I don't know about cutting carbs to 20 grams a day. Seems to me that such an extreme restriction would rob the body of essential nutrients.
I was on a low-carb diet for years and it did me a world of good. After a bout of hepatitis I just fell apart. For the first time I was getting fat and developing an, I guess, arthritic condition in my joints. Not only did the diet rid me of the fat but it gradually reversed the joint problem.
I was able to stay on that diet because I kept it simple. I got a good idea of the carb content of foods and kept the carbs down to about 50 grams a day. On weekdays, that is. On weekends I went in the other direction.
I took example from a diet meant for bodybuilders. That was to keep the carbs to 30 grams a day during the week and go slightly in the other direction on weekends. I'm not a bodybuilder so I gave myself much leeway with the diet.
I believe that few people will stick to any sort of diet that is not simple.
Although I felt fine, I eventually got off the diet for the reason you mentioned, concern about nutrition.