Malnutrition: Causes, symptoms and support

Many of us associate malnutrition with unplanned weight loss, but the reality is far more complex. Malnutrition isn’t always visible. It can develop due to nutritional imbalances, underlying medical conditions, hormonal changes, or lifestyle factors – even in people who appear to be eating well or are at a healthy weight.

If you’re wondering what malnutrition really means, what can cause it, and how to address it, you’re in the right place.

Malnutrition explained

Malnutrition occurs when the body isn’t receiving the nutrients it needs to function optimally. This doesn’t just refer to calories; it can also involve deficiencies or imbalances in vitamins, minerals, protein, fats, or carbohydrates.

Over time, these gaps can affect both physical and mental health, leading to symptoms such as fatigue, poor concentration, frequent illness, hormonal disruption, or reduced recovery from illness or injury.

I often see clients who are eating regularly and maintaining their weight, yet are still malnourished due to poor absorption, restricted diets, or increased nutritional needs that simply aren’t being met.

For example, someone with an underlying condition like coeliac disease may absorb fewer nutrients from food due to intestinal damage, despite eating a balanced diet. This can lead to low calcium and iron levels, which may affect bone health or even cause anaemia. Others may develop malnutrition as a result of hormonal imbalances, medical treatments, or long-term dietary restriction.

What can cause malnutrition?

Malnutrition rarely has a single cause. It’s usually the result of several factors working together.

Underlying medical conditions

Certain conditions can interfere with digestion, absorption, or appetite, increasing the risk of malnutrition. These may include:

• Coeliac disease
• Crohn’s disease or ulcerative colitis
• Small Intestinal Bacterial Overgrowth – or SIBO
• eating disorders or long-term disordered eating
• cancer and cancer treatments

Inflammation, gut damage, nausea, pain, or food avoidance can all reduce nutrient intake or absorption over time.

Nutritional imbalances

Even without a diagnosed condition, a lack of dietary variety can lead to nutrient deficiencies. I commonly see:

• iron deficiency, leading to fatigue and anaemia
• vitamin D deficiency associated with bone pain, muscle weakness, and low mood
• protein deficiency, which can impair healing, reduce muscle mass, and weaken immunity

These imbalances often develop gradually and are easy to miss until symptoms begin to interfere with daily life.

Hormonal imbalances

Hormones play a key role in how the body uses and distributes nutrients. Conditions such as hypothyroidism, hypothalamic amenorrhoea, or polycystic ovary syndrome (PCOS) can alter metabolism, appetite, and nutrient requirements.

In practice, this may show up as persistent fatigue, weight changes, low energy, mood changes, or menstrual disruption – symptoms that are sometimes dismissed without considering underlying nutritional status.

Lifestyle and life stage factors

Every day life can also contribute to malnutrition. Common examples include:

• restrictive diets for weight loss or symptom management
• busy or stressful lifestyles that disrupt regular meals
• ageing, where appetite may decrease, but nutrient needs remain high

Athletes, older adults, and people managing chronic stress or long-term health conditions are particularly at risk.

Signs and symptoms of malnutrition

Some common symptoms of malnutrition to look out for include:

• persistent fatigue or weakness
• hair thinning or hair loss
• brittle nails or dry skin
• difficulty concentrating or memory issues
• digestive symptoms such as bloating or diarrhoea
• unplanned weight loss – or sometimes unexplained weight gain

These symptoms are often subtle at first, which is why malnutrition can go unnoticed for months or even years.

What to do if you think you may be malnourished

Addressing malnutrition requires a personalised approach, particularly when medical or hormonal factors are involved. This is where working with a registered dietitian can make a real difference.

Identify the root cause

The first step is understanding why malnutrition may be occurring. With my clients, I assess dietary intake alongside medical history, symptoms, and, where appropriate, recommend blood test results. Without identifying the underlying cause, nutritional issues are unlikely to fully resolve – sort of like filling up a leaky bucket. 

Build a balanced, realistic nutrition plan

Rather than relying on generic advice, nutrition support should be tailored to your individual needs. This may involve:

• correcting specific nutrient deficiencies
• supporting gut health and nutrient absorption
• adjusting meal patterns to suit appetite, energy levels, and lifestyle
• ensuring adequate protein and overall energy intake

The aim is to create a plan that is both nourishing and sustainable.

Practical tools for everyday life

Long-term change matters. Practical support might include meal planning guidance, supplement advice where appropriate, or condition-specific recipes that make nourishing yourself easier and more enjoyable in day-to-day life.

Where do I start?

If you suspect malnutrition or you have a condition that puts you at risk, seeking support early can make a significant difference. This is particularly important if you’re experiencing ongoing fatigue, digestive symptoms, or have a diagnosed medical condition that affects nutrition.

Addressing nutritional issues sooner rather than later can help prevent longer-term complications and improve energy, sleep, and how you feel day to day. If you’d like to discuss your concerns and explore whether personalised nutrition support is right for you, reach out to take the first step.