What is an effective dose?

May 05, 2020 7 min read

This information was written by Harriet Smith, Registered Dietitian, in October 2019.

Oral nutrition supplements (ONS) are commercially produced products, prescribed for patients with disease-related malnutrition who are struggling to meet their nutritional requirements through an oral diet alone.1 Registered dietitians determine a patient’s ONS requirements based on clinical judgment; as an evidence-based profession the dietitian needs to justify the type, volume and duration of ONS used. Currently the optimal dosage of ONS is likely to vary considerably according to patient need.

Recent London audit data indicates 57-75% of ONS prescriptions are inappropriate.2 Of those initiated appropriately, few patients are followed-up to ensure ONS remain indicated, resulting in significant costs to the NHS.2 Malnutrition in England is estimated to cost £19.6 billion per year; more than 15% of the total public expenditure on health and social care.3 The National Institute for Health and Care Excellence (NICE) suggests that improving identification and treatment of malnutrition has the third highest potential to deliver cost savings to the NHS;4 therefore, it is important that the amount of ONS being prescribed is effective, both clinically and financially. This article will provide an overview of the current evidence relating to optimal dosage of ONS in the context of current prescribing guidelines.




Current prescribing

Most ONS prescriptions range from one to three supplements per day, with benefits typically seen in patients receiving at least 300 kcal/day.1 Prescribing Guidelines for ONS differ according to local trusts and clinical commissioning groups (CCGs); although many trusts consider a clinically effective dosage of ONS to be two sachets/bottles per day (depending on the product), which provides approximately 500-600 calories per day. Many of these recommendations are based upon national prescribing guidance from Prescqipp, the Malnutrition Universal Screening Tool (‘MUST’) Explanatory Booklet and the Malnutrition Pathway (see Table 1) and/or clinical experience.5, 6, 7


ONS compliance

ONS is only effective if it is consumed and compliance rates vary considerably across care settings. A systematic review paper from 2012 by Hubbard et al. looked at ONS compliance across different care settings and the influence of patient and ONS-related factors. They identified 46 studies (n=4328) which reported compliance or allowed compliance to be calculated and found mean compliance was 78% (67% in hospitals and 81% in community settings) and mean intake of ONS was 433 kcal/day.8

Patient compliance across a heterogenous group of unmatched studies was positively associated with higher- energy ONS and greater consumption of ONS and total energy intakes. However, compliance was unrelated to the amount or duration of ONS prescribed; this suggests the number of calories provided by the ONS is an important factor when it comes to improving patient compliance.


What is an optimal dosage?

Based on the Hubbard et al. paper,8 the 46 studies included in the review reported a wide range of calorie prescriptions from ONS. A simple analysis of the ONS prescriptions reported in the paper shows that calorie prescriptions ranged from less than 300 calories/day to more than 900 calories/ day, according to the calorie banding in Figure 1. The most frequently reported calorie range from ONS prescriptions was 400-600 calories per day.

The Hubbard et al. paper would suggest that it is likely to be a range of calorie intakes that have been associated with improved clinical outcomes, depending on the patient group and setting. This concurs with the calorie ranges provided by guidance in national publications.6, 7 As mentioned above, standard ONS typically provides 300 calories per serving. Since most trusts and CCGs consider 500-600 calories to be a clinically effective calorie range from ONS, it is easy to see why prescribing standard ONS twice-daily has become recommended practice.

However, there are now high-energy ONS supplements designed for once-a-day usage, which provide a clinically effective number of calories (>300 calories) in one bottle. The idea of a one-a-day dosage is that it allows flexibility in how and when the ONS is taken, particularly since studies have shown that when ONS are taken in small doses, compliance is very high (93%). This suggests that the use of high-energy ONS taken in smaller doses may help to improve compliance,8, 9 especially in patients with reduced appetite who may struggle to consume two standard ONS bottles (400 mls) per day.


Previous concerns around the one-a-day concept

The PrescQIPP Guidelines state: “Avoid prescribing less than the clinically effective dose of two sachets/bottles daily that will provide 600-800kcals/day. Once daily prescribing provides amounts that can be met with food fortification alone and will delay resolution of the problem.” 5 Whilst there is some evidence for managing malnutrition with dietary advice alone (dietitians are encouraged to adopt a food-first approach), data on clinical outcomes or cost is limited.10

Additionally, care should be taken when using food fortification to ensure requirements for all nutrients including macro and micronutrients are met. Finally, acute and chronic disease may adversely affect appetite and a patient’s ability to purchase, prepare and consume home-made fortified meals and drinks.11 Thus, food fortification techniques are only effective if it is realistic and sustainable for the patient and carer alike.

Existing research into the benefits of ONS has shown that:

  • ONS can improve energy and protein intakes, reduce complications and readmissions to hospital, improve hand grip strength and body weight, with little reduction in normal food intake12

  • ONS help to improve functional status (handgrip strength) and quality of life and reduces hospital readmissions13

  • ONS are a clinically and cost-effective way to manage malnutrition, especially in patients with a low BMI, living in the community setting14


Clinical benefits of ONS include

Reductions in complications (e.g. pressure ulcers, poor wound healing, infections) and mortality (in acutely ill older people)12, 15



This article has highlighted the limited evidence base for optimal dosage of ONS. Whilst the protocol in many trusts is to prescribe standard ONS twice daily, ONS is only effective if it is taken by the patient. Current literature has shown that providing high-energy ONS is associated with improved patient compliance, whereas volume and frequency of ONS had no effect. Put simply, it appears to be the amount of calories, not the number of bottles/sachets of ONS that matters; this is supported by the Managing Adult.

Malnutrition in the Community Pathway, which advocates a calorie range of 300-900 kcal/day for clinical benefit. Prescribers may therefore require further education and guidance to better understand the factors that influence ONS compliance. Local trusts and CCGs must take this into consideration, perhaps by placing greater emphasis on a clinically effective range of calories rather than volume or frequency of prescriptions.

Previous concerns relating to once daily prescribing are not supported by scientific literature and are most likely referring to standard ONS, providing approximately 250-300 calories per bottle/sachet. There are now high-energy ONS supplements available which provide a clinically effective amount of calories in one serving, making it a convenient option for patients with reduced appetite. Thus, prescribing high- energy ONS once-a-day versus multiple standard ONS daily may help to increase compliance, manage malnutrition and potentially deliver cost savings to the NHS. The optimal dosage of ONS warrants further investigation, however this “quality, not quantity” concept is an important message to highlight to healthcare professionals, especially registered dietitians considering their own prescribing practice.



1. Gandy J (Ed.) (2014). Manual of Dietetic Practice; chapter: 6.3 Oral Nutritional Support. Wiley-Blackwell. (2014).

2. Forrest C, Wilkie L (2009). London Procurement Programme Clinical Oral Nutritional Support Project. London Procurement Programme.

3. Elia M (2015). The cost of malnutrition in England and potential cost savings from nutritional interventions (short version). A report on the cost of disease-related malnutrition in England and a budget impact analysis of implementing the NICE clinical guidelines/quality standard on nutritional support in adults. Accessed online: https://www.bapen.org.uk/pdfs/economic-report-short.pdf

4. NHS England (2015). Guidance - Commissioning Excellent Nutrition and Hydration (2015- 2018). Accessed online: www.england.nhs.uk/wp-content/uploads/2015/10/nut-hyd-guid.pdf (Aug 2019).

5. Prescqipp. (2017). Guidelines for the appropriate prescribing of oral nutritional supplements (ONS) for adults in primary care. Accessed online: www.prescqipp.info/media/1512/b145-ons-guidelines-30.pdf (Aug 2019).

6. Elia M, et al. Malnutrition Action Group. (2003). The ‘MUST’ Explanatory Booklet: A Guide to the ‘Malnutrition Universal Screening Tool’ (‘MUST’) for Adults. BAPEN. Accessed online: www.bapen.org.uk/ pdfs/must/must_explan.pdf (Aug 2019).

7. Malnutrition Pathway Consensus Panel. Managing Adult Malnutrition: Including a pathway for the appropriate use of oral nutritional supplements (ONS). Accessed www.malnutritionpathway.co.uk/ons (Aug 2019).

8. Hubbard GP, et al. (2012). A Systematic Review of Compliance to Oral Nutritional Supplements. Clin Nutr.; 31(3): 293-312.

9. van den Berg GH, Lindeboom R, van der Zwet WC (2015). The effects of the administration of oral nutritional supplementation with medication rounds on the achievement of nutritional goals: A randomized controlled trial. Clin Nutr.; 34(1): 15-19.

10. Baldwin, C and Weekes, C.E. (2011). Dietary advice with or without oral nutritional supplements for disease related malnutrition in adults (review). Cochrane Database Syst Rev.; (9): CD002008.

11. The National Institute of Health and Care Excellence (NICE) (2006). Nutrition support for adults: oral nutrition support, enteral tube feeding and parenteral nutrition. Clinical guideline [CG32]. Accessed online: www.nice.org.uk/Guidance/CG32 (Aug 2019).

12. Cawood AL et al. (2012). Systematic review and meta-analysis of the effects of high-protein oral nutritional supplements. Ageing Res Rev.; 11(2): 278-296.

13. Norman K et al. (2008). Three month intervention with protein and energy rich supplements improve muscle function and quality of life in malnourished patients with non-neoplastic gastrointestinal disease - a randomized controlled trial. Clin Nutr.; 27(1): 48-56.

14. Elia M, et al. (2016). A systematic review of the cost and cost effectiveness of using standard oral nutritional supplements in community and care home settings. Clin Nutr.; 35(1): 125-137.

15. Stratton RJ, Elia M. (2007). A review of reviews: A new look at the evidence for oral nutritional supplements in clinical practice. Clin Nutr Suppl.; 2(1): 5-23.