Amyotrophic lateral sclerosis (ALS) is an adult onset, neurodegenerative disease that is characterized by the loss of upper (corticospinal) and lower motor neurons. ALS is a multifactorial disease whereby a combination of genetic and environmental factors may contribute to disease pathogenesis. While the majority of studies indicate that the underlying causes for ALS pathology may be due to multiple defects at the cellular level, factors that have recently been identified to be associated with survival could lead to the development of beneficial interventions. In ALS, a higher pre-morbid body mass index (BMI) and the maintenance of BMI and nutritional state is associated with improved outcome. This review will focus on the associations between body composition and adiposity relative to disease duration and risk, and will discuss current evidence that supports the benefits of improving energy balance, and the maintenance of body mass through nutritional intervention in ALS.