Clinical Nutrition: Basics

In clinical medicine, nutrition is considered a part of treatment, not a patient-centered issue. Malnutrition and protein deficiency in hospitalized patients are associated with increased rates of infection, longer hospital stays, and increased complication and mortality rates. European and international clinical nutrition guidelines explicitly state that nutritional assessment and timely nutritional support should be a standard part of medical care, not an optional extra. [1]

The prevalence of nutritional risk in hospitals is very high. Studies show that 20% to 50% of hospitalized patients are at risk of malnutrition or have already developed nutritional deficiencies. However, a significant portion of these patients do not receive targeted nutritional therapy. Malnutrition is often masked by edema, obesity, or the severity of the underlying disease, so without systematic screening, it goes undetected. [2]

Clinical nutrition encompasses more than just "diet" but a full spectrum of interventions: from adaptations of standard hospital meals to specialized enteral and intravenous parenteral nutrition formulas. Current guidelines use clear definitions that distinguish general dietetics from clinical nutrition as a therapeutic tool. This approach helps incorporate nutrition into standard treatment alongside drug therapy and surgical interventions. [3]

Clinical nutrition occupies a special place in intensive care units, surgery, oncology, gastroenterology, and geriatrics. In these areas, disease outcome is closely linked to protein and energy reserves, muscle mass, and inflammation levels. Specialized guidelines on clinical nutrition in intensive care, cancer, inflammatory bowel disease, chronic renal failure, and other conditions emphasize that ignoring nutritional issues deprives the patient of a significant portion of the potential treatment effect. [4]

Nutrition in clinical medicine is considered an interdisciplinary task. It involves physicians of various specialties, dietitians, clinical pharmacologists, nurses, and, when necessary, rehabilitation specialists. Without teamwork, it is impossible to simultaneously assess needs, select a nutritional plan, monitor tolerance, and promptly adjust the plan. Ideally, clinical nutrition is integrated into the patient's care from the first day of hospitalization and continues after discharge, especially for chronic diseases. [5]

Table 1. The role of clinical nutrition in the treatment system

The treatment objective	How does proper nutrition affect
Reduction of complications and mortality	Reduces the risk of infection, pressure ulcers, and postoperative complications
Reducing the length of hospital stay	Accelerates recovery and improves tolerance of therapy
Supporting the effect of drugs and operations	Provides a resource for healing and immune response
Maintaining muscle mass	Prevents sarcopenia and functional dependence
Improving the quality of life	Reduces weakness, improves appetite and exercise tolerance

Nutritional assessment and screening in hospital

The first step in clinical nutrition is a systematic assessment of the risk of malnutrition in all hospitalized patients. Guidelines recommend the use of standardized screening tools based on a combination of weight, body mass index, unintentional weight loss, decreased appetite, and illness severity. This approach allows for the rapid identification of individuals requiring in-depth assessment and intervention. Screening is recommended upon admission and regularly throughout treatment. [6]

A comprehensive nutritional assessment includes several components. The physician collects a detailed dietary history, clarifies weight changes over recent months, assesses functional status, the presence of comorbidities, and analyzes laboratory parameters. Not only the scale readings are important, but also the distribution of fat and muscle mass, the presence of edema, sarcopenia, and sarcopenic obesity. For elderly patients, the risk of falls and functional dependence are assessed separately. [7]

In the past decade, there has been increased attention to the concept of "nutrition risk," which takes into account not only current status but also the expected severity of the disease and planned treatment. A patient with cancer undergoing major surgery or aggressive chemotherapy may require active nutritional support even with a relatively normal body weight. Guidelines recommend the use of comprehensive risk scores to make timely decisions about initiating clinical nutrition. [8]

Energy and protein requirements are assessed based on the clinical situation. Indirect calorimetry is used when possible, but most departments use calculation formulas and correction factors based on basal metabolic rate. Current guidelines emphasize the importance of avoiding both underfeeding and overfeeding, especially in critically ill patients in intensive care, where excess caloric intake is associated with complications and does not improve outcomes. [9]

Micronutrient needs are assessed in parallel. Deficiencies of B vitamins, vitamin D, iron, zinc, selenium, and other micronutrients are common among hospitalized patients and can exacerbate illnesses. European micronutrient guidelines offer recommended dosages for various patient categories, emphasizing the need for individualized adjustments in cases of severe deficiencies and malabsorption syndrome. [10]

