One of the foremost proponents of Pure Beer was MP W. Cuthbert Quilter. The following is a quote from an article he wrote in 1887.
"As regards the effect upon the health of the nation of so-called beer of the various kinds, I cannot do better than give the following statements of Mr. W. C. Young, public analyst for the districts of Poplar, Whitechapel, and St. George's-in-the-East; and of Dr. Bernays, the eminent chemist of St. Thomas's Hospital.
Mr. Young says:—1. Barley Malt contains important nitrogenous and mineral constituents, possessing valuable nutritive, digestive, and strengthening properties.“The Nineteenth Century Vol XXI” edited by James Knowles, 1887, Pages 130.
2. Maize Malt, saccharine, and other malt substitutes do not contain these matters, or only in very small quantities.
3. Beer brewed from barley malt differs from that brewed from any of its substitutes in containing the above-mentioned important constituents.
4. Beer brewed from malt substitutes is practically only a solution of alcohol, so that of all the properties a beer should possess, it has only the worst—that of intoxication.
5. The alcohol produced from barley malt is purer than that from maize, rice, &c., the latter containing appreciable quantities of fusil oil.
6. Beer brewed from these substitutes will not keep sound for more than a few days.
7. After a long study of the subject, I have been assured by a gentleman who was for many years a Medical Officer of Health for one of the poorest quarters of the East End of London, that in the majority of cases which had come under his notice of the worst form of confirmed drunkenness, he could trace the effects to the continual drinking of such beer, or what is commonly known as 'fourpenny ale.' He attributes much of the squalor, dirtiness, and wretchedness of the poor in his parish to the use of this 'fourpenny ale.'"
In case you're wondering "fourpenny ale", or X Ale, was the standard Mild of the day. It was so called because it cost fourpence a quart. I never realised Mild could be so bad for you.