How a vegan diet could affect your intelligence

The vegan diet is low in – or, in some cases, entirely devoid of – several important brain nutrients. Could these shortcomings be affecting vegan’s ability to think?

Zaria Gorvett
BBC
Tue, 28 Jan 2020 00:01 UTC

It was the late 1880s in the city of Rajkot, India. The meeting was to take place on the banks of the local river – and discretion was essential. Mahatma Gandhi, who was just a teenager at the time, hadn’t told his parents where he was going; if they had found out, they would have been shocked to death.

As it happens, Gandhi was having a picnic. And on this occasion, India’s future national hero – and one of the most famous vegetarians in history – wasn’t planning to dine on cucumber sandwiches. No, for the first time in his life, he was going to eat meat.

As he later wrote in his biography, Gandhi was raised as a strict Vaishnava Hindu, so he had never even seen meat before this fateful day. But his picnic companion was a shady character with an unusual obsession – the idea that meat held the key to being physically and mentally strong.

In the end, Gandhi braved the meat. It was as tough as leather.

The idea that avoiding meat is bad for our brains makes some intuitive sense; anthropologists have been arguing about what our ancestors ate for decades, but many scientists think that there was a lot of bone-crunching and brain-slurpingon the road to evolvingthese remarkable 1.4kg (3lb) organs. Some have even gone so far as to say thatmeat made us human.

One reason is that intelligence is expensive – the brain devours about 20% of our daily calories, though it accounts for just 2% of our body weight – and what better way to find the enormous array of fats, amino acids, vitamins and minerals these fastidious organs require, than by feasting on animals which have already painstakingly collected or made them.

But though it’s hard to imagine our ancestors choosing turnips over tuna, today it’s a different story. According to the latest statistics, there are around 375 million vegetarians on the planet. In the West, veganism has ditched the hippie stigma to become one of the fastest-growing millennial trends; in the United States, it grew by 600% between 2014 and 2017. Meanwhile in India, meat-free diets have been mainstream since the 6th Century BCE.

On the one hand, recent concern about the nutritional gaps in plant-based diets has led to a number of alarming headlines, including a warning that they can stunt brain development and cause irreversible damage to a person’s nervous system. Back in 2016, the German Society for Nutrition went so far as to categorically state that – for children, pregnant or nursing women, and adolescents – vegan diets are not recommended, which has been backed up by a 2018 review of the research. In Belgium, forcing a vegan diet on your offspring could land you a spell in prison.

But on the other, if abstaining from meat had any real impact on our brains, you would think that we would already have noticed. So is it really damaging our intellects, or is this all just fear of the unknown?

Ideally, to test the impact of the vegan diet on the brain, you would take a randomly selected group of people, ask half to stop eating animal products – then see what happens. But there isn’t a single study like this.

Instead, the only research that comes close involved the reverse. It was conducted on 555 Kenyan schoolchildren, who were fed one of three different types of soup – one with meat, one with milk, and one with oil – or no soup at all, as a snack over seven school terms. They were tested before and after, to see how their intelligence compared. Because of their economic circumstances, the majority of the children were de facto vegetarians at the start of the study.

Surprisingly, the children who were given the soup containing meat each day seemed to have a significant edge. By the end of the study, they outperformed all the other children on a test for non-verbal reasoning. Along with the children who received soup with added oil, they also did the best on a test of arithmetic ability. Of course, more research is needed to verify if this effect is real, and if it would also apply to adults in developed countries, too. But it does raise intriguing questions about whether veganism could be holding some people back.

In fact, there are several important brain nutrients that simply do not exist in plants or fungi. Creatine, carnosine, taurine, omega-3, haem iron and vitamins B12 and D3 generally only occur naturally in foods derived from animal products, though they can be synthesised in the lab or extracted from non-animal sources such as algae, bacteria or lichen, and added to supplements.

Others are found in vegan foods, but only in meagre amounts; to get the minimum amount of vitamin B6 required each day (1.3 mg) from one of the richest plant sources, potatoes, you’d have to eat about five cups’ worth (equivalent to roughly 750g or 1.6lb). Delicious, but not particularly practical.

And though the body can make some of these vital brain compounds from other ingredients in our diets, this ability isn’t usually enough to make up for these dietary cracks. For all of the nutrients listed above, vegetarians and vegans have been shown to have lower quantities in their bodies. In some cases, deficiency isn’t the exception – it’s completely normal.

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.

“I think there are some real repercussions to the fact that plant-based diets are taking off,” says Taylor Wallace, a food scientist and CEO of the nutrition consulting firm Think Healthy Group. “It’s not that plant-based is inherently bad, but I don’t think we’re educating people enough on, you know, the nutrients that are mostly derived from animal products.”

