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The Vegan Studies That Weren’t

Article at a Glance
  • Many of the studies which purportedly support a 100% Vegan diet are actually based on food frequency questionnaires administered largely to omnivores. Omnivores who eat less meat are often lumped into the same categories as Vegans.
  • Some large scale studies show that, when it comes to mortality risk, Pescetarian diets are healthier than Vegan diets.
  • Men seem to gain more benefit from giving up meat than do women.
  • Ultimately, the issue of whether it is beneficial to go Vegan comes down to each person’s unique genetic makeup.
The Vegan Studies That Weren’t

Most of us can agree: eating less meat is better for our health and better for the planet.

But how far should we take it?

John Mackey, CEO of Whole Foods, and a staunch advocate of a plant based diet, acknowledges in his book “The Whole Foods Diet” that most people can be healthy eating around 10% of their calories from animal products. Many plant based physicians disagree and advocate for a 100% “pure” Vegan approach.

The problem with strict Vegan diets is there are very few pure “Vegan studies” to guide us. Most of the studies the plant based community relies on to advocate for a 100% Vegan diet are population studies that use food frequency questionnaires to ask omnivores just how much animal protein they eat. Benefits are seen in those who consume less animal protein, but not zero animal protein. China Study author, T. Colin Campbell’s own work, such as this study showed that a diet of 5% animal protein turned off cancer, but 20% turned it back on in rats exposed to aflatoxin.

Understanding epidemiological studies

When plant based advocates talk about all the science that supports their movement, they are almost by definition talking about epidemiological studies. Epidemiology looks at patterns within populations and then infers causation, but it doesn’t establish causation. For example, some studies show higher levels of osteoporosis in populations that drink milk and eat dairy products. Are the increased cases of osteoporosis caused by the acidic nature of milk products that causes the body to leach calcium from bones to neutralize PH balance, or are the cases of osteoporosis caused by vitamin D deficiency and changes in VDR receptor genes between populations in northern climates vs. populations that live closer to the equator?

We don’t know and epidemiology won’t be able to tell us. Only clinical trials, which control for all variables, can give us something approaching that kind of certainty. It is for this reason that many take a dim view of nutritional epidemiology. I am not necessarily one of those people. Without epidemiological studies, we would have very little data on how food affects our health, so I see these studies as valuable. So too does longevity expert Dr. Valter Longo who factors in epidemiology as one of five pillars in his personal scientific method. However, we must also acknowledge that population studies have their limits. It’s discouraging to watch Kip Anderson in What the Health trolling diabetes associations waving studies in people’s faces. The studies he cites show benefit for people eating meat, it’s just that they are eating less of it!

Which is not to say that there isn’t a link between type 2 diabetes and eating certain quantities and types of meat, but it doesn’t follow that eating meat causes type 2 diabetes in all people.

Red Meat and Type 2 Diabetes

For example, this study cited by the film What the Health as proof that eating meat causes type 2 diabetes (a claim widely made in the movie) is actually a retrospective cohort study that went back through old data collected by previous studies in order to reach new insights.

The data presented relies on food frequency questionnaires which asked people how often they ate red meat. The lowest category of consumption was “never or less than once per month, which allows for the existence of Vegans and meat eaters within the same category. This is not a study that followed people on a Vegan diet vs. meat eaters. Does this mean that the study’s findings, that red meat consumption is associated with an increased risk for type 2 diabetes, are invalid? No. But, neither can the study be represented as a “pure” Vegan study. The group with the lowest risk of type 2 diabetes included people who eat red meat about once a month, which is decidedly not Vegan.

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Plant based diet and mortality risk

We’ve written previously about this Harvard study which found decrease in mortality risk over an 18 month period in people who ate less animal protein, but not zero animal protein. When the data for people without a chronic condition, or lifestyle risk factor, was isolated, the study found no statistically significant risk of early mortality for meat eaters. The study was prospective. Rather than try to isolate people into clear groups and track results from the jump, people were asked what they’d eaten and then the authors went hunting for associations.

There are two takeaways from the study, one of which is that people with a chronic illness can benefit greatly from eating a vegetarian diet. The other is that healthy meat eaters don’t have the same level of immediate urgency to change their ways. But this study was only conducted over an 18 month period, are there any studies that compare strict Vegan vs. Pescetarian vs. Vegetarian diets and gauge risk for certain diseases over longer periods of time?

As a matter of fact there are, and the results aren’t as clear cut as the plant based world would have us believe.

Pescetarians live longer than Vegans?

Let’s break down some of the best studies we have which compare the mortality rates associated with various popular diet types.

