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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.

© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021, Rationale: Cancer is associated with muscle wasting. However, optimal protein intake has not been determined, limiting the efficacy of nutritional interventions. This systematic review aims to assess the effect of protein intake on muscle mass of patients with cancer types with high prevalence of sarcopenia during treatment, in longitudinal studies. Methods: MEDLINE, CINAHL, and Scopus databases were searched following PRISMA guidelines. Longitudinal studies written in English, including adults with high sarcopenia prevalence cancer diagnosis, submitted to (chemo)radiotherapy, with assessment of protein intake and muscle changes during treatment, published until 4 October 2020 were included. Studies including supplementation with substances, such as n-3 fatty acids, specific amino acids, or proteins, were excluded. Study appraisal was independently conducted by two reviewers, and a qualitative research synthesis was performed. Results: Overall, 575 records were identified, of which, eight studies were included (one randomized clinical trial and seven uncontrolled before and after studies). Patients with head and neck (n = 5), lung (n = 2), and esophageal cancer (n = 1) were included, comprising a total of 554 participants. The studies presented heterogeneous methodologies, objectives, and methods to assess body composition. Overall, participant groups with a mean protein intake below 1.2 g/kg presented muscle wasting, with one exception, while those reporting a mean intake above 1.4 g/kg, maintained muscle during treatment. Conclusions: Our findings show that protein intakes below 1.2 g/kg, even when within the recommendations, have been associated with muscle wasting during treatment. Only intakes above 1.4 g/kg have been associated with muscle maintenance. High-quality research is needed to establish an optimal dose response.

Background: Despite being recognised that nutritional intervention is essential, nutritional support is not widely accessible to all patients. Given the incidence of nutritional risk and nutrition wasting, and because cachexia management remains a challenge in clinical practice, a multidisciplinary approach with targeted nutrition is vital to improve the quality of care in oncology. Methods: A literature search in PubMed and Cochrane Library was performed from inception until 26 March. The search consisted of terms on: cancer, nutrition, nutritional therapy, malnutrition, cachexia, sarcopenia, survival, nutrients and guidelines. Key words were linked using “OR” as a Boolean function and the results of the four components were combined by utilizing the “AND” Boolean function. Guidelines, clinical trials and observational studies written in English, were selected. Seminal papers were referenced in this article as appropriate. Relevant articles are discussed in this article. Results: Recent literature supports integration of nutrition screening/assessment in cancer care. Body composition assessment is suggested to be determinant for interventions, treatments and outcomes. Nutritional intervention is mandatory as adjuvant to any treatment, as it improves nutrition parameters, body composition, symptoms, quality of life and ultimately survival. Nutrition counselling is the first choice, with/without oral nutritional supplements (ONS). Criteria for escalating nutrition measures include: (1) 50% of intake vs. requirements for more than 1−2 weeks; (2) if it is anticipated that undernourished patients will not eat and/or absorb nutrients for a long period; (3) if the tumour itself impairs oral intake. N-3 fatty acids are promising nutrients, yet clinically they lack trials with homogeneous populations to clarify the identified clinical benefits. Insufficient protein intake is a key feature in cancer; recent guidelines suggest a higher range of protein because of the likely beneficial effects for treatment tolerance and efficacy. Amino acids for counteracting muscle wasting need further research. Vitamins/minerals are recommended in doses close to the recommended dietary allowances and avoid higher doses. Vitamin D deficiency might be relevant in cancer and has been suggested to be needed to optimise protein supplements effectiveness. Conclusions: A proactive assessment of the clinical alterations that occur in cancer is essential for selecting the adequate nutritional intervention with the best possible impact on nutritional status, body composition, treatment efficacy and ultimately reducing complications and improving survival and quality of life.