The Royal Society for the Protection of Birds said it holds little nutritional value and suggested instead giving them a range of alternatives, including cake crumbs, crushed biscuits, grated cheese, leftover jacket potatoes, breakfast cereal, overripe strawberries and porridge oats.
Granary breads with seeds are marginally healthier than cheap white sliced loaves but still simply fill the birds up without doing them enough good.
Experts say the issue is particularly important at the time of year when young are being raised.
Val Osborne, head of wildlife inquiries at the society, said: “There are many other household foods that would be much better for them.
“Bread doesn’t actually contain any of the vital ingredients to provide birds with the energy they need to breed and feed.
“The RSPB is asking people to consider alternatives such as porridge oats, cake crumbs and potatoes.”