Malnutrition is associated with poor nutritional, clinical and patient-centred outcomes. It also places a significant strain on health and social care budgets.1 2 In the United Kingdom (UK), the overall cost of malnutrition is estimated to be around 15% of the total public expenditure on health and social care (£23.5 billion).3
Oral nutritional supplements (ONS) are a clinically and cost-effective way to manage disease-related malnutrition.4 ONS products come in a range of styles (i.e. milk-based, juice-based, yoghurt-based, dessert, plant-based, savoury), formats (i.e. liquid, powdered, pudding-style, pre-thickened), types (i.e. high protein, low volume), energy densities and flavours.5 6 A recent survey (2019) of 207 Registered Dietitians explored practitioner preferences and clinical practice for recommending ONS. Nutritional value, patient palatability, acceptability, tolerance, and existing hospital contracts were considered the most important factors when making ONS recommendations.7
The effectiveness of ONS depends on adequate intake. ONS compliance is defined as the percentage of a prescribed amount of ONS consumed by the patient per day.2 It is important to achieve good ONS compliance to optimise the patient’s nutritional intake and to reduce waste.8 This article explores the role of powdered ONS products in patient compliance, and considers the literature to support their use and implications for clinical practice.
Powdered ONS Products
The PrescQIPP B145 Guidelines (2017) for the appropriate prescribing of ONS for adults in primary care recommends that powdered ONS should be considered first line choice of ONS when prescribed ONS are indicated, as they are the least costly preparation.9 According to an audit of ONS prescribing trends at hospital discharge, very few patients were discharged on cost-effective powders despite local approaches to improve the quality of prescribing and cost control, which included: ‘1. Monitoring the ratio of powder to liquid ONS product usage in adults: target of 80% powder; and 2. A ‘Dietitian only rule’: all ONS recommendations to prescribe on discharge from the acute hospital must be endorsed by a dietitian’.10
Prescribing guidelines for ONS differ according to local trusts and clinical commissioning groups (CCGs); guidelines may refer to the amount of calories, rather than the number of bottles/sachets of ONS. The Managing Adult Malnutrition in the Community Pathway advocates a calorie range of 300-900 kcal/day for clinical benefit,6 based on systematic reviews and meta-analysis including a broad range of patient groups.11
Table 1 provides an overview of different powdered ONS products and their nutritional composition.
Table 1: Examples of Powdered ONS Products
Powdered ONS Category
Powdered ONS Product
Energy (kcal) per serving*
Protein (g) per serving*
AYMES Shake, Complan Shake (Nutricia), Energie Shake Powder (Anaiah Healthcare), Ensure Shake (Abbott), Foodlink Complete (Nualtra), Fresubin Powder Extra (Fresenius Kabi)
*Range across different brands when constituted as per directions on packet
A Question of Compliance
It is evident that there are differing opinions with regard to the suitability of powdered ONS. Concerns raised include their suitability in vulnerable individuals 12 and that their reconstitution may have a negative impact on compliance.13 With a greater range of powdered products being available and a potential cost benefit compared to ready-to-drink, there exists a renewed opportunity for further studies on compliance to powdered ONS.
A recent, small, cross-over study 14 involved adults with a range of diseases who lived at home and received ONS prescriptions. In this study, patients whose ready-to-drink or powdered ONS prescriptions had recently been swapped, were asked to rate both products. It was reported that patients preferred the ready-to-drink ONS, which was accompanied by a greater compliance. No differences between the types of ONS in terms of thickness, mouth feel, and taste were reported, but patients rated the ready-to-drink ONS as more convenient, easier to use and prepare, with a better consistency.
Whether or not these results are clinically significant is uncertain. Firstly, the results were not corrected for volume. In this study, prescriptions were changed either from a ready-to-drink, energy dense, low volume ONS (125 ml), to a powdered ONS (reconstituted to >230 ml) or vice versa. Systematic reviews suggest significantly greater compliance and energy intakes with the use of small volume, energy dense ONS compared with standard ONS.8 Thus, volume differences may have, to some degree, accounted for improved compliance with the ready-to-drink ONS.
Secondly, the study omits important information on the variety of flavours offered, the duration of the patient’s previous ONS prescription, or indeed the duration of the new ONS regimen (prior to completing the study questionnaires). These variables may have influenced the study findings. For example, taste fatigue and monotony, which tend to occur when ONS are consumed regularly over prolonged periods, are thought to contribute to poor ONS compliance.15
Emerging Evidence-Base for Powdered ONS
It is important to highlight that there is a very limited evidence-base for powdered ONS and patient compliance. There is also a need for studies comparing the effectiveness of powdered and ready-to-drink ONS in the treatment of disease-related malnutrition. A study in cancer patients demonstrated a preference for ONS made up with fresh milk which suggests a preference towards powdered products.16
A recent abstract presented at the European Society for Clinical Nutrition and Metabolism (ESPEN) Virtual Congress in September 2020,17 suggests that powdered ONS products are convenient, easy-to-use and demonstrate excellent compliance. Data from five ONS acceptability studies were pooled and analysed. These studies involved older, community-dwelling patients with or at risk of disease-related malnutrition who were compliant with ONS (powdered and ready-to-drink). Participants commenced a 7 to 30-day intervention of a new powdered ONS (calories and protein matched) following dietetic assessment.
