This is a terminology problem - there is no specific definition for wheaten bread in the way that there is for wholemeal. Any clues from the labelling as to the content? And does it have any added fat?
If not, then brown bread is 3 syns a slice and I would use that as a guide.
I found the nutrional content for Tesco wheaten bread and its 3 syns a slice! yum! I cant imagine its like soda bread - I think it would be much better for you - but yep - its a terminology thing - and something you really are missing out on in England!! Yummy!
