This article was written by Nutritionist and Dietetically Speaking Intern Hanna Tejani and reviewed by Registered Dietitian Maeve Hanan.

Our brain is extraordinary, and it needs plenty of energy to fuel all the functions it carries out. Hence, proper nutrition plays a vital role in brain function.

This fascinating organ accounts for 20% of our total energy needs whilst only taking up around 2% of our total body weight! (1)

The brain is responsible for a whole host of neural processes. It is the central hub where 85 billion neurons are involved in our ability to make decisions, feel emotions, remember information, spark ideas and more (2). 

With 3 million individuals in the UK either suffering or at risk of malnourishment, it is important to understand how this impacts our brains (3). 

Being malnourished can have a big impact on our brains and can impair some of the key functions we need for basic survival. This article will delve deeper into what exactly happens to the malnourished brain.

Brain Structure

The brain is an extremely complex organ, so to help understand this vital command centre, we can break it down into 3 distinct regions, each responsible for different tasks.

The Forebrain: 

This contains the largest part of our brain – the cerebrum (4). It is responsible for understanding and interpreting our surroundings including what we see, feel, and hear. The forebrain also plays a role in regulating our emotions, learning new information and coordinating movement (5).

The Midbrain: 

This part of our brain connects the forebrain (cerebrum) to the hindbrain (the spinal cord). The midbrain is key in regulating our movement and processing audio and visual cues – including controlling our eyes and eyelid movement (4).

The Hindbrain: 

This part of the brain is essential for our everyday survival and is under our subconscious control, meaning we carry out these processes without even being aware that we are doing so. This includes our breathing, heartbeat, and dilation of blood vessels (6).

1. Structural Changes to the Brain

During early life, nutrition is crucial in neural development, and pregnant mothers are commonly advised of the importance of nutrition on the development of their baby (7). Furthermore, studies have attributed malnutrition within the first years of life to a reduced brain volume in young adults (8).

However, the effects of good nutrition on the brain are not limited to infants and children.

The brain can actually shrink in size as a result of malnutrition.

In a study conducted on 475 adults (around the age of 80 years old), the link between malnutrition and structural brain changes were investigated. The MRI brain scans revealed that there was a significant association between low vitamin B1 intake and severe structural changes to the brain (9). These lesions on the brain have been associated with decreased cognitive function and an increased risk of stroke and dementia (10).

Moreover, a study that investigated energy intake and brain structure in those with anorexia nervosa found that cognition was impaired, especially if the onset was during adolescence. However, this damage has been shown to be reversible through recovery (11, 12). 

2. Reduced Reward Response, Emotional Changes and Inflexibility

We know that our desire to eat is made up of a multitude of contributing factors including palatability, sensory appeal, and preferences towards different foods. A key feature of this desire is our brain’s reward system. This system takes hedonic pleasure (liking) and salience (wanting) and converts it into a desire or reward that is associated with eating food (13).

A good way to understand this is by looking at the animal kingdom. Monkeys will seek out bananas by their yellow skin and association with the taste of the fruit itself, and the positive experience of eating the banana further increases their desire to eat bananas! (14)

At the core of this incredible system lies a very important neurotransmitter – dopamine. Dopamine is produced in the midbrain and its release stimulates the limbic areas of the brain such as the nucleus accumbens. Dopamine is typically triggered by pleasant foods and its levels are elevated in the nucleus accumbens when we eat foods that taste good. This provides more incentive for us to eat these foods.

Research has shown that when protein is restricted in the diet, it interferes with the pathways that are responsible for producing dopamine, therefore leading to a blunted response in our desire to eat (15, 16).

In addition to this, there is emerging research suggesting that some eating disorders could be related to a dysfunction in our food reward response, where foods are hedonically liked too much or too little. Although, more research is still being conducted in this area as it is a ‘chicken or egg’ situation where further understanding is required to see what comes first (17).

In addition to this, our brain also regulates our emotions. Studies have found that poor diet in early life can result in an inflammatory response that activates the areas of our brain that regulates emotions. This constant inflammation impairs the functioning of these regions which can also cause issues with remembering information and cause depressive-like behaviours (18). 

3. Issues with Thinking, Concentration and Problem Solving

We have all been there, losing concentration mid-way through the day only to realise we accidentally skipped lunch. Well, there is a very good reason why we feel this way. We mentioned above that the energy needs of the brain, and some of this energy goes towards problem-solving. 

A lack of energy (i.e. by not eating enough or leaving long gaps between eating) can affect our ability to process information and concentration. 

In addition to this, malnutrition can have an impact on our sleeping patterns which indirectly also affects our ability to concentrate, and problem solve (19).

