The number I've heard is 50g+.

I'm curious why you're losing muscle, that isn't typical on LC diet. Are you getting plenty of calories and protein? Protein should be at least .85g per KG of reference body weight (your goal weight).

So for you minimum of 45g up to around 79.5g unless you're very active then you can go up to around 2g per kg, 106g.

You might need to increase your thyroid dose. Best to get it checked out.