Final answer:
The question addresses the history and evolution of the fast food industry, its impact on American eating habits, and food technology, which relates to Social Studies at the High School level.
Step-by-step explanation:
The question concerns the historical development of fast food in America, particularly relating to the French fry innovation, and touches on broader themes of nutrition and food science within the context of the fast-food industry. Mention of the meeting between Simplot and Ray Kroc suggests a historical business dealing that is relevant to the subject. Furthermore, the reference to Americans' fast food consumption habits and the changes in these habits over time pertain to aspects of social studies and health.
The mention of trans fats and their regulatory status relates to both health and law. The question also engages with the history of food technology and manufacturing processes, as indicated by the inquiry into the Lamb Weston factory and the product development processes in the food industry highlighted by the discussion about artificial flavors and 'kid testers'.
Given the questions' scope and depth, encompassing history, nutrition, social trends, business, and technology within the context of the food industry, the subject aligns best with Social Studies, and the grade level would be High School, given the complexity and the expectations of analyzing historical and contemporary issues.