Modern diets can leave us short on essential fatty acids. Barbara Pinho looks into how this is affecting our health and our brains in particular
‘How are bananas and apples alike?’
This is an unusual question, and one you would expect to hear at the supermarket. But it’s one that researchers asked more than 2000 people to study the human brain. In a recent paper, Claudia Satizabal and her colleagues at University of Texas in the US studied cognitive function in middle-aged adults and how the blood levels of omega-3, an essential nutrient, could impact the brain. According to their results, people with more omega-3 fatty acids in their blood had better cognition.
‘We saw that people with higher omega-3 perform better in a similarities test, that basically tests for abstract thinking,’ explains Satizabal. The people being studied start by responding to questions that assess the ability to recognise patterns between objects, namely an apple and a banana. According to Satizabal, it starts with easy questions in which similarities are obvious, such as in fruits. Then the test moves on to more complex comparisons. People with higher levels of omega-3 in their blood performed better in finding these patterns and thinking logically.
‘This was a little bit surprising to us because this is a younger cohort. They’re not sick or anything; they’re just normal people. And you don’t expect to see changes in cognition at such a young age; you typically see cognitive differences once you start entering older ages,’ she adds.
This isn’t the first time scientists have looked at how omega-3 impacts human health. Dozens of previous studies have shown that higher levels of omega-3s in the blood relate to better cardiovascular health, reduced inflammation and sharper cognition.
‘Epidemiologic studies are pretty consistent to show the benefits of omega-3; that is one of the most consistent things in the literature,’ adds Satizabal.
Omega-3s in human health
Half a century ago, scientists looked at the Inuit population to study omega-3s and human health for the first time. Indigenous to northern Canada and Greenland, the Inuit have a diet rich in fish and meat with few vegetables and fruits, given the cold and remote locations they live in. Despite their fatty diets, scientists saw a remarkably low number of cardiovascular incidents in the population. To find out why, two Danish researchers studied Inuits’ lipidic profiles in the 1970s. They drew hypotheses on the role of fat in the body and how the intake of foods rich in omega-3s could affect human health. The field has developed since then, and omega-3 fatty acids are far more familiar nowadays.
Omega-3 fatty acids are one of the main polyunsaturated fatty acids (PUFAs), alongside omega-6. Like all PUFAS, omega-3 and omega-6 are made up of long chains of carbon atoms with a carboxyl group at one end of the chain and a double bond three or six atoms from the other end, hence the name. Many forms of omega-3 exist, but the most studied are the alpha-linolenic (ALA), eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids. Humans need them all in their bodies. Fatty acids are, after all, one of the core components of many cellular structures like cell membranes. The brain itself is a fatty organ – the fattest in the whole human body – with two-thirds of its weight deriving from phospholipids. ‘We are talking about something that is a prerequisite for life; it’s like salt or water; it’s in everybody,’ says Clemens von Schacky, physician and chief executive of Omegamatrix, a company that provides domestic blood testing of omega-3.
Diet is the only way to get these essential fatty acids. Omega-6s are in foods like plant oils, seeds and some nuts like walnuts and pine nuts. Omega-3s, on the other hand, are found in animal sources like fish oils. Despite their importance, consumption of omega-3s varies around the world.
Does the world have enough omega-3?
In 2015, researchers in Canada and the US reviewed almost 300 studies and created a global survey of omega-3 levels in the bloodstream of the population. For the regions with available data, Japan, South Korea, Papua New Guinea and Norway ranked highest, with people having healthy amounts of blood omega-3s, namely EPA and DHA. On the lower end was most of the world, including the UK. Ken Stark, researcher in nutritional lipidomics at the University of Waterloo in Canada, analysed the data and explains that the results are, nevertheless, limited. According to him, more studies – and more data – are needed to understand the regional and global consumption of omega-3s fully.
The team was, however, able to draw some conclusions. The researchers saw that in countries where seafood consumption is higher, omega-3 bloodstream levels are higher as well. They also saw that people have lower levels of omega-3 in countries where Western diets prevail. Western diets include large portions and consumption of red meat and ultra-processed foods, like sugary drinks, fast food and sweets like candy and biscuits. They are poor in vegetables, fresh fruits, whole grains and seafood.
To Schacky, there are many reasons as to why omega-3 levels vary so much around the globe, and diet is definitely one of them. According to him, fewer people are eating fish, and those that do eat them, are not finding the right amount of nutrients. ‘They [fish farmers] feed salmon with corn and have now turned salmon into a vegetarian for financial reasons,’ he says. ‘Consequently, the amount of EPA and DHA in salmon has been cut in half between 2006 and 2015.’
The drop in nutrients is concerning to him, and so is the change in dietary patterns.
Omega-3s and the modern diet
Since humans exchanged the hunting knife for the sickle, their diets changed forever. But what started with the ploughing and harvesting of wheat 12,000 years ago has changed drastically more than once. And the most recent food revolution happened rather recently – the nutritional transition of the 1970s.
‘The nutritional transition happened many decades ago in … Western Europe and North America,’ says Benjamin Allès, epidemiologist at Paris University 13, France. ‘Back in the day, people were taking a lot of time to cook, even when they had low incomes. Now, we have switched to a diet that includes more and more ready to eat meals and fast foods.’
Everything is related to what people can afford – not everyone can access seafood
Ultra-processed foods make up a large portion of the world’s calories, particularly in Western countries. In the UK alone, they account for more than half of total energy intake. The same doesn’t happen in all countries, particularly in regions where there is a strong culture of cooking and eating traditional food, like the Mediterranean basin and developing nations. But that doesn’t mean that it isn’t coming. ‘The ultra-processed foods industry first entered the market of developed countries. Since those markets got saturated, it’s now going into developing countries,’ explains Fernanda Rauber, nutritional epidemiologist at the University of São Paulo in Brazil. ‘For now, 20% of calorie intake in Brazil comes from ultra-processed foods, but we’ve been seeing an increase in consumption in the past few years. This is happening in other countries as well,’ she adds.
