The view that more protein is better generally prevails, though some people advocate occasional protein fasts (for example, and recently, Mark Sisson, a former advocate of high-protein pretty much all the time). Protein Fasts supposedly help with, among other things, protein absorption on high protein days and with the autophagy/recycling of proteins (thereby perhaps mitigating the risks of a high protein diet)...

By protein fasting once a week, you are essentially allowing your body a day to use its digestive machinery to perform self-maintenance. This is because dramatically lowering your protein intake once a week induces autophagy (What Is Bulletproof Protein Fasting)

I'm wondering, though, if protein fasts are necessary on an intermittent dieting regime? I think (but can't find them again) that studies using nitrogen balance suggest that by morning most people have depleted their amino acids (particularly if they aren't enjoying casein before bed).

Mark Sisson seems to think intermittent fasting is enough?

Intermittent fasting imposes periods of zero protein and zero food, giving your body a dose of autophagy and a respite from mTOR/IGF-1 activation, and likely making higher protein intakes on feeding days safer

Will resistance training in the morning while fasted, and staying in a fasted state until 10 am or even 12 pm (similar to the Lean gains early morning routine), provide enough protein recycling that protein fasting (say, once a week) isn't really necessary?

Or is it still beneficial to do a whole day protein fast regularly (aiming to get under 15g or 25g ...)?

NOTE: By a protein fast I mean still eating other macronutrients but avoiding food that is more than about 2% protein by weight.

FURTHER NOTE: To make the 'Physical Fitness' context of the question clear - I'm pondering if low protein days are necessary in an intermittent fasting regime because:

  • they could increase physical fitness (better protein absorption, healthier mitochondria/more energy, autophagy/general health, this being the main benefit)

or conversely they could

  • limit recovery (through, for example, extended time without proteins for recovery, particularly for people who train often and fast [a little] often).

FURTHER NOTE: To put the question differently I could ask, "How much autophagy and protein recycling occurs during intermittent fasting, particularly in the post-workout fasted hours at T = 14h to 17h, compared to 24-40 hours of low-protein (25 g or even less) and minimal exercise?"

  • Every "citing" he has in that blog doesn't link anywhere and everything I can find on this topic links back to this blog. I'm very skeptical.
    – DeeV
    Nov 4, 2016 at 15:21
  • @DeeV Of Mark Sisson's blog? Of the Bulletproof site? Or Leangains? Or just protein fasting altogether?
    – lithic
    Nov 4, 2016 at 19:16
  • I was referring specifically protein fasting as it pertains to this question, but I'm actually skeptical of Bulletproof diet in general. Dave Asprey is a software engineer turned self-proclaimed diet guru that claims to have "hacked biology". He has made some, sometimes really outlandish, claims without much proof. gizmodo.com/…
    – DeeV
    Nov 4, 2016 at 19:21
  • There's a Skeptics question regarding at least one of his claims. skeptics.stackexchange.com/questions/14692/…
    – DeeV
    Nov 4, 2016 at 19:23
  • Of course, I agree. All that, and more, needs to be taken with a healthy dose of scepticism. But the medium is not always the message. I erred in linking to that blog, granted. But my question still stands without reference to those sites ... How long a break, if any, from protein is helpful for fitness and health?
    – lithic
    Nov 4, 2016 at 19:50

1 Answer 1


To induce autophagy you need to fast for a longer period of time then the 16 or 18 hours of a fasting window during IF, you need to be fasting for at least 3 days.

During IF you already protein fast during the fasting window, and any protein you are taking in later, after the training, will be used to recover and build anyway, which the latest studies shows needs to be no more the .80gm per kilo of body weight, as any more then that did not show any improvements, apart from spiking more insulin and rendering the state of ketosis normally associated with IF pointless.

You do not need on IF doing a day of protein fasting, if you want to fast the all day, do it as this will increase further the secretion of growth hormone as does heavy training during the fasting window, which is stop muscle breakdown during long period of fasting.

I fast from 8pm to 12 am, train at 7.30am during my fasting window with just a coffee, 5 times a week with heavy weight, I am 51 years old and I am gaining muscle, lean muscle while losing fat. To do this on IF your proteins need to be present every day, better no more then 3oz per meal, the rest should be made up by the fat and vegetable content to provide you with the energy to metabolise everything while keeping the vital level of insulin low enough not to gain fat but enough to allow the storing of proteins within the cells.

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