Taking into account that this book was written 40 years ago, it's a remarkable text. Any groundbreaking text, when read decades later, does suffer from appearing dated and less complete than other more modern books on the same subject, but one has to bear in mind that any seminal work will, by its very nature, have less depth than those texts that follow it.
Szekely discusses the personal ethics of vegetarianism; cites centuries of well-known geniuses who were all vegetarians and then proceeds to show why freely choosing vegetarianism as a way of to a healthy life is both scientific and not as hard as one would expect, if one is used to eating flesh.
There are excellent discussions on toxic foods (including flesh) and why each food group is good or bad for the body. The first few "ten commandments" of vegetarianism may be suited to a slower, more restful world than the one we live in today, but the final quote from Henry B Stevens which Szekely uses applies not only to the food we eat but our whole way of life:
"If violence were no longer at the centre of our daily diet and land use, it would soon cease to be the foundation of our public affairs where at present war requires more than half the national budget."
While the statistics of how much of any nation's budget is allocated to war and defence weapons may vary depending on the century and the culture, that sentiment, coupled with Szekely's rational explanation of vegetarianism as a healthy way of life, is enough to turn the most ardent meat-eater into a vegetarian.