Before I start, I’d like to make a disclaimer that I am not anti-vegan, and this is not a post intended to slam vegans, or veganism. If a client is already vegan, I would never discourage them from being vegan or try and convert them to an omnivorous lifestyle. If they’re struggling, I try and help them optimize their health in a way that best suits their personal needs.
It’s also worth mentioning that there are several well documented and thoroughly researched perks to going vegan. Vegans tend to be thinner, leaner, and have better mobility. That’s our primary goal, isn’t it? Vegans have significantly fewer heart and digestive issues. Then there’s the major environmental issues like carbon emissions and water usage. Going vegan can be very good for your health and the planet. 
However……
Like everything; there’s a bit of nuance to these points.
Starting with the nutritional issues, I believe that the common belief amongst omnivores that vegans suffer from malnutrition is overstated. This belief stems from the idea that vegans can’t get enough protein, iron and B12. The B12 concern is valid, but both protein and iron is found in a bunch of plant sources like lentils, nuts and cruciferous greens, and tofu. Even if they are “incomplete proteins” eating a variety of products ensures that you can get enough protein and iron in your diet. That being said, there are quite a few nutrients critical to brain and muscle function that are found almost exclusively in meat products. B12 is one of them, but there’s also creatine, choline, HMA, and D3 (when sunlight is limited) to name a few. All of these can be added to the diet by eating fortified foods and supplements, but most of those supplements are coming from animal products and it takes careful planning to be able to make sure you’re getting the supplements you need.
Even with careful planning, however, those vitamin deficiencies can catch up with you. It’s very common for vegans to be told by their doctor that they need to start eating meat. According to a 2014 study by the Humane Research Council, In the US, it’s estimated that 84% of vegans eventually “lapse” and nearly 60% of that 84 cite health reasons. That being said, qualitative data suggests that they’ve found a middle ground, like eat fish once a month or going lacto-ovo-vegetarian. It’s not straight to Texas BBQ every night.
We are designed to eat meat. Humans have teeth and enzymes designed to digest and break down animal products into nutrients our body needs and there are several nutrients that our bodies can almost exclusively get from meat. Many organizations, including but not limited to the CDC, American Dietetic Association, and Healthline.com, say that a well-planned vegan diet is nutrient sufficient. However, I’ve yet to come across an independent (i.e not already vegan) source, that outright recommends veganism to promote optimal health. Even world-famous vegans in the fitness industry like Tony Horton say it’s not optimal for everyone. The closest I’ve found is The British Heart Society stating that we should only eat fish twice a week and 70g or less of red meat per day. For the average person that equates to 40-50% of your weekly protein intake should come from animal products. The “or less” suggestion means you can go as low as 20%. That sounds perfectly reasonable and my clients who follow similar guidelines tend to perform better than those who push the pendulum too far in one direction or the other.
The other huge point for me is availability. We are all bio-individual and have unique systems of support and needs. While a vegan diet might work for one person it might be completely inaccessible for another. Your health needs might dictate that you need some red meat every so often. Your local grocery store might not stock the foods you need to have an effective vegan diet. You might not have access to the resources that allow you to take an educated approach to vegan dieting. You could also live in a climate that outright prevents you from going vegan. Depending on how strict you want to go, the usage of bees and animal fertilizers could even prevent you from getting the plant sources you need.
As a health coach, it’s impossible for me to know all these nuances for each and every client. If someone is battling severe internal inflammation, needs a craving crusher, or wants to lose weight quickly, I’ll prescribe a nutrient dense 2 week or 1-month vegan food plan to help reach their goals. If you’re already vegan and it’s working for you, then great! Keep up the great work! For others who are seeking long-term goals with everlasting effects, however, I tend to steer my clients away from veganism for the same reasons why I direct them away from any overly restrictive diet: Restrictive diets set us up for failure. While they can provide some excellent results in the short term, often what we’re restricting ourselves from are nutrients we need. Then we get irresistible cravings. Then we lapse. Or another area of our health we weren’t thinking about starts to fail, and we’re told to change. With both of those routs we feel like a failure and the good habits we’ve developed start to unravel.
If you want to read more about adopting a vegan diet, here is the annotated bibliography for this post:
4 reasons why some people do well as vegans and others don't
British Heart Association on dietary protein
Why most vegans lapse within a year
7 nutrients you can't get from plants
Proper supplementation for brain health for vegans
Is a vegan diet healthier than eating meat and dairy?: A study of identical twins and athletic performance.
Suggested Reading:
Wilding: Returning Nature to Our Farm; by Isabella Tree (Don't you just love that name?)
The Game Changers; Documentary on plant based proteins and athletic performance.How Not To Die; by Michael Greger M.D. and Gene Stone
Food Can Fix It; by Dr. Mehmet Oz
The TB12 Method; by Tom Brady