D. de Quélus, the author of the 1720 Natural History of Chocolate is a hard man to pin down. He goes by Quélus, Chélus, Caïlus, or Caylus. In The Universal Dictionary of Trade and Commerce, the author of the entry on cacao refers to Quélus as “a judicious traveler who had lived 15 years in the American islands, and who assiduously observed all that he asserts” (n.p.). That is indeed how Quélus presents himself in the preface to the treatise. He identifies himself as a person who has not only traveled, but also performed "Chymical Analysis" on chocolate in the hopes understanding its wonderful effects and defining chocolate as clearly as possible. As the result of these experiments, Quélus claims that chocolate should be a dietary supplement, a “vehicle” for health.
During the seventeenth and eighteenth centuries, empiricism led to the development of early chemistry and it gave science a new authority. Many previous cacao scholars attested to chocolate’s use as an indigenous medicine that was able to treat a wide variety of ailments including impotence, thirst, digestion, and fatigue. Writing in the high age of natural history, Quélus instead promoted chocolate as a “vehicle” to supplement a regular diet, not as medicine in its own right. Taken this way, he argued, people could balance their health needs and restore themselves to a healthy state: “when there is a Necessity for such, Chocolate may serve for very proper Diet, and an excellent Vehicle, wherein to take a Medicine at the same time” (Part III/Chapter II/Section II). A twenty-first century analogy to chocolate the way Quélus prescribed it would be vitamins or fish oils that do not necessarily fight a disease but can promote a healthy state.
Chocolate writers including Antonio Colmenero and Thomas Gage had claimed that chocolate may result in obstructions and opulations of the body if consumed in excess and preached moderation or, in Colmenero’s words, “mediocrity.” Quélus instead discovered in his experiments that chocolate would only add more nourishment and fat to a person’s body and bring enhancements, not cause harm: “Chocolate is a Substance very temperate, yielding soft and wholesome Nourishment, incapable of doing any Harm” (Part II/Chapter I). Therefore, Quélus counsels readers to enjoy chocolate as much as they wish to, all the while balancing the humors.
That said, under certain conditions, moderation is best. Quélus advises people who maintain a “juicy” diet with plenty of fat and wine to stay away from chocolate.
On the contrary, I would not counsel the daily Use of it to such who are very fat, or who are wont to drink a good deal of Wine, and live upon a juicy Diet, or who sleep much, and use no Exercise at all. (Part II/Chapter II/Section IV)
"Juicy” substances such as fat and wine were mostly consumed by wealthy people whose bodies were extremely biased towards the warm humor. Therefore, chocolate as a hot drink would only bring more nourishment than was necessary and result in an imbalanced state.
Chocolate naturally has a cold property. Most chocolate writers beginning with Colmenero were concerned that this intrinsic coldness could harm people who were already suffering from a cold humor. As a solution, they suggested that spices be added to the beverage, as Mesoamericans had done, in order to balance out its cold state. However, Quélus counters that
if this intrinsick Coldness is no more to be feared, it must be own’d, that it will be henceforward ridiculous, if not pernicious, to join it with hot acrid Spices, more likely to alter and destroy its good and real Qualities, than to correct the bad ones which it has not. (Part II/Chapter I)
He argues that chocolate should not be tempered. Chocolate is already balanced and beneficial to health as is; the coldness is only a part of chocolate that should be embraced. Artificially adding hot ingredients to chocolate could diminish its beneficial state and cause more imbalances in the body when consumed.
Writing for the age of empiricism, Quélus tried to perform repetitive experiments to identify chocolate for the public. He chose practical experiment over the wisdom of the past as his guide to chocolate’s benefits. Indeed, he points out that though the reader might notice “its Resemblance to the particular Treatises of Colmenero [and] Dufour...Upon examination, so great a Difference will appear, that no one can justly accuse me of having borrow’d anything from these Writers” (Preface). By heavily relying on experiential results, he identified chocolate’s unique role as a dietary supplement and its temperate values. Through this treatise, chocolate could maintain its authority as a health product in the eighteenth century, one that could be consumed without fear. However, by the end of this era, chocolate migrated towards becoming a candy that is a mutant form of cacao without any healthy benefits.
Postlethwayt, Malachy. The Universal Dictionary of Trade and Commerce. Vol. 1.  London: W. Strahan, 1774.
Quelus, M. de. Natural History of Chocolate and Sugar. Trans. R. Brookes. London: J. Roberts, 1730.