[Featured image modified from Yanalya – Freepik]
A UK based study into the health benefits of vegetarian diets – the largest of it’s kind to date – has just published its findings in The American Journal of Clinical Nutrition showing that long-term diets reducing or eliminating meat and other animal products did not lead to significant reductions in early death. Not only does this call into question the claimed health benefits of vegetarian diets, but is also challenges recent warnings about the risks of eating meat.
The study by Appleby et al at the Cancer Epidemiology Unit at the University of Oxford wanted to find out if previous evidence indicating protective effects of vegetarian diets against certain chronic diseases actually translated into extended life (i.e. reduced mortality).
They used data from two UK based studies that tracked a total of 60,310 persons recruited between 1980 and 1993 and tracked until 2014, representing a total of over 1 million person-years of follow-up.
Based on a simple questionnaire participants were categorised to one of five dietary groups: Regular meat eaters – who ate meat 5 or more times per week; Reduced meat eaters – who ate meat less than 5 times per week; Fish eaters – who avoided meat but ate fish; Vegetarians – who ate eggs and/or dairy products but no meat or fish; and vegans who ate no food of animal origin at all. These dietary patterns were rechecked every five years.
During the study period over 5000 deaths were recorded, providing data to estimate the relative risk of death among each group. The graph above shows the relative risk of death for each group after adjustments for the usual suspects: smoking, alcohol, age, marital status, supplements etc. As you can see there was very little difference between the groups.
Although the vegans appear to have a raised risk, there is more uncertainty in the association as they were the smallest diet group. This is indicated by the larger 95% confidence interval whiskers, so the apparent increase is actually non-significant. It might be tempting to use these data to criticise vegan diets, but that would not be statistically valid.
This is still interesting, as the vegan group had several dietary factors which conventional wisdom would expect to be in their favour: they consumed the lowest level of saturated fat and had the highest intakes of fruit, vegetables and fibre. All of these would usually be considered part of a healthy diet. In contrast, the meat eaters had the highest levels of saturated fat and the lowest levels of fruit and vegetables, yet their all-cause mortality was similar to that of the vegans.
So what about earlier studies which found evidence for protective effects from vegetarian diets, and those that indicated an increased risk of bowel cancer from red meat – you know – the ones that made the headlines and six o’clock news? How do we square those with the ‘no overall difference’ found in this study? The answer appears to be that each diet increases risks of some diseases whilst reducing risk of others.
When Appleby et al looked at the causes of death between the groups they found some clearly significant differences, which we will look at below. This is somewhat surprising considering that the overall mortality was so similar between groups, but it highlights how focussing on a single cause of death can lead to mistaken conclusions. Let’s take a look at some of those between-group differences.
Colorectal cancer
Following October’s media frenzy surrounding the decision of the WHO to classify red meat as a ‘probable carcinogen’ and processed meat as a ‘definite carcinogen’ statistics appeared in many papers claiming to quantify the increased risk of colon cancer caused by consuming red or processed meat. One such from the Guardian on the 26th October 2015 said:
An analysis of data from 10 studies estimated that every 50 gram portion of processed meat, if eaten daily, increases the risk of colorectal cancer by about 18%… [whilst] data from the same studies suggest that the risk of colorectal cancer could increase by 17% for every 100 gram portion of red meat eaten daily.
Fortunately, we can put these claims to the test as in the new study Appleby’s group gives us the daily intake of processed meat for each diet group:
| g/day | Regular meat eaters | Reduced meat eaters | Fish eaters | Vegetarians and vegans |
| Red meat | 70 | 21 | 0 | 0 |
| Processed meat | 24 | 8 | 0 | 0 |
If the stats in the Guardian are to be believed, then the regular meat eaters should have about a 20% increased incidence of colorectal cancer than the non-meat eaters. But what did the Oxford study find?
Note: vegetarians and vegans had to be combined in this sub-analysis as the sample size would otherwise have been too small.
