I’ve been doing the 18/6 fasting. I’ll read that fasting will aid in weight loss and get you over plateaus. Then I’ll read that if you calorie restrict you won’t lose weight because your body holds on to fat stores because it thinks there’s a food shortage. Seems like fasting is ultimate calorie restricting, so is it actually causing me to hold on to body fat? I’ve been at 130 for what seems like 6 months. I started Keto at 145 lbs 7 months ago and lost 15 pounds instantly and stayed at 130. If I fast I stay the same weight. If I feel like I have eaten too much (all Keto food), I stay the same weight. I can still grab handfuls of blubber on my hips and back even though I’m technically idea weight. I’d kinda like to lose it but nothing I do makes any difference. I’m not complaining. I’ve never been abled to maintain such a low weight, not go hungry, and enjoy such delicious foods.
Fasting is Good but Calorie Restricting is Bad? Doesn't make sense to me
By fasting and eating well your BMR will stay up. Calorie restriction is a downhill course for your BMR. Fast/feast is what’s recommended by knowledgeable fasters. The biggest problem people run into with fasting is either eating too little or too much after a fast. It’s tricky. Try examining your stall from different angles.
Good luck sorting this out. 
Intermittent fasting is not calorie restriction (necessarily). It’s time restriction. Fung is clear about this. You eat about the same, just in a different time interval. Extended fasting is a different thing. Yes, if you fast multiple days you are restricting calories. I’m sure Fung has figured out how to deal with it to prevent overall metabolic slowdown. Even so, if you restrict calories for a long enough time period, your metabolism has no other way to cope other than make you very tired or slow down to burn less calories. There are a few folks on this forum with experience on VEF (very extended fast) who can advise more specifically.
Fasting may be a way for calorie restriction but it’s not necessarily the case. I almost always do IF since ages and I easily overeat sometimes. The same is true for keto.
Calorie restriction is what allows me to lose fat and it never harms my metabolism if I don’t starve. Eating a bit below our need is fine.
But even starvation causes fat loss (if we have any to lose) as we can’t make energy from nothing and we eat way less than our need in starvation. It slows down our metabolism, we lose significant amount of muscles and probably feel way worse. The human body does its best, spares energy but it has limits and it’s actually not a good idea to barely keep the host alive so they are too weak to have a chance to get food… But it’s another topic, not the case when I eat at a small deficit (apparently. I obviously can’t calculate this, that’s not possible but experience can help a bit) and loses fat just fine without a problem. Well I can’t avoid high calorie days so maybe that helps too.
And these things are a bit more complicated for many people, I don’t even get a little bonus on keto (or some penalty if I eat sweeteners, for example), I need to restrict my calories just the same as on any other diet. I don’t do that forcefully, that’s not my style but I choose a woe that helps me to eat less without problems. Both fasting and lowering my carbs intake helps. But even their combination can’t ensure fat-loss. I just have a way less chance for overeating, maybe a tiny chance to lose fat (basically zero) and I feel better.
Longer term fast is totally calorie restriction, you eat 0 calories for long and it surely causes quite quick fat-loss as we can’t make energy from nothing. But if it continues for “long” (just some days so not really long), our metabolism suffers. It’s complicated, it matters if you have those fasts often or not, surely there are individual factors… I personally never want to do fasting for 3+ days, that’s way too long, for my metabolism and my protein need alike. My fat reserves aren’t so big either, it may be a better option to lose fat for someone heavier who doesn’t even get hungry at a longer fast. But I would be still careful with that.
Keto (extreme low-carb or not) and fasting (IF or EF) may be important tools to lose fat for many but they are way, way more than that. And they are good for maintenance and even bulking for several people, they don’t necessarily keep us from eating a lot. They just make it possible or easier in many cases. It vary. I met someone who massively overate on OMAD, it just was not suited for them. I doubt I can easily overeat on OMAD and surely not massively. On keto? That’s easy. But some people starve on keto, they just can’t eat enough. It’s very individual.
I’m not qualified to perscribe anything to anybody but here is how it worked for me. I was nudging the overweight limit (175 lbs, 5" 9"). I wanted to reduce body fat to near highschool trim and got that done with time restricted eating (16/8) Sunday - Friday and eat nothing on Saturday. I delayed food until noon, and ate break even calories, so any weight lost was the calories I burned on Saturday. This made hungry times predictable which made it easier. Once I started eating at noon I wasn’t hungry again until mid morning the next day at worst. Some times, on the no food day, I felt no hunger all day if there were enough distractions. Getting rid of carbs and getting adjusted to that blunts hunger signals. The low carb effect is magnified if you do low heart rate aerobic work which is fat burning. It blunts my hunger by reinforcing fat adaption. If your body is very good at using fat for fuel it never needs to say it’s hungry because there’s always plenty of food on board, even in the leanest of us.
I got down to the 130’s. People I barely knew said I was too thin. They were right. I’m back to the mid 150’s. At least 10 lbs of that is lean tissue (aka muscle). I’d love to add 10-15 more lbs and stay at 13% body fat without sacrificing overall health or aerobic fitness. Time will tell.
My favorite quote from Dr Fung:
“The secret of success is NOT to limit some of the calories all the time (deficit dieting), which lowers metabolism. Rather, to limit ALL the calories SOME of the time… which is called Fasting.”
Equilibrium comes to mind; you simply may not have enough body fat to fast anymore so adrenaline and the other things in it are going to store fat rather then burn up what your eating when you do eat.
Fasting is pretty expansive as a term. But Fung and Megan Ramos have noted that things like One Meal a Day or time restricted eating (which is probably a better term for 18/6) are better for maintenance than losing weight.
If you’re not losing weight on 18/6 the issue probably isn’t metabolism related.
Anecdotally, 18/6 or thereabout is my default eating style - I’ve never been a snacker or someone who wants to eat when I wake up - and this included when I weighed 320 pounds. Longer fasts - I’ve been doing 3 fasts of 36+ hours each every week for the last five - do seem to work.
I found this post from the Fungster himself to be a very good explanation of the difference between fasting and calorie restriction: