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Adult malnutrition and the role of Oral Nutritional Supplements (ONS)

Kate M. Forde BSc MPH RD is Specialised Nutrition Executive – Foods for Special Medical Purposes at Dairy Industry Ireland, and is an experienced dietitian.

She answered our questions ahead of the release of a series of videos and factsheets on adult malnutrition and Oral Nutritional Supplements (ONS).

What is malnutrition and why is it important?‎

Malnutrition is a serious condition that occurs when a person’s diet does not contain enough nutrients to meet the demands of their body. This can affect growth, physical health, mood, behaviour and many of the functions of the body, including its ability to heal or repair. You can also become malnourished if your diet does not contain the right balance of nutrients. It is possible to eat a diet high in calories but containing few vitamins and minerals. This means you can become malnourished, regardless of your body size1.

Weight loss and malnutrition can increase a person’s risk of serious but potentially avoidable complications. It is associated with poorer response to therapy and poorer outcomes, which can really impact a person’s overall quality of life. That is why it is so important. It also has a particularly negative impact on older people as it can adversely affect their function, mobility and independence2.

People who are considered malnourished experience more complications than those that are well-nourished. For instance, the risk of infection is greater in hospitalised malnourished patients and, in the community, malnourished patients are likely to visit their family doctors more often. The annual healthcare costs associated with malnutrition are enormous, estimated at €170bn3 across Europe, for example. However, malnutrition is usually relatively simple and inexpensive to treat, especially if detected early. Research has shown that raising awareness of malnutrition, effective screening programmes and early treatment leads to better patient outcomes3.

Who is at risk of being malnourished and what are the risk factors?‎

Anyone is at risk of becoming malnourished at some point in their lifetime and it can often be difficult to recognise as there are many factors that could contribute to that risk. A loss of appetite coupled with unintentional weight loss signal that an individual has an inadequate intake of energy, protein and other nutrients, which contributes to the risk of becoming malnourished.

Other factors that can contribute to malnutrition are1:

  • If someone has eaten little or nothing for the last five days
  • Or if they are likely to eat little or nothing for the next five days or more due to certain medical conditions
  • If the body is unable to absorb nutrients from the diet or normal foods as expected
  • Some underlying conditions can mean your body is likely to need additional nutrients than it did previously
  • If teeth are in a poor condition, eating can be difficult or painful
  • If swallowing food is difficult or painful (the medical term for this is dysphagia and there are a range of causes, such as a blockage in your throat, damage to the nerves used in swallowing or sores in the mouth)
  • A loss of appetite as a result of losing your sense of smell and taste
  • Physical disability or other impairments could make it difficult for you to cook for yourself
  • Taking many different types of medication at the same time can disrupt the body’s ability to absorb and use nutrients efficiently
  • The body may have an increased demand for energy at times, e.g. if it is trying to heal itself after a serious injury or surgery
  • Social factors can also contribute, such as low income, living alone and being socially isolated, having reduced mobility and lack of transport with restricted access to amenities
  • Mental health conditions may affect your ability to look after yourself
  • Older people may become malnourished gradually if poor health begins to affect their ability to feed themselves properly. Malnutrition then, in turn, makes their health worse.

These are just some of the considerations that will be taken into account during a nutritional assessment by a healthcare professional. Malnutrition can develop rapidly during periods of acute illness or more gradually, depending on the circumstances. This highlights the importance of nutrition screening, which takes less than 5 minutes and can identify those at risk2.

How is malnutrition identified and treated?‎

A diagnosis of malnutrition is usually made following a nutritional assessment by a trained healthcare professional, based on factors such as weight, unintentional weight loss, or whether something, such as a health condition, has impacted a person’s ability to absorb nutrients from their diet. Any other medical conditions or investigations a person may be undergoing are also taken into account1.

There are validated screening tools that use a practical, simple method as the first step in identifying people who are at risk of being or becoming malnourished and who are likely to require a nutritional intervention2. There are many nutrition screening tools available, but the most commonly used validated screening tools are the ‘Malnutrition Universal Screening Tool’ (MUST) or the ‘Mini Nutrition Assessment’ (MNA). The MUST is a five-step screening tool to identify adults with malnutrition used in all healthcare settings. The MNA is a validated nutrition screening and assessment tool comprised of six questions that is specially used for those aged 65 and above2.

Screening should be undertaken in all healthcare settings, such as on admission to hospital both as an inpatient and outpatient appointments and weekly thereafter if there is a clinical concern. All residents of care and nursing homes should be screened on admission, with screening repeated monthly given the high prevalence of malnutrition in these populations. Moreover, screening should be carried out at initial registration in GP surgeries, repeated where there is a clinical concern and at other opportunities, such as health checks or vaccinations4.

