In this edition of The Naked Scientists, what science has to say about whether a vegan diet is a healthy diet…
In this episode
00:46 - Were our ancestors vegan?
Were our ancestors vegan?
Peter Ungar, University of Arkansas
The term "veganism" is a modern one. It was first coined in 1944 by Donald Watson who would go on to found the Vegan Society. But did our ancestors also choose to reject the consumption of animal products as many people do in the 21st century? Chris Smith spoke with Peter Unger, a paleoanthropologist and evolutionary biologist at the University of Arkansas. He is also the editor of Human Diet: Its Origins and Evolution…
Peter - Well, there's actually a limited amount of information that we have on the diets of our ancestors. Most of that information comes from direct evidence, like the teeth of the ancestors themselves or indirect evidence like the context, the bones, and the plant materials that are found alongside them in the fossil record.
Chris - What clues can we get from teeth, then?
Peter - You can look at the wear patterns on the teeth, both gross and microscopic, to say something about what animals actually ate in a moment in time in the past. You can look at the shapes of the teeth to say something about what the animals had evolved to eat, what their ancestors were selected to eat. You can look at the chemistry of the teeth and say something about the properties of the foods that were used to build those teeth. What it tells us is that we're not very specialised. We don't have the specialised teeth of carnivores, animals that chew and slice through tough meat and sinew. We don't have the flat teeth with the parallel ridges of enamel for grinding tough vegetation. We have very generalised teeth that basically suggest that we evolved for a fairly broad diet. Of course, it's very difficult when you ask what our ancestors evolved to eat because the question that I always come up with is, what ancestors, right? Are we talking about ones that lived 500,000 years ago, a million years ago, 5 million years ago? Also, where? Human ancestors and our near cousins living in different parts of the world likely ate different foods depending upon the environments they lived in.
Chris - What does eating meat do for your evolution? What does it drive or what does it enable you to unlock that, were you to forgo meat eating, your evolution might take a different path?
Peter - As our ancestors developed an increasingly broad diet, they began to consume meat as part of that broadening diet. Is meat necessary? Absolutely not. But when it's the easiest to obtain high calorie resource, then of course they would take advantage of it. Ultimately, humans are dependent on grass, whether we're talking about corn and wheat and rice, or we're talking about consuming animals that consume grass, there's just too many of us to not have to take advantage of this wonderful approach that nature has taken to generating energy from the sun. Rather than consuming the grass directly or consuming plants, some of our ancestors were probably forced to take these large mammals.
Chris - Is there any possibility or is there any evidence that some cave men and women were vegetarians or even vegans?
Peter - There is not a lot of evidence either way, to be honest with you. Researchers are beginning to develop tools that we hope will allow us - in terms of bone and tooth chemistry - to come up with numbers for the amount of meat consumption, but those are still in the works and on the ground level. We do have some evidence from more recent human relatives like Neanderthals and the amount of nitrogen in their teeth, which gives you an idea of whether animals are eating animals or eating plants, the position in the food pyramid, and it appears that Neanderthals in some places consumed mostly plant material and Neanderthals in other places consumed mostly meat. But I think the point is that, again, humans are so broad in the diets they eat. We are the broadest spread species on the planet, and the reason for that is we can find something to eat no matter where we roam.
05:38 - Why people go vegan, and what they eat
Why people go vegan, and what they eat
Alice Guillaume, Cambridge Food Hub
What exactly does the modern day vegan diet look like? And how healthy is it? Chris Smith went to meet Alice Guillaume from the Cambridge Food Hub. Alice has been on the show before, and she also happens to be vegan…
Alice - I would say there are three main reasons that I know people choose to become vegan and they can overlap between the reasons, or include all of them. Environmental reasons are important. Wanting to reduce the impact of your diet on things like land use, water use, carbon emissions, but ethics and particularly ethics of animal rights. Then, the third reason might be health reasons. So wanting to make positive health decisions. So I'd say those three are the main reasons that I believe people would choose to be vegan.
Chris - Are there grades of veganism?
Alice - That feels quite controversial and I'm sure that whatever I say, others might have a different opinion. At its purist, it is strict, but you will find people that choose, they might eat eggs that their own chickens have produced, for example. Or some people do eat honey even though it is an animal product. Whether those people then strictly define themselves as vegan, or are trying to follow it to the best of their abilities... Personally, I'm not very pure about things. I think people need to make the decisions that are right for them and how they live. Medication, for example, often can contain lactose from milk or gelatin, so sometimes people have to make compromises. I think, from my perspective, the important thing is to try and reduce the amount of animal products that we consume. I would never say to anyone they have to be completely pure about it but the most concrete definition of veganism would be removing the animal products from all those different aspects of your life.
