Written by Katherine Nicholls
Katherine Nicholls
Nutritionist Resource Content Team

Last updated 4th April 2024 | Next update due 4th April 2027

Malnutrition essentially means ‘poor nutrition’ – when the human body contains an insufficient, excessive or imbalanced consumption of nutrients.

On this page, we explore the causes and symptoms of malnutrition and how to spot the signs that you or someone you know needs treatment. We will also look into the common types of treatment for malnutrition, and the support available to help sufferers maintain a healthy nutritional intake in the long-term.

What is malnutrition? 

Malnutrition refers to deficiencies, excesses or imbalances in a person’s intake of energy and nutrients. Malnutrition can affect people of all ages, genders and health, although it tends to be more common in developing countries where there are shortages of food. In industrialised countries, however, more and more people are being diagnosed with the condition, with factors such as diet, alcoholism, mental health problems, and digestive disorders cited as common causes.

The two types of malnutrition are:

  • Undernutrition (subnutrition) – When a person’s diet is lacking in nutrients and does not provide them with an adequate amount of calories, sustenance and protein for maintenance and growth. Undernutrition can also occur if the body cannot efficiently use food as a result of an illness.
  • Overnutrition – When a person’s diet is getting far too many nutrients for the body to cope with. Usually a result of people choosing to eat more food than they need, but in rare cases it can be caused by excessive supplement intake.

What are the causes of malnutrition?

Poor diet

As explained above, the most common causes of malnutrition are diet-related – getting too much, or not enough food. In less developed countries many people will develop undernutrition as a result of food shortages and famine.

In more wealthy and industrialised nations such as the UK, food is more accessible but a lot is fatty, sugary and devoid of any nutritional value. When our diets become too heavily laden with these types of foods our health suffers and we can start to develop symptoms of malnutrition that reflect overnutrition. 

Illness and medical conditions 

Illnesses and health problems can also cause malnutrition, especially as they can impact eating habits. For example, if an illness leaves a patient with symptoms of dysphagia (difficulty swallowing), they may not be able to consume enough of the foods that they need for healthy nutrition.

Digestive disorders and stomach conditions are further causes of malnutrition. Crohn’s disease for example disrupts the body’s ability to digest food and absorb vital nutrients, meaning the patient’s health can suffer. On the other hand, people who suffer from digestive complaints such as IBS might avoid eating certain foods, which means they could be missing out on vital nutrition. 

Other medical conditions that can cause malnutrition include:

  • Conditions that suppress appetite, such as cancers, diseases of vital organs and persistent pain or nausea.
  • Persistent diarrhoea.
  • Taking lots of different medications at the same time can affect how the body breaks down nutrients.
  • Kidney failure.
  • AIDS makes sufferers more susceptible to undernourishment because they cannot absorb valuable vitamins, calories and iron.
  • Excessive sweating can lead to loss of nutrients.
  • Gastritis – often caused by excessive alcohol consumption – is a digestive complaint that can seriously limit how much food and nutrients the body can ingest.

Mental health problems

People suffering from mental health problems are more likely to have poor nutrition as they can find it difficult to look after themselves properly, especially if they struggle to communicate their needs to carers. Research conducted by Alzheimer’s Disease International (ADI) revealed that half of people with dementia and Alzheimer's will end up showing signs of malnutrition.

Depression can also impact our diets and how we look after ourselves, while people suffering from more acute psychological disorders such as anorexia nervosa and bulimia will severely limit the amount of food they consume and how many nutrients can be absorbed through the digestive process.

Physical factors

A whole host of physical factors can contribute to poor nutrition. If a person has a disability or impairment, they may find it difficult to go shopping or cook. Poor dental hygiene, such as badly fitting dentures or painful gums can also prevent people from eating properly and getting the right amount of nutrients. A lost sense of smell or taste can put people off eating altogether. 

Social factors

The environment can significantly impact diet, and people surviving on low incomes and/or in poverty are more likely to develop symptoms of malnutrition. Although malnutrition due to inadequate food intake in the UK is rare, there are still circumstances where neglect and poverty can lead to undernutrition, particularly in children. Living alone and being socially isolated may also affect a person’s eating habits, while those suffering from alcohol or drug dependencies are likely to have little appetite.

Taking too many nutritional supplements

While overnutrition is commonly associated with overeating, it can also stem from taking too many nutritional supplements. Many people take vitamins and supplements as part of a healthy diet and lifestyle, but in rare cases, excessive consumption can lead to vitamin and iron poisoning.

Synthetic nutritional supplements should be taken with caution and you should always consult a medical professional before taking supplements as a means of correcting a severe deficiency.

What are the symptoms of malnutrition?

The symptoms of malnutrition refer to the way someone feels as a result of poor nutrition. Physical and emotional symptoms vary depending on the severity of malnutrition and the causes behind it.

Some of the common symptoms of undernutrition include: 

  • depression
  • aching joints
  • soft and tender bones
  • breathing difficulties
  • tiredness and fatigue
  • lower sex drive
  • low blood pressure
  • lower body temperature
  • diarrhoea
  • dizziness
  • bleeding and/or swollen gums
  • irritability
  • loss of reflexes and lack of coordination
  • scaling and cracking of the lips and mouth

Symptoms of overnutrition can include:

  • obesity
  • type 2 diabetes
  • diarrhoea
  • bleeding
  • high blood pressure
  • heart problems
  • hair loss
  • difficulty walking

What are the signs of malnutrition?

