To maintain weight, it’s not enough to just do a diet for a couple of weeks. It’s important to change your lifestyle, build new habits, make new eating part of your life. And I think it’s cool that modern weight loss platforms like https://unimeal.com/ are focused on showing that it’s not enough to just quit sugar for a while. Try making a meal plan that you don’t need to quit. Or even don’t want to.
Any diet book can help you lose weight, but keeping the weight off is the real challenge. Most people gain back more weight than they lose after ending a diet.
As someone who went from 100kg to 85kg, I know how challenging it is to maintain a lower body weight because there isn't a day that my body doesn't fight me to try and get back to being overweight again.
The important thing is to build good eating habits, setup your environment properly, and ensure adequate physical activity. Some people might need drugs like Ozempic to make any progress, but it's a lifelong commitment.
No book but videos / YT channels, articles, blogs about ketosis and nutrition, spread over many many years. Mark Sisson, Low Carb Down Under, Anthony Chaffee, Shawn Baker..and many many others that come to mind. Main point is to learn about nutrition. Actual information. Not the garbage from the medical/food industry. Understand fatty acids, carbohydrates, delve deep into ketosis.
Next thing is to start burning calories. I can safely say that gym is waste of time. Actually the biggest waste of time. Walking is not bad but running is the best.