I am not sure about that. Autolysis starts after about ~3 days, so one meal every three days halts autolysis just as it is starting.
Regarding the immune system, I am sure it takes longer than 3 days.
Now, to strengthen your immune system after fasting, make some homemade sauerkraut. The probiotic count in that is very high, and it is very cheap and easy to make. The reason being that the bacteria in one's tract comprise two-thirds of their immune system.