In a word, none.
Seriously, bread is high carb, high salt, high GI, inflammatory, acid-forming and scores 100 on the Insulin Index
Unless organic and artisan made, it will usually be made using the Chorleywood Process (80% of British bread is made like this) which takes only 3.5 hrs from flour to packaged loaf and 2 hours of that time is cooling it down enough to package ! CBP uses additives during the process which don't have to be declared on the ingredients label.
Under UK law all flour other than wholemeal must be fortified with (and it's industrially-made rather than naturally occurring) calcium, iron, niacin and thiamine. Some manufacturers also add vitamin D.
Some nutritionists and doctors, for example Janette Jackson, author of The Drop Zone Diet and Dr Sarah Hallberg MD (recommend her TEDx lecture on YouTube) say that eating a wide variety of natural foods is better than fortified foods and supplements.
Increasingly, people are becoming intolerant of proteins in bread such as gluten.
Lastly, most wheat, corn (maize) and soya in the U.S. is genetically modified now. Although the EU says that anything over 0.9% must be labelled, if you're eating non-organic bread you have to read labels.
Eating a lot of bread won't help your diabetes.