Hi Katie, this is a great question and I apologize I missed it. I have linked 3 studies below for you to read and gather more information on this.
This is all going to depend on the specific diet (whether it is whole foods based, with plenty of veggies, fruit, whole grains, healthy fats, and legumes) or if it is processed (highly inflammatory, with processed sugar, wheat, and oils increasing inflammation).
Here is a direct quote from study #3:
“At the level of bioactive compounds occurring in plant foods, primarily carotenoids and flavonoids seem to modulate inflammatory as well as immunological processes. In conclusion, there is convincing evidence that plant foods and non-nutritive constituents associated with these foods modulate immunological and inflammatory processes. By means of anti-inflammatory activities, a plant-based diet may contribute to a lower risk of cardiovascular diseases and cancer. A high intake of vegetables, fruit, and whole wheat as recommended by all international nutrition authorities provides a wide spectrum of bioactive compounds at health-promoting concentrations.”