My daughter recently bought me some inulin to try as she had heard it can help you sleep.
I can't honestly say it helped me sleep at the time, but a side effect is that it is helpful with bowel movements!!
More recently I took some on holiday with me - for my bowels, and this time I do think it helped me sleep! It may depend on why you're not sleeping - initially I think I had things on my mind whereas more recently I didn't, but was having trouble dropping off.
Anyway, I thought I'd share just in case it is helpful to anyone else. I mix a teaspoonful in a glass of water before bedtime - not every night, but just if I think I need a little help with bowels or sleeping!