I have done the keto diet and lost 14 lbs. A true ketogenic diet is 10% carbs, 25% protein, 65% fats. Fiber carbs do not count, though you are not allowed high carb fiber sources like beans. I personally would get most of my fiber from nuts, seeds, and a fiber supplement. Yes, keto flu can happen, but there are ways to mitigate it. Up your sodium intake a bit. Take a potassium and a magnesium supplement. I did watch my calories on keto. I'm not sure how well keto would fit with vegetarian. Most of my protein on keto came from meat (fatty and lean). If you have questions I'll answer them the best I can.