Oral nutritional supplements (ONS) are commercially manufactured high-energy and/or high-protein supplements to be taken orally. ONS are available in liquid, semi-solid or powdered style products. 

They are often referred to as ‘sip feeds’. All ONS provide energy (calories) in the form of protein, fat and carbohydrate and most also contain some vitamins and minerals in varying quantities. ONS are available in milk, juice, savoury and yoghurt flavours.¹

What about dietary counselling to improve nutritional intake?

Dietary counselling should always be part of the first-line treatment for improving an individual’s diet. This dietary advice should be provided by a trained healthcare professional. 

For patients who are malnourished the emphasis in dietary advice should be on improving the energy and protein content of the diet. This can be achieved by increasing the number of meals per day (generally three meals and three snacks are recommended). 

Energy and protein content of the diet can also be improved by food fortification, which means adding protein and energy-rich foods to the diet, for example adding extra butter, cream, cheese, skimmed milk powder, jam and sugar to meals. This type of dietary advice does not follow typical healthy eating recommendations for the general population, however it may be appropriate for malnourished patients in the short term until nutritional status is improved.^2,3

When should I prescribe ONS?

The main prescribing indication for ONS is to improve a person’s nutritional intake. Generally speaking, the evidence available tells us that ONS have the greatest benefits when they are prescribed to patients who are malnourished (BMI <20kg/m²) or ‘at risk’ of malnutrition as identified by a validated nutrition screening tool.⁴

Ideally patients should have a full nutritional assessment by a dietitian prior to the prescribing of ONS. Nutrition screening tools such as the Malnutrition Universal Screening Tool (MUST)⁵ carried out by trained healthcare professionals can also be used to identify patients who might benefit from ONS. There is little evidence for the prescribing of ONS with well-nourished patients in any setting. 

How common is malnutrition and who is most at risk?

While the prevalence of malnutrition among the general healthy adult population is low (1-2%),⁶  recent Irish data showed that almost one-third of patients admitted to hospital from the community were at risk of developing malnutrition.⁷

The highest-risk patient groups include those with chronic disease, eg. malignancy and gastrointestinal disease, and older persons (>65 years), especially those with poor social circumstances, eg. living alone (difficulties cooking and shopping).⁴

What outcomes can I expect from prescribing ONS to my patients?

The use of ONS has been associated with clinical, functional and economic benefits when they are prescribed to patients who are malnourished or at risk of malnutrition. 

Typical clinical outcomes are weight maintenance, weight gain and increased protein and energy and micronutrient intakes. Functional outcomes include improved handgrip strength and improved activities of daily living. 

Some studies have also shown improved quality of life. ONS have been shown to have economic benefits in some studies, eg. shorter hospital stays and reduced incidence of complications post-surgery.⁴

How much ONS should be prescribed for a patient?

Assessment by a dietitian is needed to determine current dietary intake and the number/volume of ONS required to supplement the diet. 

It is recommended that no more than 500-600 calories from ONS should be provided per day unless patients are under the care of a dietitian, eg. two 200ml bottles of an ONS with an energy content of 1.5kcals/ml would provide this amount per day.⁸

Are there problems with compliance with ONS?

A recent review of ONS supplementation studies has reported that average compliance with ONS is 78% in studies where patients were followed for approximately six weeks after initiation of ONS.⁹ However, many patients in the community setting are often prescribed ONS for much longer time periods – in some cases over two years – and it is not known how good compliance is in the longer term. 

Compliance may be improved if patients are monitored regularly and offered choice of ONS. The Health Service Executive (HSE) recently changed the maximum length of ONS prescriptions in the community to one month so that there are greater opportunities for regular monitoring of patients. 

What is the difference between nutrient content of ONS and what are the new trends emerging?

The brands and types of ONS available are constantly increasing. Historically, standard ONS were available in cans and had an energy density of approximately 1kcal/ml. This type of ONS has largely been phased out and standard products usually now contain 1.5kcal/ml. 

The recent trend in recent years has been for more energy-dense supplements in smaller volumes, eg. greater than 2kcal/ml. There is some evidence to show that this strategy may result in improved compliance by patients and increased energy and protein intakes.⁹

There has also been an increase in development of disease-specific ONS products such as pre-thickened liquid ONS for use with patients with a diagnosis of dysphagia, and ONS containing n-3 fatty acids have been used with some success with some patient groups, ie. pre- and post-surgery.

