A grain of wheat is the seed of a plant. It consists of 3 main parts: the endosperm, the bran, and the sprout. The endosperm is very starchy and has no significant nutritional value. The bran, the outer shell of the seed, contains fibers. Finally, sprouts are where most of the nutrients such as iron and various vitamins are found. Thus, if we grind, for example, whole grains into flour, this will contain all the parts of the grain of wheat.
However, what is the case with the classic white flour, which we use most often? This type of flour is highly processed. It started from the same seed, but after many modifications, only one of the 3 initial parts remained: the starchy endosperm. Bleaching factors are added to the processed grains to make the final product look more appealing to the eye, as well as some nutrients after the natural ones have been removed. Therefore, processed products lack the nutrients and fiber that whole grains offer us.
Finally, it is worth mentioning that by consuming whole grain products energy will be absorbed slowly and steadily, as our body will have to process complex carbohydrates, which requires a lot of time and therefore provides us with energy for longer. This does not happen with the consumption of refined grains, as in that case, we consume simple carbohydrates.
Source: “The Body Book”, Cameron Diaz & Sandra Bar