Might I question the discourse used in this post? Since you assume a singular American diet, I'd like to point out 1. the persistent importance of regionalism and intersectional identity in determining American foodways, and 2. the various layers of consumption associated with urban/suburban/rural habitation, ethnic background, etc.

My own specialization is Asian American and US Empire history, so I can speak on that, for instance. In Hawaii, the postwar diet saw the emergence of SPAM (the canned kind), in conjunction with the creolization of cuisines that developed there as culture and language creolized.

Talking more about immigrant cultures and their foodways, Jimiliz Valiente-Neighbours writes in "Mobility, embodiment, and scales: Filipino perspectives on local food" (2012) that the popular turn towards local organic food (predicated upon an Edenic desire to pastoralize America in its cultural memory) is fraught with contention for the Filipino community in the US. V-N refers to translocality (the local San Diego, the local baranggay in the homeland, all simultaneously at work) as a way of describing foodways and how immigrant cultures negotiate with popular American food discourse.

Anyway, I hope I could show the diversity of American diet and foodways in the 20th century. Just to challenge your "we" singular cultural discourse a little further, remember that food and culture are diverse and are often contentious even within themselves.

Some readings I could suggest:

The Spring 2011 Radical History Review, edited by Daniel Bender and Jeffrey Pilcher, "The Radicalization of Food History."

Donna Gabaccia, We Are What We Eat

Margot Finn (Michigan) and Adrienne Rose Johnson (Stanford) are some emerging scholars in the field as well. Anything by Jeffrey Pilcher, Krishnendu Ray, Daniel Bender, Camille Begin, and Donna Gabaccia.