You get used to low carbs. At first, your endurance is low, but your body quickly adapts.
The diet is also a personal things, it depends on how your digestion is.
Non-starchy veggies can provide some carbs. Now that I use a lot of digestive enzymes, I've tried nuts for a few days and notice that I digest them a lot better (used to see a lot of pieces of them in the feces...). I will experiment with soaking, I feel it could make a big difference.
Meat wise, liver has some easily digestible carbs in the form of glycogen. It should be organic and shouldn't be eaten too often (too high in copper).
One thing is sure is that when you will restore your intestinal health, your athletic performance will greatly increase.