I can speak to how the Enlightenment affected the French diet (and to some extent medicine) through the emergence of restaurants. Lets say I was visiting France. Before this era, if I wanted a meal in France as a visitor, I had few options. I could visit the master caterer in his guild, but the guild system was highly organized and he could not legally prepare the meal; he could only serve it. Even something like a meat pie would involve several different guilds, namely the Pastry Cooks' guild, the Meat Cooks' guild, and then the Caterers' guild.

The pre-Enlightenment era was characterized by a focus on groups, as you can probably tell. Your fellow guild members were likely the same people you went to church with, and so on. All of this changed in the last few decades of the Enlightenment. The French court was in a lot of debt during the 1760s and decided to start selling off guild titles to raise funds; these titles were heavily governed before this, requiring years of training to obtain. A man named Mathurin Roze de Chantoiseau purchased the title of 'cook' in 1766 and opened up the first establishment known as a restaurant. The initial definition of 'restaurant' was a food or drink meant to restore strength to the ill or tired. For instance, consomme, wine, and cordial all made excellent restaurants.

Chantoiseau's establishment was successful for quite a few reasons. Firstly - and speaking quite explicitly to your question here - these restaurants (the consumable item - not the establishment) lacked any use of spices. Before the Enlightenment era, expensive spices were used by rich French aristocrats, racking up the national debt; of course, most people did not take kindly to this. Also, spices were reminiscent of bad cooking, used to cover up food that tasted off. Lastly - and perhaps most significantly - spices were used before this to balance the humors; it was widely believed that certain foods have certain properties. Ever wonder why many of our parents and grandparents recommend spices for the cold? It was believed - and still is by so many - that spices were warm and that the cold was simply a lack of balance. The solution was to balance cold with hot to prevent illness, and the application of spices as medicine was part of the reason why they were in such high demand. This changed around the Enlightenment, when it became evident that Paris' air was noticeably toxic. People became less concerned with maintaining these balances and more concerned with diseases like tuberculosis, characterized by general fatigue and coughing. It was also believed that a heavy meal would increase fatigue, so restaurants were perfect because they were light and restorative; there was this idea that consuming restaurants would ward off fatigue and chest-related symptoms. For these reasons, the lack of spices in Chantoiseau's dishes appealed to people.

Earlier on I discussed how the era prior to the Enlightenment focused on groups of people; The Enlightenment - in contrast - cultivated the individual, and these ideas perpetuated into the post-Revolution era. Restaurants were places where people could gather and discuss their ideas with colleagues and acquaintances over a broth. They could express themselves in these establishments. Soon thereafter, restaurants transformed into something closer to how we know them today, serving extravagant dishes with all sorts of ingredients - not just restorative broths. These were now places where an individual could cultivate personal taste; this was the same rhetoric championed by Enlightenment thought as the focus was on individualism, not groups or guilds.

Sources:

Eliot Shore, “Dining Out: The Development of the Restaurant” in Paul Freedman, ed, Food: The History of Taste

Jeffrey Pilcher, Food In World History