Are ONS a suitable alternative to a daily multi-vitamin?

The short answer is no. For most liquid-style ONS, more than four packs per day would need to be consumed in order to provide 100% of vitamin and mineral requirements for the average adult. 

What are the costs associated with ONS? 

Generally the unit of cost of prescribing ONS is more expensive in the community setting than in the hospital setting. This underlines the importance of appropriate monitoring of patients discharged from hospital to the community on ONS. 

It should also be considered that if ONS are prescribed for patients who are malnourished the evidence shows that ONS may provide good value for money in terms of improved outcomes and reduced healthcare utilisation.⁴

Should overweight or obese patients be prescribed ONS? 

Overweight and obese individuals may not be malnourished, however they may be at risk of malnutrition. If an overweight individual with acute or chronic disease has a history of significant unintentional weight loss (Greater than 5-10% of body weight in three to six months) or has been identified as at risk of malnutrition using a nutritional screening tool, they may well require a period of ONS supplementation.

Prescribers of ONS should avoid prescribing ONS to well-nourished overweight or obese individuals as this may cause further weight gain and may exacerbate weight-related medical conditions.

What are the top tips to ensure appropriate prescribing of ONS? 

• Ensure that a nutritional assessment has been carried out on a patient before ONS are prescribed, at the very least weight and height and body mass index (BMI) kg/m² (weight/height²) should be measured and recorded. This also allows for improvements to be measured over time. 
• Identify and treat the underlying causes of malnutrition. Poor appetite can be caused by modifiable factors, for example side-effects of medications, constipation, or difficulties shopping and cooking. 
• Ensure that dietary advice is provided prior to or in addition to prescribing ONS.
• ONS are intended to supplement dietary intake, not replace it. ONS should be taken between meals rather than with or just before meals to maximise food intake.
• Ask patients about taste preferences and provide samples of ONS before prescribing to reduce wastage. Most ONS manufacturers provide a free sample service.
• Explain the purpose of prescribing the ONS to the patient and what outcomes you expect during the period of treatment.
• Monitor, monitor and review. A healthcare professional would not prescribe an expensive drug without monitoring the outcome with a patient, therefore the same rigour should be applied to ONS. 
• If the patient is being discharged home from hospital investigate the possibility of follow-up by the GP, community nurse or community dietitian to monitor their nutritional status so that ONS can be discontinued if they are no longer necessary.

References 

1. Letoha A. (2002) Foods. In Monthly Index of Medical. Specialities (MIMS). pp. 214–224. Dublin: Medical Publications (Ireland) Limited
2. Thomas B, Bishop J. eds. (2007) Manual of Dietetic Practice, 4th edn. Oxford: Blackwell
3. NICE (2006) Nutrition Support in Adults: Oral Nutrition Support, Enteral Tube Feeding and Parenteral Nutrition. London:
4. Stratton R, Green C, Elia M. (2003) Disease-Related Malnutrition: An Evidence-Based Approach to Treatment. Oxford: CABI Publishing
5. Elia M. (2000) Guidelines for Detection and Management of Malnutrition. Maidenhead: malnutrition advisory group (MAG) standing committee of BAPEN
6. Morgan K, McGee H, Watson D et al. SLÁN 2007: Survey of Lifestyle, Attitudes & Nutrition in Ireland. Main Report. Dublin: Department of Health and Children 2008
7. Russell C, Elia M. (2011) Nutrition screening survey of the UK and Republic of Ireland in 2010. A Report by the British Association of Enteral and Parenteral Nutrition (BAPEN). Available at www.bapen.org. Accessed 20/03/2010
8. Health Service Executive (2009) Suggestions for prescribing oral nutritional supplements in primary care. Written communication to General Practitioners and Directors of Public Health Nursing. (Unpublished)
9. Hubbard GP, Elia M, Holdoway A, Stratton RJ. A systematic review of compliance to oral nutritional supplements. Clin Nutr 2012; 31(3): 293-312
10. Kennelly S, Kennedy NP, Corish CA et al. Sustained benefits of a community dietetic intervention designed to improve oral nutritional supplement prescribing practices. Journal of Human Nutrition & Dietetics 2011; 24: 496-504