Of the non-meat eaters, only the fish eaters had a significantly reduced risk of dying from colorectal cancer, a whopping 40% fewer fish eaters dying of that cause. Yet contrary to expectations, the vegetarians and vegans gained no significant benefit from avoiding meat. This is weird. And it challenges many of the putative mechansisms by which meat might initiate cancer. The front runner in the cancer-inducing steaks (pun intended) is thought to be the oxidation of fatty acids by heme iron (from fatty red meats), but if that were the chief mechanism then vegetarians should be protected from colon cancer to the same extent as fish eaters.
One possibility would be that fish may contain protective factors, rather than red meat containing harmful ones. But this seems unlikely, as the regular and reduced meat eaters ate similar amounts of fish per week as the pescatarians. There is something fishy going on here…
Looking at deaths from all kinds of malignant cancers it is possible to distinguish between vegetarians and vegans, and the picture again is much of a muchness. The fish diet is the only group showing a significant difference:
The second biggest killer after cancer is cardiovascular disease, so lets take a look at what this study found.
Cardiovascular disease
It is commonly assumed that meat eating is associated with heart disease. Indeed meat, animal fats and saturated fats are often conflated, and in many people’s minds all contribute to cardiovascular disease. Yet in this study there was no statistical difference between the diet groups for deaths from cardiovascular disease in general or ischaemic heart disease in particular.
In the case of cerebrovascular disease (which includes stroke), however, an interesting picture emerges:
In this case meat eating appears to be protective, with the vegan’s having a significantly increased risk of dying from cerebrovascular disease. There is possibly a smaller raised risk for fish eaters too, although the broad 95% confidence intervals make it hard to draw any firm conclusions. These findings are strange as there were no obvious dietary differences between the vegans and fish eaters when it came to the usual ‘culprits’ saturated fat, total fat, fruit/vegetable consumption etc. As the authors conclude:
Differences found for specific causes of death merit further investigation.
Strengths and weaknesses of this study
Usually observational studies can be criticised because they can only demonstrate correlation not causation. However, when a sufficiently powered observational study like this one finds no correlation (all 5 diets being essentially equal with respect to mortality) then de-facto there can be no causation.
Conclusion
The take home messages seems to be:
- Vegetarian and vegan diets do not appear to be especially protective, and meat eating is not especially harmful.
- Fears about red and processed meat and colorectal cancers appear unfounded.
- Whilst choices around vegetarian v non-vegetarian diets can indeed change risk factors in relation to specific diseases, they are unlikely to affect overall life expectancy.
Does this mean there is no point in trying to eat a healthier diet? No. For one thing, if you have a heightened risk of a particular disease – because you have a specific medical condition, genetic weakness, or family history for example – then it makes sense to eat a diet that minimises that risk. In such a case it will improve your overall mortality risk.
Secondly, the participants in this study were all eating ‘standard’ versions of these diets with macronutrient ratios close to the national norms, i.e. high-carb with lowish protein and fat. Below I have listed the participants’ macro nutrient consumptions and compared them to the national average taken from NDNS data 2011/12. You can see from the variations (+/- figures) that none of the participants’ diets varied much from this norm.
| Baseline diet; All participants | Energy, % | UK average (NDNS 2012) |
| Protein | 14.6 ± 2.8 | 17 |
| Carbohydrate | 48.9 ± 7.1 | 50 |
| Total fat | 31.5 ± 6.0 | 35 |
| Saturated fat | 11.1 ± 3.5 | 12.6 |
So this study tells us nothing about the long term benefits of a low-carb, gluten-free or paleo diet. What it does show though, that there is little reason to worry about your meat intake and even less reason to be distracted by vegetarian or vegan health rhetoric.
SOMETHING MUST BE LACKING IN THE VEGAN DIET. COULD THIS BE DUE TO LACK FATTY ACIDS LIKE OMEGA 3 AND 6 , FOLIC ACID, B12 OR OTHER MICRO NUTRIENTS?
Yes, that is correct. A lot is missing from the diet of many vegans. A good, attentive, well thought through vegan diet could be really good, especially if they then add in some offal, eggs or cheese along with all the wonderful vegetables! That’s my kind of diet.
