- Introduction to nutrition and the brain
- Energy demands of the brain
- Food and behaviour
- Food and psychological wellbeing
- Food and cognition
- Specific nutrient qualities
- The importance of our diet
The effects of different foods on our behaviour and cognitive performance have been known for years without needing to be examined closely – caffeine stimulates the brain; when kids have too much sugar, they turn “hyper”; and chocolate makes us all feel good. For centuries these experiences have been known and our dietary behaviours reflect this.
In recent years the idea of nutritional effects on the brain have been developed further and extensive research into effects of food on brain functions that are not clearly evident or observable have emerged. The effect of certain foods on brain development, mood disorders, cognition (thinking), disease states and ageing has promised to be an essential area of research, development, non-pharmacological treatment and preventative measures.
The brain is an extremely active organ which demands an extremely high percentage of the overall daily energy requirements supplied by food. PET scans and MRIs show which brain areas are utilising the greatest amount of energy by monitoring the glucose utilisation. This has enabled us to understand of brain development and maturation at different ages.
For infants, 87% of their daily energy intake supplies the brain. In children between the ages of 6-12 years, 30 – 45% of their energy is utilised in the brain. During infancy to early childhood synaptic connectivity is at its greatest rate and therefore glucose utilisation is high. By adulthood, cortical organisation is relatively stable and accordingly the energy demands of the brain decrease to 20-25%.
The effect of certain foods on behaviour has been a recent area of interest with the rising number of children diagnosed with attention deficit hyperactivity disorder (ADHD). It has been found that a high proportion of children with ADHD are iron deficient or essential fatty acid (EFA) deficient or both.
Other theories regarding nutritional disturbances associated with the aetiology of ADHD include general under-nutrition and the increased amount of junk food that children are consuming from a very young age.
More information on diets for ADHD
The effect of poor nutrition can lead to suboptimal functioning indirectly by exacerbation of stress, sleep disturbances and fatigue. Although these states are not considered “diseases” they are daily stressors that effect psychological wellbeing. A flow-on effect exists between fatigue and suboptimal cognitive functioning, in other words, our ability to think is affected. This in turn has a negative effect on self esteem and performance. This is a classic example of a psychological cycle. All aspects of the cycle impact psychological wellbeing which feeds lower self-esteem. It is becoming more necessary to evaluate the function of diet on these factors before turning to medicines.
Perhaps one of the greatest effects of nutrition on brain functioning is on our cognition (thinking). The effects of poor diet on sleeping patterns, energy and mood all indirectly affect day to day functioning of the brain at work or school. Cognition is also indirectly affected by the development of other brain functions, for example nutrition is essential for the development of the sensory systems such as hearing and vision and the integration of these processes, the sensorimotor system. Sensorimotor systems are the coordination between sensory functions and motor (movement) functions. An example of a sensorimotor function would be seeing a ball (sensory) and putting up hands to catch it (motor). These processes mature before cognition as they are essential components needed for learning and memory. Therefore without full and healthy development of these systems, optimal cognitive maturation is not achieved.
Direct effects of nutrition on cognition are seen during neurodevelopment and then again during the ageing process. At these times especially, nutrients are of utmost importance to optimise the way the brain thinks and functions.
Neurodevelopment begins before birth and continues throughout life. Neurodevelopment is development of the nervous system including the brain. Cognitive maturation is a process of neurodevelopment which involves ‘fine-tuning’ the brain into a mature functional thinking system. During life, millions of connections (synapses) are made in the brain as we learn, this is called synaptogeneisis, and is a very important aspect of neurodevelopment. Other important aspects of cognitive maturation are myelin formation (to aid conduction of nerve impulses through the neurons) and dendrite formation (to aid the transfer of information from one synapse to another). The hippocampus as well as frontal and prefrontal cortex are the major areas of brain development required for cognitive maturation.
Nutrients are thought to act as a “trigger” for these brain development processes, without which development is stunted and brain physiology and structure are impaired. This impairment can be temporary if the availability of the essential nutrients are only deprived in the short-term. However, in critical periods of development it may only require deprivation of essential nutrients for a short time before permanent damage occurs.
The nutritional requirements throughout the pre-, neo-, and postnatal stages influence immediate and long term cognitive maturation and performance. At this critical stage of neurodevelopment any insult or stimulus, or in the case of nutrition the lack of, has the potential to permanently damage the brain. The greatest brain growth occurs 3 months before birth up to around 2 years of age. It is at these stages that synaptic plasticity is at its peak and the energy requirements of the brain are maximal. The synaptic connections made during this time impact the way the brain is structurally and functionally organised (cortical organisation) throughout life.
A lot of recent attention has been directed towards the effects of nutrition in neurodegeneration. Neurodegeneration can be thought of as the opposite of neurodevelopment. It is the breakdown of synapses and shinkage of the brain (atrophy). Neurodegeneration is an ageing process and is associated with dementia.
