What science says about plant-based diets (Vegan)

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Curious what others have concluded after looking into the science-based evidence backing the vegan movement?  It's really difficult to argue against the evidence showing in nutrition science studies.  Then we have the environmental implications which I am sure we have all been made aware of the negative consequences of mass animal agriculture.  Economically, when you combine the medical and environmental consequences, it's just completely illogical to continue consuming not only fossil fuels but animals as we have been.  What are your thoughts on why so many people choose to turn away from the evidence supporting plant-based diets?  Have you looked at the evidence yourself?  If we wish to believe as many true things and as few false things as possible then surely we are required to avoid ignorance especially concerning matters that have massive negative consequences if we neglect to examine the claim and its evidence.  I would really love to hear what others thoughts are on this!

As it happens I just made a video on evidence-based practise and diet plans. I wasn't going to upload it yet, I was going to wait and refine it (re-record it to get the running time down sometime next week), but here's the raw "draft" version:

https://youtu.be/lNTx8362Q5A

Here are the two systematic reviews on DASH:
http://www.ncbi.nlm.nih.gov/pubmed/26990451
http://www.ncbi.nlm.nih.gov/pubmed/25149893

And here's the evidence document for AGTHE. No doubt you will find other government evidence publications (grey literature) for other government-developed diet plans. On page 1 it notes that there's Grade B evidence (under the NHMRC guidelines) for the Mediterranean diet - i.e. "body of evidence can be trusted to guide practice in most situations".

The long and the short of it is that DASH and the Mediterranean diet have been studied a lot, just from skimming the two systematic reviews for DASH it appears there's Grade B if not Grade A evidence under the NHMRC guidelines for its use in clinical practice (and in fact it is used in clinical practice). The AGTHE is also based on evidence-based practice, you'll note that it incorporates the recommendations made from evidence. Other popular/fad diets (Pale, Atkins, other high protein diets, veganism, vegetarianism, 80/10/10, etc) are not supported by the body of evidence - with of course the sole exception of the Mediterranean diet. I should note though that the Mediterranean diet is quite restrictive in your food choices, certainly more-so than DASH or AGTHE so it's not at all surprising. The main studies that exist on veterinarian diets look at SDAs in the USA, they're purely observational (Level IV under NHMRC), and they would show a high risk of bias (many possible and probable confounders).

And on that I'll note that iron deficiency is the most prevalent nutrient deficiency in the developed world, and inadequate calcium intake is also very high. When people chose to follow a vegan diet they put themselves at higher risk of developing problems from long-term health outcomes, and self-supplementation is both not advised, and likely contributes more harm than good. But even if that wasn't the case, just have a look at the common side-effects of iron supplementation.