Hi Bruno,
1) As I understand it, you have tried two different diets, (a) being a ketogenic diet, and (b) a non-ketogenic diet where you have no food past 4pm, and maybe (c) a ketogenic diet where you had no food after 4pm. Is this correct?
The dietary modifications I have done are a little different than your a, b and c delineations.
I've done the following a few times in the past three years:
a) three forms of ketogenic diet (KD): meat, vegetarian and vegan
b) one-meal-at-midday (not KD)
c) meals before 4pm (not KD)
b) and c) have I think
grossly the same effect. I'll call that early-meal-timing (EMT, let's say)
I think if I combined KD and EMT, I think there might be some muscle wasting. KD needs to have a lot of regular, little doses of protein in my experience. So I haven't really done your "c", except for here and there.
I apply dietary shifts (KD, EMT) and carb loading at different times of the month now. It's become very natural and fluid. Some shift are predictable; like a little carb-loading around female cycle and KD after the cycle. That seems very natural.
4) How does (a) compare to (b) in terms of which benefits and disadvantages you get? Do you feel that (a) is more powerful/beneficial, or is (b) just as good? Is (c) better than either (a) and (b) done in isolation, or are there diminished returns?
I always share the effects of the KD with people I know and I'm enthusiastic about KD because it can completely uncover an upbeat happy personality and acheless body (or ache-reduced body) that's been swamped by too many carbs for too many years. For me years of Lyme infection and treatment were brought to an end when I used the KD; so I have a strong appreciation for it. There are lots of medical reports of its application and benefit beyond the seizure control for which it was established 100 years ago.
I also recommend people consider it because it is a form of elimination diet: a person can really see how their body fares without some foods and what happens with the reintroduction of those foods. This is very useful.
Ketogenic diets need to be done in isolation for at least a week and I think one gets to see their complete merit in about a month. The change can be drastic. Like Nick and Fitter noted, lunch coma goes away and this has a huge effect on work and study life.
After four weeks, I think one will not see new improvements, but may have some vitamin deficiencies. That's an area of debate. Me, I just take a vitamin supplement.
3) Besides the benefits, do these diets suffer any disadvantages?
A ketogenic diet is replacing one source of craving (sugars) with another (proteins).
So an early-meal-timing diet (EMT) works directly on one's issues with craving and cultivating self-discipline and contentment, and a KD plan can't really do that: if one ignores protein cravings on the KD one can set themselves up for wasting.
2) You claim that (a, b) and (c) benefit your meditation practice, correct? How so, in what ways? Is your concentration better? How about your energy, strength, endurance, fatigue, amount of sleep required, mindfulness, etc?
So any dietary change develops concentration because one has to deliberately counteract the relentless firing of the brain that is firing signals to ask for past chemical set-points. In inducing the KD and in EMT diet, the brain is firing off lots and lots of "requests" per second to ask that its blood sugar set-points be met. It takes lots and lots of counter thoughts to not act on those "requests" for a few days as blood sugar set-points lower, establish a new (lower) normal. So that's concentration: one is just applying constant counter-thoughts to brain firings until a new normal is achieved. That's my perception of it.
While setting a new normal in relation to food and the brain's set-points, one becomes really, really aware that there are many, many, many little ways (distractions) by which the brain gets cycles of pleasure to buffer its sense of stress.
Now taking this to cushion one gets very interesting results. The first two days of a retreat the brain is deprived of thousands of little pleasure tweaks it makes all day long and on top of it the brain is re-setting its blood sugar due to EMT retreat diet and further the person...well, it's normal to have a stress narrative around that whole package. So the first days of retreat seem like hell for the brain.
So sitting on the cushion the first few days is a lesson in brain's ability to recruit pleasure in a form of triage. First, there's day dreaming. A good day-dreaming mind can make a person look like a "good" meditator because one can get so enveloped in a story and sit still due to that story envelopment.
