Science behind Egg Fast


I promise, I really have searched (both here and on Google) for this info but I’m not finding anything. It’s been claimed that people can lose 3 or more pounds in just 3 days, and lots of people attest to this. But HOW is one losing that much in that short a period of time? Is it simply water? Muscle? I didn’t think it was possible to lose that much “fat” in that short a period, especially when you’re not really restricting calories during an egg fast.

Anyone know or even have a hunch why this seems to work for some people and if it’s really beneficial weight loss or just a temporary morale booster?


It probably works for the same reason zero (or nominal) carb works. I do “egg week” every so often, all eggs all week, with butter. I love it and I feel great, plus I usually lose a little bit.


But is it humanly possible to lose 3500 (or more) calories by eating this way? HOW???

(Doug) #4

The most we can lose is really about 1/2 lb. per day, with eating nothing. Lots of wacky, silly claims are out there, but that’s the bottom line. It’s normal to lose water weight on many types of diets - this is often part of the “fast weight loss” that’s claimed, but of course it’s regained when one goes back to ‘normal’ eating.

Eggs are great food - and fully compatible with low-carb, but there’s nothing magical about them.

(Bacon is a many-splendoured thing) #5

Firstly, the relationship between calories and mass is not what it is assumed to be. Calores don’t actually weigh anything, as you can verify by heating a sealed container containing 1 kg of water to 100°C and then letting it cool to 20° (room temperature). The container of water will remain the same weight, despite losing 80 (kilo)calories.

Second, the body does not actually make use of calories; it converts glucose and fatty acids into ATP, carbon dioxide, and water. It is the carbon dioxide and water exhaled in our breath that account for the loss of fat mass on a ketogenic diet. (Michael Eades just posted a fascinating video about this on YouTube, which has been linked on these forums in a couple of places.)

Third, a very high percentage of the protein included in our daily calorie intake is never metabolised. There is a high ATP cost needed to convert amino acids into either glucose or a fatty acid, before they can be metabolised, so the body prefers to use amino acids for structural purposes and only metabolises them under dire circumstances (i.e., when starving).

So for all these reasons, the relationship between caloric intake and “weight” loss is problematic.


K, that’s pretty much how I’m feeling about it. I can’t find any science to prove that we’re actually losing “weight” by eating an egg fast, unless you want to count water weight. But as you said, eggs aren’t harmful so I may just do it for a day or two, if for no other reason than to shake things up a bit.

(Bacon is a many-splendoured thing) #7

Eggs contain very high-quality protein, and in a good proportion with their fat content. They also contain very little carbohydrate, if any. This makes them an excellent low-insulin food. So it is possible to lose fat on an egg “fast,” provided that one stops eating when satisfied.

As Dr. Fung warns, however, it is better to either eat to satiety or to fast completely, because the body can cope easily with both situations. Short rations, however, signal the body that there is a famine going on, so it had better hang on to everything it can.

(Doug) #8

I would think that just eating eggs will practically guarantee weight loss. It’d be hard to eat enough eggs to balance things, energy-wise, i.e. you’re going to be running at a deficit, and the body will make up the needed energy by taking it from fat storage.

Also, as Paul said:

In general, protein takes more energy to digest than do fat and carbs. It’s 10-35% from what I’ve read, so a substantial thing. Looking at it from a caloric standpoint, 1000 calories (for example) of carbs or fat is pretty much what the effective intake is, minus a little bit - some energy does get ‘wasted’ digesting them. But for protein it can be as much as 350 out of the 1000 that don’t really end up as ‘intake.’


Wow, love the info, guys - keep it coming! I didn’t want to fall for one of those “too good to be true” fads and I really need to understand WHY I’m eating a certain way and exactly what it’s doing to my system. It sounds like I should keep going (all I’ve had today so far is eggs) but what scares me is that in the past when I only have a couple of eggs, not only am I hungry very quickly but I also get a BG rise and fall. I guess not enough fat or too much protein (which I understand excess protein converts to carbs/glucose?)

The egg fast diet says you are to eat eggs, cheese and fat. I may try it for my next meal or two and see how I feel physically, since feeling good is always the number one priority.

