You will not lose muscle on a 3 day fast, and the weight loss won’t be as dramatic either. Typically people put the weight back on - most of the weight lost is water weight as it is. 3 days is a general reset and is typically not considered a prolonged fast which could cause more of a general weight loss.
Dry fasting helps to clean out the body which would be in part contributing to why you are struggling to gain weight. There is so much mucus inside the average person that causes lack of absorption and contributes to malnutrition and malabsorption. If you continue to dry fast and keep up a good diet with calorie-dense foods, I am certain you will be able to gain weight easily :)
Do you have other symptoms than heart arrythmia?
Currently, I’m making the hypothesis that oxytocin is behind some of the benefits of prolonged/intermittent dry fasting. Zinc seems to be needed for the oxytocin / oxytocin receptor link and I wonder if you could be deficient in it.
In no special order:https://www.researchgate.net/publication/350631256_IS_OXYTOCIN_THE_PANACEA_FOR_LONG-COVID> A convincing cure for COVID-19 remains elusive, but beyond the horizon looms long-COVID. However, here, we propose a treatment: oxytocin. In this hypothesis paper we provide an underlying mechanism for long COVID: the oxytocin neuron could be infected by SARS-CoV-2 leading to a reduction in plasma oxytocin. It is postulated that the reduction in plasma oxytocin leads to the variable multi-system, remitting and relapsing nature of long-COVID. Numerous experimental data can be shown to correlate with oxytocin and long-COVID symptoms and conditions, thus providing strong circumstantial evidence to support our hypothesis
https://www.intechopen.com/chapters/51098>Zinc also improves the stability of oxytocin, and the stabilization effect is correlated with the ability of the divalent metal to interact with oxytocin. Zinc is essential for the binding of oxytocin to its cellular receptor [25,26].
Intermittent drinking, oxytocin and human health>Our hypothesis; regulating drinking behaviour through intermittent bulk drinking could increase oxytocin signalling
Gaining weight, especially muscle, is extremely easy to do when fasting
You will become very insulin sensitive and I have added on 5kgs of body mass (mostly half fat half muscle) after 5 day dry fasts if I ate enough. When I kept eating keto during the refeed I kept losing body fat but gained weight anyway post fast.
My next test will be to refeed with mostly protein and fat. Just meat, eggs, and water.
However, I’ve always felt best when drinking soylent foods post fast. Especially Mana but huel, particularly huel black edition, works very well. Mana is tastier though.