To grow grain:
As you may have heard before, it’s not just us humans who eat grain products. No, also quite a lot of animals are fed with grain! And now imagine this: about 80% of all grain is given to animals, such as cattle, pigs or chickens, as feed. The reason for this is meat fattening. This is because to get one calorie in meat, cattle must consume seven plant calories.
So only 20% of the grain is processed into food for us humans. And of that 20%, only 3-4% of the grain becomes whole grain products (Here’s some info on whole grains). The other part, the majority, becomes wheat flour, which, compared to whole wheat flour, is poorer in nutrients and minerals.
To take a look at other sources of information, a website (see below) is also mentioned here. On the page you can see how the use of cereals looks in Germany. There, namely 60% is used as animal feed and 20% are grain products for humans. The remaining shares find their use in industry or as seeds.
So, in summary, most of the grain is fed to livestock and only a small portion is processed into grain products.
Münzing-Ruef, I. (1999): Kursbuch gesunde Ernährung. The kitchen as a pharmacy of nature. Munich: Zabert Sandmann GmbH, p. 211
http://www.bauernhof.net/nahrung-fuer-mensch-und-tier/ (retrieved, on 07/11/2017)