This critical review delves into the profound implications of malnutrition on disease progression and the convalescence process. Malnutrition, encompassing both undernutrition and overnutrition, serves as a pivotal determinant of health, significantly influencing the immune system's ability to combat infections and chronic conditions. The review elucidates the biological underpinnings that render malnourished individuals more susceptible to severe disease manifestations and hinder recovery. It highlights the dual burden of malnutrition, where undernutrition and obesity each contribute uniquely to disease exacerbation. By synthesizing current research, the article sheds light on how malnutrition not only predisposes individuals to a higher risk of disease but also complicates treatment outcomes, making recovery a more arduous process. Additionally, it examines the socio-economic factors that perpetuate malnutrition, suggesting that addressing these root causes is essential for effective intervention. The review advocates for integrated strategies that combine clinical and public health approaches to mitigate malnutrition's impact, emphasizing the need for comprehensive policies that encompass nutrition education, food security, and equitable healthcare access.