Chris - How long have you been vegan?
Alice - It's difficult for me to remember exactly when I became fully vegan. I briefly transitioned through vegetarianism, but it started when I went to university. I became quite involved in environmental activism and a lot of people that I was doing things with were vegan. I began to understand the impact of my diet on the planet and it felt like something that I had complete control over. I was always somebody who was turning off the lights, turning off the taps when I'd brush my teeth, but I remember learning a fact. It was something along the lines of: if you don't eat one beef burger, you've essentially saved the same amount of water as having showers instead of baths for a whole month. It was something like that. It was about the water impact of eating meat. And I thought to myself, why am I doing all these other small changes when there's this one big change that I have complete control over in my own life? That's why I decided to become vegan. And. I'd eaten meat my whole life before then, so it felt a bit of a struggle. I felt like I was going to be missing out on things, but I really tried to spin it in a positive way to think about all the new foods that I would have access to. It really broadened my cooking. It made it more exciting. I tried different cuisines from around the world and overall it's really been a positive thing. And now animal products are not something that I miss.
Chris - How do you keep yourself healthy? And did you go into this with an eye on the health side of it? Because this is a programme ostensibly about the science and the health of veganism. There have been a number of reports recently where people are saying, look, this is not a healthy diet. How do you make sure you don't end up in trouble from a health perspective, especially as a young woman, because young women tend to be more prone to iron deficiency and that kind of thing, for example?
Alice - Of the people that I know, the people that are the most aware of what they eat and the nutrients they're getting are the vegans because it's almost drilled into you that you're going to become deficient. It means that people are very aware of what they eat and very aware of where they can get certain things from. They are more likely to take supplements, for example. I was aware of the health aspect, aware of the different elements of your diet that you need, proteins and nutrients and things like that, and also aware of the health benefits, increased consumption of whole foods and fibre in particular. My diet consists of a lot of pulses, for example, things like chickpeas and lentils and beans, which are a great source of fibre. I'd say that there's an increased consumption of fruit and vegetables. The way I had it described to me, which I really liked, is if you remove meat and dairy from your plate, there's more space for fruit and vegetables and nuts and seeds and pulses, all things that are really good for you. I think it's worth saying that I think that you can be an unhealthy vegan or a healthy vegan. You can have a diet that is high in processed foods, for example.
Chris - Do you get yourself checked out? Do you go to the GP and say, well, can I have a blood test to look at my haemoglobin level, make sure I'm not anaemic, etc.?
Alice - I don't, but I think it's a good idea. I have given blood fairly recently, so that's a good way of getting those things checked as part of that process. I'll be honest, it is something that has been on my mind just because if you're experiencing symptoms like fatigue and things, you do want to know, right? Have I got all the balance correct? But again, a vegan diet can increase your chances, but all of us have the potential to have nutrient deficiencies. And actually one of the leading causes of diet related ill health is lack of fibre. Basically, people don't eat enough fruit and vegetables, and I think that that's something that you can really gain potentially if you become vegan, depending on what foods you're choosing to eat.
11:17 - Are vegans B12 deficient?
Are vegans B12 deficient?
Peter Julian Owen, University of Cambridge
Peter Julian Owen, a consultant orthopaedic surgeon at Addenbrooke’s hospital in Cambridge. He is also the co-founder and chair of CluB-12, which attempts to understand the importance of Vitamin B12…
Peter - I founded CluB12 very shortly after a tragedy in our family where my daughter took her life. She'd been vegan for three years and I must confess my memory of vitamin B12 from medical school was a bit distant, and we knew she should be taking it on a vegan diet and encouraged her to do so, but it transpired that she hadn't been taking it and it was more sporadic and she'd become a bit anxious. So, we said, take your B12, unbeknownst to us that she should have had intramuscular. She had oral and three weeks later she became psychotic and took her life. It just turned our world upside down. It's quite clear to me there's a lot of ignorance within medicine about the significance of this very important molecule.
Chris - It's a horrible thing to have had happen to you. How did you link that to the B12, though?
