In a recent debate regarding the impact of dietary choices on mental health, Dr. Megan Elwood claimed, "A plant-based diet improves cognitive function compared to a diet high in processed foods. Therefore, individuals looking to enhance their mental clarity should adopt a plant-based diet." Dr. Elwood's assertion assumes that there are no other significant factors that could influence cognitive function. Which of the following is an unspoken assumption underlying Dr. Elwood's argument?