Reverse dieting is something I am quite familiar with. Coming from the typical (outdated) competitor background, low cals, low carbs, low fat (low damn everything except for cardio!!) a reverse diet was a good option for me at the time. After several low cal lose-gain weight cycles, cutting carbs, restrictive diets, and bingeing, the list goes on, I had a very poor relationship with food and had all but given up. With the help of my coach my calorie intake has more than doubled over a period of around 10 months.
The purpose of a reverse diet is to increase metabolic capacity. This is what is claimed, however this is not actually true in the sense that your metabolism/BMR doesn't actually change. Your NEAT however, does. This often gets incorrectly correlated to 'eating more but still losing weight so its magic' it is not.
Your body, when fuelled correctly, will function correctly. And this means metabolism will actually work at the rate it’s designed to work. By eating too fewer calories the body will try to make do on this. It will try its best to function on less fuel, and most of the time it will also try to do MORE on less. The problem with this is that you cannot trick your body. You can try to, and you may get away with it short term, but sooner or later your body will say hey, I need more wtf are you doing to me? And you will binge. No one can stay compliant forever on an amount that is designed to make them starve to death. Your body wants to survive, it wants to be a little bit fat, and it wants to protect itself from starving.
The 'reverse diet' has since become quite controversial. There are some claiming that it magically increases metabolism. It doesn't
While I believe there is benefit to slowly adding calories in SOME cases, for most, it is a waste of time being in a larger deficit than required for any longer than necessary. Standard practice after a diet phase is to get back up to maintenance as soon as possible.
When one increases calories, the natural response is to move more. It happens subconsciously. We eat more, we have more energy to burn. Our NEAT goes up - our non exercise activity thermogenesis, our day to day moving around.
If you are in a deficit, you have low energy as it is and you don't feel like doing an awful lot. Those waiting side of stage to compete and often just lying down somewhere trying to preserve their energy. Had they eaten a decent serve of carbs, then this would be a different story.
So when once increases calories (generally by way of carbs on a 'reverse') then what happens is they have more energy, so they move around more - they can train harder at the gym, they have energy to get up and move around more - and as such, their energy expenditure increases. So, they are technically still in the same calorie deficit, they are just eating more and also burning more.
But the belief is that somehow as they are eating more (yet still losing weight!) that it is magic, and increasing metabolic capacity. It is not. The law of thermodynamics still stands.
I also used to believe this, but quickly learned that the increase in NEAT is a far more sensible explanation.
If someone has had a hard time getting used to the idea of going from a fat loss phase, to now a gaining phase without prior experience of a gain, then this might be a little tricky for them to get their heads around so in this case it can be helpful for them going slow. The process does have merit in that regard, and there is a lot to be said of competitors who are afraid to ever eat more than 1200 cals a day - for them being able to slowly increase but not see the scales jump up, then this can help.
But aside from that, generally it is best to stay on as high a cals as you can, all of the time. Always diet on as many calories as possible.
So in terms of the reverse diet, it is not some magic thing that increases metabolic capacity, but it still can be a useful tool in some cases to help those who may be a little intimidated by the thought of actually having to eat more