It may disappoint you slightly to learn that Garmin elevation is hugely innaccurate. Spot elevation is fairly good (ie. when you're stood still), but I've found it to be as much as 100% out on runs before. For example, a hill reps session off road last year I worked out from a map at around 2000ft total (250ft/rep x 8) and yet the Garmin read around 4200ft!
Fell Runners use a simpler formula based on climb/mile. Although it's now metric so I can't remember it exactly.
Using your formula the Borrowdale Fell race (as an example) comes out around 410-425% depending upon the precise route taken (7000ft in 16.5miles). Most of my runs would be well over 100% and probably closer to 200% each time.
Actually, fasting isn't like that at all. I sometimes fast for a day and regularly miss lunch out. I have no reason to lose weight and no intention of doing so. I do it for two reasons. Resting my gut (I have crohns) and increasing my ability to burn fat for energy (helpful for distance running). I also train on empty regularly and find it perfectly agreeable. It can't have hindered my training much either, I ran 10m on Sunday morning over the hills without any food beforehand and didn't really eat until about 11:30. I'm not advocating always doing these things, but just pointing out that the human body is perfectly capable of fasting with no adverse effects.