Over the past few weeks I’ve received three emails from patients informing me that they watched the Netflix documentary, You are What You Eat, and this documentary motivated them to go vegan.

Nutritionists everywhere release a collective sigh whenever a new documentary is released on nutrition. They are always riddled with bias and half truths and they are produced in a sensationalized way that motivates people to jump onboard.

I won’t lie – this is a long post, but worth it!

You are What You Eat documents 22 sets of genetically identical twins over 8 weeks, while one eats vegan and the other eats meat. Food is supplied for the first 4 weeks and then for the remaining 4 weeks each twin must make their own meals, based on the study requirements.

Before I get into the study, I want to say this – I can help any vegan, vegetarian or omnivore of all walks of life, create a healthy, vibrant, optimal diet. For the first five years of my practice I ran a 28 Day Vegan Challenge, helping reintroduce people to plant-based eating. And, for full transparency, I’m not vegan.

In 2023, around 1.1% of the world’s population was vegan and approximately 4% of the U.S. population was vegan. It’s interesting, with these small numbers, how we hear about vegan eating as often as we do.

Here’s how I replied to my three patients:

If you want to go vegan or vegetarian, it’s a personal decision. Sometimes its an ethical or moral or religious decision. What I don’t want is for people to be pushed into a major dietary change by unfounded fear.

Here’s what I see clinically: you’ll likely feel better for three -twelve months and then energy will start to dip. This is because omega 3, Vitamin A, Vitamin B12 and iron levels will begin to dip after reserves have been used up. Humans are poor converters of beta-carotene to vitamin A. Around 45% of the population carries at least one gene variation that reduces BCMO1 enzyme activity. This can result in a marked decline in the ability to convert beta-carotene into Vitamin A. There are multiple combinations of these heritable variants. Some variant combinations can result in a conversion rate nearly 70% lower than normal!

Vitamin A cannot be sourced through non-animal food sources. Vegans rely on beta carotene conversion and should supplement directly with Vitamin A. If you look up carrots and vitamin A, site after site will state that carrots contain vitamin A. They do not. They are calculating beta carotene and the potential conversion into vitamin A.

The two omega 3 fatty acids are eicosapentaenoic acid EPA and docosahexaenoic acid DHA. You can source both EPA and DHA directly through fatty fish, and through supplementation of fatty fish. If you look up vegan sources of omega 3, the results will list plant foods like chia seeds, walnuts, flaxseeds, etc., yet none of these foods have EPA or DHA in them. They do contain a distant precursor to EPA, called alpha linolenic acid ALA.

Humans are also poor converters of ALA to EPA. The overall conversion efficiency from ALA to EPA is estimated at 8%. Research suggests that the estimated conversion of ALA to DHA was estimated .4%- 1%. ALA sources will not provide DHA and this is very important for brain health and during pregnancy, for the baby’s brain health.

B12 deficiency can show up later, between 1-5 years on the diet. B12 sources include animal proteins and B12 is not found in vegan foods. Nutritional yeast may have trace amounts, but this won’t provide enough B12 to keep you out of deficiency. Studies have shown that anywhere from 56-75% of vegans are B12 deficient.

For men and some women, undesired weight loss may occur (this can be positive, and desired, but this can also turn into a wasting state, especially if your very active). Let me be clear, there are vegan athletes and there are plenty of people who eat vegan that do well. It takes a lot of effort to get enough variety and then supplement to meet your body’s macro and micronutrient needs. Vegan diets cannot be simplified and they

Opinion Science (Driven by Self Interest)

We’ve all been victims of opinion science for some time, although it sure feels like this is coming at us more regularly now. For any study, book or documentary, we always need to look at who funded and led the study.

Do you remember the book, The China Study? Regardless of its title this is not a study, but an opinion piece written by an author who’s vegan. He reviewed observational data collected by China (observational data shows no cause and effect) and he claims that this data confirms that vegan eating was better for us – unfortunately, the author, Dr. Colin Campbell left data from specific provinces out that would have shown the opposite – it’s been debunked.

Or have you heard of the book, Skinny Bitch – that was written by vegans to scare people with factory farming stories? Instead of going vegan, the book should have introduced people to developing relationships with farms and really knowing where their food comes from.

Remember when eggs were demonized for causing cholesterol issue and heart disease – completely debunked.

Let’s Look at the Study

The Netflix documentary, You are What You Eat, documents a Stanford study run by Stanford University’s Professor Christopher Gardner. This short 8 week study, involved identical twins, and the research suggested that adopting a healthy vegan diet could lead to better cardiometabolic outcomes compared to a healthy omnivore diet. Based on the study, Gardner recommends that clinicians consider this dietary approach an alternative for patient health management. Again, this was a short 8 week study, so this claim is a bit of a leap.

The first thing that I do when reviewing a study is to scroll to the bottom of the publication and review study funding and author disclosures. It’s important to note Gardner’s background and potential biases. Having adopted a mostly vegan lifestyle for over four decades, he leads the Stanford Plant-Based Diet Initiative (PBDI), launched with support from Beyond Meat. The study was funded by Kyle Vogt—a prominent figure in vegan investment circles— and it raises questions about the influence of financial backing and personal beliefs on scientific research.

The study’s duration, a mere eight weeks, and the fact that it compared very limited markers, has drawn criticism for not adequately assessing the long-term impacts of a vegan diet. Gardner has run a lot of studies and I don’t question his ability to run a study. The study’s approach and funding sources, including ties to vegan advocacy, have led me (and many) to be skeptic about his objectivity. He was also in The Game Changers and What The Health, both Netflix documentaries whose overarching message was promoting a plant-based diet and basically scaring people about eating animal products.

The trial aimed to identify dietary impacts on heart disease markers, specifically LDL cholesterol. They only compared one marker for this, LDL-C. While the vegan diet showed improvements in LDL-C and insulin levels, the methodology and reliance on high-carbohydrate intake has led to more questions. We’ve no idea what would happen if this was followed for 3 months or 6 months (the latter timeframe is considered a ‘long term’ study).

Also, the emphasis on LDL-C cholesterol as a primary outcome measure really oversimplifies the complex picture of cardiovascular health.

Over the 8 weeks, the vegan group did experience some weight loss and insulin improvements, but this may not fully justify the vegan diet’s health benefits, considering the potential for nutritional deficiencies without careful supplementation, as I discussed prior. Also, the vegan group consumed an average of 200 calories less than the omnivore group. This alone could account for the improvement in insulin and LDL-C and weight loss. The correct study design should have been based on equal calories for both groups.

Gardner’s motivations and the PBDI’s goals—focusing on issues beyond basic nutrition, such as animal rights and environmental concerns—suggest a shift from traditional nutrition science to advocacy. It raises concerns about the influence of personal values and external funding on dietary guidelines and public health recommendations.