Let's do some beer-math
In this case beer made of barley, which is the preferred raw material. An average beer has 43 calories per hundred gram according to USDA’s database. Of 1 kg of barley you can produce approximately 730 gram malt. This malt in turn is converted to 4.7 liter of beer (this according to FAO's Technical Conversion Factors). We estimate, based on FAOSTAT categories of use that 20% of the barley is used for brewing, 132,886,519 tonnes * 20% * 4.7 gives 124,913,328,000 liter of beer, which equals 53,712,730,970,000 calories. This would be 21 calories per capita and day (assuming that also infants drink beer!), 1% of our energy intake.
If we compare that with the direct use of barley as food, 20% of 132,886,519 tonnes of barley has 94,000,000,000,000 calories which means we lose almost half of the energy by making beer out of barley.But then we also have “dregs” the rest product that is mainly used as animal feed, so some of this enters our food in another way.
(busy working with my new book)