Okay, so here is the story in a nutshel.

2007-2009 - regularly rode 150 miles a week, in great shape
June 2009 - broke my tibia into little bits riding a horse, bed ridden for months, multiple surgeries
April 2010 - Gained weight due to couch potato status started Medifast diet(lost 34lbs)
September 2010 - finally able to walk well enough to start riding my bike again, left quad is obviously smaller than right. Clearly significant muscle wasting from underuse for months.
Today - After just a week of riding I notice that I am not getting winded AT ALL riding at at just 1 mph slower than my previous (2009) average speeds on the same course.

This makes no sense. I am out of shape with muscle wasting in my left leg. I had expected to take many months to get back to where I was. The only difference is the diet. I am on a very high protein, very low carb, low calorie(900), low fat diet. I am in ketosis. I lost 34 lbs but that only puts me where I was prior to the break, so it isn't a weight issue.

I should be huffing and puffing like mad, but the cycling is abnornally easy.

Anyone else switch to a low carb, high protein diet and notice that they don't get winded?