What is safe amount of carbs to avoid muscle catabolism in a low-cal diet?

I am 6'1/210/14% bf. Looking to shed 20 pounds. what is a safe min carb intake to avoid major muscle loss? 100 grams, 50 grams?

That will be totally dependent upon how you respond to dieting, what actual diet you do, any aides you utilize, when you do cardio, how you do it, when you train, what you eat after training, etc. It's hard to give one answer, you really can't. Some do a CKD to lose fat, and those diets do not have carbs daily, so it's not all about carbs. It's about protein and fat even more-so than carbs when you talk anti-catabolism.

~SC~