Over the past 25 years I've entered ketosis on very low carb diets like Atkins. I've entered multiple time because I keep falling off the wagon and put on a lot of weight very quickly. What I have noticed is that my muscle mass has decreased and my metabolism has dropped drastically. I am now 70 years old, so maybe some of the muscle loss can be attributed to age catching up. But the metabolism drop to about 1600 calories is not.

It is well known that on a low calorie diet (around 1200 calories) and doing only a small amount of exercise, muscle mass will be lost and in time the metabolism will fall. My guess is that when I start a ketogenic diet (very lo carb and low calories) it takes a number of days to enter ketosis. Of course after entering ketosis any calorie deficit is made up by the liver converting body fat into energy producing triglycerides and ketones. But during the few days that it takes to enter ketosis, there is no difference between this ketogenic diet and a low calorie diet. If entering ketosis numerous time (like 30-50 times), surely the body will take reactive action and use muscle and reduce metabolism to counter the diet (energy deficit) until kitosis is achieved each time.

If this is correct then it is not a good idea to to lower the calories while entering ketosis. But if there is no deficit in calories, why would the liver start converting body fat into energy producing triglycerides and ketones (if not needed)?

As you can see I am puzzled even after this long time of dieting. Where am I going wrong?