Will the MC make me GAIN weight?

Hi everyone, am really desperate for some answers!

So I am hopefully going to start a 21 (will push to 30 if I can!) Day cleanse starting May 19th. I have been on a low-carb diet since October, sort of Atkins-style. I definitely practice more "clean" atkins rather than "dirty" atkins ("dirty" atkins is when people basically live off cheese and heavy cream, lots of very greasy food, pork rinds etc). I don't handle dairy well so the only dairy I ever eat is maybe a bit of feta or goats cheese on a salad. A typical day for me is
Breakfast- 2x egg omelette cooked in butter with spinach and mushrooms
Lunch- salad with lots of leafy greens, avocado, red onion, pickles, any meat- usually mackerel, tuna, smoked salmon, chicken or ham, drizzled with extra virgin olive oil
Dinner is usually fairly simple, just meat and vegetables. Sometimes will make something like a fish pie using coconut milk and cauliflower mash, or a shepherds pie again using cauli mash instead of potatoes.

So as you can see it's fairly "clean" but very low carb. I try and stay under 20g of NET carbs per day.

I am really worried with the Master-Cleanse that with all the carbs and Sugar from the syrup that I will actually gain weight. I've read a few posts saying that if you follow a low carb diet then a Master-Cleanse is not recommended at all. I also read only lady's review saying as soon as she went back to her low carb, meat based diet she gained all of the weight back. I desperately want to give the Master-Cleanse a go since I am unable to budge the last 20lbs. I really like low-carbing as it takes away all of my Sugar cravings, keeps me full for a long time (before when I was on a low fat diet I found I was always hungry/craving things but that disappears on a low carb and higher fat diet) so I definitely want to stick with it after the cleanse. But will the cleanse be completely pointless for me?
Sorry for the long post. Really hope I can get some answers!