Researcher Network member, Imogen Allen and co-author, Samuel March, give their opinion on the research that was used to support a recent BBC Future hosted article on vegan diet and intelligence.
On 28th January 2020, BBC Future hosted an article by Zaria Gorvett called “How a vegan diet could affect your intelligence. ” Its clickbait title is perfectly worded to draw in social media users desperate to assuage their cognitive dissonance by reinforcing the comforting belief that consuming animal products is essential and necessary to their health.
The content within the article isn’t without a semblance of balance. It’s credible and accurate in several respects. However, it doesn’t consider the overall evidence base around vegan health and nutrition, nor does it acknowledge the presence of brain benefiting nutrients that are more rich in vegan diets. It cites some questionable research, and whilst it acknowledges its limitations, it nevertheless uses it as a springboard to a series of “could”, “may” and “might” extrapolations, which give the illusion of discrediting vegan diets, without actually robustly substantiating anything.
A heavy starter
Gorvett pulls no punches in the opening paragraphs. In short succession she cites studies that claimed “meat made us human” and studies which claim plant-based diets “stunt brain development”, are “unsuitable” for children and rounds off by mentioning that “parents who force a vegan diet on their offspring in Belgium could even one day find themselves in prison.” She does this fairly dispassionately, without pinning her colours to the mast, and does actually go on to provide some balance later on in the article. However, most bloggers have remarked that the majority of readers don’t read past the point they are first required to scroll. By this point in Gorvett’s article, those readers coming only to quell their moral doubts will have got what they came for, and left.
She then goes on to cite a most peculiar study conducted on 555 Kenyan Schoolchildren. One group of children on an already deficient “de-facto vegan” diet was given some additional meat. The studies found that, over time, this group gained a “significant edge” in non-verbal reasoning tests over their counterparts who were given a similar calorific boost through milk or “plant-based” diets. The “plant-based” control group were not given beans, pulses, leafy greens, tofu or other plant-based staples, but pure oil. For what it’s worth, even the oil group was alongside the meat group in outperforming the milk group on arithmetic ability tests.
Gorvett acknowledges (by way of quite the understatement) that “more research is needed to verify if this effect is real, and if it would also apply to adults in developed countries, too.” Why mention such a flawed study at all? No reasonable academic would afford it any weight in a serious discussion regarding the necessity of meat in the average diet of consumers in developed countries. Instead, Gorvett leaves the academically uninitiated with the hanging implication that the effect might be “real”. A semblance of balance; but no more.
A “unsettling” main
Kenyan schoolchildren, Gorvett’s apparent priority, dealt with, she moves onto the “meat” of her analysis. She cites a number of “brain nutrients” which she says “simply do not exist in plants or fungi” or exist “only in meagre” amounts. She mentions vitamin B12, vitamin D3, iron, omega-3 fatty acids, choline, carnosine, creatine and taurine. Faced with the potential for deficiency, Gorvett’s draws a conclusion that is a feat of ambiguous, semi-substantiated alarmism; stating
“For now, the impact these shortcomings are having on the lives of vegans is largely a mystery. But a trickle of recent studies have provided some clues – and they make for unsettling reading.”
It’s not clear why Gorvett is so unsettled as, in fairness to her, she does acknowledge that many of these nutrients can be synthesised from algae, bacteria or lichen and added to supplements and substitutes. Taking a nutrient by nutrient approach, most recent studies contain few surprises and little cause for alarm.
Vitamin B12
It has been known for a while that vegans are more prone to vitamin B12 deficiency compared to non-vegetarians. Gilsing et al. (2010 ) found that 52% of vegans were classified as deficient (<118 pmol/l) compared to 7% of vegetarians and one omnivore. That said, it is worth acknowledging that a more recent study found only marginal deficiency to exist across all dietary groups owing to consumer widespread use of supplements (Schüpbach, 2017). As found by Selinger, Kühn, Procházková, Anděl, & Gojda (2019), “regularly supplementing vegans had similar levels of [vitamin B12] as non-vegans”.
Vitamin D
Dietary intake of vitamin D and plasma vitamin D levels have been found to be lower in vegans (Crowe, Steur, Allen, & Appleby, 2011; Hansen, Madsen, & Jørgensen, 2018). For example, Crowe et al. (2011) found levels of 25(OH)D concentrations were on average 77 nmol/l compared to 55.8 nmol/l in vegans. That said, it is important to note that despite having lower plasma levels in summer and winter, all groups had similar levels of deficiency ranging between <1-8%. It is difficult for anyone to achieve an adequate plasma vitamin D status from the diet alone (The Vegan Society, 2019). Therefore, supplements may be advisable to all dietary groups, not just vegans.