(Bacon is a many-splendoured thing) #10

More likely the former than the latter. The picture is fairly nuanced, and Amber O’Hearn, who is supposed to have said that gluconeogenesis is not supply-driven, says that that’s not precisely what she said. However, Dr. Phinney says that too much protein is likely to inhibit ketogenesis. I don’t pretend to understand these very intelligent people’s descriptions of what actually goes on, but I think it’s safe to say that we still have more to learn.

Also, allow me to remind everyone that, apart from sugars, carbohydrates are all glucose molecules bonded in different ways. If we have an enzyme to digest a given carbohydrate, it becomes glucose in our blood stream and has to be dealt with by insulin. If we lack the enzyme to digest a given carbohydrate (for example, we can’t digest cellulose, because we lack cellulase), then we call it fibre. And similarly, proteins are proteolysed into their constituent amino acids. So the body doesn’t “see” carbohydrate and protein, it sees glucose and amino acids.


It’s definitely not fat for many of us (not like I could do a single day but that’s not the point) but as people are different and “you will lose this or that much” is something I ignore 100%… :smiley:

I am not sure we don’t restrict calories on an egg fast… I definitely did, not forcefully, well the force was the awful food, my body rather wasn’t hungry… I would have missed my usual amount of eggs or at least other protein if I hadn’t been nauseous from all the excessive amount of fat (well, the ratio, the amount was small). Maybe I messed up the tense here, it isn’t my forte…

I wouldn’t think it’s so great for fat-loss but surely works for some people. I have read it’s for some very stubborn cases where saner things doesn’t help…?

But you won’t lose much fat in a few days, no matter what you do (especially without extreme activity with little food as that is effective at losing fat and muscle galore, some ultramaratoners probably could tell tales). I would rather eat properly instead of suffering an egg fast but I really hated all the 8 hours I heroically did it (I knew I am incompatible with the thing, I just got too curious after some years)… Fat fast was MUCH better for me. And it worked similarly as fat with very little protein actually satiates me so my energy intake dropped. The egg fast had more protein but I couldn’t even ate more than an egg at a time so I got hungry again and again while I hated the food so much my appetite was non-existent. I love fat and egg, by the way, just not in that ratio. I was more free on fat fast, I had various items so it worked better for me. I lost nothing noticeable, of course, it’s impossible for me in a short time (I got paranoid about my protein after 1.5 days and stopped :D) but it was an interesting experiment and sometimes I plan to make another fat fast day or at least a meal in that style… But I prefer to eat both fat and protein if possible, much nicer.

They contains a significant amount, a big part of my carb intake comes from them. But it’s animal sugar that doesn’t feel like plant carbs, it seems… And it’s still not much, of course, I don’t eat so many eggs, it’s 6g carbs at most.

Maybe it’s not true for everyone considering what I saw from people but I totally agree, at least in the case of many of us! If I start to eat, I need a proper meal, especially for my first meal. My SO always needs a proper sized meal so he never ever eats a bite outside of his meals.

Do egg fast have rules about how many times to eat? I remember such stupid ideas for fat fast (I mean, as a general rule, it’s definitely not stupid individually if that suits the one in question)… Ignored, obviously and had one meal on fat fast :slight_smile: It is a low-cal thing and I was shocked I could pull it off, 1000 kcal is way too tiny for my first meal normally.
I had many tiny meals on egg fast but they were super close together as I got hungry all the time, normal with tiny meals.

I don’t think we should worry about famine if it’s a short “fast”, it’s probably not long enough to cause even very temporal problems due to it. Both egg and fat fast is for a few days only.

But it’s egg fast, 10g fat and potentially some cheese per egg.
It probably ensures an energy deficit for most of us, possibly for various reasons…
But you are right, only eggs do that too, very few people can eat their maintenance calories in eggs only. Even I am super far from it, I just stop after 12 eggs, at least in one sitting but even waiting isn’t effective enough.

And now I am curious about what would I do if I tried some kind of “egg fast” again… Beyond failing and ending up eating a ton of meat as well. After flirting with carnivore a lot, just eggs (and fat) feels more miserable than ever!

