Right, I have one question about ketosis in general and then one about running, possibly they are linked though.

After reading the Low Carb Performance book over xmas I decided to give it a go starting about 3 Jan. I do a weekly slow mixed road/trail run of about 8 miles which (high carb) never caused me any trouble. Last week (5 days into low carb experiment) about 5 miles in I started to feel lightheaded so walked for about a mile before resuming running at a slower pace. Felt awful afterwards for hours. This was the first time I had tested using Ketostix as they only arrived that morning (cannot buy them without prescription in UK). It tested MAX on the scale. I think almost certainly I was dehydrated on my run as for some reason I had drunk hardly any water that morning (normally have a lot more before a run) and also I'd had a coffee.

Have been keeping carbs low (not counting, but must be under 50) every day. Interestingly, having tested with Ketostix, after the first time it's always been about midway down the scale. I know Ketostix aren't the best way of measuring ketosis, could that be down to hydration though?

Had one day of slightly higher carbs at the weekend (again didn't count, probably at the lower end of 100-150 though) and will probably do this every week. Tested with Ketostix over the next couple of days and again tested to the middle of the scale.

Tested again before my run this morning and it tested totally negative. Not sure why this would be. Am I not in ketosis? Or has my body just completed it's "adaptation"? Anyway, felt great on the run. Didn't feel tired at any point and finished faster than I started.

Just wondering what this all means, and whether it would be a good idea to go low-carb all week and then "carb up" for a meal a day or two before my long run? What do other low-carb runners think?