You can get all of the nutrients you need from a vegan diet except vitamin B12, and that’s only because we wash produce so thoroughly nowadays. If we’re talking about deficiencies though, it is important to remember that meat-eaters usually don’t have a perfect diet either and can also be lacking nutrients, such as fiber and vitamin B12.
The trouble with most of the research is the vegans are eating more healthily than the standard UK diet, so the ‘average’ meat eater is not much of a benchmark. Worryingly, this study suggests that even that advantage didn’t help the vegans live longer. That would suggest that a healthy non-vegan diet might be the best, but there was no specific category for that so we don’t know. The closest would be the pescatarians, and they do come out quite well probably not because they avoid meat, but again, because they are trying to eat more healthily overall. In the end you make your choice and live with the results, which on an individual level will vary from person to person anyway. Good luck with your diet, I hope it works out for you. If it doesn’t keep an open mind – you can always change later.
The study of diets is fraught with confounders, its difficult to do control studies hence the confusion. It is easy for people on one side of the meat v no meat argument to pick a hole in the other sides positive research. My advice to anyone would be to keep it simple. Look at the populations that do not get heart disease in any significant numbers, do not get cancer in any significant numbers like some of the pre westernized african nations amongst others. Now what do they eat ?, lots of veg and whole food starch. Maybe occasional meat but not much. What can you say about this kind of diet. Well it is certainly not causing heart disease. OK if you eat like this and it turns out that western stress from urbanized living is the real culprit or maybe poor social circles from large community living are the real villains in heart disease then it may be you will get it anyway. But you can at least feel sure that your diet was not the problem. However if you eat loads of meat the pro meat people might be right and you have nothing to worry about but its difficult to be sure. Finding the same level of evidence of meat eating pop’s with as low rates as pre western Ugandans is pretty hard to come by. Finding a meat based diet for people with heart disease that reversed the condition is pretty much non existent.
Bad Studies do exist and thus post is a perfect example of meat eater.biased rhetoric. A nutritarian vegan diet is undeniably healthier than a mTOR boosting meat eating diet This article is like a training wheels pigeon holed view of reality. LOOK around and we see vegans leaner and healthier, less constipated or bloated and having smaller waists. I can write a book about this but I don’t have the time. More.important things to tend to.
Hi Ivan, you are right about bad studies, but this one is considered sound. Similar findings were found in Australia too. If you can point me to a specific weakness in the paper I would be very interested to know. I have to say that in my experience vegans come in all shapes and degrees of health which is the problem with anecdotal evidence. Have you always been vegan or is this something you started recently?
I think you should first try a vegan diet first. Then we will talk further. With this article I get the idea that it has been examined from a meatier perspective.
Indeed it is a meatier perspective that I come from Ronald. Meatier in the sense of a greater research and logic base.
I was a vegan in my late 20s, and my husband was vegetarian for 28 years! We are extremely glad for the meatiness of our research! I hope you keep an open mind, as we did.
If I took you down my local Veggie community group when they have a bring some food for social get togther evening you would see that being veggie is no guarantee of healthy eating. When I have attended I always make a point of eating before I go. Show me a whole food meat based intervention trial that has reversed heart disease.
I’ll sum up what he said : I have bad arguments but in my opinion, I am right. I could say some smarth thing (doubt it), but I’m to busy so you have to trust my superior intellect (here you go)
The data shows what I suspected, that Veggies/Vegans eat more carb’s. If we had the data on the carbs I would imagine they are consuming far more unhealthy, high glycemic carbs as well which would explain the heart disease figures. You only have to go to a vegan/veggie gathering to realise that it is not a whole food plant based gathering. What I would love to see is a head to head healthy meat eater cohort Vs WFPB group V Healthy Pescetarian group. Any such studies ?