Iron
Some research suggests that iron deficiency may be more prevalent in vegans, but findings are varied. One study found 40% of vegan women to be iron deficient (Waldmann, Koschizke, Leitzmann, & Hahn, 2004). An extensive literature review on vegetarians also demonstrated that this group have a higher prevalence of depleted iron stores (Pawlak, Berger, & Hines, 2018). On this basis, it may logically follow that vegans would also be at similar risk. However, Schüpbach (2017) demonstrated that the prevalence of iron deficiency is similar across all dietary groups including vegetarians and vegans. Additionally, whilst based on a small sample size, Haddad, Berk, Kettering, Hubbard, & Peters (1999) found vegan (n-15) and nonvegetarian (n-10) women to have a similar prevalence of iron deficiency (<12 ug/l), 27% and 20% respectively. The same study on men also found neither dietary group to have iron deficiency. Finally, Selinger, Kühn, Procházková, Anděl , & Gojda (2019) also reported that despite vegans having lower ferritin and haemoglobin levels, there was no indication that vegans had a higher risk of iron deficiency. Iron deficiency is the most common nutrient deficiency in the world (WHO, 2020), so it’s important for everyone to know how to obtain iron from plant foods. Iron rich plant sources include lentils, chickpeas, beans, tofu, leafy green vegetables, fortified breakfast cereals. Whilst absorption of non-haem iron is lower and absorption may be reduced by some substances present in plant food such as phytates, oxalates and polyphenols (Nomkong, Ejoh, Dibanda, & Gabriel, 2019), sufficient consumption of plant based foods/meals rich in iron and vitamin C should be plenty. The most important factor affecting iron absorption is the body’s need for iron (SACN, 2010).
Omega- 3 Fatty Acids
Regarding long-chain omega-3 fatty acids, vegans consume almost no eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from food sources. Although “there is no convincing evidence that vegetarians or vegans experience adverse effects”, evidence suggests that there is a “clear inverse association between EPA and DHA intake and risk of cardiovascular disease, and limited evidence for cognitive decline, depression and age macular degeneration” (Saunders, Davis, & Garg, 2013). Therefore, vegans may choose to add these fats to their diets using microalgae supplements, particularly during pregnancy, breastfeeding and childhood due to the role of these fats in brain, nerve and eye development.
Choline, Carnosine, Creatine and Taurine
Concerns about lower levels of choline, carnosine, creatine and taurine in the vegan diet were also mentioned. However, creatine, carnosine and taurine are not essential nutrients because our bodies make them. Supplementation of these isn't thought to be essential for vegan health, although some athletic individuals may benefit from creatine supplementation.
In terms of choline, this nutrient is widely distributed in plant foods because it’s present in cell membranes. Soya products, quinoa and broccoli are some of the best plant-based sources. Amaranth, artichokes, Brussels sprouts, buckwheat, corn, mushrooms, oats, wheat germ and whole wheat products are also good sources. Choline requirements and intakes in different dietary groups are poorly defined due to a lack of research and there is no target set for this nutrient in the UK. This isn’t thought to be an area of concern for people eating balanced and varied vegan diets.
Selective supplementation can play an important role in the transition to a lower emission, cruelty-free diet with the focus on vitamins B12 and D, iodine and selenium. Whether this is “unsettling reading” is a matter for readers.
Skipping courses
Whilst Gorvett seems keen to serve up (often using bold highlights) any quote which paints vegan diets in a bad light, the article fails to consider a number of other brain benefitting nutrients which vegans generally consume more of, as well as other positive effects of vegan diets.
Schüpbach (2017) found vegans to have considerably higher plasma levels of magnesium, vitamin C, vitamin E, vitamin B1 and folic acid compared to omnivores.
Like vitamin B12, dietary intake of folate is also protective effect against cognitive decline. This is because of the role these nutrients play in preventing the build-up of homocysteine (Tucker, 2016).
Vitamin E is a potent antioxidant and can protect brain cells from oxidative stress linked to ageing and has also been repeatedly associated with better cognitive performance (Weber, La Fata, & Mohajeri, 2014).
Vitamin C is important for neuronal differentiation, maturation and myelination and is involved in the modulation of cholinergic, catecholinergic and glutaminergic systems (Travica, Ried, Sali, & Scholey, 2017). Although the positive memory effects of vitamin C in cognitively intact individuals are more unclear, individuals have been found to have higher plasma vitamin C levels compared to those suffering cognitive impairment (Travica et al., 2017). This could be due to other potential confounding variables but is an important finding, nonetheless.
Furthermore, plant-based diets are richer in a variety of phytochemicals which may also have a positive cognitive effect. For example, Davinelli et al. (2016) recently wrote how it is becoming increasingly clear that diets “rich in phytochemicals can modulate cellular response pathways, playing an important protective role to attenuate pro-inflammatory and oxidative damage”.
Finally, higher BMIs and hypertension have been linked with reduced cognitive function and increased risk of dementia in adults (Cournot, Ansiau, Fonds, Ferrières, & Ruidavets, 2006; Gustafson, Rothenberg, & Blennow, 2003; Novak & Hajjar, 2010; Rosengren, Skoog, & Gustafson, 2005; Whitmer, Gunderson, Barrett-Connor, Quesenberry, & Yaffe, 2005). As vegans tend to have lower BMI’s and lower blood pressure, these factors alone may give them a cognitive edge and even reduce their risk of later dementia (Tai Le & Sabaté, 2014).
Conclusions
In concluding, Gorvett cites a number of reasonable and balanced perspectives and, on the face of it, leaves the question very much open. Most of the perspectives she cites conclude that it seems possible to have a healthy diet as a vegan, that there is a risk of certain deficiencies, but that these can be addressed with substitutes and supplements, so long as the consumer maintains a degree of dietary vigilance. This is nothing new or controversial.
The issue with the article isn’t so much what is said, but how it’s said and the things that are either left hanging, or unsaid: the rhetorical questions inspired by flawed research, the invitations to extrapolate, the semblance of balance, the fact that every bold, highlighted quote militates against a plant-based diet…it’s like Gorvett set out to prove vegan diets make you less intelligent, but never quite found the conclusive evidence she was looking for.
The views expressed by our Research News contributors are not necessarily the views of The Vegan Society.
References
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