This post is meant to explain why we should eat plenty of good keto food early on, as we adapt to this new way of eating.
The credit goes to Jason Fung/Megan Ramos (among others) for most of my understanding of this, but any errors involved are mine alone, and I’m mixing in the fat-adaptation bit to explain the early processes of this system. Jason/Megan look at it from the POV of fasting, and the question I was trying to answer on the forums was regarding 1MAD (one meal a day), but as that is fasting, I think it’ll make sense.
This post also assumes that you’re not able to eat the amount of energy you need in one meal. I could do this SO EASILY as a carbage eater, but eating keto? Zero chance. I struggle at 2MAD, let alone 1MAD. (We are not discussing maintenance here, that’s a different kettle of oily, oily fish).
Your body looks at the amount of energy you feed it, and diligently works to use that amount (i.e. it adapts). It obviously doesn’t want to burn more than it’s got available, or you’ll eventually die, or less, because why would it not use the fuel available to it? (This is called homeostasis, where the body (brilliantly) balances all the competing demands and supplies to keep things just as they are.)
So you teach your body that you’re going to feed it a good amount of food that it can comfortably utilise. It uses it to run your brain, heat your body, do things to food, build proteins-bone-muscles-etc, let you exercise, :poop:, etc.
In the initial stages of keto (adaptation phase), your body wants carbs/glucose. After all, that’s what it’s been using for decades, and it’s the easiest fuel it can use. You are teaching it to not use this, but to use fat as the main fuel source instead. So the last thing you want to do is restrict that fuel. Teach it that there’s an abundant supply, make it realise that it’s all good, it just has to make the switch.
So you keep throwing fat/protein into your (formerly pie, now probably meat) hole until your brain gets the message and your body switches over, at which point, for most people, you’ll discover that your appetite decreases, sometimes dramatically. It took me (and Cha) about eight weeks for this to occur.
It’s at this juncture – once fat adaptation has occurred, and your body is used to its new fat fuel and a good amount of it – that 24-36 hour fasts come in (I told you I’d get back to 1MAD stuff). Your body is happy burning its baseline fuel amount that you’ve been feeding it, and so when you 1MAD it, or 0MAD it, it burns that amount of fuel anyway.
Where does your body get that extra energy from that it is used to, and that you didn’t give it today? Body fat. It doesn’t much care where the energy comes from, as long as it gets it. You’ve taught it to work at a particular rate, and it sees no reason to stop, so it continues doing what it’s been taught to do. Then you feed it the usual amount again, and this reassures it that this is normality, then you take it away, then you give it back.
As Megan said in a talk I listened to the other day, “mix it up.”
The reason for this is that the body does NOT run on the super-simple Calories In-Calories Out (CICO, which I find to be an incredibly appropriate-sounding acronym) principle that we’ve been taught for years. Basic principles of thermodynamics be damned – that would be fine if everything had hormones controlling things like we do, but obviously they don’t, so it’s a very flawed model/analogy. So we run into the problem that the input affects the output which also affects the input, which is a major confounding factor. (Example – if you do a large amount of work (energy expenditure), you will get really hungry, which obviously affects the energy intake, showing they’re not discrete variables that you can independently control as CICO insists.)
Your body is smart, it adapts. Therefore, if you regularly feed your body a small amount of energy each day, it will learn to run on that small amount of energy because it is diligently working to keep you alive, that being its #1 goal. It doesn’t give a damn if your goal is to lose weight, its goal is that you to stay alive. OTOH, if you feed it a good amount of (good quality) energy each day, it will happily use that to optimally run your body. Then you fast it, and it burns that energy amount anyway, using your body fat to make up the deficit you have deliberately engineered.
TL;DR You need to teach your body to burn a good amount of good food, so eat as much as you should, not to a daily deficit. Then create that deficit on an irregular basis via fasting (i.e. 1MAD, 0MAD, or more.)
 Note that this doesn’t really get into the “insulin is a hormone, keto is basically a hormone control diet” aspect of it, which I’ve deliberately not gone into here. The above is radical enough as is, without complicating it further.
 Sorry this got out to 900 words…