This is the book that will help you fine-tune and optimise your LCHF/keto regime.

I went on the keto diet in 2019 and, with very positive reinforcement from early results, have kept it up since. Given the health benefits, I plan to remain on in indefinitely. But things gradually change, fat may creep back up, and constant monitoring and tuning is needed. This book helped me get back on track.

The Art and Science of Low Carbohydrate Performance, by Jeff Volek & Stephen Phinney 

These highly qualified authors offer an in-depth understanding of the biology of ketosis, backed by scientific experiments from the literature and their own experience. They advocate regular measuring to monitor the efficacy of any interventions, just as I had already been doing for years, so I immediately liked them.

I was primarily just cutting carbs. But my daily measurements showed I was only achieving very mild ketosis (0.5 to 1 mmol/l). They helped me understand that the balance of my food intake contained too much protein and too little fat, and that too much protein won't allow you to stay in deeper ketosis. (They explain why).

By acting on that, I could halve my body fat in three months: it had crept back up to 18% and I brought it to 9% (monthly average). Wow. Evidence-backed results.

Another eminently actionable contribution was the wealth of tables with the content of various kinds of food. Really specific and detailed. I keep referring to them.

Last but not least, this book is specifically written for athletes and goes in depth into how and why keto will provide superior endurance in a way that carb-fuelled nutrition can't. Although I am not a professional athlete, I have been running a dojo for 20+ years. As a martial arts coach I perform intense physical activity regularly and these insights helped me improve my own athletic performance.

Perhaps slightly too technical as a starter book. But for people who have already seriously committed to keto, it's the go-to resource to get the most from it.