Convenience, ease of use and overall acceptability were rated on a scale by the patient or carer. Results showed that overall compliance to ONS at baseline was good (79%) and this increased to 88% following the intervention. All participants that completed the study (n=64) reported the convenience of powdered ONS to be acceptable, with 70.3% reporting that they ‘liked’ or ‘liked very much’ the convenience of the powdered ONS. Only 3% reported difficulty in preparing the ONS. Mean time to prepare the powdered ONS was 1 minute 47 seconds. These pooled results suggest that short-term compliance to powdered ONS is excellent. The researchers concluded that powdered ONS are also easy to use and prepare, and convenient for the intended user. 17 However, further research into powdered ONS and compliance, across a range of patient groups, is needed.
Wider ONS Compliance Issues
In addition to the product presentation, many other factors affect ONS compliance (see Table 2). The systematic review8 of 46 published trials suggests that overall compliance to ONS varies across different care settings. The review also found that many factors influence ONS compliance, such as variety (flavour, volume and form of ONS), energy density and the patient’s age (older age has been negatively associated with compliance). Compliance could be altered by reduced taste or smell function, dysphagia, and gastrointestinal symptoms.15
As previously mentioned, prolonged and repeated consumption of ONS, regardless of presentation, is also known to contribute towards lower compliance rates.8, 15
It could be argued that inappropriate prescribing of ONS may also contribute towards poor compliance. Inappropriate ONS prescribing is thought to encompass a range of clinical scenarios, including:18
Prescribing in the absence of a clinical indication (overprescribing))
Prescribing incorrect doses or durations of treatment that extend beyond the original clinical indication (misprescribing)
Failure to prescribe for patients with a clinical indication for ONS (underprescribing).
A recent review of ONS prescribing habits (conducted by Interface Clinical Services) examined prescribing data from 4,168 patients, which was gathered over three months.19 Whilst the majority of patients in this review were already on ONS that had previously been deemed suitable for their needs, 38% of ONS prescriptions were changed or stopped.19 Inappropriate ONS prescriptions place additional strains on NHS staff, resources and budgets. To increase compliance, healthcare professionals must ensure that ONS prescriptions are clinically indicated and appropriate.
Limited staffing in long-term care and nursing establishments may also affect ONS compliance. For example, it has been reported that staff spend less than one minute per resident encouraging consumption of ONS and/or meals.20 Providing patients with verbal encouragement at mealtimes along with nutrition support education from suitably qualified healthcare professionals are also important determinants of ONS compliance.20 Finally, shared decision making and multidisciplinary team working are important for optimising ONS compliance. Research has demonstrated that ONS compliance is reduced when patients, relatives and carers are unaware of the importance of nutrition support in the context of malnutrition. Conversely, patient compliance is improved when the patients, relatives and carers are included and engaged in the delivery of nutritional care plans.21
Table 2: Factors Affecting Compliance to ONS
Taste distortion in illness23
Lack of knowledge of ONS purpose24
Eating environment/social factors28
Effect of treatments29
Presentation/ability to prepare12
Inappropriate prescribing18, 19
Inadequate review10, 19
Inadequate patient/carer instruction21
Lack of accompanying dietetic support7
Lack of encouragement21
Time ONS are offered29
ONS products are a clinically cost- effective way to manage disease-related malnutrition.1 However, ONS is only effective if it is consumed, and compliance rates vary considerably across care settings. When clinically indicated, powdered ONS products are the least costly supplements available and are increasingly recommended in primary care settings as first choice of ONS, with ready-to-use ONS reserved for those who are unable to make up powdered products.
A clinically effective dosage of ONS is considered to be 300-900 kcal/day.11 It is possible to meet this using powdered ONS products. Prescription of ONS should be consistent with local prescribing guidelines whilst being tailored to the patients' needs and preferences. Recent clinical research suggests that powdered ONS products are convenient, easy-to-use and demonstrate excellent compliance. However, there is a need for more research into compliance and ONS presentation in a variety of patient groups and settings.
In addition to the product presentation, many other factors affect ONS compliance. To achieve optimal compliance, a variety of flavours, volumes, and textures can be used, served at different temperatures, according to the patient’s requirements. Appropriate prescribing, individualised dietetic assessment, and regular monitoring to assess ONS suitability are needed to improve compliance.
2. Seguy D, et al. (2020). Compliance to oral nutritional supplementation decreases the risk of hospitalisation in malnourished older adults without extra health care cost: Prospective observational cohort study. Clin Nutr.; 39(6): 1900-1907.
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