An early identification of risk or presence of malnutrition is pivotal even in normal times. Therefore, it is crucial to assess the individual nutritional status in all subjects admitted to the hospital, even more during the COVID-19 pandemic. Untreated malnutrition is associated with longer hospital stay and higher risk of comorbidities, which may seriously impair patients’ body functions and quality of life, as well as survival rates [40,78]. Also at the community level, malnutrition and nutritional risks may have long-term consequences on health and body functions. Prevention and treatment of malnutrition and nutritional deficiencies may impact the prognostic outcomes at any level and in any stage of life. Through shared genetic and environmental factors (the epigenetic phenomena), nutritional problems can span generations creating a vicious cycle of malnutrition, negatively affecting body composition and health status throughout the life-course, and indirectly posing a risk of developing non-communicable diseases in later life [58,79]. Intervening through programs that simultaneously involve the entire family household, from grandparents to grandchildren, may therefore represent a strong strategy to interrupt the so-called “intergenerational cycle of malnutrition” [79] and should be pursued by both geriatricians and pediatricians.

Several screening tools are available to identify people at risk of malnutrition or already malnourished. However, implementing these during the COVID-19 pandemic is challenging. Rapid instruments can help clinicians assessing nutritional status. To date, there might be difficulties to retrieve information directly from patients about recent dietary intake or weight changes because of health problems (i.e., severe respiratory conditions, cognitive decline, low level of consciousness) [80]. It must be recognized that it may be difficult to obtain information from caregivers or relatives because of the limited access to the hospitals. Video conferencing aids may help retrieve information about nutrition from relatives or caregivers (i.e., weight loss, reduced dietary intake) [81]. The utilization of even simple instruments such as scales and/or stadiometers may be difficult during this emergency circumstance for various reasons (i.e., unavailability in COVID+ facilities, hygiene reasons, containment measures) [82]. In such cases, clinicians should still consider self-reported or estimated values. Additionally, the most accurate techniques to assess body composition (i.e., dual-energy X-ray absorptiometry, bioelectrical impedance analysis, magnetic resonance imaging, computed tomography) may not be available in most settings or of difficult implementation during the COVID-19 pandemic. Indeed, alternative measures such as mid-arm muscle or calf circumference, even if less accurate, should be considered in older subjects [81]. As for pediatrics, there is a vast choice of growth charts or standards available for clinical practice: international, national, for healthy subjects, or even disease-specific. Generally, it is suggested to use the official WHO growth standards, developed to differentiate infant’s growth according to the early type of feeding in the first years of life [83]. Most recently, the United Nations Children’s Fund (UNICEF) has proposed that the risk of undernutrition in children may be monitored directly by caregivers through the use of a user-friendly mid upper arm circumference (MUAC) tape, thus decreasing the risk of exposure to COVID-19 by reducing health center visits [84]. Although the validation of the UNICEF MUAC tape is still to be ascertain, the innovative design of this new tool provides caregivers with a safe way to monitor the child’s nutritional status even during the COVID-19 emergency.

A step forward in the monitoring of nutritional issues and muscle loss has been the proposal of a new app named Remote-Malnutrition APP (R-MAPP) [85]. This application has been recently developed to remotely identify older people at risk of malnutrition and sarcopenia during the COVID-19 pandemic. R-MAPP includes two validated questionnaires: The Malnutrition Universal Screening Tool (MUST) and the Strength, Assistance with walking, Rise from a chair, Climb stairs, and Falls (SARC-F) to rapidly screen for malnutrition and sarcopenia, respectively. Given that both pediatric and geriatric population may share similar challenges regarding nutritional imbalances during this pandemic, the development of an application similar to R-MAPP but aimed at assessing nutritional status in the entire household environment, may represent a good starting point to address the negative consequences on nutritional status posed by the COVID-19 pandemic. Of course, when developing an “all age inclusive” R-MAPP, attention should be paid to the fact that neither MUST nor SARC-F are validated for the pediatric population, therefore, it would be necessary to use different screening tools to assess nutritional status in the youngest. Malnutrition screening tools specifically designed for the pediatric community setting, such as the Electronic Kids Index (E-KINDEX) or the Nutrition Screening Tool for Every Preschooler (NutriSTEP), may be employed. However, a recent survey pointed out that community setting specific malnutrition screening tools are not as accurate [86]. Therefore, for the purpose of remote screening of malnutrition during the pandemic, developing a different tool may be preferable, perhaps adapting the more accurate malnutrition screening tools validated for the hospital setting.