Peter - Back in med school I was taught about megaloblastic madness and that was the term for vitamin B12 deficiency. And sure enough, when you go back into it, anxiety, depression and psychosis are all part of the B12 deficiency spectrum. Presentation wise, only 15% of people present with an anaemia or megaloblastosis, which is the megaloblastic bit of that megaloblastic anaemia. So 85% of people will present with a neuropsychiatric problem. That's the first part of this ignorance because we don't appreciate that we look for for an anaemia with B12 deficiency. Georgina had said, I feel a little anxious, I think I should have been taking my B12, and we've since looked at her diaries - we wouldn't have done before she took her life - and found some writings, 'I'm going to stop being vegan. I'm going to eat some eggs, have some fish, change my diet round.' Tragically, too late to turn it around. With a dietary change, when you're that deficient, you need intramuscular B12. The reason being that three milligrams of our body is vitamin B12 when we've got enough, when we are replete. Very small amounts. But if we drop down to a milligram, there are severe consequences of that. To get your body back up, with two milligrams, and only absorbing two micrograms of a tablet going past the absorption part of your bowel called the ileum, you are not going to take that B12 level in the cells back up very quickly. It'll take you 200 days, perhaps. But you can give an injection and you can get 100 micrograms of the milligram into the cells. The other 900 micrograms drifts out in the urine. But you can see how having an injection every other day, after 10 days, you've put another milligram back into your cells and that's how you replenish someone and get them through these dreadful situations.
Chris - What does B12 do in the body?
Peter - The textbook would tell you the molecule attaches to an enzyme, so vitamin B12 is a co-enzyme in the main part of the cell called the cytosol. It works on an enzyme called methionine synthase, and that's part of a cycle, like you might know about the Krebs cycle. This is called the one carbon cycle and and that creates little methyl groups, carbon with three hydrogens, which is a building block for nature; for DNA, for RNA and many processes in the body. If you don't have a functional one carbon system, you can't methylate and that has dramatic consequences. There's another enzyme in the mitochondria which are for energy production within the cell called Methylmalonyl-CoA mutase, and that also has vitamin B12 as a co-enzyme. That might be responsible for the energy people seem to lack in B12 deficiency.
Chris - Where do we get most of it from?
Peter - We get ours because we eat animal products and the animals that we eat, or the products we eat, have managed to filter out the B12 for us. So if you put that the opposite way round, if you think of a vegan diet, that is an exclusion diet, so you won't get any B12 of any significance in a vegan diet.
Chris - Does that mean then that anyone eating a vegan diet is probably B12 deficient or is at least at very high risk of becoming B12 deficient?
Peter - People feel it might take two or three years to become significantly B12 deficient, but unless you supplement or find another source of B12, you will become B12 deficient.
Chris - Are the supplements all right? If you just eat some supplements and you're vegan, will you get enough B12?
Peter - The problem with the supplement is that the human body is used to having a drip feed of B12 in every meal. So if you take a large dose of vitamin B12, you will only capture two micrograms of it through the very specific uptake mechanism. But you can absorb a little just passively through your whole bowel, about 1%. The problem with that is the rest of that B12 goes into your colon, and there are some studies that show it changes your biome. There are even studies to show it turns the B12 into an non-vitamin called pseudo B12. And pseudo B12 has been found in some diseases in the body. It's a whole science we've yet to understand. There's another issue with the supplements that the active form that defines it as B12 is attached to the bottom of that disc. But at the top, that's what defines what we would find in the shop. We'd find a methyl B12 or a cyano B12 or a hydroxy B12, and the cyano is the most stable and doesn't react to light, but the methyl slowly degrades. Some of our members within our group cluB12 have been testing supplements from the shops. And yes, there are degradation products. They're not what they say they are on the tin. So a good varied diet is more likely to give you the nutrients you think you're getting.
18:17 - The health pros and cons of a vegan diet
The health pros and cons of a vegan diet
Tom Sanders, King’s College London
What exactly does the science say about vegan diets, and what are the main points of nutritional concern? Tom Sanders is emeritus professor of nutrition and dietetics at King’s College London. Tom has been researching vegan diets since the 1970s…
Tom - The nutrient that is most likely to be lacking in a vegan diet is going to be a vitamin B12. It may be quite low in calcium depending on the food selected and the protein quality will be a bit lower, but it won't be so low to be a problem. The diet itself, because it's derived from plant foods, means that some of the minerals, things like iron, all calcium and zinc, can be the absorption of them from plant foods can be not very good, and be influenced by other components in the diet. So sometimes that can be a problem. But really there are only a few things that are really missing in vegan diets.
