Normally the body uses various sources for energy. In everyday life mostly a mix of fatty acids and glycogen, and to a lesser extend amino acids, and more obscure things like lactic acid if available, right?
For the past 30 years or more, since being a teenager I've been having crashes and since earliest childhood problems with strength/endurance/simple things like walking up inclines or running/lifting weights/etc/basically any kind of exercise. I kind of have the feeling that my body is mostly running on gycogen because the amount of energy is so limited and then I hit the wall. I've been running for 6 years now, but still don't get further than 10km without bonking. When I'm active in any way (also working behind a computer) then I can fast a max of 2 hours. Every attempt at trying to stretch this, or to be less dependent on (mostly slow) carbs ends in a massive crash that leaves me feeling miserable for several days. Every attempt at trying to be active before breakfast ends in a crash. Sometimes, just having a dinner with 7g more protein and 7g less carbs results in a crash. Don't ask how I felt over Christmas, trying to enjoy pork tenderloin for three days. The annoying thing is that I'm not the only one in my family with this issue. I never really thought it was an issue until my sis asked me to help with understanding something for her. And now I got sucked into this.
So basically, is there a way to teach your body to provide a steady flow of energy without being sick the whole time? I've been on a few trips lasting 2-3 weeks where carbs were more limited than I'm used to, and I felt weak, confused and miserable the whole time. Btw, my blood sugar is fine, and this is not a weight loss questions.