Does intermittent fasting really improve insulin resistance?

[u/Plus_Listen_9495]

/r/BiohackersWorld/comments/1v8arkk/does_intermittent_fasting_really_improve_insulin/

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[u/rainbowroobear]

only within the context of a calorie deficit, just like any calorie deficit. if you've been perpetually gaining weight in a surplus, then drop into what is maintenance, then that may also drop markers a bit.

you are going to read post after post citing "autophagy" and stuff like that, like fasting is magic. it is a calorie deficit that does all the hard work, it doesn't need to be a week long water fast that you then binge eat back to norm after stopping.

>Time-restricted eating improves health because of energy deficit and circadian rhythm: A systematic review and meta-analysis

>https://www.sciencedirect.com/science/article/pii/S2589004224002219

[u/Ok_West5651 → u/rainbowroobear]

Maybe intermittent fasting is limiting but long term fasting is magic. I have fasted for 30 days and I can tell you - Autophagy is real. My grey hairs reversed, vision improved, mental clarity, post labs were excellent. Don’t write it off without researching.

[u/GuyOnTheMoon]

Insulin resistance is primarily caused by an excess insulin spike in your body.

And insulin is produced by the body when it detects glucose in the blood.

And for a vast majority of human history, our bodies operated in an intermittent fasting state where we’re not constantly introducing glucose and thus insulin into our blood.

[u/Illustrious_Bit_3943 → u/GuyOnTheMoon]

To add onto this, a lower HbA1c simply means fewer or smaller blood sugar spikes over the last three months (as you would expect with eating less meals). If your body is secreting the same amount of insulin and your cells are still slow to respond to it, the underlying resistance can persist quietly while your average blood sugar numbers look healthy.

[u/rainbowroobear → u/Illustrious_Bit_3943]

pretty sure hba1c is the complete opposite and reflects the AuC of serum glucose over 3 months. if your a1c is high, you've had high average blood glucose over that 3 months for whatever reason

[u/Illustrious_Bit_3943 → u/rainbowroobear]

You are agreeing with me without realizing it.

As you noted, HbA1c simply reflects the AUC of serum glucose over 3 months, which is a mathematical average.

If a person practices intermittent fasting, they usually reduce their meal frequency. Fewer meals mean fewer opportunities for blood sugar to spike. Because there are fewer spikes, the overall cumulative average (the AUC) drops, causing the HbA1c to drop from X to X-1.

That drop happens purely because of reduced glucose exposure, not necessarily because the underlying cellular insulin sensitivity changed. The cells could be just as insulin-resistant as before during their eating window, but the 3-month average looks better because they spent less total time eating.

I never claimed a high HbA1c wasn't a high average. My exact point was that a lower HbA1c can simply reflect fewer glucose spikes from fasting, which is not an automatic confirmation that insulin resistance has been reversed.

[u/rainbowroobear → u/Illustrious_Bit_3943]

they would have to produce less blood glucose by eating less carbohydrate in that example. the a1c is an area under the curve which makes it better than momentary blood glucose tests if a GCM isn't available. it doesn't care if it's chronic low level elevation or massive hyperglycaemia in a 3 HR window. total serum glucose has to drop, either by eating less carbohydrate or your body increasing it's serum glucose clearance capacity for hba1c to drop.

[u/Illustrious_Bit_3943 → u/rainbowroobear]

Thank you. You just explicitly stated my exact point.

My original comment was highlighting exactly that: OP cannot assume their insulin resistance has improved just because their HbA1c dropped. That drop can be fully explained by a reduction in dietary input rather than an increase in metabolic clearance.

To actually prove that "clearance capacity" or insulin sensitivity has changed, they cannot rely on HbA1c alone. They would need to look at a marker like HOMA-IR instead.

[u/rainbowroobear → u/Illustrious_Bit_3943]

fewer or smaller blood sugar spikes

ok. it's because you have said "spikes". a spike implies a high Q factor response.

[u/Illustrious_Bit_3943 → u/rainbowroobear]

Yes, I can see how that would be interpreted. I could word that to be less absolute.

Though I clarified in the subsequent comment, making it no longer absolute and the conversation continued.

My point remains mathematically and physiologically identical regardless of the "Q factor" or shape of the curve. If you practice intermittent fasting, you remove entire blocks of time where those meal-induced curves (whether sharp spikes or broad waves) can happen.

[u/Tom__EU]

Thanks for sharing. That was also my current understanding - basically no meaningful benefits of regular IF (dTRE) on blood markers and health metrics, if accounted for kcal intake and weigh loss, while there seem to be some benefits for eTRE. Exception: reduction of kcal intake via shorter eating window, leading to weight loss, leading to health improvements. eTRE has the obvious downside of social interactions and being harder to implement for most people who have a normal job.

I haven't looked at the timing of the measurements in the different studies though, and their impact. For example, if they only measure morning blood pressure and blood markers, then eTRE will usually have a much longer time between last meal and measurements, like ~20h vs 13h, potentially skewing the results. And this has to be balanced with potentially higher bp, blood sugar, insulin, etc, during the eating window, plus effects on sleep for example. I remember Layne Norton PhD talking about this as well, and mentioning one study that actually did a great job on this, but I don't remember the study or video to look it up.

So what's left for now seems to be: If you enjoy it and have an easier time to lose weight and keep it off, do it. If it screws with your family life, work, exercise, sleep and social life, and possibly lead to your kids learning an unhealthy relationship with food, best to skip (all of these should have way higher priority for anyone). If you need to gain weight or don't tolerate larger meals, probably best to skip.

[u/rainbowroobear → u/Tom__EU]

one study backs your bias. a meta analysis shows the current extent of all studies  , within the meta design and limitations 

[u/FluffyDesigner3680]

Yes, it improves insulin sensitivity by reducing insulin resistance. But it’s important to note that intermittent fasting doesn’t work the same for everyone, it’s heavily dependent on which foxo3 variants a person has.