat adapted if I have lost my sugar cravings and can go 6 or 7 hours between protein/fat meals with no hunger. (Great site, great questions) If there are posssible tests in these areas which are not too expensive similar to ketosis strips which are cheap and in chemist shops then someone should develop them as it could be really encouraging to know that even if those scales remain solidly unmoving day after day you may be doig something good inside.
on July 13, 2013
at 03:16 PM
I can't speak to knowing the difference, but I can tell you that I've been diagnosed and overcome muscle wasting disease when my muscles were cannabalizing themselves. It is absolutely a real thing and isn't something to be ignored. I'm not entirely sure which symptoms were related to the muscle wasting or other metabolic issues I had at the time, but for me, I was incredibly exhausted. I had muscle fatigue (had to rest walking up the stairs while caring my child who was small at the time) and chronic joint pain and joint weakness.
Like I said, this is a time when I was also dealing with a metabolic issue as well so I can't be exactly sure which is related to which as far as symptoms go, but I do want to stress the imporance of muscle wasting and its damage on the body. Even after I have worked through healing my digestive tract, it has taken me nearly 3 years to rebuild my strength and muscle tone lost during that time.