In conclusion, the ideal remote malnutrition screening app should specifically investigate unintentional weight loss/gain, changes in eating behaviors, presence of underweight or overweight in subjects of all ages, with reliable age-specific nutritional screening tools. The app should also include a complementary (not compulsory) section for the subjects to provide current weight and height information (thus allowing the app to compute nutritional-relevant body composition indexes). Finally, the app should specifically address growth in pediatric subjects, as well as provide a dedicated section to investigate the presence of sarcopenia (i.e., through the SARC-F score) in older subjects. The use of new technologies such as smartphones “apps” may also be considered to deliver physical exercise designed to include also activities that are targeted to both the youngest and the oldest populations. However, particular care should be paid when trying to apply such technologies at the extremes of life. The use of smartphone in children may be criticized as it is recognized that longer screen-time in the young population has negative effects, including (paradoxically) increased risk of developing obesity. Oppositely, older people may experience difficulties in understanding basic functioning of smartphones, let alone mastering the download and understanding of medical apps. In this sense, pediatricians and geriatricians should join effort by finding ways to implement the use of new technologies without disrupting the fragile environment of our youngest and oldest generations. Once again, this could be achieved through the mediation of a caregiver, but more extensively, it could represent an occasion to develop interactive digital tools that promote the monitoring of nutritional status and the implementation of nutritional strategies for the entire household (grandparents, parents, and grandchildren), shifting the standard of care from a diseased-focus system to a life-course approach.

Protein deficiency needs to be prevented at both the extremes of life, especially in COVID-19. Older adults need at least 1.0 g/kg of body weight/day to prevent muscle loss. The protein intake should be increased to 1.2–1.5 g/kg of body weight/day in the presence of acute or chronic diseases. In severe forms of COVID-19, characterized by high catabolic processes such as wasting syndrome, the intake of proteins may be increased up to 2.0 g/kg of body weight/day [55,56,57]. In children, the prevention of acute protein-energy malnutrition requires different intakes, according to weight, age, and severity of the disease. To date, there is no specific indication for the management of ICU admitted pediatric patients with a diagnosis of COVID-19, but the standard guidelines for nutritional support in PICUs are valid tools to direct the nutritional support in this category [87,88,89]. In addition to protein intake, it is mandatory an adequate caloric provision since if energy intake is not sufficient to meet demands, body fat, and muscle are catabolized to provide energy [90]. Determining caloric needs is best based on direct measurement of resting energy expenditure [91]. However, a driving value for energy intake of 27–30 Kcal/kg of body weight/day can be recommended in older people [81] and the Schofield equation can be used in children [91]. Both energy and protein intakes should be adjusted to nutritional status, disease status, pre-illness physical activity level, and preferences [92]. During hospitalization, nutritional status may also be assessed by measuring specific nutritional-relevant biomarkers. Visceral proteins such as albumin, pre-albumin, retinol binding protein (RBP), and transferrin are especially useful to detect eventual alterations in the protein pool. Specifically, both RBP and pre-albumin have a short half-life (12 h and 2–3 days, respectively), therefore, a reduction in the levels of these two proteins may indicate acute nutritional status changes. Conversely, the monitoring of protein with longer half-life, such as transferrin and albumin, may help highlighting chronic changes in nutritional status. Finally, among the blood values that are less likely to be measured routinely, IGF-1 is considered a useful parameter for early detection of protein-energy malnutrition [93]. All these protein-energy markers are useful to complement the clinical nutritional assessment. Indeed, no single marker can assess overall nutritional status given that each of these has its own limitations especially in the acute phase response and in other disease conditions (i.e., renal and liver failure). However, the levels of these biomarkers may be of interest in providing information about catabolic and/or anabolic conditions [94]. Given that the vast majority of these biomarkers are influenced by inflammatory states, the clinical interpretation of their levels along with the inclusion of an inflammatory marker (i.e., C-reactive protein) should, therefore, be recommended.

