For me personally I am unable to absorb the amount of fat the Keto diet recommends. And some carbs, like fiber, are important to include. I found minimizing my carbs, eating smarter, certainly play a big part in both my breathing and weight.
As Jean recommends, the Mediterranean diet is a nice balance of everything we need!
Good luck!

Thank you Jean for your reply. I will also look into a Mediterranean Diet as well.

I have found that a diet that follows the Mediterranean diet works really well for me and allows me to eat pretty normally. Russ is sort of one-of-a-kind, and is able to do a lot of things that most of us ordinary humans with COPD can't do. His disease is also small airway disease almost exclusively, as I understand it, which is quite different from what most of us with COPD have. Give the diet a try, but do understand that you may not begin to have the results he does.....although half those results would probably look pretty good to most of us!