A high glycemic index causes your blood sugar to spike. A spike to blood sugar causes an imbalance of hormones (especially testosterone for men). This imbalance of hormones then causes the sebum production to raise and that causes pimples.

White bread has a glycemic index which is considered high so it will cause sugar spikes. However whole wheat bread has a lower glycemic index which doesn't really cause your blood sugar to spike.

Some people say the gluten in bread also cause acne. I don't know that much about that but I always eat whole wheat bread without having any problems!

I changed from white to wholemeal as part of my health and skin care routine.even after changing you still need to limit the amount of slices/bread you eat,ok saying whole meal is better than white,then thinking i can eat as much as i like,dont think its the case,you need to limit the amount as well as the type of bread.