Chris - What should a person do to make sure that they don't miss out on those things? Because there's a lot of focus on what people might be missing, but there's not so much focus on what they're including. So what's the best way to approach this?
Tom - I've always said if you’re looking at a diet, you want to have a good staple food. So in the West, our staple food is based on wheat. So we eat bread and all things made from flour and bread. And that's a good start. And then if you can mix the cereal with a legume or a pulse we call it, so beans, lentils, things like that, it gives you a very high quality protein, mixing the two together. And the other thing, which I think you need to make sure you have is plenty of fruit and vegetables, you need to be quite careful though with young children not to feed them too many fruit and vegetables because they've got small stomachs and then they can't eat the other foods, for example the cereals and the beans that provide most of the nutrients.
Chris - I was going to ask you about that because there must be times in our life when our needs change for various reasons. You've mentioned one of them I was going to bring up, which is little kids because they must have a bigger demand for calories to grow, for example. But another time is when you're growing a little kid, you're a pregnant woman. And if you are for instance, an elderly person who's broken something needs to get better from a surgery in hospital for example, you're going to need different energy and different dietary constituents at those points. Are there any things that people should bear in mind at those points in their lives for example?
Tom - Nutrient requirements are greatest in the first few years of life when growth is most rapid. And in slightly older children, around the adolescents going through puberty, there is also a big increase in energy and food requirements. But in older children, they're able to go and select food for themselves and eat more food. Women actually don't need to eat more food during pregnancy because the body makes a number of adaptations to cope with improved absorption of some nutrients. But it's very important when women go into pregnancy, they go into pregnancy with a good diet.
Chris - What about breastfeeding?
Tom - Breastfeeding, I think the important message I think is, it's very important that mothers who are vegan ensure they've got a good source of vitamin B12 because if the mother doesn't eat enough vitamin B12, the level of vitamin B12 will be low in the mother's milk. And that can cause vitamin B12 deficiency in the baby.
Chris - Researchers including yourself, have looked over the years at the relationships between different diets and disease outcomes. So when one does those sorts of studies, are people better off eating plant-based diets and, and in some cases extreme plant-based diets like vegans, do they have lower rates of certain diseases and higher rates of others? How does it break down?
Tom - When I first looked at it, we were trying to establish were there any problems with vegans compared with mixed diets, omnivores we call them. And our overall conclusion early on was the health of vegans differs little from that of omnivores. And I still probably stick with this. Many people who follow vegan diets also have other healthy aspects of lifestyle. They tend to be non-smokers, don't drink much alcohol, and take a lot of physical activity. And those are all good things for health. So if you adjust for those things in the analysis, there's not a huge difference. There's probably a lower risk of heart disease. And we can attribute that, I think, to the very low intake of saturated fatty acids and a slightly higher intake of polyunsaturated fats. They have low blood cholesterol levels. When it comes to cancer, we don't really have a huge amount of evidence on cancer and vegans because the largest number of, I think, we've got pulled together is only about 8,000-10,000 people followed for 15, 20 years. If we look at vegetarians compared with meat eaters, there's not any difference in risk of colorectal cancer, which is the one you might think that might be protected on. And I suspect that's the case for vegans. There's some suggestion that vegans might be at lower risk of prostate cancer, which affects elderly men. There's some suggestion that some blood cancers might be lower in vegetarians and vegans and some of these are, we know, due to infections. But it may be something more to do with lifestyle than to do with diet. But overall, I don't think there's really a huge difference in cancer compared with the effects of things like tobacco or alcohol.
Chris - And lastly then. In your view, vegan diet - good thing, bad thing?
Tom - I think it's what people want to do and I understand there are a variety of reasons why people follow vegan diets. Some of them do it because they believe they are concerned about climate change. And there are other groups like the Janes for example, in the Indian sect who follow for religious reasons. And you can follow a vegan diet, but you've got to be very careful. It's okay if you supplement it with vitamin B12, I think you need to watch out about calcium intake. But you can do that by selecting the diet properly.
Are vegans Omega-3 deficient?
Philip Calder, University of Southampton
Omega-3 is a healthy fat that is typically found in oily fish and fish oil supplements. It obviously presents a problem for vegans because they don’t eat fish. So does that remain a sticking point in a vegan diet? To find out more, we put in a call to Philip Calder, professor of nutritional immunology at the University of Southampton. Philip is a leading expert on Omega-3…
Philip - Omega-3s are a type of fat that we get from the diet. Now people probably assume that fat is bad for us. In fact, there are some fats that are healthy, there are some essential fats and Omega-3 are among these healthy fats.
