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Malnutrition causes, symptoms & treatments

Malnutrition is a state in which a deficiency of nutrients such as energy, protein, vitamins and minerals causes measurable adverse effects on body composition, function or clinical outcome.

What is malnutrition?

Malnutrition basically means ‘poor nutrition’. The National Institute for Clinical Excellence (NICE) define malnutrition as ‘a state in which a deficiency of nutrients such as energy, protein, vitamins and minerals causes measurable adverse effects on body composition, function or clinical outcome.’ The World Health Organisation define it slightly differently as ‘deficiencies, excesses, or imbalances in a person’s intake of energy and/or nutrients.’ Interestingly, this latter definition includes overnutrition, where there is an excess of energy or nutrients, such as in the case of overweight and obesity. Based on this definition, the majority of people in the UK are suffering from a form of malnutrition.

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What are the types of malnutrition?


Insufficient energy intake can lead to a low BMI in adults and stunted development in children. In the UK, undernutrition is most common in older people and those with health conditions that affect their appetite or ability to absorb nutrients. Over 10% of people over 65 suffer from malnutrition. Our ability to taste and smell reduces as we age and this can impact our appetite. Loss of teeth as we get older can also mean it is more difficult to digest certain foods. Older adults who live alone are at considerably higher risk of malnutrition compared to older adults who live with others. Increasing the energy density of foods (adding calories) can be an effective way of preventing malnutrition in older adults and those with limited appetites.

This can be achieved by food swaps such as switching to full-fat dairy products. These increase the calorie content without significantly increasing the volume of meals. Having additional energy-dense snacks throughout the day can also prevent unwanted weight loss in older people. Undernutrition is also a problem for those who suffer from eating disorders such as anorexia nervosa. This can have a serious effect on the functioning of the body’s organs potentially leading to death.


Overnutrition is a very common problem and much more prevalent than undernutrition. Excess energy intake can lead to overweight, obesity and increased risk of heart disease, stroke and type 2 diabetes Currently, 67% of men and 60% of women in the UK are overweight or obese, while 1 in 5 Year 6 children are classed as obese.

Micronutrient imbalances

Vitamin and mineral deficiencies can trigger specific health problems, for example, a lack of calcium can contribute to osteoporosis. A lack of iron, folate and vitamin B12 can lead to anaemia, a condition characterised a reduced number of red blood cells or haemoglobin concentration. This can cause fatigue, weakness, shortage of breath and dizziness. Iron deficiency is the most common form of micronutrient malnutrition globally. Women of childbearing age are particularly at risk due to menstruation and pregnancy. Those following a vegan diet are at risk of experiencing deficiencies of vitamin B12, as this is only found in foods of animal origin.

For this reason, it’s important that those following plant-based diets select foods that have been fortified with vitamin B12 or take supplements. Excess micronutrient intake can be just as dangerous as insufficient intake. This is normally only a problem that results from supplement use as it is rare to achieve toxic levels of micronutrients through food.

What are the causes of malnutrition?

Malnutrition (undernutrition) is caused by a lack of energy or nutrients, either as a result of a poor diet or problems absorbing nutrients from food. Certain health conditions increase the risk of malnutrition including dementia, depression, anorexia, and digestive conditions such as Crohn’s disease. As well as being a consequence of ill-health, malnutrition is also a cause of it as nutrient deficiencies can compromise your immune system and impair your body’s ability to repair itself.


What are the symptoms of malnutrition?

Some of the symptoms of malnutrition (undernutrition) include:

  • Unintentional weight loss
  • A low body mass index
  • Feeling tired
  • Impaired immunity
  • Loss of appetite
  • Children not growing or gaining weight at the expected rate

How can you treat malnutrition?

To treat malnutrition, you first need to identify the factors that are causing it. These could be:

  • psychological, such as grief or anxiety leading to a loss of appetite
  • physiological, such as difficulty swallowing, dental problems, or a lack of mobility
  • socioeconomic, such as poverty, living alone or being socially isolated

Strategies for addressing the underlying causes will then need to be developed on an individual basis. For example, an older adult who lives alone with limited mobility might benefit from having a regular delivery of frozen meals that can be easily prepared.

How can you prevent malnutrition?

The best way to prevent malnutrition is to eat a varied diet, broadly in line with the Eatwell Guide. This includes lots of fruit and vegetables, whole grains and sources of protein. Eating too little food or omitting whole food groups will increase your risk of nutrient deficiencies. Seek advice from a health professional If you are experiencing unexplained weight loss or any of the other symptoms of malnutrition.

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