Cutting a whole food group out of your diet can be dangerous, unless you take steps to make sure you're getting the required vitamins and stuff from other sources.
I tried Keto for a couple weeks, so like the opposite of Veg/an? I even made sure I wasn't getting too much carbs/sugar from stuff like peppers (max half a day, eaten with plain quark) Apparently I was a bitchy mess. All I remember is drinking way too much black coffee, thinking about all the food I wanted to eat but couldn't, and not having energy for much else after tracking what food I ate and its calories and how 'much' else I could eat for the rest of the day. One day after work, I cracked open an energy drink and walked home to somehow counterbalance the calories I had drank, and then thought "this is fucking madness"