One of the most well-known challenges for vegans is getting enough vitamin B12, which is only found in animal products like eggs and meat. Other species acquire it from bacteria which live in their digestive tracts or faeces; they either absorb it directly or ingest it by snacking on their own poo, but unfortunately (or fortunately, depending on how you look at it) humans can’t do either.

To see how crucial B12 is for the brain, take what happens when we don’t get enough of it. In children, the consequences of B12 deficiency can be life-altering. “There are some tragic cases of children whose brains failed to develop because of their parents being ill-informed vegans,” says Benton. In one example, the child wasunable to sit or smile. In another, theyslipped into a coma.

Later in life, the amount of B12 in a person’s blood has beendirectly correlated with their IQ. In the elderly, one study found that the brains of those with lower B12 were six timesmore likely to be shrinking.

Even so, low B12 is widespread in vegans. One British study found thathalf of the vegansin their sample were deficient. In some parts of India,the problem is endemic– possibly as a consequence of the popularity of meat-free diets.

Another nutrient that’s scarce in the typical vegan diet is iron. Though we often associate it with blood, iron also plays prominent role in brain development, and is essential for keeping the organ healthy throughout our lives. For example, one 2007 study found that giving young women iron supplements led to significant intellectual gains. In those whose blood iron levels increased over the course of the study, their performance on a cognitive test improved between five- and seven-fold, while participants whose haemoglobin levels went up experienced gains in their processing speed.

It’s surprisingly easy to slip into iron deficiency, even though it makes up 80% of the inner mass of the planet we live on. Up to two billion people are thought to have a shortage of the element worldwide, making it the most common nutritional inadequacy. Vegans areparticularly prone, because the form that’s most readily absorbed by the body is “haem iron”, which is only found in animal proteins. One German study found that40% of the vegans they looked at were consuming lessthan the recommended daily amount.

Other common deficiencies among vegans include D3, omega-3, selenium, folate and iodine. Though the body can make D3 when the skin is exposed to sunshine, this doesn’t make up for the extra that vegans are missing from their diets. In the winter months, when the sun is weaker, omnivores living in the UK havenearly 40% more vitamin D3in their blood than vegans.

Of course, some of these things can easily be acquired from supplements. But others are so obscure, vegans are unlikely to have even heard of them – let alone realise they could be missing out.

One example is taurine. This enigmatic amino acid is one of themost plentifulin the human brain, where it’s thought to underpin several important processes, such as regulating the number of neurons. It’s often added to caffeinated energy drinks, because of the (possibly mistaken) belief that it can provide an immediate cognitive boost.

Though there are small amounts of taurine in some dairy products, the main dietary sources are meat and seafood. “Some species have the ability to make all the taurine they need,” says Jang-Yen Wu, a biomedical scientist at Florida Atlantic University. “But humans have a very limited capacity to do this.”

For this reason, vegans tend to have less taurine in their bodies. No one has looked into how this might be affecting their cognitive abilities yet, but based on what we know about its role in the brain, Wu says vegans should be taking taurine tablets. “People can become deficient when they restrict their diets, because vegetables have no taurine content,” he says.

In fact, the holes in our current understanding of what the brain needs to be healthy could potentially be a major problem for vegans, since it’s hard to artificially add a nutrient to your diet, if scientists haven’t discovered its worth yet.

“There are so many unknowns,” says Nathan Cofnas, a biologist from Oxford University. “And when you deviate from the typical diet for your species, to one which has not been tested and properly established to be healthy or good for the brain, you are conducting an experiment and you are taking a risk.”

Take choline: in the brain, it’s used to make acetylcholine, which is involved in a number of tasks, including relaying messages between nerve cells. It’s fundamental to our ability to think – even insects have it in their tiny brains – and the body can’t produce enough of it on its own.

And yet: “It’s a very understudied nutrient,” says Wallace. “I believe we’ve only considered it essential [something you have to get from your diet] since the late 1990s.”

There are small amounts of choline in lots of vegan staples, but among the richest sources are eggs, beef and seafood. In fact, even with a normal diet,90% of Americansdon’t consume enough. According to unpublished research by Wallace, vegetarians have thelowest intakes of any demographic. “They have extremely low levels of choline, to the point where it might be concerning,” he says.

For vegans, the picture is likely to be bleaker still, since people who eat eggs tend to have almost double the choline levels of those who don’t. And though the US authorities have set suggested intakes, they might be way off.

Wallace points to a 2018 study, which found that the babies of women who consumed twice the amount considered “adequate” – around 930mg each day – in the last third of pregnancy enjoyed alasting cognitive edge. For comparison, the average vegetarian getsroughly a fifth of that amount.