I'm not as advanced as some, but I've been doing what I like to think of as a hybrid version of a V-Diet (currently on my 2nd time around). I eat one solid meal a day, aiming for similar macronutrient profile that I'd get with a shake (40-50 gms protein, less than 10 gm carbs, and whatever fat is necessary or unavoidable in the meal).
Typical solid meal: piece of fish or boneless skinless chicken breast or 8 oz steak, with a big-ass bowl of broccoli or sugar free cole slaw or cauliflower, maybe a half-pat or full pat of butter. The daily meal schedule: I like to have 2 shakes for meals, then train, then a post-workout whey shake, then my solid meal, and casein shake before bed.
Drinking shakes all day keeps me motivated not to cheat on my solid food, and gives me something to look forward to at the end of the day. I've been cheating by drinking a scoop of whey protein during my workout (15-20 grams, in lots of water, with a scoop of Leucine and Creatine). I've found this really helps keep me going in the gym.
I also do my own weight training routine, not the V-Diet workout. I don't like full-body training, and I think training heavy (low reps) is important. I have found that the "NEPA" off-day walks are super important... you burn calories without any impact on your nervous system.
I actually think the V-Diet would work better if you have some muscle. I don't think beginners have the muscle mass needed to burn calories around the clock.
I lost 15 pounds my first time on this approach (6 months ago) and this time (3 weeks in) I've lost 8 pounds. I'm 48 years old and 5'11, I went from 235 to 220-218, then lost a few pounds over the next few months. This time, I went from about 212 to 204, and I still have one week to go.
My experience was that even a week or two after the diet, I was still burning fat at an accelerated rate, even though I was adding additional solid food. I've been training since the 70's, mostly as a recreational trainer (I have average genetics at best, but I don't play sports so I train with weights). I hope to bench 300 pounds by the end of the year (just missed a triple with 275, a few weeks ago... solid double though). So I'm nothing special in the gym, but I'm not a beginner either.
The V-Diet does have some good concepts... for one, it's extremely regimented, which is good for people with poor portion control. You know exactly what you're supposed to be eating, and you know if you screw up. It's much easier to take in 'hidden' calories (or pretend you're not cheating) when you are eating solid food.
Also, by eliminating the solid food, you are dumbing down your taste buds, making it easier to keep it strict. When you are eating tasty food all day, it increases your appetite.... suddenly, you find yourself eating more than you're supposed to. I don't know if protein-sparing modified fasts are healthy long term, but for 28 days I think it's okay.
And the concept of making a lot of diet progress quickly is a good one... it keeps you motivated to stick to your diet after the PSMF is over. A diet that takes a long time to lose fat on might retain a bit more muscle mass, but progress is so slow that (IME) it's too easy to lose motivation... why not eat a second helping, when your diet barely seems to be working anyway?
By seeing progress fast, it keeps you motivated later. Also, this diet teaches you that being hungry is not an emergency... it teaches you how to cope with reasonable amounts of hunger, and it teaches your body not to panic in-between regular feedings.
Finally, I am starting to think that people who make regular attempts at getting cut have an easier time losing fat than the guys who rarely attempt to lose fat. A seasoned BB competitor would have an advantage over a first time competitor, when it comes to losing bodyfat IMO. I think the body responds better to regular dieting, than it does to the very occasional diet.
No scientific basis for that statement, just my opinion. But I think just like anything else, the more you do something the better you get at it... dropping bodyfat is probably no exception, IMO.
I plan on doing this type of diet twice a year... every six months. I lost 4 or 5 inches off my waist so far... I think I might finally have good abs some day (in the next year for sure). And the post diet rebound seems to be great for gaining lean mass and strength. It seems the calorie restriction primes you for a good rebound.
By the way, even though I take liberties with the V-Diet (with my daily single meal) and do my own workout plan, I've found other aspects to be crucial to success: lots of fish oil, casein protein over other types, flax meal for fiber/fats, lots of water, the NEPA (non-exercise physical activity) on off days. Fat burners/mood elevators (Hot-Rox or yohmbine) do seem to help keep you going.
Sorry this post was so long, but I've been having a good experience with it.