My experience: 5 years ago I lost over 30 lbs on a low-GL diet, and did over 3 months of P90X to get myself fit to walk up Ben Nevis. On the day I weighed 129 lbs and no problems on the ascent (4000' of up), which I accomplished in the average time, even though I was nearly 60. The descent however was agony, even with supports on both knees and use of trekking poles.

I have not been up Ben Nevis again, but since then I regained most of the weight, and lost it again through IF, to average about 123/124 lbs. I can't say I feel absolutely nothing in my knees when descending the Fells, but I don't need supports and carry only one pole, more for balance.

Was 5 lbs the critical difference? I don't think so. Many IFers report significantly decreased joint pain quite early in their weight loss journeys. I am sure a real low carb WOE will accomplish the same.