I am very sure eating only eggs and meat would make me lose fat too (maybe a few additional rules but maybe even without…?). In a way more enjoyable way (still a bit miserable, I want my dairy). Slower too but it’s more sustainable and I have time…

What? Eggs are very fatty. About 66% fat, perfect for me personally though lower-fat sounds better, actually… Egg fast is… IDK but it’s insanely high fat.
Eggs have a cute amount of protein and I would need at least 22 eggs for my minimal protein (very high-fat is a bit different and almost no protein like in fat fast is very different so yep, my egg fast had about 6 eggs but it lasted for 8 hours so it’s not informative)… That’s 220g fat on egg fast? Not a fat-loss diet for me (if I could do it but I can’t. but I wouldn’t need so many eggs anyway, on high-fat
16 would do…?).

Getting very quickly after a few eggs… That sounds very normal. Some people get satiated for hours - and I fail to get satiated at all. I am hungry even after 10-12 as it’s a too tiny meal… Eggs were my top satiating items on vegetarian carnivore but I still need my calories… More like my protein and fat, a lot from both.
Meat is better. Why we don’t have “meat fast”? Or do we? Or is that too normal and it has no such name. (People tends to think meat is protein. Nope, meat is 0-99% fat, take your pick. Very flexible.)

I am looking forward to your experiences!


I have no idea how long I will do this. Today so far I’ve had 6 eggs, a cheese stick, 4 ounces of cream cheese, and 4 tablespoons of mayo. My food tracker says that equals: 4 net carbs, 46.6 grams protein, 95.4 grams of fat, and 1058 calories. Since it’s about 8:00 in the evening and I usually stop eating at 9:00, I will probably have 4 ounces of cream cheese as my “snack” and call it a day.

That’s not really a big calorie deficit for the day but it is a big carb decrease from my usual 30 grams or so. Will I do this again tomorrow? Depends on how I feel. I will go play an hour’s worth of a recreational sport (in a fasted state) and then have a few eggs when I get home, about 1:00 p.m., which is a 16 hour fasting window. If the sight of eggs doesn’t make me squirm, then I’ll have some more during the day. But I’m not going to punish myself if I’m miserable, I’m just giving it a try out of curiosity, and because it’s a pretty quick and easy way to get me meals prepared, eaten and cleaned up after. Gotta love that part!

I’ve been having a hard time getting back into ketosis after a slip-up a week ago so maybe, if nothng else, this will put me back unto ketosis. Even if that’s all it does, I will be happy with that and use the egg fast approach in the future if I’m struggling to get into ketosis. I try really hard not to get OUT of ketosis, but sometimes, sh/t happens.

(Bacon is a many-splendoured thing) #13

According to the food composition database of the U.S. Department of Agriculture, a 50 g egg contains 0.365 g of carbohydrate, consisting of

Sugar amt. (g) Type of data Date of measurement
Sucrose 0.035 Analytical 1/1/2003
Glucose 0.17 Analytical 1/1/2003
Fructose 0.035 Analytical 1/1/2003
Lactose 0.035 Analytical 1/1/2003
Maltose 0.035 Analytical 1/1/2003
Galactose 0.035 Analytical 1/1/2003

So not too much sugar; less than one percent, anyway.


I have read about 0.5g carbs per egg (a normal sized egg is 52g without shell here). As I wrote, I gain a big part of my carbs from eggs, the amount is significant even if it’s still low. One of my carbiest items on carnivore though I have “worse” :wink:

Indeed, eggs aren’t very carby but they have no negligible amount. They can raise our carb intake significantly if our allowance is tiny like 20g a day. Carbs add up and most people count animal sugars as well.

Oh thanks for the details, I am kind of curious what kind of sugars my food items have but not enough to look it up in most cases. Glucose in eggs, no surprise but it has all those others as well, that’s new…


yea you are not losing all those lbs in ‘fat’ from your body. inflammation factors come down, bloat and more BUT it can be a beneficial ‘use sparingly’ in the walk down toward ones goal.

egg fast basically is this: An egg fast is a short-term, restrictive ketogenic diet that includes mainly eggs, some cheese and some added fat like butter. It lasts three to five days and may aid short-term weight loss. Still, it may have potential risks like nutritional deficiencies — particularly if you follow it for longer than advised. It forces one into ketosis.

gotta remember ANY food can be an egg fast LOL in that you can eat say, 2 strips of bacon for each meal. You can eat a can of tuna for each meal. Any food that restricts, is controlled, is a keto plan food to push one into ketosis and keep ya there will get mostly the same results.

