- White bread is not devoid of nutritional value

But it is processed food, which means it has indeed lost some nutritional value. Moreover, the way white flour is processed by our body is different from the way wheat or oats is - in very simplistic terms, the reduction of fibre content in white flour means that when it is consumed and processed, glucose / sugar from it is released very quickly into our body. Our body can handle that, once in a while. But repeated sugar spikes (and falls) isn't good for the health. And that is why doctors today (especially in India) advise you to eschew white flour in favour of others (wheat, oats, millets etc.). But yeah, the way you consume it, with other foods, matters too (and from your other comment, it does appear you follow a reasonably good diet, with a healthy outlook - without unduly obsessing over it).