Scientists speculate that when the whole grain is milled and becomes whole-wheat flour, the digestion and absorption process is still fast and can induce higher insulin responses.

Theoretically, milled grains are less beneficial than whole grains that are not processed.

According to Harvard's website, the glycemic index of white bread and whole wheat bread is the same. The glycemic index depends mostly on the particle size of the food. When whole grains are milled, the particles are similar in size to those of white flour.

Thicker penne have a lower glycemic index than thinner penne. Pasta left al dente also has lower indices than pasta left to mush.

The amount of fiber, minerals, antioxidants, and phytochemicals are just as important as the glycemic index.

What makes nutrition confusing is the news cycle and fad diet books warning against gluten and carbs, and the marketing of meaningless things like multigrain bread. The science, however, is not confusing.