Table 2. Key elements of nutritional status assessment

Evaluation element	What does it include?
Screening upon admission	Weight, body mass index, weight loss, appetite, disease severity
Anthropometry	Weight, height, waist circumference, muscle circumference
History of nutrition	Change in diet, duration of loss of appetite
Functional state	Fatigue, grip strength, self-care ability
Laboratory indicators	Markers of inflammation, iron, vitamins, microelements

Therapeutic diets and dietary modifications

The basic level of clinical nutrition is the adaptation of standard hospital meals to the needs of the individual patient. Inpatient nutrition guidelines recommend a flexible dietary system that takes into account nutritional risk, age, comorbidities, tolerance, and preferences. The key goal is to ensure adequate protein and energy intake without compromising control of underlying conditions, such as diabetes or heart failure. [11]

In many cases, increasing the density of the diet partially solves the problem. This is achieved by adding protein and energy components to meals, eating small but frequent meals, and including specialized drinks high in protein and energy. This approach is especially useful for patients with a poor appetite, those who tire of large portions, and for older adults with difficulty chewing and swallowing. [12]

A number of diseases require a special diet. For example, in chronic renal failure, it is important to monitor protein, sodium, potassium, and phosphate intake; in chronic liver disease, the emphasis is on adequate protein and energy while limiting sodium and alcohol; in inflammatory bowel disease, the dietary focus varies depending on the activity of the process and the condition of the intestine. International guidelines on clinical nutrition for specific diseases emphasize that standard "table diets" are often insufficient and require adaptation. [13]

The nutrition of patients with swallowing difficulties, cognitive impairments, and high caregiver dependency requires special attention. In such cases, it is important not only to select the right consistency of food but also to organize the feeding process, train staff and relatives in safe techniques, and monitor the risks of aspiration and choking. Guidelines for clinical nutrition in geriatrics emphasize that proper nutrition in this group of patients impacts survival no less than the choice of medication regimens. [14]

Even in relatively mild conditions, clinical nutrition can help improve treatment tolerance. For example, in cancer patients, individually tailored nutrition reduces fatigue, improves tolerance to chemotherapy and radiation therapy, and reduces the risk of treatment interruption due to complications. It is important that a dietitian be integrated into the oncology team, rather than being brought in only in the later stages of severe exhaustion. [15]

Table 3. Examples of therapeutic diets in clinical practice

Clinical situation	Basic principles of the diet
Chronic renal failure	Control of protein, sodium, potassium, phosphates, sufficient energy
Chronic liver failure	Adequate protein, sodium restriction, prevention of deficiencies
Diabetes mellitus	Even distribution of carbohydrates, control of saturated fats
Inflammatory bowel disease	Individual selection of the volume and composition of food, sometimes elemental mixtures
Geriatric patient with dysphagia	Changed consistency, safe feeding techniques, increased diet density

Enteral Nutrition: When Regular Food Isn't Enough

When a patient is unable to obtain sufficient protein and energy through conventional routes, and the gastrointestinal tract remains functional, enteral nutrition becomes the primary method of clinical nutrition. It can be administered via a nasogastric or nasoenteric tube, gastrostomy, or jejunostomy. International guidelines emphasize that the enteral route is preferred whenever possible, as it preserves intestinal function, promotes the maintenance of microbiota, and is less expensive than parenteral nutrition. [16]

Enteral nutrition is particularly important in intensive care, surgery, and severe infections. Early initiation of enteral nutrition in intensive care patients is associated with better glycemic control, a lower incidence of infectious complications, and a shorter hospital stay compared to no nutritional support. However, recent studies emphasize the need for an individualized approach: overly aggressive early feeding may increase intolerance and gastrointestinal complications. [17]

The choice of formula and administration regimen is determined by the clinical situation. There are standard polymeric formulas, specialized products for renal, hepatic, and respiratory failure, as well as formulas for patients with severe malabsorption or short bowel movements. Additionally, the choice of bolus, cyclic, or continuous administration is considered. Comparative reviews show that the choice of regimen should take into account tolerability, aspiration risk, and departmental organizational capabilities; there is no universally "best" option. [18]

Complications of enteral nutrition can be divided into mechanical, infectious, and metabolic. Mechanical complications include tube displacement or obstruction, mucosal trauma, and aspiration of contents. Infectious complications include catheter-associated infections during gastrostomy and soft tissue infections. Metabolic complications include diarrhea, constipation, hyperglycemia, electrolyte deficiency or excess, and refeeding syndrome. Prevention of complications requires proper access and formula selection, adherence to nursing techniques, and regular monitoring. [19]

