http://www.bbc.co.uk/mobile/lifestyle/health/ask/common/bread/index.shtml said:
Brown v white bread
Bread of any type is healthy because it's high in complex carbohydrates and low in fat and sugar. It's also a good source of iron and calcium.
The extra health benefits of brown bread come from the wheat grains which give it its colour. Wholewheat grain is a good source of fibre, protein and B vitamins. With white bread, the husk of the grain is removed and only the inner part is used.
Brown bread
Wholemeal and granary contain much or all of the wheat grains, and these are the healthiest.
Other types are made from finely milled wheat where all the bran (and therefore most of the protein and vitamins) has been extracted.
White bread
In the UK white bread must, by law, be fortified with extra minerals or vitamins. In fact, it may have twice the calcium of wholemeal (although wholemeal has more iron and up to three times more zinc).
Also, beware of added salt in all breads. High salt intake can lead to high blood pressure, strokes and even some types of cancer.