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 women.
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?
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. Similarly, the work of noted longevity expert Valter Longo, advocates for eating more protein after age 65 to maintain muscle mass.
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. Do milk products cause the increased cases of osteoporosis, 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?
- Only clinical trials, which control for all variables, can give us something approaching that kind of certainty. For this reason, many take a dim view of nutritional epidemiology.
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 a retrospective cohort study that went back through old data collected by previous studies 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.
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.
- 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.
- 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.
- In the Orlich study, 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:
|Pooled analysis (Key et al., 1999)
|UK: EPIC-Oxford/Oxford Vegetarian study (Appleby et al., 2016)
|AHS-2 all (Orlich et al., 2013)
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 2
|Ischemic Heart Disease
|Occasional meat eaters
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.
|Adventist Health Study 2
|Occasional meat eaters
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.
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, and is not the longevity “magic bullet” many claim it to be.