A key principle when working with enteral nutrition is dynamic assessment of effectiveness and tolerability. It is important to daily analyze actual protein and energy intake, the volume of residual gastric contents, the presence of diarrhea or constipation, changes in laboratory parameters, and the clinical picture. If well tolerated, the feeding volume is gradually increased to target values. If complications arise, the regimen and formula composition are adjusted, or temporary supplementation with parenteral nutrition is considered. [20]

Table 4. Main indications and contraindications for enteral nutrition

Indications	Contraindications or relative limitations
Inability to eat adequately on one's own, functioning intestines	Complete intestinal obstruction
Severe swallowing disorder	Uncontrolled bleeding from the gastrointestinal tract
Condition after major operations	Severe hemodynamic instability
Intensive care patients at high risk of malnutrition	High risk of aspiration if airway protection is not provided
Chronic neurological diseases	Refusal of the patient or legal representatives with a safe alternative

Parenteral nutrition: when the intestines don't work

Parenteral nutrition is used when the gastrointestinal tract cannot provide adequate nutrient delivery or its use is dangerous. Classic indications include severe intestinal failure, acute ischemic bowel necrosis, severe malabsorption, some severe forms of pancreatitis, prolonged postoperative intestinal paresis, and situations where enteral nutrition is technically impossible. Guidelines emphasize that parenteral nutrition should not replace enteral nutrition if the latter is feasible and safe. [21]

Parenteral nutrition can be total, when all requirements are met intravenously, or supplemental, when it is used to compensate for deficiencies in enteral or oral nutrition. In intensive care and oncology, a combined strategy is often used, whereby enteral nutrition is continued as much as possible, and the missing energy and protein are administered parenterally. This approach leverages the advantages of both methods and reduces the risks associated with total intravenous nutrition. [22]

Parenteral nutrition consists of amino acid solutions, glucose, fat emulsions, electrolytes, trace elements, and vitamins. Dosage is calculated individually based on body weight, clinical condition, liver and kidney function, the presence of fever, and the degree of stress. Guidelines emphasize the need to avoid excess calories, especially glucose, as this increases the risk of hyperglycemia, infections, and fatty liver disease. [23]

Parenteral nutrition is associated with a number of potentially serious complications. These include catheter-associated infections, central venous thrombosis, electrolyte imbalances, refeeding syndrome, hyperglycemia, and liver and gallbladder dysfunction. Review studies emphasize that these risks can be significantly reduced by strict adherence to aseptic technique, proper selection of vascular access, regular monitoring of laboratory parameters, and a gradual increase in exercise in patients at high risk of refeeding syndrome. [24]

The decision to initiate parenteral nutrition requires the involvement of an experienced team and a clear monitoring plan. Target protein and energy levels must be established, the frequency of glucose, electrolyte, liver, and renal function monitoring must be determined, and the feasibility of transitioning some of the nutrition to the enteral route must be regularly assessed. As soon as bowel function permits, a gradual increase in the enteral component is recommended, while the volume of parenteral nutrition is reduced. [25]

Table 5. Examples of clinical situations when parenteral nutrition is indicated

Situation	Features of parenteral nutrition administration
Acute intestinal failure	Total parenteral nutrition until bowel function is restored
Severe malabsorption	Long-term therapy, often at home in chronic forms
Inability to pass a tube and enteral nutrition	Full or partial coverage of intravenous needs
Resuscitation when enteral route is impossible	Temporary support followed by transition to enteral nutrition
Cancer patient with intestinal obstruction	Individual choice between total and supplemental parenteral nutrition

Clinical nutrition for chronic diseases and special groups

In chronic diseases, clinical nutrition becomes part of a long-term treatment strategy. In cancer patients, proper nutrition helps combat cachexia, maintain muscle mass, reduce fatigue, and improve tolerance to chemotherapy and immunotherapy. Guidelines for clinical nutrition in cancer emphasize the importance of early involvement of a dietitian, even before significant signs of malnutrition appear. [26]

In inflammatory bowel disease, nutrition serves several purposes: preventing malnutrition and micronutrient deficiencies, maintaining weight and growth in children, and reducing inflammatory activity in some cases. In some cases, a complete enteral diet is considered as an alternative to drug-induced remission in children. Adult patients often require individualized recommendations regarding food volume and composition, formula selection, and dietary adjustments during periods of exacerbation and remission. [27]