Wait A MINUTE! You cherry picked! Right off the bat you base all this off of a NCBI study that, as you stated, showed not difference in overall mortality, meaning, sure, vegetarians and vegans die too. But, this study also says:
“There were significant differences in risk compared with regular meat eaters for deaths from circulatory disease [higher in fish eaters (HR: 1.22; 95% CI: 1.02, 1.46)]; malignant cancer [lower in fish eaters (HR: 0.82; 95% CI: 0.70, 0.97)], including pancreatic cancer [lower in low meat eaters and vegetarians (HR: 0.55; 95% CI: 0.36, 0.86 and HR: 0.48; 95% CI: 0.28, 0.82, respectively)] and cancers of the lymphatic/hematopoietic tissue [lower in vegetarians (HR: 0.50; 95% CI: 0.32, 0.79)]; respiratory disease [lower in low meat eaters (HR: 0.70; 95% CI: 0.53, 0.92)]; and all other causes [lower in low meat eaters (HR: 0.74; 95% CI: 0.56, 0.99)].”
All of which clearly indicates a less meat is better for you!
Hi Jeff. You are right that if you look at particular causes of death you can come to different conclusions depending on which disease you pick (circulatory, cancer etc). This is the problem with much of the research and health debate concerning meat vs vegan diets – when you pick one disease you might reach a particular conclusion, such as the familiar headline that “red meat is associated with increases colon cancer”. However, that might not be relevant if meat eaters die less of respiratory disease and all other causes (as the data you quote indicates). How can we assess the pros and cons of each diet across all the different outcomes? All cause mortality. Overall mortality is a measure of how many people have died by a certain age. The fact that there is no difference in mortality between vegetarians and omnivores shows that neither diet helps one group live longer (on average) than the other.
[Also, I’m not sure how you came to the conclusion from the quote above that it ‘clearly indicates a less meat is better for you!’ as it states that meat eaters have less chance of dying from respiratory disease, pancreatic cancer and all other causes, whereas vegetarians have less chance of dying from pancreatic and lymphatic/hematopoietic tissue cancers. Rather hard to draw a firm conclusion from that, surely? Again, that’s why all cause mortality is so important]
There have been around 3 or 4 such studies and the majority show that vegan/veggie diets benefit overall. Also I am not aware of a meat based diet that has reversed heart disease
When you say ‘benefit overall’ are you referring to all-cause mortality? If that is so, then why does it not appear to benefit UK and Australian populations? (see our article on the Australian study here https://wordpress.com/read/blogs/32878195/posts/4617)
The PURE study found no link between saturated fat and mortality, but rather carbohydrates seemed to be the culprit. The video is well worth a watch: (https://rosemarycottageclinic.wordpress.com/2017/03/03/cardiologist-attacks-diet-dogma-at-2017-symposium/)
As for heart disease, in Europe the the evidence is overwhelming: countries that eat more animal products have the lowest rate of heart disease – its a very powerful association. (https://rosemarycottageclinic.wordpress.com/2017/11/19/carbohydrates-not-animal-fats-linked-to-heart-disease-across-42-european-countries/)
I think sat fat is not the elephant in the room with regard to heart disease but it has been shown to create endothelial dysfunction using brachial arterial flow measurement. It could be therefore that while its not a main culprit you do need to avoid it if wanting to reverse heart disease.
I agree on carbs, here is my take on the China study data
In his rebuke of Denise Minger Campbell makes a valid point that univariate analysis is fraught with danger.
What he means is analysing one variable to an effect can be misleading as other variables may be playing a part.
For example he cites that with wheat there is a predisposition for higher wheat consuming regions to be lower green plant eating regions. This would tilt the results somewhat if we accept that green plant is protective.
Indeed there are 23 regions where wheat exceeds grenn plant consumption and 41 where green plant exceeds wheat.
Looking at wheat alone and comparing it with average consumption of wheat across all regions, when it is above average heart disease stands at a high 23.24
But what would we expect to happen if wheat was greater than average wheat consumption but so too was green plant greater than average green plant consumption. Would we expect HD to be below 23.24 ?. Well it comes in at 26.33 from 7 regions
Wheat greater than average but plant less than average HD = 21.8 from 15 regions
Wheat less than average but plant greater than average HD = 8.91 from 19 regions
You say:
“1. Vegetarian and vegan diets do not appear to be especially protective, and meat eating is not especially harmful.