Additional information on protein synthesis/anabolism and protein turnover/catabolism can be gathered by the monitoring of urine creatinine and urinary nitrogen excretion. Other useful biochemical markers for the assessment of nutritional status include hemoglobin, total protein, serum cholesterol and blood lymphocyte count, as well as the evaluation of specific micronutrients deficits (iodine, folate, vitamins, and other essential micronutrients in general) [93,95]. Particular attention should be paid to the refeeding syndrome in patients who are severely malnourished since the target of energy intake should be gradually achieved and monitored carefully in these cases. In those subjects who fail to ingest adequate amounts of energy and nutrients with natural foods, multi-nutrient formulas providing both macro- and micronutrients should be considered [96]. If it is not possible to meet nutritional demands per os, as in the case of COVID-19 patients requiring mechanical ventilation, enteral nutrition should be initiated as early as possible to reduce complications [97]. Given the risk of refeeding syndrome, it is also recommended close monitoring of serum levels of phosphate, magnesium, potassium, and thiamine during the first three days after enteral or parenteral nutrition, which should be promptly supplemented in case of even mild deficiencies [92]. The nutritional status should be mandatorily addressed upon admission within a hospital setting, either COVID-19 related or not. For instance, several studies have now suggested a link between vitamin D deficiency and immune system dysfunction in patients with COVID-19 [98]. It has also been suggested that an adequate micronutrients nutritional status may help in preventing viral infections and severity of illness [99]. Some vitamins (i.e., vitamin A, B6, B12, D, E) and minerals like as zinc and selenium seem to promote a correct immune function [100]. Therefore, low levels of these micronutrients have been correlated with negative clinical outcomes in viral infections. Several studies suggested an association between low levels of vitamin D and worst outcomes in COVID-19 patients [101,102,103,104,105]. Furthermore, in the last decade vitamin D deficiency has been associated with some other viral conditions like as influenza, human immunodeficiency virus and hepatitis C [81]. However, some authors have questioned an association with influenza [106,107]. It has been also observed that COVID-19 infection may be associated to the risk of developing hypocalcemia and hypomagnesemia [108]. To date, the antioxidant properties of magnesium as well as its role as an inhibitor of the release of inflammatory cytokines, are well recognized [109]. However, low levels of other micronutrients (i.e., vitamin A, E, some B vitamins, zinc, and selenium) have also been suggested to play a role in mediating negative outcomes during viral infections [81]. Indeed, a close monitoring of the levels of these compounds is generally recommended. Addressing micronutrients deficiencies in COVID-19 patients may result in better outcomes for infected subjects. Many studies are investigating the potentials of providing micronutrients supplements to help busting up the immune system, thus ameliorating the immune response to SARS-CoV-2 infection. To date, only a few of these studies have already been published, while a larger number has yet to finalize the enrolment phase of the clinical trial. In a study from Tan et al., the authors report that COVID-19 infected subjects older than 50 years who received a combination of vitamin D, magnesium and vitamin B12 during hospitalization were less likely to require oxygen therapy or intensive care support as compared to subjects who did not receive the supplements [110]. Regarding vitamin D, Annweiler et al. [111] report that regular bolus vitamin D supplementation previous to COVID-19 infection was linked to less severe COVID-19 symptoms and better survival in infected older subjects, but no significant difference in illness outcomes was observed when bolus supplementation was initiated during hospitalization. Similarly, Murai et al. [112] observed no significant reduction on length of stay among COVID-19 hospitalized patients who were administrated a single high dose of vitamin D3, compared with placebo. On contrary, a pilot study in Spain determined that the administration of high dose vitamin D at early admission and during the first seven days of hospitalization significantly reduced ICU admissions in 50 hospitalized COVID-19 treated with hydroxychloroquine and azithromycin versus hydroxychloroquine alone [113]. Likewise, Ling et al. [114], found that patient who received vitamin D supplementation in the first 7 days of hospitalization had a reduced risk of COVID-19 mortality. Concerning zinc supplementation, in a study from Carlucci et al. [115], it was observed that COVID-19 patients treated with hydroxychloroquine and azithromycin who were also supplemented with zinc sulphate had lower mortality or transfer to hospice rate, as well as an overall increase frequency of being discharged home compared to subjects who were treated with hydroxychloroquine and azithromycin alone. However, a smaller study investigating the association between zinc supplementation and survival of hospitalized patients did not found any difference [116]. Finally, regarding vitamin C, there is currently many trials investigating its potential role in ameliorating COVID-19 outcomes [117]. Initial results published by Zhang et al. [118], indicated a promising reduction of 28-day mortality in subjects treated with intravenous vitamin C for 7 days. Further evidence on the positive effects of macronutrients supplementation on COVID-19 outcomes might emerge from the ongoing clinical trials currently investigating the topic. An updated list of the current trials investigating the topic was provided by Di Matteo et al., in a review paper investigating food potentials in influencing COVID-19 outcomes [119]. Other elements that are currently being investigated for their immuno-modulatory action are polyunsaturated fatty acids (PUFA) and probiotics, as recently reported by Lordan et al. [120].

However, despite the importance of preventing and treating micronutrient deficiencies, there is no evidence that micronutrient supplementation in non-deficient subjects would be protecting against COVID-19 or improving clinical outcomes of the infection. Indeed, the European Society for Clinical Nutrition and Metabolism recommends an intake of vitamins and minerals according to daily allowances in order to maximize general anti-infection nutritional defense [81].