That is a good question. I think any answer to that one would be a bit speculative. So I’ll speculate 
As GLP1’s stabilizes blood sugar levels (blood glucose homeostasis) it may make fasting more “comfortable” and with the appetite suppression, more “endurable”.
I personally would not fast for longer than 24 hr without water but if one were to fast with adequate water/hydration, I’d speculate that would be OK.
If the fast is intended to be for weight loss, I would not bother with fasting. With GLP1’s weight loss can be very steady and predictable once settled into the routine. With that process leading to the goal of ideal weight maintenance and potentially a lower maintenance dose.
If the fast was for other reasons, fasting occasionally could be a reasonable addition to a healthy routine that includes GLP1’s. But I do not have any clinical info regarding this and have not done any searching to see.
As always, consult your physician 
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mccoy
#125
This issue has been raised in the thread on Longo’s fast-mimicking -diet. It’s a 5-days very low-calories, low protein, vegan stint. Conceptually, it may be harmful. Pra tically it may be not. There are no studies on it apparently.
Edit: While re-reading my question, it appears that a low-carb version of the FMD might avoid to overstimulate insulin secretion, especially if simple carbs/sudden peaks are avoided.
In Water only, short fasts, there would be no glucose input hence no stimulus to insulin secretion hence no amplification of a glucose signal which is not there.
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LukeMV
#126
Anyone notice an increased heart rate on these medications? How significant is the increase? I know there was a little discussion earlier in the thread but not much.
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Davin8r
#127
Yes, they have a direct effect on the SA node of the heart. For some it’s just a few extra BPM, but for me it’s like 10. My Oura Ring thinks I’m constantly overtraining/under-rested because of it.
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RapMet
#128
For me not enough to notice. I’m usually 54-60 rested, and last 10 days in RT my rested rate has not gone over 60, though it hasn’t been under 58 either, so maybe 2–3-point difference. I did however notice a change based on monophases for some reason, about 5 rate difference. I have no clue how that can be, or if there is something else that might affect it but haven’t been able to pinpoint. As weird as it sounds, I tend to have better and deeper sleep when a full moon also. Go figure, welcome to our universe. LOL
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LukeMV
#130
I don’t really have much fat to lose, but I think I’m going to microdose Retatrutide soon to suppress my appetite a bit and maybe get other benefits. I’m thinking I’ll start at 0.5mg per week and try not to go above 1mg per week.
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Davin8r
#131
You may not get much appetite suppression at that dose, but it should still cause some weight loss.
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LukeMV
#132
I’m going to go slow and base it off how I feel, so I’m not sure what dose I will eventually land on. I don’t want to kill my appetite but if I can lose the desire to snack, that would be nice.
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RapMet
#133
I started Retatrutide about 10 days ago at 2.5 mg per week and first week the suppression of appetite was pretty significant. I just ate for sake of eating but wasn’t hungry much. On second week then the appetite returned but maybe at 70% of normal. What I find helpful is the fact that I don’t have any cravings for certain foods which I used to. I lost first week about 2lbs, but second week is almost over, and I haven’t lost much could end up being 0.75lb. After few weeks at 2.5mg I plan to go 1mg for a while and perhaps continue 0.50-0.75mg for a long time. BTW, I haven’t noticed any side effects at all.
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RapMet
#134
If you don’t need to lose much, I would do 1mg and then adjust based on how you feel and what you are trying to achieve. Seems pretty potent as 2,5mg I’m doing is definitely suppressing my appetite. I decided to start with 2.5 as I need to shed at least 20, but I’d be happier with 30. It will be a slow journey, but I feel I’ll get there.
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mccoy
#135
Ditto for me, presently I’m finding that 1000 mg of berberine does have this effect, some days pretty pronounced, other days milder. I love the feeling of rising above the desire for food. Letting discrimination govern, not some neurological signal coming from the GI or the hypothalamus.
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My biggest health concern is my overweight status. I need to lose 20 lbs to get to my ideal weight. I’ve been losing weight slowly, but I think I need to add Retatrutide to get down to the level I want. Then I’ll cut back to maintain. Thank goodness for GLP-1s. They really make losing weight quite easy.
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LukeMV
#137
Just took my first 0.5mg dose of Retatrutide this morning. Hoping for appetite suppression and a bit of a body recomposition effect. I think I will dose 0.5mg every two or three days depending on how I feel. I’m kind of excited about this.
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Davin8r
#138
I wouldn’t get your hopes up about appetite suppression at that dose, but I’ll be interested to hear what happens!
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LukeMV
#139
I can just increase the dose until I get a little bit of the appetite suppression then. I don’t want to completely eliminate it, so I’m gonna wing it and see how it goes.
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So retatrutide has a T1/2 of 6 days, similar to tirzepatide. Roughly 2 mg of RT is similar to 2.5-2.6 of TZ. A starting dose would be 2 mg of RT every 6-7 days. I think 0.5 mg doses are likely to have no impact as it is too small of a dose … however, I guess if done every 2 days … then would be almost 2 mg/week which would be a minimal starting dose.
My experience with TZ with counseling and effort put in, is most folks end up on 3.75 mg/week during losing weight and then to maintain ends up being in the 2.5-3.75 mg/week range. So equivalent on RT would be 2-3 mg.
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LukeMV
#141
Thanks for sharing your clinical experience. I have spoken to several individuals, who are also fitness enthusiasts like myself, that microdose it with more frequent injections to eliminate side effects and swear by the results. They’re also not trying to lose a lot of weight but are hoping for some benefits, so this is what I plan to do as well. I figure it can’t hurt to take a small amount. If I get zero benefits, I can live with that.
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Depends on one’s goals. If losing weight is a component, then pursue standard dosing, as very few people end up having an issue with 2-3 mg/week, it is when it goes up that we have problems (and yes, I’m sure I’ll have a testimonial from someone who had all types of problems, but it isn’t typical).
If looking for GLP agonism, then semaglutide is likely most potent on just that receptor. Then if feel need BBB penetrance then putting in a little dulaglutide with SG/TZ/RT is sensible if worried about AD or PD (which I personally am).
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Davin8r
#143
I’d be interested to see data on non-obese, non-diabetics taking GLPs and how much different the sensitivity to the medication and dose required is by comparison. From my personal experience and anecdotally online, it seems like people who just want to lose, for instance 15 or 20 pounds, and who already exercise regularly and eat a good quality diet (other than excess calories), might generally be very sensitive/responsive to even low doses of GLP meds. I lost 20 pounds and had highly significant appetite suppression from just 2mg/week dose of tirzepatide, for instance. @Steve_Combi also had substantial weight loss from low doses of tirzepatide and then retatrutide. I also got significant elevation of heart rate even at that low dose, so the “sensitivity” seems to cut both ways.
My brother, by comparison (obese non-diabetic) has needed to up his dose (currently 7.5 q week) to get anywhere near the same effect.
Retatrutide just seems to be not as good at appetite suppression compared with similar doses of tirzepatide, for most people (although every bit as good if not better with weight loss, due to glucagon agonism and/or much higher potency agonism of GIP compared to tirzepatide).
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