There are three studies which are particularly interesting in how they approach the effect of diet on mortality, those by Orlich et al, Appleby et al and Key et al all three of which are summarized nicely in the book Vegetarian And Plant-based Diets In Health And Disease Prevention. I’ve pulled some of the interesting tables out of the book to share as they’re quite an eye-opener.

Firstly, they looked at all-cause mortality for a variety of diets compared to a standard western meat-heavy diet, 1 would be a standard diet so anything lower than this is better, anything higher worse. Straight off the bat, you can see in the studies by Key and Appleby that a vegan diet isn’t associated with any improvement whereas vegetarian, pescetarian and even occasional meat (classed as less than 1 portion a week for Key, 5 portions for Appleby) perform better. The bold numbers indicate that this improvement was considered significant.

But what’s really interesting to me are the results from the Orlich study, where they split by sex. When grouped all together we see improved risk for all diets with vegetarian and pescetarian showing a significant improvement. If you look closely you can see that the vegan score has actually reduced as well, but not significantly so. One explanation for this is likely a high variation in the group of results. When split by sex we see evidence of this variation, with men seeing a very positive effect and women seeing little beneficial effect at all. Indeed in this study men seem to have better outcomes than women when following any meat-free diet.

Orlich study by gender:

 
Vegan
Other Vegetarian
Pescetarian
Occasional/Low Meat Eaters
Pooled analysis (Key et al., 1999)
1.00
0.84
0.82
0.84
UK: EPIC-Oxford/Oxford Vegetarian study (Appleby et al., 2016)
1.00
0.93
0.91
0.93
AHS-2 all (Orlich et al., 2013)
0.85
0.91
0.81
0.92
AHS-2 men
0.72
0.86
0.73
0.93
AHS-2 women
0.97
0.94
0.88
0.92

The AHS-2 study by Orlich then broke things down further looking at particular disease types. The most interesting to jump out is the result for ischemic heart disease, where we see a clear beneficial effect for a pescetarian diet.

Adventist Health Study 2All CausesCancerIschemic Heart DiseaseCardiovascular DiseaseOther
Vegan
0.85
0.92
0.90
0.91
0.74
Other vegetarian
0.91
0.90
0.82
0.90
0.91
Pescetarian
0.81
0.94
0.65
0.80
0.71
Occasional meat eaters
0.92
0.94
0.92
0.95
0.99

Given that heart disease is more frequent in men do they see an even greater improvement? It seems that way and not just for pescetarians. Below you can see that men on a vegan diet see a huge improvement in cardiovascular and ischemic heart disease risk, with vegetarian and pescetarian diets also offering a strong benefit. For women this effect was limited to those on a pescetarian diet, although again it was a very strong effect.

  
Cardiovascular Disease
  
Ischemic Heart Disease
 
Adventist Health Study 2
All
Men
Women
All
Men
Women
Vegan
0.91
0.58
1.18
0.90
0.45
1.39
Other vegetarian
0.90
0.77
0.99
0.82
0.76
0.85
Pescetarian
0.80
0.66
0.90
0.65
0.77
0.51
Occasional meat eaters
0.85
0.75
0.93
0.92
0.73
1.09

So some really interesting data there, especially if you’re a man currently eating a traditional meat-heavy diet. It is also really important to point out that these studies are based on mortality, they provide no information on quality of life or other such metrics.

Key takeaways

The data above is compelling and would indicate that men can benefit the most from vegetarian and vegan diets, although, in our view, some of this comes down to genetics.

But, I really wrote this post to get a simple message across: the epidemiological data presented in favor of a strict vegan diet is often driven by omnivores who ate less meat, but did not eat zero meat. In other words, many of the supposed Vegan studies aren’t vegan studies at all. When direct comparisons are made between vegans and other diets, veganism doesn’t always stack up like you’d think.

This not to say that a plant based diet is unhealthy or that we should all eat steak at every meal. To the contrary, research by Dr. Valter Longo, demonstrating that the amino acid profile of animal protein is inflammatory, should be taken seriously. But a vegan diet, even when done intelligently, carries with it a very real risk of nutrient deficiency.

It’s especially important for kids, who are being bombarded with plant based messaging at every turn, to know that vegetarianism is often a healthier alternative to the vegan diets that put many of us in caloric deficits. (R)

Dr. Aaron Gardner, BSc, MRes, PhD

Dr. Aaron Gardner, BSc, MRes, PhD is a life-scientist with a strong background in genetics and medical research, and the developing fields of personalized medicine and nutrition. Read his full bio here.

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