How long until you are OUT of being fat adapted?

(Michael - When reality fails to meet expectations, the problem is not reality.) #21

Until now, testing of RER (see second link below for discussion) was pretty much limited to big, bulky expensive equipment. We’re on the cusp of cheap home devices. So the days of guessing whether or not you’re ‘fat adapted’ are soon over. Still waiting for my device to arrive. When I purchased in June I was advised of November shipment. Just fired off a query asking if shipping is imminent or not.

(Bob M) #22

I’ve found that after almost 6 years of low carb/keto, I can eat things like ice cream, and a lot of it, 1-2 times over a weekend, and not only be fat adapted, but be in ketosis on Monday. If I didn’t know what carbs did to my blood sugar and the like, I’d try to test to see how long it took me to get completely not fat adapted. Too many variables, though, like working on the house. Right now, I’m running from the basement to the second floor and back again, all weekend. With that kind of work, carbs are getting used up too quickly.

I bet type of carbs also play a role. Ice cream tends to make a short, quick peak, whereas pizza makes high blood glucose for a long time. The AUC (area under the curve) of ice cream is much smaller than the AUC of pizza. I’m sure this affects things.

(Jane) #23

Looking forward to seeing the data from your new toy when you get it!

(Michael - When reality fails to meet expectations, the problem is not reality.) #24

:man_facepalming: Me too!


I’ve heard such things. I got fat adapted after 7 weeks, quite suddenly. At least I can’t imagine what else it could be. The changes were great (in more than one meaning).
I’ve heard it’s gradual. Maybe it changes or it’s different for others, I never did keto for very long, only for months. But many people notices a big difference somewhere around 3-8 weeks. Surely not all, I experienced changes people have much earlier due to being in ketosis.

About the original question… It’s somewhat a mystery I think but as many of us feels different when fat adapted, we can take an educated guess, at least regarding our individual case.
I feel nothing or close to that when I go into/out of ketosis. Sometimes I feel something but I usually look at my carb intake and weight to take a guess. But fat adaptation is different. It can’t be 100% but I am sure enough about what happened with me.
So, fat adaptation changed my hunger and satiation quite drastically. I went off keto soon and continued my low-carb lifestyle with the occasionally carby day. It was fine, the changes stayed with me and I lost fat easier off keto but fat-adapted than on keto without fat adaptation. Both is the best, I don’t know why I couldn’t stick to keto but I came back from time to time and it was obvious to me I always will.
Years passed and I had carbier times too, not just days. Probably low-carb but with too much carbs. And if I managed to avoid severe carb poisoning, I started to feel my hunger getting stronger again. My fat adaptated hunger is very soft unlike my old one. I had something in between, I dropped my carbs asap and my hunger got soft again.
Then OMAD came and my hunger got rare. Keto, OMAD and fat adaptation all have some effect on my hunger and easier, longer-term satiation. I could try out keto without fat adaptation only once, it had no effect on them but now there’s a difference. So I combine all three now and I am glad fat adaptation seems to stay with me. If this type of hunger means that.

(Jane) #26

I don’t have any personal expereince because I like the way I feel on keto too much to go off more than an occasional meal.

But going by some of the posts I’ve seen on the board where people went off keto and came back several months later and struggled a bit, I would say MONTHS, not days or week to lose your fat adaptation.

Now, you can gain weight pretty quick eating too many carbs but it is mostly water and will come back off if you go back to keto. But that’s not the same as losing your fat adaptation.

I know the few times I measured my ketones when not fasting, but the day after a higher carb day I was surprised at how fast I was making ketones again. You really do burn the carbs up quickly - the key is can you get back on keto without the hunger monster rearing its ugly head. If so, then still fat-adapted in my book.

(Alec) #28

I have a late n=1 entry to this debate. I was solid keto for 2 years ish from 2018-2020, but then fell badly off the wagon and have tried a few times to get back on.

Since a few weeks ago, I have been on my latest attempt to get back on, and I have been focussing on fasting first, as some other approaches didn’t work for me.

It has been a good 18 months since I have had any lasting period on low carb/keto. Have I lost my fat adaption? Nope. I am doing 42 hour fasts twice a week with absolutely no trouble at all. If anything easier than when I was full time keto. At the end of a 42 hour fast, zero hunger.

Maybe it is because I have lots of new fat to burn? No idea, but in my case my fat adaption has not diminished at all despite eating a carb laden diet for 18 months.

(O Kina Alford) #29

I’ve read this entire thread looking for the answer you just gave. I was strict keto for about 2 years…definitely fat adapted…But after about 6 months of being off the wagon, I just cut out the carbs again and I was curious as to whether I am still fat adapted or will have to go through the entire process again. I have only been back on for 2 days and I have always (when doing keto) eaten 12 net grams of carbs a day. In these 2 days I haven’t felt any fatigue and my workouts have been fine, so I think I may still be fat adapted, but was hoping to get some confirmation.


Same here, as long as you don’t go back to carb binging it definitely seems we keep the metabolic flexibility to go right back to burning fat for fuel. I do TKD now so I have about 30g carbs preworkout and sometimes after, usually once or twice a week I’ll do a half descent carb up (only good ones) and when I decide to pull them again there’s zero pushback, I deplete and start burning fat again, no keto flu, no energy issues, no nothing.


That’s amazing. I fell off and am getting back on again almost exactly how you did. Thank you for this.