Ive been thinking about this Charles. I think you may well be spot on with the size of the potato, good thinking
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Thought it might be worth mentioning for anyone else looking in, that something similar happened to me - I thought potato felt a bit spiky - when I revisited 3 and paid speciall attention to timing, it seemed to settle my blood sugars really well

then it was easier to sort out the potato. Nowadays, I'll choose a sweet potato. Seratonin being my strongest leg so often its through the winter for me. I also prefer it in chunks with salt and black pepper as its less sweet than when I mash it