Chris - Why are they essential? What does that actually mean?
Philip - So essential usually in a nutritional sense means we can't make that nutrient ourselves and we have to get it from the diet. So there are two essential fats. One of them is called linoleic acid, that's an Omega-6 fat. And the other is called alpha-linolenic acid. That's an Omega-3 fat. Both of those essential fats are actually made in plants. So we get plenty of those from plant foods. But the really important Omega-3 fats, we call them EPA and DHA. We can actually get those from fish. We don't get them from plants. EPA and DHA are really important to supporting how our cells work in the body. Our brain cells, our heart cells, our immune cells. And that means they're associated with better health and over a long time period, reduced risk of many diseases.
Chris - And if we don't have them, what sorts of diseases are the deficiencies of these things associated with? How might a person who's running low on these things see this manifest in their health?
Philip - So a long-term consequence of not getting enough Omega-3s would be increased risk of heart disease. Also inflammatory conditions, things like arthritis for example.
Chris - What about brain health? Because I read a report from a celebrity commentator who said that she had embraced a vegan diet and then found that she couldn't think straight a number of months later, but then went and met a salmon steak and it was like someone had injected her with 50 million IQ points literally overnight. I mean does that sound plausible and why might that be?
Philip - Well I think it might be an exaggeration, but it is true that one of these important Omega-3s I mentioned, DHA, is really important in brain function. And there are experiments and data from research showing that if babies get more DHA early in life, they have better cognitive function. Maybe they have improved learning abilities, improved behaviour and so on. It's a small difference, but it does seem to be a consistent finding. Now later on in life it's believed, although it's been difficult to demonstrate, that having more DHA in the brain, which we'll be getting from our diet of course, helps with our cognitive function. Of course, you can get Omega-3 supplements that sometimes we call fish oils. These obviously come from fish, but now there are supplements on the market which are algal oils. And these are for all intents and purposes, these are equivalent to fish oils that are suitable for people who choose not to eat fish or take fish oil supplements.
Chris - So have people actually looked at, say, vegan diet consumers and compared their levels of these Omega-3s with people who are not eating that diet, do they tend to be on average deficient in these oils?
Philip - One of the problems is we can't define deficiency of Omega-3s with a number unlike some of the vitamins and minerals where there's a clear cutoff for deficiency. But we do know that vegans particularly have a lower intake of EPA and DHA. I think that's obvious because the main source is fish. And they also have lower levels of EPA and DHA in their blood than vegetarians. And vegetarians have lower levels than omnivores. But having said that, it's not that the levels are extremely low, that's actually been quite well described now. So they're lower but they're not totally absent, let's say. So that asks some other questions about our body's ability to make those important Omega-3s if we're not getting them from the diet.
Chris - And if a person is chronically low in them, do we have documented evidence then that there is an association with an increase in inflammatory states, heart problems, and possibly cognitive problems?
Philip - So we know that from two types of science. One is what we call observation and that's where you look at people's intake or the levels of these fatty acids in their blood at a point in time. And then you find out what happens to them maybe in 10, 15, 20 years time. So we know that people who start with a higher intake of EPA and DHA or who have more EPA and DHA in their blood, they have a lower risk of all of the things I mentioned, particularly heart disease. So I think that's a relationship. The other is in trials where people have been given EPA and DHA usually through supplements because that's easier to do in a human trial. There are beneficial health impacts. So I think that's quite clear. But I think we also have to keep in mind that there is an Omega-3 that I mentioned earlier on that we get from plants like rape seed oil for example. Flax seeds and flax seed oils are very good sources and we do have the capability to convert a little bit of that alpha-linolenic acid into these, I'm going to call them fish-type Omega-3s in our own body. So we are able to make our own EPA particularly in small amounts.
Chris - Do you think it's an advisory, like a healthy vegan diet or is it better to be vegetarian?
Philip - That's a really difficult question to answer. Many diets can be healthy and many diets can be unhealthy. So you know, an omnivorous diet can be an extremely unhealthy omnivorous diet or it can be a very healthy omnivorous diet. And I think with vegans it's roughly the same. So I think it's possible to have a healthy vegan diet so long as people are attentive to the things they're not getting enough of and maybe seek out ways which might be supplements to make sure they're getting enough of those nutrients.
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