Screening, however, is only ever designed to be a quick way of identifying those who are at significant risk of nutritional problems so that further detailed nutritional assessment can be undertaken by a trained healthcare professional, such as a registered dietitian2.

The main treatment option for somebody identified by these screening tools is to increase the energy calorie and protein content of their diet. Consideration is also given to the need for the right balance of vitamins and minerals. Calories in food are what give your body energy. Protein is known as the ‘building block’ of the body, helping it build, repair and maintain strength1.

A dietitian or other healthcare professional will discuss what changes can be made to a person’s diet to increase the energy calorie and protein content. They will develop a recommended diet plan depending on individual circumstances and food preferences. They will also provide someone with support to make these dietary changes, with the aim to ensure nutritional adequacy of their diet over long periods. In addition to these dietary changes, depending on the circumstances, oral nutritional supplements (ONS) may also be recommended to achieve a person’s nutritional requirements.

What are Foods for Special Medical Purposes (FSMPs), such as Oral Nutritional Supplements (ONS)?

Foods for Special Medical Purposes (FSMPs) are designed to meet nutritional needs arising from a wide range of medical conditions that affect people of all ages, from infancy to old age. They are food products created for the dietary management of people suffering from a disease, disorder or medical condition that either temporarily or permanently affects their ability to achieve a suitable nutritional intake using normal foods5.

Oral Nutritional Supplements (ONS) are a type of FSMP that are tailor-made food products with specific amounts of energy (calories), protein, fat, carbohydrates, vitamins and minerals5. There are many different types of ONS:

  • Powders that can be made up into drinks using fresh milk or water or added to drinks and/or foods and recipes
  • Ready-to-drink milk-based or juice-style drinks
  • Pudding type ONS for those who may have a difficulty swallowing  

ONS are available in a choice of flavours and textures, so that anyone who needs them is able to find a product that suits them. This promotes enjoyment of the products, thereby encouraging better compliance and ensuring that they are adequately nourished. A healthcare professional will help someone to decide which one is best for their needs and preferences.

ONS are an effective and non-invasive solution to tackle malnutrition and provide functional benefits in those who are typically able to consume some normal food, but not enough to meet all of their nutritional needs3. These products are consumed across all healthcare settings – in hospitals, care homes, clinics and in private homes, but should only be used based on the recommendation of, and used under the supervision of, a healthcare professional. This necessary and continued supervision by a healthcare professional clearly distinguishes FSMPs, including ONS, from other food types3.

How do ONS address malnutrition and how do they fit into a patient’s nutrition management or care ‎plan?‎

ONS are foods that contain specific amounts of energy, protein, vitamins and minerals that you would normally get from a healthy balanced diet. They are specifically designed for people who may not be able to eat enough food to meet their needs through their regular diet alone. They are designed to improve the amount of nutrients you get to help maintain your body weight or to help cope better with illness and recover more quickly.

There are several reasons why ONS may be prescribed in addition to dietary changes. For example, a person may have unintentionally lost weight due to illness as they find it more difficult to eat normal foods because of their symptoms. Certain conditions can impact a person’s appetite, cause taste changes or make it difficult to swallow normal foods, making it too difficult for them to increase their intake of normal foods.

The supervising healthcare professional will help decide which ONS is best suited to the person and their condition. Importantly, they should explain the need to take ONS, how many to take and for how long they will be needed. In most cases, they will only be needed while someone is having difficulty eating a normal diet or until they have reached a healthy weight. The healthcare professional should regularly review their progress while they are taking ONS, taking factors such as weight and how the person is managing with the recommended ONS into consideration, and they will ask questions about what the person is managing to eat. Regular reviews are important to make sure they are getting the maximum benefit from the ONS and that they are only taken for as long as they are needed.

It is also very important that they ensure ONS are taken alongside normal foods and are not used as a replacement for normal food or the recommended diet plan as advised by a dietitian. The purpose of ONS is to help boost a person’s current dietary intake and not replace it, so it is important that they only take the recommended dose each day. They may be taken between meals like a snack, first thing in the morning or before bed-time. Some people find that taking small amounts regularly throughout the day also helps. ONS are also very versatile and can be incorporated in favourite recipes or meals, for example in porridge for breakfast. However, it is still important that any dietary advice or changes are made under the supervision of a trained healthcare professional.


  1. HSE. Malnutrition in Ireland. Available: (accessed 5 April 2022).
  2. IrSPEN. UNDERSTANDING MALNUTRITION. Available: (accessed 5 April 2022).
  3. MNI (2018). Better care through better nutrition: Value and effects of Medical Nutrition. Brussels: Medical Nutrition Industry International.
  4. BSNA. Medical Foods Q&A. Available: (accessed 5 April 2022)
  5. SNE. Food for Special Medical Purposes. Available: (accessed 5 April 2022)