Cancer patients and survivors are at risk of poor clinical outcomes due to poor nutritional intake following cancer diagnosis. During cancer treatment, treatment toxicities can affect eating patterns and can lead to malnutrition resulting in loss of lean body mass and excessive weight loss. Following treatment and throughout survivorship, patients are at risk of not meeting national nutrition guidelines for cancer survivors, which can affect recurrence and survival. Obesity, which is highly prevalent in cancer patients and survivors, can affect clinical outcomes during treatment by masking malnutrition and is also a risk factor for cancer recurrence and poorer survival in some cancers. Appropriate and effective nutritional education and guidance by trained clinicians are needed throughout the cancer continuum. This article presents an overview of recommendations and guidelines for nutrition and weight management and provides recent examples of behavioral theory-based targeted lifestyle interventions designed to increase adherence to recommendation by cancer patients and survivors.