The Keto diet is a hot topic these days, but it's really nothing new. It's mainly a weight-loss diet with very low-carb (just those in non-root veggies) and high fat.
The idea is to train your body (it does work) to burn fat for energy instead of carbs. When that happens, you excrete ketones mostly in urine. The high fat diet (greens with plenty of olive oil, juicy meat or fish with plenty of butter, etc) stave off hunger and combat carb addiction. That's the idea.
Adjustment to a keto diet can mean enduring the "Keto Flu" for a week or two as the body readjusts to fat burning.
Everything about getting in to good shape is difficult.