The lack of certain nutrients is thought to be toxic to the brain (neurotoxicity), especially in the elderly brain. Undernutrition leads to processes which predispose the brain to shrinkage and neurodegeneration such as uncontrolled neuron (brain cell) death, amyloid-beta toxicity, oxidative stress and mitochondrial dysfunction. Research has been focussed on nutrients that may have the potential to protect the brain from oxidation and atrophy, such as EFAs and folates.
Different foods provide different nutrients which have different actions in development, maturation, growth and protection of the brain.
Dietary cholesterol from dairy products and egg yolks have been associated with brain functioning at all ages. Lipids make up 10% of the weight of the brain and are essential for the proper formation of membranes and myelin. Importantly though, excess cholesterol can build up in the blood leading to disease.
These powerful antioxidants combat oxidative stress in the brain and this is believed to have a protective effect in the ageing processes. Carotenoids are found in yellow and orange fruits and vegetables especially but all fruits are good sources of flavonoids.
Micronutrients including iron, zinc, choline, selenium, iodine, magnesium, B vitamins, and vitamins A and C play key roles in energy metabolism as well as neurological enzymatic reactions and processes. Micronutrients are specifically involved in producing functional brain lipids, neurotransmitters, DNA and RNA.
This micronutrient is essential for the enzymatic formation of thyroxin, without which can lead to mental retardation any age, although it is especially influential during infancy.
Salt and seafood are the best sources of dietary iodine.
A deficiency of iron is common, especially in females. Fatigue, lethargy, irritability, inattention, decreased IQ and apathy are seen in iron deficient individuals and have been linked to the symptoms of ADHD in children. The inattentive symptoms may be explained by the cognitive maturation delay found in studies of animals deprived of iron in their diets. Furthermore the fluidity of membranes is hardened in iron deficient individuals.
Lean meat and fish are the best sources of iron but other protein rich alternatives also provide this mineral such as eggs, nuts and legumes.
Protein intake is essential for the production of vital neurotransmitters including; dopamine, noradrenaline, histamine and glycine. One such protein is tryptophan, a precursor for serotonin which has effects on mood and memory.
Protein is largely found in meat, fish, poultry, eggs, liver and kidney, legumes, nuts, sunflower seeds and sesame seeds.
Low levels of folate (also called folic acid or vitamin B9), a nutrient found largely in leafy green vegetables, are hypothesised to be toxic to the brain, causing brain atrophy. This is especially prevalent in the cerebral cortex of patients with Alzheimer’s Disease.
Folate levels have also been associated with positive effects on mood.
Vitamin B12 deficiency is related to brain atrophy. Lean beef, salmon and eggs are good sources of vitamin B12.
Vitamin D has recently been determined to be an important neurosteroid and its receptors are widespread throughout the brain. A deficiency of vitamin D is sometimes accompanied by depression, psychosis and anxiety. Accordingly vitamin D therapy has been shown to provide mood-elevating effects.
A vitamin D-rich diet has been associated with a reduced risk of multiple sclerosis (MS) and has been utilised as an adjunctive treatment in early MS patients. Epilepsy has also been associated with a deficit in vitamin D which suggests its use may be developed as a potential adjunctive treatment for the disease in the future.
Vitamin D is also thought to play a role in the regulation of behaviour. The receptors for this micronutrient are widespread through areas of the brain known to be responsible for mediating behaviour, such as the limbic system.
The best sources of vitamin D include fatty fish, eggs and margarines fortified with vitamin D.
Essential fatty acides (EFA) cannot be synthesised by the brain and are therefore an “essential” part of our diets. Found largely in fish, EFA are necessary for the induction of myelination and providing components of the myelin sheath, which present these nutrients as important regulators of membrane fluidity. Animal studies have found that deficiency of fatty acids can lead to altered blood brain barrier functioning. EFA are also involved in producing neurotransmitters and other important peptides.
Importantly EFA are associated with auditory and visual development. Docosahexaenoic acid (DHA) is an essential omega-3 fatty acid necessary for normal neurogenesis and neurological function. DHA is specifically important for visual signalling pathways. Consumption of high levels of DHA during infancy are associated with better visual development.
Many studies have focussed on the improved cognitive and mood elevating effects in adults who consume a Mediterranean diet; namely a diet primarily comprised of fish, fruits and vegetables. People who adhere to the diet describe better self-rated health which has been found to influence overall energy and vitality.
More information on the Mediterranean Diet.
The body of evidence to support the positive effects of a healthy and varied diet is large and is an active area of research and development. It is important at all ages to focus on consuming a well rounded diet with all the essential nutrients. This is especially important for infants and children during times of neurodevelopment and then again during ageing when neurodegeneration can compromise health and vitality.
|For more information on brain health, including exercise and mental activity, see Brain Health.|
|For more information on nutrition, including information on types and composition of food, nutrition and people, conditions related to nutrition, and diets and recipes, as well as some useful videos and tools, see Nutrition.|
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