So then we might limit the day dreaming. What will the brain do now in a boring old seated posture hour after hour with no apparent way to recruit pleasure till lunch? Well, aha, energy starts to collect in the groin. That's not the effect of posture or we'd never teach sitting cross-legged to grade schoolers --- cross-legged sitting would have pornographic status, if it were inherently sexual; that arousal is just one result of the brain on a very systematic hunt for its getting pleasure chemistry no matter what situation it's in. So, hey, the hands are only a few inches above the groin... and voila, sexual craving is coming up. If there's only physical reaction, one can move one's hands to one's knees and this will help reduce the focus in conjunction with mental effort to go back to anapanasati (or whatever is the object). But if the brain is allowed a daydreaming component to the sexual arousal: what happens is fascinating --- the brain creates a hunger to be touched and then creates a sense of outer energy in the cloak of daydream form --- say the cute guy across the meditation hall or something --- and then the mind keeps bringing that sense of outer energy up to one's own body (the classic vipassana make-out daydream) and, voila, the body is just alert, aroused, upright and sort of heightening its sense of sexual pleasure everywhere all because the mind knows full well it can make some pleasure circuitry happen out of thin air, like creating a sense of separate and outer energy, cloaking it in a sexual form, and then imagining that imagery approaching oneself again and again. So the mind can create these states of yearning, dissatisfaction and gratification in thin air.
Hence 2nd jhana. One creates pleasure and saturates the brain out of thin air (on the breath)).
It's amazing and it's the same thing that happens in what one learns in mindfulness of diet. It's just that the sexual component offers the brain a much bigger pleasure cycle than just cleaning one's desk at work as a diversion.
When the brain can't get any fantastical pleasures it will hone in on sleep as the body gets achy and the subjective stress of sitting for an hour creates an aversion to which the brain wants to respond with some pleasure. So drowsiness happens.
If the jhanas are applied the brain automatically starts with a pleasure chemistry (2nd jhana) and then we wean the brain to equanimity -- where the brain is alert and neutral. If something "interesting" happens in fourth jhana, it can seem like nothing special until what pleasure hunting organ in the brain gets wind of it and starts saying, "let's have that experience again" and the brain assigns that experience a value and teaches itself that that event is a source of pleasure. So then we have to deal with an arising and passing away loop again, re-flood the brain with 2nd jhana and, again, slowly let the mind go to fourth jhana. When we just let the brain's sense of "That's a source of pleasure! What's that!!!" pass, the brain naturally diminishes the pleasure chemistry and fourth jhana naturally extends and becomes a more stable place, free of mental gradients induced by "I". This is my perception of what's happening, anyway.
That's how I sense it anyway. And so food modification is amazing for affecting meditation, by training alone.
KD will make sitting more alert, but remain food-vigilant; EMT will pass through lunch coma but help a person develop contentment and understand what is "defeating" craving-mind.
SLEEP: EMT and KD are sort of equal. Less sleep is needed, sleep is more restful. If I go to bed by 10. then I might naturally wake up at 2 or 3 and sit and that's a nice loose time for the mind.
Strength, endurance, stamina: On KD diet I have very little explosive energy and my stamina and strength are directly related to last intake of protein. Carbs on the other hand provide a powerful source of fuel for many hours. So I can eat EMT-style and still do heavy yard work in the evening. KD provides even energy but depends on very regular KD food intake.
Social: carbs have a calming effect (too many can be depressive) so eating carby meals with friends (like pizza and beer), it's just clear everyone is satisified and mellow. Eating KD with friends, there's just a constant tension/alertnes...even after steak and eggs or tofu and avacados. KD has kind of a jittery effect. So that lo-carb beer takes on the status of a god.
I re-wrote this several times and from several ways. It's hard to avoid a long answer. I recommend people consider a KD diet (meat or vegetarian or vegan versions) so that they can see for themselves how huge a difference it makes in who they think they are: personality and body make big shifts in a mere week. For meditative retreatants, it'd be fine to do, but I highly recommend the teacher/guide also know well why the EMT eating is used: this directly shows and treats craving, which KD can't really resolve because there's a wasting effect to pass through craving without satisfying it.
What do you think, Bruno? Does that help? Make sense?
[edit: typos because I continue to be unmindful of words; should really train that now...]