Hi! As a registered nutritionist I would say it completely depends on whether you can sustain the diet over the long term. Adherence is one of THE most important factors when it comes to fat loss. Slower and gradual fat loss is both better for the body and more easily maintained, though it may seem less effective at the start.
Both the HB and IF diets are renowned for being incredibly hard to follow and not very sustainable. In more recent years, fasting-focussed diets have actually been shown to be less effective than others as they can lead to increase in cortisol and inflammation! Both of which can reduce amount of fat lost.
The real question is, can you sustain it for 20 years?
I am the owner of the personal training studio Fitnessworks Balham. We don't use crashy/FAD diets with our clients. We solely recommend building good and healthy dietary patterns that focus on increasing consumption of lean protein sources, fruits and veggies! Pair this with resistance and cardio training - now that's the perfect regime! Basically, all the stuff that science actually says works.
Let me know if you found this helpful!