You're right that in the short term you might need some extra carbs, but there are plenty of primal sources of carbs. Look at some Sweet Potatoes, Yams, Squash, etc. When you first switch to a lower carb diet your body needs to adapt to fat burning, which can take a few weeks or more depending on the person. Once your body gets switched over, you can do endurance events at pretty low carb levels. Check out this guy who won the Western States 100 (thats a 100 mile run) on low carb: Western States 100 – Low Carber Wins Ultramarathon – Steve Phinney and Jeff Volek Study | Me and My Diabetes .