ONS – What Are Oral Dietary Supplements

In accordance with the formal definition established by the *European Society for Clinical Nutrition and Metabolism* (commonly abbreviated as ESPEN), **oral nutritional supplements** (referred to as ONS, derived from *Oral Nutrition Supplements*) constitute specialized formulations available in multiple physical states—ranging from liquids of varying viscosities to semi-solid creams or powdered substances intended for reconstitution. Their principal objective is to supplement the body’s daily requirements for energy and essential nutrients, encompassing both macronutrients and micronutrients. Depending on the specific formulation, these products may be presented in a ready-to-consume format—such as pre-packaged beverages in bottles or pouches—or serve as a base for preparing nutrient-dense solutions at home. Alternatively, they can be incorporated as enhancers into conventional meals or beverages to augment their caloric and nutritional density. ONS are categorized under **foods for special medical purposes** (FSMP), indicating that their administration is subject to rigorous medical supervision. They are primarily intended for patients whose capacity to adequately ingest, digest, or absorb food—or specific nutrients—is compromised, whether due to chronic illnesses, acute clinical conditions, or postoperative complications. Furthermore, ONS are employed in scenarios where a standard diet proves insufficient to meet the elevated metabolic demands of the body, a circumstance frequently observed in diverse somatic disorders (reference: Cederholm et al., publication from 2017).

Oral nutritional supplements designed for specialized medical applications constitute an extraordinarily diverse category of products, enabling precise adaptation to the distinct requirements of various patient populations. With regard to their compositional and nutritional profiles, two primary subcategories can be distinguished: **nutritionally complete formulations** and **nutritionally incomplete formulations**. The former—nutritionally complete preparations—deliver a comprehensive array of essential nutrients in quantities aligned with dietary recommendations for healthy individuals. These formulations serve a dual purpose: they function as a **dietary adjunct** for patients who encounter difficulties in consuming adequate quantities of conventional meals, and they may also act as the **sole source of energy, macronutrients, and micronutrients** in scenarios where traditional oral intake is impractical or insufficient. In contrast, nutritionally incomplete preparations are characterized by an elevated concentration of one or more selected nutrients but do not provide the full spectrum of essential dietary components. Consequently, their use is strictly intended as a **supplemental enhancement to conventional dietary intake** rather than as a standalone nutritional solution. Furthermore, these supplements exhibit variability in **energy density**, with options ranging from standard to high-calorie formulations, as well as modifications in protein or fat content (either reduced or increased proportions of these macronutrients). Certain products are fortified with **functional bioactive compounds**, such as dietary fiber, specific fatty acids, or amino acids, whereas others undergo targeted reductions in specific components (e.g., low-electrolyte formulations). Additionally, some supplements perform **modulatory functions**, such as altering the consistency of traditional foods through thickening, which can significantly facilitate ingestion for patients with certain medical conditions or swallowing disorders.

This document provides comprehensive guidelines for the use of oral nutritional supplements (ONS) as an interventional strategy in cases of existing malnutrition or high risk of its development. It details patient groups who may benefit measurably from supplementation, including elderly individuals with appetite disorders and difficulties in independent meal preparation, oncology patients with increased metabolic demands, and patients with chronic conditions such as cystic fibrosis, inflammatory bowel diseases, or chronic kidney disease. The document also presents current scientific evidence supporting the efficacy of ONS in improving nutritional parameters, body weight, and quality of life, while acknowledging the limitations of existing studies and the need for further research.

The vast majority of oral nutritional supplements (ONS) are formulated in liquid form, permitting direct consumption straight from the container. A critical consideration is the regulated pace of intake: the supplement should be ingested gradually, in measured amounts distributed over a period ranging from thirty minutes to a full hour. Given the high concentration of both energy and essential nutrients, excessively rapid consumption could overwhelm the digestive system, thereby compromising the body’s ability to assimilate these vital compounds efficiently. Furthermore, ingesting the preparation too quickly may trigger undesirable gastrointestinal responses, including a laxative effect. Some patients may experience discomfort related to the supplement’s texture or flavor profile. In such instances, it is advisable to incorporate the nutritional preparation into familiar foods—such as pancakes, porridges, desserts, soups, or main courses. Masking the supplement’s taste with complementary ingredients and presenting it within well-tolerated meals can substantially enhance dietary compliance among individuals requiring nutritional intervention.

Oral nutritional supplements (ONS) are widely accessible through both online retail platforms and brick-and-mortar pharmacy networks. The product range encompasses a diverse selection of formulations with varying nutritional compositions and an extensive array of flavor profiles, thereby facilitating personalized adaptation to the unique dietary requirements and taste preferences of patients. It is important to note that while these supplements do not require a medical prescription for purchase, professional guidance is strongly advised prior to initiation; patients should consult their attending physician to ensure appropriate product selection and to enable supervised usage. Currently, these preparations are not eligible for public reimbursement or subsidy under healthcare funding schemes.