You can lift and do cardio just fine even on full blown water fasting for a couple of weeks, or longer if you're already heavily overweight. It's not the most

You can lift and do cardio just fine even on full blown water fasting for a couple of weeks, or longer if you're already heavily overweight. It's not the most pleasant feeling in the universe, and your performance won't be anything to write home about, but you will still be pretty functional. Humans have had to go without food for a while for most of their history, so it makes sense we would have adapted to live just fine through periods of scarcity.