I used ‘tricks and tips’ for a few days in my journey too but came to find out they don’t suit me at all cause all it made me do, in truth in my tiny little personal brain, was ‘keep me on a friggin’ diet’ and that was something I wanted no part of anymore. Did years of that stuff and was SO over it ya know LOL but I have to say I tried a few days of this trick or that and in the end you can get results for sure but if you do this:

and this is why one needs extremes. One goes off the basic Keto Plan and then one can feel they need to over correct with some big trick like an egg fast and again, results come but I would focus tons more about WHY you are slipping up and why you can’t hold Keto Plan for more steady easy results on the lifestyle. See I had big slips also :slight_smile: I get it for sure but the egg fast is a correction and quick fix for a much much bigger issue, why ya going off plan in the first place? One can’t hold that usually as most of us know. Eat crap, fix it fast. Eat crap fix it fast and then usually it becomes, no fix and lose control more and more, well it worked that way for me anyway :slight_smile: Any tricks/tips can help us change for sure but we have to remember there is a much bigger picture we need to address. Long term, stay on plan etc.

wishing you the best way forward for ya!


Thank you for that awesome reply, Fang! You summed everything up perfectly and hit the nail on the head. At this stage of my life I am all about feeling better/getting healthier but not fanatical about it. It’s a bunch of little changes that I’ve incorporated into my daily life that is slowly bringing positive results. I do fine when I’m home, actually surprised at how compliant I have become and that my cravings for carby foods are far and few between, but the slip ups come when I’m at an event or restaurant or someone else’s home. I made the best choices I could last week from the restaurant menu, but I’m sure there were ingredients in some of the items that knocked me out of ketosis. I think the biggest culprit was the salad dressing. :frowning:

Such is life, and I’m no longer lamenting or obsessing over the occasional low ketone number, I’m just getting back on the horse and doing the best I can. And very good point about how almost any food could become a “fasting” food. It’s more about the restriction factor than it is the nutritional content.

So basically there really is no magic or complicated science behind the extreme weight losses I’ve read about… they are not true fat losses but instead a “whoosh” effect or a water release, and maybe a tiny bit more fat than a typical day. That’s the info I was looking for, and I guess we will always hope that there is some sort of magic to get to our goals more quickly, so maybe the Easter Bunny will come up with one!

(MC) #17

“egg fast basically is this: An egg fast is a short-term, restrictive ketogenic diet that includes mainly eggs, some cheese and some added fat like butter. It lasts three to five days and may aid short-term weight loss. Still, it may have potential risks like nutritional deficiencies — particularly if you follow it for longer than advised. It forces one into ketosis.”

This is basically my keto diet (vegetarian) with cream and cocoa fat bombs, some veggies now and then, and now I’m wondering about the nutritional losses.

I do like the idea of an egg fast though, it sounds like a good way to get back onto the keto wagon.

(Bacon is a many-splendoured thing) #18

One of the concerns is adequate protein intake, and this should not be a problem if you are eating enough eggs. The food that gives us the necessary amino acids in the correct proportions is beef (referred to as “high-quality reference protein” in the dietary guidelines), and eggs come pretty close, I understand, to matching the amino-acid profile of beef. What people usually have in mind when they mention “nutritional deficiencies” is, however, vitamins and minerals. If you are eating other things besides eggs, then I suspect you don’t need to worry, unless you start experiencing signs of some sort of deficiency.


Well I ended up doing it for about 40 hours. That’s not very long but it was long enough to get me back into ketosis and, according to the scale (which lies) I lost a pound by doing it for a day. Would the ketosis and weight loss have happened even if I didn’t egg fast for 1.5 days? Maybe. Probably. But I will use it again the next time I feel like I need a boost or jump start.


Not of fat, no. There may be an outliar like an uncontrolled hyperthyroid case that would, but in real life, no.

I’ll say this, I’ve tried every fat burn cheat there is, all the pretty good ones that are proven to work like ECA Stack, Fat burners in the 90’s when they still had amphetamine in them, all the way up to what’s been called the “worlds deadliest fat burner” (that one can do it). But eating eggs and doing it? Not gonna happen, again, not 3lbs of fat.

Having your macros right for you, and being consistent, will do the trick every time. I’m all for the cheats, but gotta have the base down first.