Which fasting pattern is better? -Fast 5 consecutive days every month or fast 15 consecutive days every THREE months?

Fast 5 consecutive days every month is pretty popular in news recently.
It is proposed by Dr.Valter Longo based on his research and clinic trail results.

To get detail information about 5 consecutive days fasting benefits, Pls google Valter Longo and FMD.

However, this forum seems to advocate much longer fasting period-- 15 days or more. So my question is :
Which fasting pattern is better or more effective? -- Fast 5 consecutive days every month or fast 15 consecutive days every THREE months?

Are there any study to compare the above mentioned two fasting patterns?
Did anyone here tried both of above mentioned fasting pattern before and how do you feel/compare after your trail?

thanks for any information or advice.
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