2. Fears about red and processed meat and colorectal cancers appear unfounded.
3. Whilst choices around vegetarian v non-vegetarian diets can indeed change risk factors in relation to specific diseases, they are unlikely to affect overall life expectancy.
Does this mean there is no point in trying to eat a healthier diet? No. For one thing, if you have a heightened risk of a particular disease – because you have a specific medical condition, genetic weakness, or family history for example – then it makes sense to eat a diet that minimises that risk. In such a case it will improve your overall mortality risk.”
Number 3 contradicts number 1. Then you suggest only eating healthy if one has a disease, minimizing risk. But, waiting to find out if you’re vulnerable to heart disease, alzheimers, stroke, cancer, etc… before eating a healthy diet is really bad advice.
Point 3 means that by choosing a vegetarian diet you may indeed reduce your risk of one disease (e.g. certain cancers) only to increase your risk of another (e.g. stroke). The all-cause mortality indicates that overall the advantages are pretty much balanced by the disadvantages so overall there is no benefit. On the face of it that means that for overall health there is no point worrying about the meat/vegetarian dichotomy. That said, (and the point I am making in the last paragraph) is that If you know you are a heightened risk of a particular disease (e.g. if you have a family history of stroke) then you might be better off with one or other diet (vegetarians seem to die more of stroke).
As to your last point about not waiting to eat a healthy diet – the question is what constitutes a healthy diet? Most people have been persuaded that meat / vegetarian is an important part of that choice, but this article shows it is not. In my experience the quality of the food – unprocessed, low glycemic index, unprocessed whole foods – is almost certainly much more important. For many of my patients a grain-free diet massively improves their health, but this isn’t true for everyone. Some have to exclude all plant foods for a time and only eat bone broth and meat to restore their microbiome. In my family many of us cannot tolerate cows’ milk but are fine with goats’ and sheep’s. I don’t have a problem with vegetarianism per-se, except that it comes with a lot of idealogical animal rights baggage that make adherents exaggerate the health claims.
What is your feelings towards oats ?
The Aventist health study shows better outcomes for Vegan/vegitarians
http://www.mdpi.com/2072-6643/6/6/2131/htm
Yes it does, but is that because they are adventists or because they are vegetarians? As the authors of the paper note: “Since this review is limited to the Adventist cohorts, the findings may not be fully generalizable to other vegetarians with different lifestyles. The studies in our review did not directly compare vegans with lacto-ovo-vegetarians, thus it may not provide adequate interpretation of the magnitude of differences in effect size between these two dietary patterns. The observed health benefits of vegetarians may be partially related to other lifestyle factors due to residual confounding.”
What really makes the UK EPIC study stand out is that it compared UK vegetarians to meat eaters. The average UK vegetarian has many lifestyle differences compared to the average UK meat eater. Just ask yourself which group are more likely to smoke? drink alcohol? eat natural food? Even with all those lifestyle advantages UK vegetarians still do not live longer!
The Aventist group is more homogeneous and therefore within it comparing vegans/veggie adventists with meat eating adventists is likely to be more representative.
Name me a meat eating study that has halted or reversed heart disease
Thanks for your comments, but this is becoming a circular argument. If the benefits of vegetarian diets were significant they would show up in the population studies I previously mentioned (UK EPIC, Australian, European or PURE). Unless you can provide convincing evidence why these are flawed then no amount of evidence on specific sub-populations or isolated risk factors is relevant to this article.
The fact remains that in the Adventist group non meat eaters live longer although Pescitarians trump both. Given that the group means that control for other factors is tighter I would be more inclined to rely on this study.
