Fasting while on GLP1s — has anyone given it a go?

Clavicular's Hammer

Clavicular's Hammer

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Years back I used to fast, and I appreciated both the way it made me feel and the sharpness of mind it brought. I haven't done it in a long time, but I'm thinking this weekend might be the moment to try again. Is there anyone in this community who fasts while taking a glp1?

Because gastric emptying slows down on these medications, you'd need to be extra cautious about overeating once the fast is broken.
 
Yes. On a GLP it's far simpler.

As for the upsides—where would I begin when it comes to how beneficial fasting is..

At minimum I go 24 hours (that's what I consider an actual fast) 2/3 times per week, and I really like that time. If I think I'd gain from it, I can stretch to 48 and beyond.

Beyond that, every other day I follow OMAD, which I guess a few people would count as fasting.
 
I recently completed a fast lasting 3 days. During and afterward, I felt okay.

I also do intermittent fasting every day. Typically, there are 16-18 hours between my last and first meals.
 
Before I started glp, I used to fast. These days though, I wouldn't risk it. Getting in enough food to keep up with how much I move is already a struggle. I found out the hard way what happens when I don't eat enough — I hit a wall and totally ran out of energy right in the middle of a day full of activity. The odd part is that back when I was fasting, this never happened. I could go for days without any trouble. What actually changed, I don't know, but something did.
 
I've been doing intermittent fasting for 15 yrs — nothing before 12 noon, and I eat 1-2 x a day. GLP type peps definitely make it simpler, though in my case fasting is so habitual that I never actually feel real hunger.
 
Scorpio73 said:

I've been doing intermittent fasting for 15 yrs — nothing before 12 noon, and I eat 1-2 x a day. GLP type peps definitely make it simpler, though in my case fasting is so habitual that I never actually feel real hunger.
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Hmm, going by that definition, I suppose that includes me as well? I wake up very early, have breakfast and lunch, and then I don't eat anything else for the rest of the day.
 
Clavicular's Hammer said:

Years back I used to fast, and I appreciated both the way it made me feel and the sharpness of mind it brought. I haven't done it in a long time, but I'm thinking this weekend might be the moment to try again. Is there anyone in this community who fasts while taking a glp1?

Because gastric emptying slows down on these medications, you'd need to be extra cautious about overeating once the fast is broken.
Click to expand...
Throughout the whole period I was working toward my goal, I stuck with intermittent fasting.

8/16

These days I still have black coffee in the morning, even though fasting isn't part of my routine anymore.

With Tirz, staying fasted from 8pm until 12pm became simple, and I believe it was a net positive for me.

Since I needed cream in my coffee only after lunch, I began mixing a vanilla protein shake into my coffee instead — it tasted great! I continue doing that too.
 
Clavicular's Hammer said:

Years back I used to fast, and I appreciated both the way it made me feel and the sharpness of mind it brought. I haven't done it in a long time, but I'm thinking this weekend might be the moment to try again. Is there anyone in this community who fasts while taking a glp1?

Because gastric emptying slows down on these medications, you'd need to be extra cautious about overeating once the fast is broken.
Click to expand...
I haven’t done a water fast while on GLP-1s yet. Most days, though, I keep my eating window to 4-6 hours, and that works okay for me. Intermittent fasting has been part of my routine for roughly 10 years — mainly because it fits my schedule, not because it helped me shed pounds (clearly it didn’t do that for me LOL!).

Honestly, I’d guess that on GLP-1s, ending a fast might make it simpler to avoid overeating. There are times when I’m extremely hungry if I barely ate the day before, yet once I have 400-600 cal, I feel full. Tell us how it turns out, and best of luck!
 
I've been following this pattern every day for the past 3 weeks: 05:00AM through 12:00PM. Really, though, the window opens at bedtime for me. So think of it as 10:00PM to 12:00PM.
 
What's strange is that for about 6 months I did weekly fasts lasting 24-48 hrs. Once I started GLPs, fasting became more difficult for me, though I do reach fullness sooner when eating — the catch is I'd need at least 2 meals per day. My guess is glucagon is involved.
 
For more than a year, fasting was my only tool to stop myself from putting on weight too quickly, so I stuck with it. On glp…once I had been in maintenance for a while..after roughly a year I began introducing small items in the morning, and my weight stayed stable.

Breakfast has never really been my thing, so continuing to fast wasn’t difficult. Before glp, I was so rigid that even coffee with a splash of creamer was off-limits until my fasting window closed.

These days I just eat whenever I feel like it. Almost every day I’ll have coffee with some calories in it, or if hunger hits I’ll go for something high protein like eggs. I steer clear of big morning/noon meals since I want to be hungry for dinner.

On vacation I’ll do pancakes and that sort of thing for 1 breakfast day, but that’s typically the extent of it—eating a large breakfast kills my dinner appetite and wastes money.

Either way…I no longer worry about whether I’m getting into ketosis. If I wake up starving then I eat.

Back when I did keep up fasting during my early days of glp…it made fasting so easy for me. It was great. I didn’t feel like my blood glucose was low or anything like that.

My 2 cents
 
I do fast, though it isn't something I set out to do.

