Flax (same as linseed) seeds do the job and you can get them fresh whole or ground from here http://www.flaxfarm.co.uk/ they're really friendly and helpful. Also their flax oil is fantastic, the best and heathiest thing on salads. I buy the 2.5 litres sold for animals and divide it into containers and freeze it, it's so much cheaper that way. I take 1/2 a tablespoon of whole flax every morning in water that cures constipation easily but I find swallowing stuff easy I know some people don't! If you can swallow a pill dry then you can take flax this way. You can use ground flax too sprinkled on pretty much anything. If it's ground you get the nutrients as well as the fibre (your digestion can't break down whole flax seed). Also try the flax bread recipe.