End of 3rd Low-Carb Week: Where does my energy come from?

I posted this email in the “Joy of Running” email discussion list at the end of the 3rd week of low-carb nutrition. The title was “Where Does My Energy Come From?”

Hi Guys, So...

I started a low carb nutrition 3 weeks ago. I eat eggs, bacon/sausage, cheese, nuts, fresh vegetables for breakfast. A large mixed salad with olive oil and vinegar, plus cheese, nuts for lunch. Some serving of meat and vegetables for dinner. At least two fruits. Some cottage cheese or yogurt (both full fat, not low fat) for dairy. I do not NOT eat sugar, flour, bread, pasta, grains. I do not feel hungry. I eat as much as I feel I need. I do not hold back on calories, only carbs. I do not have any cravings for anything I do not eat.

While most runners want to lose 5 lbs, I have lost 11.5 lbs in 3 weeks. For the interest of science, here are my weight measurements every day since my new nutrition:

Week zero (pre-low-carb) : 171 lbs
Week 1: 171, 167, 167, 166, 164, 163, 165 (avg: 166)
Week 2: 163, 163, 164, 162, 162, 162, 161 (avg: 162)
Week 3: 161, 162, 163, 161, 161, 160 (avg: 161)

This morning I was 159.5 lbs, so 11.5 lbs down since 3 weeks ago.

The first two weeks I had good and bad runs. Bad runs were on hot & humid weather where I sweated a lot and end up aborting the run (happened twice). The third week (this one) I felt better, ran easier, stop sweating (sweating less than normal, for the same effort.)

Every morning this week, Tue, Wed, Thu, I went for a 10 mile run in the morning. The first day I ate a few nuts, being afraid to run without eating anything. The other two days I ate nothing and felt fine. Yesterday (Friday) was normally my rest day. I had an afternoon snack and then joined my wife for an easy 5 mile run at 10 min/mile pace. Back at home I was NOT hungry so I did not eat anything.

This morning I got up and went out at 6:30 am for a group run. I did not eat anything. Now, you would expect that being on a low carb diet and having run 5 mile last night without eating dinner, I would have completely exhausted my glycogen reserves so it would not be possible to run 10 miles this morning without some high carb breakfast or at least some Gatorade. I only had a few sips of water before I left home.

Well, I ran 10 miles at 8:10 average pace (mile 4 was 7:42) I felt that my running was effortless. I did not feel tired, or out of energy. I actually held myself back because tomorrow I am running the River Run half marathon.

So, where does the energy come from? Am I really burning (mostly) fat instead of (mostly) glycogen?

I feel I have more strength than ever. I am up to running 60 miles/week (average each of the last 3 weeks). I am really perplexed. It appears that without carbs I am running better. It goes against everything we have been told about runners needing to eat lots of carbs because they are energy and without carbs we will hit the wall.

I see myself as running a science experiment on myself. So far the results are very encouraging :)