Ultra-processed foods pose a range of health risks: they promote obesity and are linked to cancer, cardiovascular disease and early death. Furthermore, when it comes to omega-3, research shows that people who consume more of these foods tend to have lower levels of the fatty acid in their blood. Stark also saw this in the global map: the countries where people eat the most ultra-processed foods correlate with lower omega-3 levels. Given that ultra-processed foods only seem to bring bad news, the question remains as to why millions choose to eat them every day.
‘Everything is related to what people can afford,’ says Satizabal. ‘Not everyone can access seafood, especially in the US, where you have food deserts; if you have fish, it is basically fried fish.’ A food desert is a region with little access to fresh food and an abundance of fast-food chains. In the US, they are common in low-income areas.
It’s also a matter of convenience. Because ultra-processed foods are portable, quick to consume and virtually available everywhere, people tend to grab them. ‘In today’s society, people no longer have the time to cook; they don’t have the time to eat either. And these products are marketed in a way that responds to this need,’ adds Rauber.
Vegan and vegetarian diets have almost no EPA and DHA
Another dietary shift that impacts omega-3 consumption is the turn to vegetarian products. More and more people worldwide are eating plant-based meals. In the UK alone, the number of vegans is four timeshigher now than in 2014, with 600,000 people opting for this diet. Plant-based diets tend to be healthier than Western ones because adopters eat more fresh fruits, vegetables and whole grains. Studies report better cardiac health, improved weight loss and lower incidence of certain cancers. Yet, given that omega-3s are most commonly found in animal products, there’s an issue with omega-3 shortage. ‘These two diets [vegetarian and vegan] are pretty much in fashion right now, but they are devoid of sources of EPA and DHA,’ Schacky adds.
Plant-based diets become more complicated when we look closely at what products people actually consume. Allès and his colleagues studied the consumption of ultra-processed foods in different diets and saw a trend. ‘Vegans have the highest contribution of ultra-processed food to their diet, but not all vegetarians and vegans have the same nutritional quality.’
According to him, vegetarians and vegans that have adopted the diet recently tend to consume more ultra-processed foods. This increased consumption could be related to the fact that meat substitutes like vegetarian sausages, burgers and plant-based drinks are all heavily processed. So, besides the lack of omega-3 in vegetarian products, the extraordinary consumption of ultra-processed foods – themselves poor in omega-3s – makes plant-based diets quite low on the fatty acid.
While there’s the big challenge of low levels of omega-3 around the world, calling it a deficiency could be inaccurate. According to Stark, it’s pretty tough to be omega-3 deficient because every diet – even Western ones – will have some amount of the nutrient. ‘So then, it becomes a question of “Does additive omega-3 provide beneficial effects?” and that’s hard to tease out, especially when you’re talking about neural cognition,’ he adds.
Omega-3 and the brain
Research shows that omega-3 can improve brain cognition throughout all stages of life. In a study, scientists gave tuna fish oil to infants during the first five years of their life and then measured academic performance up until they were nine years old. They saw that kids with higher omega-3 levels had better literacy and numeracy performance. Another studyin young adults shows that people who take supplements of DHA have better memory, and reports on seniors at risk of dementia show that those who take omega-3 supplements experience less decline in brain performance.
‘What the epidemiologic studies tell us is absolutely clear. At any age, whatever parameter you look at, in terms of cognition, it correlates with the omega-3 index,’ explains Schacky. Yet despite the overwhelming number of studies showing clear correlations, pointing to causality is a challenge. ‘When you’re talking about heart diseases, you can measure events fairly clearly. Whereas the brain is such a grey area,’ says Stark.
This is not just the brain and heart; it goes far beyond that
To fully understand the brain, studying thought would be ideal – but that’s complicated. Besides assessing logical thinking, researchers study other parameters like memory and processing speed. Yet, despite the different tests one could perform, it’s complicated to evaluate brain health by looking at variables that could be seen as abstract. This is why Satizabal and her colleagues assessed more than cognition in their recent study and dived into a more visible variable: brain size. The team scanned all participants’ brains to study the brain’s volume and composition while relating those values to omega-3 levels in the blood. They saw that people with higher levels of omega-3 had larger hippocampal volumes. This correlation has been reported before: the more the omega-3 index, the bigger the brain seems to be. And the opposite has been reported as well: lower omega-3s in the blood correlate with brain atrophy.
In Schacky’s view, our brains are changing fast because of global omega-3 levels. ‘This is happening to the brains in the world: they are getting smaller and smaller, they’re working less and less well,’ he adds. He believes if blood levels of omega-3s don’t improve, the human brain might be different 70 years from now.
But how much should these levels improve? Satizabal argues that there’s no need to take over the fish market. One of her findings shows that people don’t need to consume huge amounts of fish to improve their health. ‘As long as you just mix in a couple of meals per week, that will be really good for your brain health. It’s like an investment you’re doing to keep things working well,’ she adds. In turn, vegetarians and vegans could take supplements or consume vegetable products rich in omega-3, like seaweed.
But doing nothing would be the worst course of action, especially since omega-3s impact the whole body. ‘This is not just the brain and heart; it goes far beyond that,’ Schacky says. ‘All the cells in the human body need to have some omega-3s to work well. And if you look at it from this perspective, increasing omega-3 levels now becomes more and more important.’
Barbara Pinho is a science writer based in Porto, Portugal
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