Did a quick google and found this:
Is it all right to continue the ‘Sole Source’ programme if giving blood? The ‘Sole Source’ programme should not be followed for one week preceding blood donation and for one week after. In fact, a centre will refuse to take blood if they know the donor is on a very low calorie diet, because blood viscosity and volume are affected by the ‘Sole Source’ programme.
I remeber asking this question when I was on CD last yr. I think the answer was yes as long as you are feeling ok. I havent got round to it yet.....but you just reminded me there is a session in Hatfield tomorrow!
There may be an official answer, but I think thats what we were told last time!