It really depends on the body, people with weak immune system would be needing a lot of nutrients in their body so they are not allowed to skip their meals. I don't believe in these types of diet either, as long as you can control your eating habits you can definitely lose weight (doesn't apply to people with sickness tho)
It depends on body types which is not related to the immune system for sure. Skipping meal for any body type is not a good habit because it can damage your digestion cycle and also leads to the excess acidic content generation which keeps secreted to help in digestion.