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Understanding malnutrition in children

Key learning points:

- Malnutrition in children is rare and the majority of thin or short children are adequately nourished

- It is more common in infants and preschool children, who quite commonly have periods of weight faltering and benefit from advice and support from the health visitor

- Where malnutrition is suspected in older children identify and manage the underlying causes; simply offering dietary advice or supplements may make behavioural eating problems worse

Infants and young children are at a much higher risk of undernutrition than adults, but malnutrition in children is now much less common in the UK than it used to be. 

Cheap food and the social welfare system mean that food poverty in childhood is no longer a major issue, with obesity now a much larger problem. However many parents worry at some time that their child is not getting enough to eat, particularly if they are fussy eaters, and they may present their concerns to primary care.

The challenge then is how to identify the few true cases, without mislabelling many healthy children.

What is malnutrition and how does it affect growth?

Malnutrition strictly speaking describes any state of unhealthy nutrition, including obesity (overnutrition) and conditions such as Vitamin D (rickets) or iron deficiency. However this article will use malnutrition in its popular meaning of undernutrition.

A simple definition of undernutrition is that this occurs where the net intake of food energy is less than the requirements of the body for maintenance, growth and activity (1). The effect malnutrition then has depends on its severity and duration. In the short term it will lead to loss of body fat. This is often seen after childhood illnesses such as gastroenteritis or viral infections, but usually rapidly reverses once the child is better.

However, if malnutrition continues, this will progress to slower gains or loss of body mass (wasting), then slower growth (stunting). Finally, if very severe it will lead to a gradual shutdown of various body functions, such as the immune system and hair growth.

Malnutrition in adolescence can also cause delay in the onset or progress of puberty and periods may stop in older teenagers.

How is malnutrition diagnosed?

You cannot diagnose malnutrition by taking a dietary history, which tends to be very subjective and inaccurate (see Box 2). Assessing nutritional status depends on measurement of various parameters of growth as well as a few signs and symptoms that may be seen in very severe malnutrition only. None of these measures are 'tests' for malnutrition, as nearly all can also occur in well-nourished children.

Box 1 lists a range of possible signs and how useful they are at different ages. In general these signs in isolation are unlikely to be meaningful, but the more signs are found together, the stronger the likelihood of malnutrition (1).

In order to find out how extreme or unusual measurements are, you have to plot them on a centile chart. This compares them to healthy children of the same age and gender. New UK charts have recently been produced (2,3) and their instructions and supporting materials on the Royal College of Paediatrics and Child Health website provide a lot of supporting information (

In the UK, children who just have low height or weight are unlikely to be malnourished. Short stature tends to be inherited, so short children often also have short parents, but it can also just occur out of the blue and only rarely because of underlying endocrine factors (4).

Similarly, some children are just naturally slim and light. So if a child is growing steadily along a low centile for weight or height (or both) this is not likely to reflect undernutrition. If they are extremely short or light - below the 0.4th centile - they should be investigated at some time to rule out other underlying problems, but malnutrition is still unlikely to be the explanation.

Many children show weight loss after illnesses but any infant who shows weight loss that doesn't reverse within a week or so is likely to be malnourished.

Over time a malnourished infant will show slow weight gain, which shows as a fall in the weight centile. This is most commonly seen in infancy and would usually be called weight faltering. Small and short term drops in the weight centile are common, so concern should only be raised if the fall is substantial and sustained over more than two measurements: only around 1% will fall though two weight centile spaces.

Malnutrition is most likely in a child whose weight has dropped down the weight centile chart since birth by more than 2 centile spaces and who is also thin or short (1). 

Thinness is measured using body mass index (BMI). BMI varies a lot though childhood, and always tends to be much lower than adult levels, so this either needs to be calculated (weight (kg) Height (m)2) and plotted on a BMI centile chart, or you can use the lookup provided on the RCPCH growth charts (

Thinness in a child tends to make everyone think a child is not eating enough, but while a high BMI is a good way of identifying obesity, a child with a low BMI is likely to just have a lean build (1). However, a BMI below 0.4th centile is rare enough to justify further assessment.

What should raise concern in older children is unintentional weight loss: for example less than 1 in 200 school children will lose more than 2kg. A sustained drop in BMI below the normal range should also raise concern - but there can be huge variation in BMI due to variations in height measurement over time - this is only meaningful if the height centile is unchanged.

Assessing and managing weight faltering in infants and preschool children

Infants and preschool children need to eat a lot more in order to grow and are at higher risk of malnutrition than older children and adults; about 2% of infants will become significantly malnourished in the first year of life (1). This is usually due to a combination of child factors such as minor illnesses, low appetite and slow development (5).

Maternal factors play a surprisingly small part in most cases, but maternal mental health issues and child protection issues are associated with increased rates of weight faltering. Assessment by the health visitor will usually identify modifiable dietary issues and their advice can lead to subsequent improvement (see Box 1) (6).

 Major underlying medical problems often result in weight faltering, but in these rarer cases the children will be obviously unwell. There is no evidence that prescribing high-energy milks and drinks will improve weight gain and these drinks may delay transition onto solid foods.

Assessing and managing malnutrition in older children and adolescents

As children move into mid-childhood they naturally tend to slim down and parents may become concerned, but the great majority of thin or short children will in fact be adequately nourished.

The thin adolescents can be particularly challenging to assess as downward centile crossing commonly occurs as a result of differences in the onset of puberty. New specialist UK charts can help assess whether this is truly abnormal, as well as whether puberty is progressing as it should (3).

A child who is thin and has recently lost weight, or who was not previously thin, merits investigation, with management then directed at the underlying causes. Possible underlying problems to be considered are inflammatory bowel disease, depression and eating disorders.

Severely disabled children are at increased risk of undernutrition, but such children are also often naturally thin and short, so they would require more specialist assessment.

The worst thing to do in this age range is to just advise parents that they need to increase the child's dietary intake. This will not address the child's underlying problems and is likely to worsen or induce behavioural eating problems (see Box 2). Prescribing high-energy supplement drinks will also blunt the appetite, while there is no evidence that they increase overall energy intake in children (7).



1. Wright CM, Garcia AL. Child undernutrition in affluent societies: what are we talking about? ProcNutrSoc 2012;71(4):545-555.

2. Wright CM, Williams AF, Elliman D, Bedford H, Birks E, Butler G, et al. Using the new UK-WHO growth charts. BMJ 2010;340:c1140.

3. Moy R, Wright C. Using the new UK-WHO growth charts. Paediatrics and child health 2013;24(3):6.

4. Cheetham T, Davies JH. Investigation and management of short stature. Archives of Disease in Childhood 2014;99(8):767-771.

5. Shields B, Wacogne I, Wright CM. Weight faltering and failure to thrive in infancy and early childhood. BMJ 2012;345:e5931.

6. Wright CM, Callum J, Birks E, Jarvis S. Effect of community based management in failure to thrive: randomised controlled trial. BMJ 1998;317(7158):571-574.

7. Poustie VJ, Russell JE, Watling RM, Ashby D, Smyth RL. Oral protein energy supplements for children with cystic fibrosis: CALICO multicentre randomised controlled trial. BMJ 2006;332(7542):632-636.