The longest living populations ie Blue zones are also either low or no meat eaters
Taken from adventist II
“There were 2570 deaths among 73 308 participants during a mean follow-up time of 5.79 years. The mortality rate was 6.05 (95% CI, 5.82–6.29) deaths per 1000 person-years. The adjusted hazard ratio (HR) for all-cause mortality in all vegetarians combined vs non-vegetarians was 0.88 (95% CI, 0.80–0.97). The adjusted HR for all-cause mortality in vegans was 0.85 (95% CI, 0.73–1.01); in lacto-ovo–vegetarians, 0.91 (95% CI, 0.82–1.00); in pesco-vegetarians, 0.81 (95% CI, 0.69–0.94); and in semi-vegetarians, 0.92 (95% CI, 0.75–1.13) compared with nonvegetarians. Significant associations with vegetarian diets were detected for cardiovascular mortality, noncardiovascular noncancer mortality, renal mortality, and endocrine mortality. Associations in men were larger and more often significant than were those in women.”
Thanks, I think you have made your point. But again, if this applied to vegetarians and vegans generally (other than among Adventists) then why would it not show up in the UK, Australian, European populations and the PURE study?
Can you point me to where the PURE study does an analysis of Veggie v meat ?
https://www.researchgate.net/profile/Jenny_Chang-Claude/publication/12821350_Mortality_in_vegetarians_and_nonvegetarians_Detailed_findings_from_a_collaborative_analysis_of_5_prospective_studies/links/00b4951c85790392ce000000/Mortality-in-vegetarians-and-nonvegetarians-Detailed-findings-from-a-collaborative-analysis-of-5-prospective-studies.pdf
You think you get any real science out of a couple thousand SELF DESCRIBED UK “Vegans” you are silly fools.
Wait a minute – I think I understand your frustration with this data. I, being a vegetarian, feel that frustration myself. But I appreciate that this article – and some of the comments in it, including the mention of the adventist study – is helping me getting a more nuanced image of the data. Calling someone a ‘fool’ is not adding to that sense of nuance and constructive dialogue that I would like.
The balance of studies show vegans, veggies and pescatarians live longer and have less disease on the way. The Oxford study does not show this but I do not think that it is as controlled as the Adventist study. Couple this with the fact that the Blue Zones tend to be low or no meat eaters and the evidence starts to look pretty sound, a whole food plant based diet is best. Can anyone show me a meat based diet that has reversed heart disease in the same way that Ornish published in the Lancet way back in 1991 and in the way that Essseltyn and Macdougal have successfuly managed since ?.
Thank you for an interesting article. It is somewhat frustrating to read data that seems to contradict what I thought was true, but also enlightening. Thank you, Keir and Afifah, for your work and for your careful way of answering questions 🙂
The Oxford study consisted of ethical vegans (hot whole food plant based) Vs healthy eating meat eaters. A better formed study is the Adventist health study which is far better controlled and shows Vegans/Veggies ahead on most scores to their meat eating counterparts and if you want to trump both groups go Pescitarian according the Adventist health study
That should have read (not whole food plant based)
How many studies and trials and…. have the Adventists done or caused to be undertaken? I believe the number is above 2,000 which begs the question, – why the continued gathering of evidence to support the same conclusion ?
One well-powered, properly conducted and in-depth RCT will have done the job.
Methinks they protesteth too much.
Hi Keir, probably you know all about it by now, but it seems that the vegan population in the Oxford study was particularly keen to junk food. After all chips and coke is a vegan diet, too.
They also found that adding a proper supplement of B12 to a whole food plant based diet (not simply junk food vegan) can lower the value of homocysteine to the correct place, and avoid the higher mortality by strokes.
There’s four videos on this by Dr. Greger.
Thanks Nico, there are, as you suggest, better or worse diets that come under various headings. Of course supplementation with B12 is always necessary on any vegan diet, as it is an essential to life, and isn’t in plants. This alone should be sufficient to assure people that a vegan diet is not the natural diet for humans. It is possible, with supplementation, to live healthily as a vegan, for some people, but not all vegans by any means. A couple of years of veganism is about the longest to maintain health, after that most, including Dr Greger, lose muscle mass, lose testosterone, voices go higher, sexual function fails. Tim Shieff, the parkour and free running champion lost all sorts of normal functions while vegan (and heavily sponsored as such) and he only recovered when he reintroduced animal products. Here is a frank discussion about it that I heard months ago https://www.youtube.com/watch?v=xzfD74ZvtdA.
The article is dishonest and a complete misrepresentation of the study.