There is a growing body of evidence that suggests that specific deficiencies can result in poor concentration and memory, mind-blanks and even lack of motivation (20). These include:

• Vitamin B1: also known as thiamine, you can find this vitamin in foods such as peas, bananas, oranges, nuts, wholegrains, and liver.
• Vitamin B5: or pantothenic acid can be found in chicken, been, liver and kidneys, eggs, mushrooms, and avocados
• Vitamin B6: this vitamin also goes by pyridoxine. Foods containing B5 include pork, chicken, fish, soya beans, oats, banana, and milk. 
• Vitamin B12: aka cobalamin and good sources include meat, fish, milk, cheese, eggs, and some fortified breakfast cereals. As you can tell we get cobalamin from mainly animal sources so if you are vegan, you may need a B12 supplement!
• Zinc: foods that are a good source of zinc are meat, shellfish, dairy products, bread, and cereal products (21, 22).

4. Less Oxygen Available for the Brain

One of the more severe consequences of malnutrition are the changes observed with reduced cardiac output and blood pressure and these are even seen in cases of acute malnourishment, especially in adolescents (23).

Low heart rate and blood pressure are particularly common in patients with anorexia nervosa – with 95% experiencing low blood pressure (24).

You may be wondering; how does this affect the brain? Our heart pumps blood around our bodies, delivering oxygen to the muscles and organs that are hard at work.

A low heart rate and blood pressure can cause the brain to become deprived of oxygen leading to symptoms including fainting, fatigue, memory issues and confusion (25).

5. Neurotransmitters Disruption 

We mentioned above how dopamine is an important neurotransmitter and the evidence base for malnutrition and how this affects our food reward system. However, dopamine is not the only neurotransmitter that is affected when we are malnourished. Serotonin is another vital neurotransmitter, and it is nicknamed ‘the happy hormone’ due to its function in controlling satisfaction, happiness, and optimism (26). 

Serotinin is also a key player in regulated hunger, sex, sleep, and memory. If we look at the life cycle of this nifty neurotransmitter, it starts out as tryptophan, an essential amino acid.

Our essential amino acids can only be derived from our diets, and low brain serotonin stores have been observed in cases of malnutrition.

Without serotonin our brain will struggle to module the vital processes that we mentioned above which is likely to have a knock-on effect on our mood (27).

6. Increased Risk of Depression, Anxiety, and Social Isolation

The repercussions of malnutrition on physical health have been well accounted for, but how about our mental health? Malnutrition is particularly prevalent in the elderly, who make up 1.3 millions of malnourished individuals in the UK. A study conducted on 3,111 older adults found that mental health was significantly affected with an increasing risk of malnutrition in this community. Though it is difficult to provide an explanation for why this occurs, some reasons proposed include micronutrient deficiencies and a low intake of energy or polyunsaturated fats (28).

Optimising nutrition intake has also been seen to improve mental health, as demonstrated in the ground-breaking SMILES trial. This study tested the link between dietary improvement as a treatment for depression. 176 participants with major depressive episodes were randomised into a dietary intervention and social support group. The dietary intervention group were supported to consume a Mediterranean-style diet that was high in whole grains, fruit, vegetables, legumes, olive oil, nuts and oily fish with moderate amounts of meat and dairy. 

The findings of this study indicated that participants in the dietary intervention group had a greater reduction in their depressive symptoms over the 3-month period when compared to the social support group (29). This provides us with some evidence for the role of nutrition interventions in alleviating the symptoms for those suffering with depression and other mental health conditions. However, it must be noted that nutrition itself will not cure these psychiatric conditions and individual treatment and support from registered health professionals is key.

7. Dietary Fat and Brain Health

Dietary fats have also gained increasing interest and investigation to understand how their intake influences brain health, especially polyunsaturated fats. 

There are two main types of polyunsaturated fats (30): 

• Omega 3: found in oily fish including kippers, herring, trout, sardines, salmon and mackerel.
• Omega 6: found in oils such as rapeseed, corn, sunflower and some nuts.

In relation to brain health, these fats have been shown to benefit a whole host of functions.

Omega-3s form part of the membrane of brain cells, have anti-inflammatory properties and are involved in cell signalling.

Therefore, dietary intake is incredibly important for brain structure and neurodevelopment. 

They have also been shown to improve thinking and reasoning abilities in older adults, cognition and protection against depressive episodes (31). We typically get enough omega 6 from our diet. However, in order to ensure we are consuming enough omega 3, it is recommended to eat around 1-2 portions of oily fish per week (30). 

Take Home Message

The science and study of the brain is incredibly complex and intricate, and this article highlights just some of the growing evidence that is available. The main point to take away is that we need to consume enough energy, protein, fats, vitamins and minerals to nourish our brain and keep it functioning at optimum level.

References:

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