In reply to GrendeI:
Where are you going, and how good is your base fitness? I had similar worries earlier this year. I'm just back from a trip to the Andes and had no fitness problems at all, despite having stopped running months ago due to sore knees, and a diet not dissimilar to yours (I convinced myself that was simply pre-altitude carb loading!)
I had a similar experience a few yrs ago, having done no exercise of any type for 3 months, went up Toubkal in winter with no dramas, much to the annoyance of my slower, less fir husband who'd spent months doing proper training.
If your base fitness is good, you should be fine, especially if you're going high and will have plenty of acclimatisation days to get used to the hills and your pack, and work on the fitness 😊