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Is there any meaningful difference between 18 and 23h fasts from a health standpoint?

Hello!

I lost roughly 50 pounds doing OMAD as a way to cut out snacking awhile ago and I’m going back to fasting in order to get back on track with weight loss, but now I get ravenous and basically feel hangry after my workout (just walking fast/light jogging) which is usually 18-19h into my fast.

I was wondering if there is any appreciable difference in the health benefits achieved by going for slightly longer periods, but less than 24h. If it makes any difference I eat in the evenings.

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Answer

For clean fasts, every hour past the 11th hour since your last insulin response is another hour of burning fatty-acids that were liberated from adipose tissue.

Edit: if you eat in the evening make sure it’s still about three hours before you go to sleep.

Answer

My advice would be:
(1) to listen to your body. If you are regularly getting hangry 18 hours into your fast, then stick to the 18:6.
(2) keep track of your own health metrics. Have your blood work done so you get values for your fasting glucose levels, triglycerides, A1C levels, etc. Are any of them out of the normal range? is there any sign you have insulin resistance?

Almost all studies on intermittent fasting focus on <24 hours, so there is limited literature on extended fasts. Here is one paper on extended fasts (really long ones!) – but be aware that one of the authors runs a center where they have people undergo water only multiple day fasts (i.e., has an acknowledged bias) https://doi.org/10.3390/nu14061183

(I include it so that you can see the blood metrics that those authors use to assess the effectiveness of the extended fast.)

Answer

The further beyond 16 hours, the more your body will be depleted of glycogen stores in the liver and muscles, and then somewhere after 20 hours or so then the body with switch energy sources again to any remaining fat on the body and does a ketosis thing and turns fat into an energy source called ketones.

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