November 7, 2018, by sarasleigh
Are Plant-based Diets Good for the Brain?
Written by Vaishali Gursal (3rd year BSc Neuroscience)
Earlier this month, a study by the University of Oxford concluded that a global switch to a plant-based diet (rich in fruits and vegetables, along with a heavily decreased consumption of red and processed meat) could cut greenhouse gas emissions by two-thirds, reduce global expenditure on healthcare and could potentially save up to 8 million lives by 2050.[i] However, homo sapiens have historically consumed both plant and animal protein to gain a variety of nutrients and minerals to keep our bodies functioning at a high capacity. Although fruits and vegetables are brimming with vitamins, nutrients and antioxidants, plant material is much harder to digest and has a low ‘bioavailability’ – meaning that it is difficult for us to absorb and utilise these nutrients. As a result, a sudden switch to consuming a plant-based diet is sure to lead to nutrient deficits and have a major impact on the way our brain functions. It may even be necessary to take additional artificial supplements that are, in nature, only available from animal protein. Around 20% of our body’s energy is directed to the brain, hence the effects of following a plant-based diet on the healthy functioning of our brain needs to be explored.
Vitamin D can be obtained from sunlight or animal foods and is vital for supporting the hippocampus (where memories are made and stored), regulating calcium levels within the brain and promoting healthy growth and development of the organ. However, those following a plant-based diet are often deficient in vitamin D. A study conducted at the University of Kentucky claimed that when rats were fed a diet low in vitamin D for several months, this resulted in free radical damage within the brain. This means that highly reactive atoms with unpaired electrons interacted with proteins, DNA and cell membranes, causing damage. Additionally, the rats performed poorly in cognitive tests for learning and memory, suggesting that a vitamin D deficient diet may lead to a decline in cognitive performance.
Vitamin B12 is obtained from animal products and is vital for the synthesis of DNA, RNA (a molecule that codes, decodes and regulates the expression of genes), red blood cells and myelin (a fatty substance that is wrapped around neurons to conduct electrical impulses and speed up communication between cells of the brain). Those on a plant-based diet need to obtain B12 from supplementation or fortified yeast. A low deficiency in vitamin B12 can result in fatigue, lethargy and memory problems. There are several studies that show a severe deficiency in vitamin B12 can result in detrimental psychological conditions, including depression, changes in behaviour and personality and psychosis.[ii] In fact, when patients present with instability in mental health, a blood test is routinely conducted to rule out vitamin B12 deficiency.
Iodine is a mineral most commonly found in seafood and dairy products. It is essential for the synthesis of thyroid hormones that control the body’s metabolism and are critical for healthy bone and brain development. Iodine can also be obtained from fruits and vegetables, although this depends on the amount of iodine in the soil where they were grown, and the type of fertiliser used. Studies in animals conclude that an iodine deficiency results in a decrease in brain weight and synaptogenesis (the generation of new connections between neurons, creating neuronal circuitry), as well as a reduction in the size of neurons in the cortex.[iii]
Iron is a mineral that can be obtained from animal products, dark green leafy vegetables, wholegrains and iron-fortified cereals. It is essential in the synthesis of red blood cells, as well as the production of neurotransmitters (chemicals that aid in transmission of signals across a synapse between two cells, e.g. serotonin, noradrenaline and dopamine). Studies conducted at Johns Hopkins Medical School found that an iron deficiency in rats resulted in impairment in learning, due to the dopaminergic and cholinergic systems (neuronal circuitries that use dopamine and acetylcholine chemical neurotransmitters to aid electrical communication between cells) being affected.[iv] This led to disturbances in circadian behaviours (e.g. the sleep-wake cycle) and cognitive impairment. A diet lacking in iron can be supplemented by iron tablets, which are available in pharmacies or can be prescribed by a GP.
Can a plant-based diet that doesn’t provide the RDA (Recommended Daily Amount) of essential vitamins and minerals be healthy if adequate supplementation is consumed?
The answer to this is largely unknown. It is important to note that taking supplements does not guarantee better health and it is very easy to consume larger-than-recommended amounts. Additionally, it is not known whether taking essential nutrients and vitamins in a tablet form has the same effect on the body and brain or is absorbed and utilised in the same fashion as consuming animal products rich in that nutrient.
As we become more aware of how our eating habits have an impact on our health and the environment, vegan and vegetarian diets have been on the rise. The consequent hype in the media about plant-based lifestyles has resulted in a variety of vitamins being branded as possible defences against various cancers, heart disease, diabetes and stroke. However, these studies have not compared the supplement in question against a placebo (an inactive tablet) in randomised controlled trials and have instead been purely observational. Furthermore, these observational studies do not fully consider possible variables between participants, e.g. exercise habits, other nutrient or vitamin deficiencies, accessibility of a plant-based diet within certain countries or the prevalence of diseases/conditions within various ethnic groups or geographical regions that are not affected by diet. [v]
Therefore, the switch from an omnivorous diet to a largely plant-based (and adequately supplemented) one will undoubtedly have a positive impact on the environment and global expenditure on healthcare, but the long-term impact this may potentially have on the healthy functioning of the brain is yet to be concretely determined by the scientific community.
References and Further Reading:
[ii] Black, M. et al (2008) Effects of vitamin B12 and folate deficiency on brain development in children, Food Nutr Bull, Suppl vol 29,2
[iii] Redman, K. et al (2016 )Iodine deficiency and the brain: Effects and Mechanisms, Critical Reviews in Food Science Nutrition, 9;56(16)
Youdim, MB. Et al (2008) Brain iron deficiency and excess; cognitive impairment and neurodegeneration with involvement of striatum and hippocampus, Neurotox Res, 14(1):45-56.
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