Cancer patients are at a high risk of malnutrition and disease-associated catabolic derangements. It is important to differentiate between 'simple' - voluntary or involuntary - caloric restriction with protein-sparing ketogenic metabolic adaptation and cachexia, characterized by the combination of weight loss and dysmetabolism, most prominently systemic inflammation. While both conditions result in the sacrifice of fat and protein stores and thus impact on treatment tolerance, complication rates and survival, the presence of metabolic derangements is especially dangerous by straining multiple organ functions. To avoid underdiagnosing and undertreating malnutrition, all cancer patients should be routinely screened for nutritional risk. At-risk patients require comprehensive assessment for contributing and treatable causes and, if available, multi-professional efforts to improve food intake, support anabolism, alleviate distress and antagonize pro-inflammatory processes. In curative settings, anabolic support should accompany or even precede anticancer treatments. Prehabilitation before major surgery, has been studied extensively, including muscle training as well as nutritional and/or psychological support. Recent meta-analyses report a consistent benefit on functional capacity and possible improvement in postoperative complications and length of hospital stay. In palliative settings, prevailing catabolic derangements require careful assessment of the individual constellation of disturbed functions and an empathic evaluation of benefits and risks of nutritional interventions. This is of special relevance in patients with an expected survival of less than a few months. Due to the complex interactions of mechanical, metabolic and psychological factors, multi-professional teams should be involved.

Patients with advanced cancer are at high risk of losing vital body resources resulting in malnutrition, immunodeficiency, impaired quality of life and worse clinical outcome. Prominent among the diverse factors contributing to this complex condition are metabolic derangements characterized by systemic inflammation, catabolism and accumulating changes in body composition. Because cure in advanced cancer still remains elusive, optimal supportive and integrated palliative care are required to allow patients to tolerate aggressive or long-term anticancer treatments, to maintain an adequate quality of life or to stay the course of advancing disease. Support needs to address and focus on all physical, psychological and social problems interfering with food intake, digestion and anabolism to maintaining adequate body resources and functions. Reliable screening for malnutrition, adequate assessment of the nutritional and metabolic status, and individualized multimodal care require the establishment of dedicated operating procedures involving experts and standardized pathways for communication among all participants involved in clinical cancer care. Therapeutic options include counseling, enriching foods, oral nutritional supplements, enteral and parenteral nutrition, metabolic modulation, exercise training, supportive care to enable and improve the intake of adequate amounts of food, as well as psycho-oncology and social support. Finally, to enable this new level of nutritional and metabolic patient care it appears necessary to establish common definitions and grading systems allowing not only for efficient treatment but allocating adequate medical resources to reach this goal.

This opinion paper presents a short review of the potential impact of protein on muscle anabolism in cancer, which is associated with better patient outcomes. Protein source is a topic of interest for patients and clinicians, partly due to recent emphasis on the supposed non-beneficial effect of proteins; therefore, misconceptions involving animal-based (e.g., meat, fish, dairy) and plant-based (e.g., legumes) proteins in cancer are acknowledged and addressed. Although the optimal dietary amino acid composition to support muscle health in cancer is yet to be established, animal-based proteins have a composition that offers superior anabolic potential, compared to plant-derived proteins. Thus, animal-based foods should represent the majority (i.e., ≥65%) of protein intake during active cancer treatment. A diet rich in plant-derived proteins may support muscle anabolism in cancer, albeit requiring a larger quantity of protein to fulfill the optimal amino acid intake. We caution that translating dietary recommendations for cancer prevention to cancer treatment may be inadequate to support the pro-inflammatory and catabolic nature of the disease. We further caution against initiating an exclusively plant-based (i.e., vegan) diet upon a diagnosis of cancer, given the presence of elevated protein requirements and risk of inadequate protein intake to support muscle anabolism. Amino acid combination and the long-term sustainability of a dietary pattern void of animal-based foods requires careful and laborious management of protein intake for patients with cancer. Ultimately, a dietary amino acid composition that promotes muscle anabolism is optimally obtained through combination of animal- and plant-based protein sources.