In patients with chronic renal and heart failure, clinical nutrition aims to balance restrictions with the prevention of malnutrition. In renal failure, following a low-protein diet without professional supervision can lead to sarcopenia and a worse prognosis. In heart failure, malnutrition is associated with increased mortality, so recommendations are increasingly shifting from strict restrictions to individualized dietary choices with sufficient protein and energy. [28]

Geriatric patients represent a special risk group. They are more likely to have sarcopenia, sarcopenic obesity, swallowing disorders, cognitive impairment, and social factors that limit access to adequate nutrition. Guidelines for clinical nutrition and hydration in geriatrics emphasize the need for regular screening, early nutritional support, the use of fortified foods, and, when necessary, enteral methods. The goal is not so much achieving an "ideal" body mass index as maintaining function and independence. [29]

Chronic home nutrition, including home enteral and parenteral nutrition, requires a well-functioning system. The patient and family must be trained in the care of tubes or catheters, aseptic techniques, signs of complications, and emergency response procedures. International practice guidelines demonstrate that, when properly organized, home artificial nutrition can be safe, improve quality of life, and reduce hospital stays. [30]

Table 6. Special patient groups and clinical nutrition emphases

Patient group	Basic nutritional tasks
Cancer patients	Prevention of cachexia, maintenance of muscle mass, tolerability of therapy
Patients with inflammatory bowel disease	Prevention of deficiencies, support of remission, growth in children
People with chronic renal failure	Protein and energy balance, prevention of sarcopenia
Patients with heart failure	Prevention of malnutrition, optimization of diet composition
Elderly patients	Screening for malnutrition, nutritional supplementation, and sarcopenia prevention
Patients on home artificial nutrition	Training, access safety, and complication prevention

Organization of clinical nutrition services and typical mistakes

Effective clinical nutrition is impossible without an organizational structure. Current guidelines and position papers emphasize the need to establish nutrition committees that include physicians, dietitians, pharmacologists, representatives of nursing staff, and administration. These teams are responsible for developing local screening protocols, algorithms for prescribing enteral and parenteral nutrition, staff training, and quality audits. [31]

One common mistake is delaying clinical nutrition. Patients often receive nutritional support only when severe malnutrition or complications occur, when intervention options are already limited. It is much more effective to identify risk early and initiate nutritional therapy before major surgery, intensive chemotherapy, or prolonged hospitalization. This proactive approach reduces the incidence of complications and treatment costs. [32]

Another common problem is the undervalued role of nurses and the lack of systematic staff training. Nursing staff are often responsible for the actual administration of formula, monitoring tolerance, caring for catheters and tubes, and recording food and fluid intake. Without their involvement, even perfectly written protocols remain on paper. Research shows that training programs and support from the nutrition team improve implementation of recommendations and reduce the frequency of errors. [33]

Finally, outdated concepts about nutrition are still common in clinics, such as a fear of early enteral nutrition after surgery, the belief that complete fasting speeds recovery, or the unjustified withholding of parenteral nutrition where it is needed. Current guidelines on surgical and intensive care nutrition clearly emphasize that the lack of nutritional support when indicated increases the risk of complications and mortality. Updates to local guidelines should be based on current international data. [34]

Advances in clinical nutrition include more accurate risk stratification, the use of indirect calorimetry, digital tools for monitoring intake, and individualized therapy based on the patient's genetics, microbiota, and phenotype. Evidence already shows that a systematic approach to nutritional support can significantly improve hospitalization outcomes, shorten treatment duration, and enhance quality of life for patients with chronic diseases. [35]

Table 7. Common mistakes in organizing clinical nutrition and how to avoid them

Error	What is dangerous?	How to fix
Lack of routine screening	Skipping patients with high nutritional risk	Introduce mandatory screening upon admission
Late involvement of a nutritionist	Delayed correction of malnutrition	Include a nutritionist in the patient's care from day one
Ignoring the role of nursing staff	Failure to comply with protocols, errors in the introduction of mixtures	Training, clear distribution of responsibilities
Fear of enteral nutrition	Malnutrition, increased complications	Updating protocols according to modern guidelines
Unjustified refusal of parenteral nutrition	Prolonged fasting when enteral route is impossible	Individual assessment of indications and risks