Or, how about I just do and “cleanse” with 23 hours of cardio per day and only drink water?
In the short term, and especially by the metric of scale weight, crash diets work. They can and will strip pretty significant amounts of weight off your body in a quite short time frame.
Of course, a lot of this is water balance shenanigans and muscle glycogen depletion. But if you are burning 3000 calories per day between your Basal Metabolic Rate and a crazy amount of cardio, you will lose body mass as well. Of course, with that level of daily deficit, you are pretty much guaranteed to lose a whole bunch of muscle mass along with it, which is pretty damn counter-productive.
So assuming you do one of these nutty cleanse things – shocking fact: a cleanse is just a crash diet with a more publicly acceptable name – and lose 20lb on the scale, what happens next?
Well, if you’re anything like the vast majority of people, and immediately go right back to doing what you were doing before, you will gain probably half of that weight back essentially overnight. Water balance shenanigans, remember? Another half will come back over the first week as muscle glycogen refills and your body works to convince itself it isn’t in imminent danger of starvation.
So you were miserable and hated your life for a month to lose 5lb. And reward yourself with cake. And two months later you are heavier than when you started, because you didn’t focus on changing anything in the lifestyle that got you fat in the first place.
A quick note about this whole cleanse thing. You hear a lot of people say that they did a cleanse that had them only drinking fruit and vegetable juices for a few days or a week and they felt a lot better, their skin cleared up, they slept better, and basically it was even better than the second coming of buddy christ. Allow me to reframe this so it makes sense in context. Take someone who is eating the Standard American Diet, which is about as terrible as a diet gets and as Lyle McDonald says would be improved by switching to only ingesting skittles and bug spray. Cut out all processed crap and get them to consume a whole bunch of fruits and vegetables which are pretty good for the average person, and fantastic for someone who probably has a ton of nutrient deficiencies from eating garbage all the time. You think they’re gonna feel better? No shit!
The same thing happens when I tell people I’m celiac (no gluten or beer or burgers or donuts or cake or fun, ever). They always say “oh, I went gluten free for a month, and I felt SO much better! I must be gluten-intolerant too!” Gluten intolerance IS a thing. But most people who feel better when they cut gluten out of their diet feel better because they switched from eating a crap ton of processed food and gigantic bowls of refined carbohydrates to eating salads with chicken on them. See a trend here? Go from eating garbage all the time to literally anything else, even NOTHING, and you will feel better.
Anyways, crash diets. They work in the short term. And they have their place in your toolkit, namely when you have been an idiot and not given yourself enough time to get into good shape for some specific event or as a way to kick off a longer-term fat loss program.
If you want good information about extreme diets that actually work and are less likely to put you in the hospital, check out Lyle McDonald’s site. His RFL program works. I don’t know anyone, myself included, who has been able to do the Extreme RFL. Good luck if you try that one. And I’m going to go on record as saying that is a Very Bad Idea, mostly if one of you tries it and dies you won’t/can’t blame me. We are not doctors.
But if you want to stay less fat, rather than just temporarily getting less fat, you should probably consider a more moderate approach, and working on changing the habits that got you to the place you no longer want to be. People who rely exclusively on crash dieting are kinda like Nascar drivers – going nowhere, but with a crap ton of stress and noise.