Tirz makes eating something I have to push myself into. Since I also have a malabsorption issue from bariatric surgery in the past, going too long without food means I could genuinely miss out on the nutrients my body needs to get through the day...that said, fasting has gotten far too effortless for me, and it just ends up leaving me feeling drained.
 
I do intermittent fasting daily, minimum 16 hours, typically closer to 18. My meals lean heavily on protein plus complex carbohydrates. Without that high protein intake, hitting my calorie and macro targets within the eating window would be extremely hard. It's a real challenge. I've cycled in and out of fasting since 2016. Combining all those years of experience with GLP1s has turned this into something effortless. You simply have to experiment and observe what works. Blood work is the strongest signal of whether it's working. I recently completed my first major panel, a 9 vial draw. Nothing will be overlooked. Results should arrive shortly.

Bill
 
spanky2026 said:

Before I started glp, I used to fast. These days though, I wouldn't risk it. Getting in enough food to keep up with how much I move is already a struggle. I found out the hard way what happens when I don't eat enough — I hit a wall and totally ran out of energy right in the middle of a day full of activity. The odd part is that back when I was fasting, this never happened. I could go for days without any trouble. What actually changed, I don't know, but something did.
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What GLP are you on?

Since reta includes a glucagon component, I figure it could be the stronger option, assuming you aren't using it yet.

Multi-day fasts were something I did prior to GLPs, though not after beginning reta—I'll need to give it a go.
 
Before I started GLP1s, I was doing keto (yes, actually testing with pee strips) and intermittent fasting. Once I was on Tirz, though, the situation flipped—I had to push myself to eat so I wouldn't drop weight too quickly. The general line for safe weight loss is no more than 2lbs per week (or over 1%). Anything beyond that tends to be water (particularly early on, since you're consuming less food and drink) or muscle! Muscle loss is something you want to avoid; it only makes maintaining the weight loss harder... and makes lifting things harder too. Think marathon, not sprint.

Reta is the one I'd strongly advise against fasting with. For one, it might push your body into starvation mode, where no weight comes off because you're not burning calories (and you get depression and sluggishness along with it). For another, the glucagon agonist could trigger ketoacidosis, which is potentially fatal.

If your body fat is already on the lower side, fasting (or even just keto) while on Reta is a genuinely terrible plan.
 
That’s an interesting point. If I end up dead, I’ll let you all know. A daily intermittent fast combined with eating properly shouldn’t produce any bad outcomes, as far as I can tell. I recall 2016, when IF was basically unknown, and everyone kept warning me it would kill me. My health was flawless — blood work and every other marker. Over the course of a year my TES climbed from 300 to 900. My cholesterol dropped from 225 to 135. With extended fasting, maybe ketoacidosis could set in. Still, doing a daily fast alongside proper eating doesn’t worry me at all. Thanks for shining a light on this.

Bill
 
Mochizuki0124 said:

What's strange is that for about 6 months I did weekly fasts lasting 24-48 hrs. Once I started GLPs, fasting became more difficult for me, though I do reach fullness sooner when eating — the catch is I'd need at least 2 meals per day. My guess is glucagon is involved.
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For a year I followed rolling 48s — 48 hours on, then 48 off. Looking back, I suspect my gut microbiome and other internal systems didn't benefit from that pattern. Still, certain aspects of fasting appealed to me a lot. I dropped 60 lbs that way.

Loose skin is something everyone on glp1 deals with, and fasting is an excellent route for that — atrophy will actually resolve it, no surgery required.
 
Clavicular's Hammer said:

Years back I used to fast, and I appreciated both the way it made me feel and the sharpness of mind it brought. I haven't done it in a long time, but I'm thinking this weekend might be the moment to try again. Is there anyone in this community who fasts while taking a glp1?

Because gastric emptying slows down on these medications, you'd need to be extra cautious about overeating once the fast is broken.
Click to expand...
In my opinion, fasting delivers great results. Early on in my Tirz adventure, I used intermittent fasting and it helped me drop that initial big amount of weight really effectively. For me, 18/6 was the schedule that suited me best. Still, a word of warning: watch out for muscle loss, since it can happen quite easily. So my own take is that fasting works well when done in stretches, but on these "meds" it matters a lot to eat properly and train hard — I'm talking 5 days a week of intense workouts — otherwise you end up with ozempic-face 🫩
 
Nate2plate said:

Mochizuki0124 said:

What's strange is that for about 6 months I did weekly fasts lasting 24-48 hrs. Once I started GLPs, fasting became more difficult for me, though I do reach fullness sooner when eating — the catch is I'd need at least 2 meals per day. My guess is glucagon is involved.
Click to expand...
For a year I followed rolling 48s — 48 hours on, then 48 off. Looking back, I suspect my gut microbiome and other internal systems didn't benefit from that pattern. Still, certain aspects of fasting appealed to me a lot. I dropped 60 lbs that way.

Loose skin is something everyone on glp1 deals with, and fasting is an excellent route for that — atrophy will actually resolve it, no surgery required.
Click to expand...
I dropped roughly 20lbs during fasting. Building muscle was a real struggle, though, since my protein intake was consistently low. These days, getting enough protein is much more manageable.
 
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