© 2016 American Association for Cancer Research. Body mass index (BMI) and simple counts of weight are easy and available tools in the clinic and in research. Recent studies have shown that cancer patients with a low normal BMI (or those with weight loss) have worse outcomes than obese patients. These results suggest that obesity has a protective effect and has been termed the "obesity paradox." In this commentary, we discuss hypothetical explanations and take a step beyond BMI or simple weights alone to present other useful and more specific body composition metrics, such as muscle tissue mass, visceral fat mass, and subcutaneous fat mass. Body composition is highly variable between individuals with significant differences seen between various races and ages. Therefore, it is critical to consider that patients with the exact same BMI can have significantly different body compositions and different outcomes. We encourage further studies to examine body composition beyond BMI and to use other body composition metrics to develop individualized treatments and intervention strategies.