The signs of malnutrition are normally detected by other people, such as your family, friends, doctor or nutritionist.  People suffering from undernutrition in particular may not be mindful of the physical changes to their bodies due to poor nutrition. 

Signs of undernutrition

The common signs of undernutrition include: 

  • loss of body fat and muscle mass
  • sunken cheeks
  • white fungal growth on the tongue
  • poor memory
  • chewing and/or swallowing problems
  • hollow eyes
  • abdominal swelling and constant bloating
  • protruding bones
  • thinning, dry, cold and pale skin
  • dry and sparse hair that falls out easily
  • apathy, introversion, self-neglect and deterioration in social interactions
  • in more severe cases, sufferers may even show signs of unresponsiveness (stupor)

In children, signs of undernutrition can also include stunted growth and considerably slow mental and behavioural development. In rare cases, some children may even develop the bone disease rickets which is caused by insufficient calcium intake. 

Signs of overnutrition

The main sign of overnutrition is obesity, however, people with undernutrition can also be overweight if their diet is high in calories but low in essential nutrients. Overnutrition caused by an overdose of vitamins usually causes digestive problems such as stomach cramps, diarrhoea, and persistent nausea.

If you are concerned that you or someone you know is suffering from malnutrition, it's important to get in touch with a medical professional. They will check for signs of malnutrition, carry out a health assessment and analyse your symptoms to reach a diagnosis. 

What are the effects of malnutrition?

As well as the various symptoms of malnutrition, the condition can also lead to complex health conditions that can greatly affect overall well-being. 

Effects of undernutrition

For those who are undereating, usually, the effects of malnutrition will only occur if a calorie and nutrient deficiency continues for a period of time. 

Some of the most common side effects of undernutrition include: 

  • respiratory failure
  • higher risk of hypothermia and pneumonia
  • weaker immune system thus increasing risk of catching an infection and longer recovery time
  • poor wound healing
  • fertility problems
  • organ failure
  • urinary infections
  • development of health conditions such as oedema, anaemia and jaundice
  • total starvation could be fatal if no calories have been consumed for a long period of time

There can also be severe consequences that result from specific micronutrient deficiencies in someone’s diet.

Below are some of the most common: 

  • Iron deficiency - can cause anaemia.
  • Zinc deficiency - affects the body’s ability to fight infection and causes skin rashes.
  • Vitamin B12 deficiency - linked to anaemia as well as problems with nerves.
  • Vitamin D deficiency - causes bone diseases such as osteomalacia in adults and rickets in children.
  • Vitamin C deficiency - can cause scurvy.
  • Vitamin A deficiency - can lead to night blindness.

Effects of overnutrition

For those suffering from overnutrition, the effects on physical and emotional health will be very similar to those caused by undernutrition. However, debilitating obesity-related illnesses such as type 2 diabetes, high blood pressure and gallstones will exacerbate these.

The health implications of excessive consumption of supplements depend on the nutrient and their intensity.

Some of the more severe side effects of very high mineral and vitamin dosages can include:

  • poisoning
  • hardening of the arteries
  • increased susceptibility to infectious diseases
  • gallstones
  • cardiac arrest
  • heart problems
  • metabolic disturbances
  • stomach problems
  • numbness
  • allergic reactions

Treatment for malnutrition

Treatment for malnutrition depends on how severe the malnutrition is and what is causing it. After an assessment and diagnosis by a medical professional, sufferers may need dietary advice and supervision from a dietitian and/or a nutritionist to safely change and improve their eating habits in the long term. For those suffering from severe malnutrition and/or showing evidence of health problems that have contributed to the condition, hospital admission may be required.

Hospital admission

Admission to a hospital will put malnutrition sufferers in the care of a number of different health professionals. These will provide support and medical attention to not only treat symptoms of malnutrition but also the underlying cause of the condition. 

Hospital admission is particularly important for those who have difficulty swallowing food, and an artificial feeding method may be needed to get vital nutrition into the body.

The most common artificial feeding treatments include: 

  • A feeding tube (nasogastric tube) that is passed down the nose and into the stomach to provide nutrients directly to the digestive system.
  • A percutaneous endoscopic gastronomy (PEG) tube that is surgically placed directly into the stomach.
  • A drip which will provide nutrients and fluids directly into a vein.

In addition, sufferers of malnutrition with swallowing difficulties may be referred to a speech and language therapist (SLT) who can assess the problem and offer advice about a special diet that can help.

The amount of time you will spend in the hospital will depend on your general state of health and the underlying cause of your malnutrition. It is often possible to return home while receiving treatment.

How can a nutritionist help with malnutrition?

The main treatment for malnutrition involves making dietary changes with the help of a dietitian and/or a nutritionist. While a dietitian will provide in-depth rehabilitation and treatment processes for malnutrition sufferers, a nutritionist is a food expert who educates clients about the importance of diet for optimising health and well-being on a long-term basis. 

Essentially, a nutritionist is ideal for seeking further help after you have recovered from the initial symptoms of malnutrition. They will devise an eating plan that caters for all your needs, dietary requirements, health conditions - such as difficulty swallowing - and nutritional goals. This will be followed up by consistent support and advice to ensure you build a long-term positive relationship with healthy eating. You can use Nutritionist Resource's search tool to find a qualified professional best suited to you.

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