Although increased weight, and particularly obesity, has been associated with a more severe clinical course of COVID-19 and risk of fatality, the course of the illness can lead to prolonged length of stay. Changes in nutritional status and weight loss during hospitalisation are largely reported in some populations, but still not explored in COVID-19 patients. Considering that patients with COVID-19 show an increased inflammatory response, other signs and symptoms, which can lead to weight and muscle loss, should be monitored. The aim of this article was to establish possible connections between COVID-19, prolonged hospitalisation and muscle wasting, as well as to propose nutritional recommendations for the prevention and treatment of cachexia, through a narrative review. Identification of risk and presence of malnutrition should be an early step in general assessment of all patients, with regard to more at-risk categories including older adults and individuals suffering from chronic and acute disease conditions, such as COVID-19. The deterioration of nutritional status, and consequently cachexia, increases the risk of mortality and needs to be treated with attention as other complications. There is, however, little hard evidence of nutritional approaches in assisting COVID-19 treatment or its management including cachexia.

Cachexia is a clinically relevant syndrome which impacts on quality of life, morbidity and mortality of patients suffering from acute and chronic diseases. The hallmark of cachexia is muscle loss, which is triggered by disease-associated inflammatory response. Cachexia is a continuum and therefore a staging system is needed. Initially, a three-stage system (i.e. pre-cachexia, cachexia and refractory cachexia) was proposed. More recent evidence supports the use of a five-stage classification system, based on patient's BMI and severity of weight loss, to better predict clinical outcome. Also, large clinical trials in cancer patients demonstrated that cachexia emerging during chemotherapy has greater influence on survival than weight loss at baseline. Therefore, becoming widely accepted is the importance of routinely monitoring patients’ nutritional status to detect early changes and diagnose cachexia in its early phases. Although cachexia is associated with the presence of anabolic resistance, it has been shown that sustained yet physiological hyperaminoacidaemia, as well as the use of specific nutrients, is able to overcome impaired protein synthesis and revert catabolism. More importantly, clinical evidence demonstrates that preservation of nutritional status during chemotherapy or improvement of body weight after weight loss is associated with longer survival in cancer patients.

In a variety of chronic and acute disease states, alterations in protein synthesis, breakdown and protein turnover rates occur that are related to the loss of body protein and skeletal muscle wasting. A key observation is the stimulation of protein breakdown in muscle and the stimulation of protein synthesis in the splanchnic area; mainly liver. An altered splanchnic extraction of amino acids as well as an anabolic resistance to dietary protein, related to stress, disuse and aging play a key role in the pathogenesis of muscle wasting in these conditions. To overcome these factors, specific dietary protein and amino acid diets have been introduced. The main focus of these diets is the quantity and quality of dietary proteins and whether a balanced mixture or solely dietary essential amino acids are required with or without higher intake levels of specific amino acids. Specifically in cancer patients, stimulated muscle protein synthesis has been obtained by increasing the amount of protein in a meal and by providing additional leucine. Also in other chronic diseases such as chronic obstructive pulmonary disease and cystic fibrosis, meals with specific dietary proteins and specific combinations of dietary essential amino acids are able to stimulate anabolism. In acute diseases, a special role for the amino acid arginine and its precursor citrulline as anabolic drivers has been observed. Thus, there is growing evidence that modifying the dietary amino acid composition of a meal will positively influence the net balance between muscle protein synthesis and breakdown, leading to muscle protein anabolism in a variety of chronic and acute disease states. Specific amino acids with anabolic potential are leucine, arginine and citrulline.

Weight loss leading to cachexia is associated with poor treatment response and reduced survival in pancreatic cancer patients. We aim to identify indicators that allow for early detection that will advance our understanding of cachexia and will support targeted anti-cachexia therapies. A total of fifty pancreatic cancer patients were analysed for skeletal muscle and visceral adipose tissue (VAT) changes using computed tomography (CT) scans. These changes were related to physical characteristics, secondary disease states and treatment parameters. Overall, patients lost 1·72 (sd 3·29) kg of muscle and 1·04 (sd 1·08) kg of VAT during the disease trajectory (413 (sd 213) d). After sorting patients into tertiles by rate of VAT and muscle loss, patients losing VAT at > − 0·40 kg/100 d had poorer survival outcomes compared with patients with < − 0·10 kg/100 d of VAT loss (P= 0·020). Patients presenting with diabetes at diagnosis demonstrated significantly more and accelerated VAT loss compared with non-diabetic patients. In contrast, patients who were anaemic at the first CT scan lost significantly more muscle tissue and at accelerated rates compared with non-anaemic patients. Accelerated rates of VAT loss are associated with reduced survival. Identifying associated features of cachexia, such as diabetes and anaemia, is essential for the early detection of cachexia and may facilitate the attenuation of complications associated with cachexia.

Muscle wasting or cachexia is caused by accelerated muscle protein breakdown via the ubiquitin–proteasome complex. We investigated the effect of curcumin c3 complex (curcumin c3) on attenuation of muscle proteolysis using in vitro and in vivo models. Our in vitro data indicate that curcumin c3 as low as 0·50 μg/ml was very effective in significantly inhibiting (30 %; P < 0·05) tyrosine release from human skeletal muscle cells, which reached a maximum level of inhibition of 60 % (P < 0·05) at 2·5 μg/ml. Curcumin c3 at 2·5 μg/ml also inhibited chymotrypsin-like 20S proteasome activity in these cells by 25 % (P < 0·05). For in vivo studies, we induced progressive muscle wasting in mice by implanting the MAC16 colon tumour. The in vivo data indicate that low doses of curcumin c3 (100 mg/kg body weight) was able to prevent weight loss in mice bearing MAC16 tumours whereas higher doses of curcumin c3 (250 mg/kg body weight) resulted in approximately 25 % (P < 0·05) weight gain as compared with the placebo-treated animals. Additionally, the effect of curcumin c3 on preventing and/or reversing cachexia was also evident by gains in the weight of the gastrocnemius muscle (30–58 %; P < 0·05) and with the increased size of the muscle fibres (30–65 %; P < 0·05). Furthermore, curcumin inhibited proteasome complex activity and variably reduced expression of muscle-specific ubiquitin ligases: atrogin-1/muscle atrophy F-box (MAFbx) and muscle RING finger 1 (MURF-1). In conclusion, oral curcumin c3 results in the prevention and reversal of weight loss. The data imply that curcumin c3 may be an effective adjuvant therapy against cachexia.

In skeletal muscle, as in any mammalian tissue, protein levels are dictated by relative rates of protein synthesis and breakdown. Recent studies have shown that the ubiquitin–proteasome-dependent proteolytic pathway is mainly responsible for the breakdown of myofibrillar proteins. In this pathway proteins that are to be degraded are first tagged with a polyubiquitin degradation signal. Ubiquitination is performed by the ubiquitin-activating enzyme, ubiquitin-conjugating enzymes and ubiquitin–protein ligases, which are responsible for the recognition of specific substrates. Polyubiquitinated protein substrates are then specifically recognised and degraded by the 26S proteasome. The present review focuses on: (1) the mechanisms of ubiquitination–deubiquitination that make the system highly selective; (2) the mechanisms of proteolysis in skeletal muscle. In particular, the role of the system in the remodelling of skeletal muscle during exercise and disuse and in recovery or regeneration that prevails during post-atrophic conditions is reviewed.