The Vegan vs. Omnivore Debate: Insights From the Research Behind the New Netflix Series, 'You Are What You Eat'

Have you watched the new Netflix documentary, You Are What You Eat? The documentary follows 4 of the 22 sets of twins who participated in a study, looking to answer the question, “What are the cardio metabolic effects of a healthy vegan vs healthy omnivorous diet among identical twins?”

In summary, it was an 8-week study where one twin was randomly assigned to a healthy vegan diet and the other twin randomly assigned to a healthy omnivorous diet. They were given prepared meals for the first four weeks so that they could become familiar with the diet before continuing on their own for four weeks, still following their respective diets.

The researchers measured LDL cholesterol as a primary outcome and insulin, weight loss, TMAO, glucose, triglycerides and B12 as secondary outcomes. In the series, they showed that vegans had a significant reduction in LDL cholesterol, fasting insulin and weight after 8 weeks.

I thought the series did an excellent job at showing the impact of an omnivore diet on the health of the planet and animal welfare. Those who weren't aware of the impact factory farms cause to the planet, surrounding communities, and animals prior to the series will certainly have a better understanding after watching the series. (Personally, I didn't know how food got to my plate until about 11 years ago! It's when I learned about the origins of my food that prompted me to make some major changes in my diet.)

While I thought that the planet and animal welfare angles were strong, I felt that the research they presented in the series was missing a lot of key information. As a vegan plant-based dietitian, I was left with lots of questions, like:

• Exactly what foods were on the vegan and omnivore plates?

• What type of education did they receive to know what to prepare on their own during the second four weeks of the study?

• What did the participants make on their own after the pre-packaged meals were no longer delivered?

• How much fiber were both groups getting?

• How are the participants eating now and did the healthy eating education, as well as the outcomes, influence their dietary habits long term?

• What was their perception of vegan food (flavor and texture) after the study?

  So I had to turn to the actual research study to see if I could find these answers. There were definitely limitations to the study, like a small number of participants (22 sets of twins) and short duration (8 weeks), plus no long-term follow up. That said, there are some key takeaways and points I think we can learn from the outcomes they found.

What foods were on the vegan and omnivore plates?

Turns out that both the vegan and omnivore groups increased their whole grain, vegetable and fruit intake compared to before the study. The biggest difference was in the type of protein they consumed with vegans eating legumes, nuts, seeds, and meat alternatives as their protein foods and omnivores consuming eggs, dairy, meat and poultry as their protein foods.

Omnivores ate 6–8 ounces meat, fish, or poultry, 1 egg, and 1.5 servings of dairy a day and had plant-based targets to include 3 veggies, 2 fruits, 6 servings grains or starches a day.

Vegans ate 6+ servings of veggies, 3 fruit servings, 5 servings legumes, nuts, seeds, or vegan meat alternatives, and 6 servings grains or starches a day. Meat alternatives included tofu, tempeh, soy nuts, and veggie burgers (and were the largest source followed by nuts and seeds).

This was not an iso-caloric diet, meaning they didn't track or count calories. Participants were instructed to eat ad lib (continue eating until they’re full).

**Side note: Eating until you're full is what I typically recommend with my clients because plant-based foods do a great job at keeping you full with their fiber and water content.

Naturally, both groups ended up eating less calories during the study compared to baseline. I assume this is because fiber intake increased when they included more whole grains, fruits and veggies. Lower calories plus higher fiber intake could certainly explain the weight loss and lower LDL levels (the exercise program they received as a part of the study most likely also contributed to those findings).

What type of education did they receive to know what to prepare on their own?

The dietitian in me questioned how 4 weeks of Trifecta meal delivery provided what the participants needed to make their own vegan meals for the next four weeks. The documentary didn’t explain this so I had to dig into the research. Turns out that participants received written instructions, class and group sessions, cooking demonstrations, and other support from health educators. The participants received a questionnaire at the end of the study asking for valuable feedback on what worked for them and what didn’t. A majority of participants (~69%) either strongly agreed or agreed that meeting regularly with the study’s health educator while receiving delivered, prepared meals during the first 4 weeks of the study helped them adhere to eating pattern recommendations in the subsequent 4 weeks. This demonstrates the importance of continuous education and follow up from dietitians when supporting clients in making dietary lifestyle changes. However, after watching the documentary and digging into the research, I still don't know exactly what the vegans made for themselves during the second 4 weeks of the study.

We do know that the vegan group increased their fiber intake from an average of 22 grams a day to an average of 33 grams a day. (The national fiber recommendations are a minimum of 25 grams a day for women and 38 grams a day for men).

What was their perception of vegan foods (flavor and texture) after the study?

A “busy lifestyle” was the highest reported barrier among participants' home meal preparation. Other noted barriers were time required to prepare meals and foods that spoil before getting used. Not a big surprise here, but I think it reinforces what I personally see in practice — people will eat plant-based if you make it taste delicious and easy to prepare. Taste and convenience are big motivators in eating plant-based. The biggest comment I get every single day from folks who want to eat more plants, but don’t, is, “If you make it for me, I’ll eat it.”

Eating out appeared to be the biggest barrier overall, with the vegan group being unsatisfied with eating out while following a vegan diet. It wasn't clear whether they received instructions on how to order when eating out or what was available locally to them. Eating plant-based while eating out is certainly doable, depending on where you live, where you go and what's available on the menu. Get tips for eating out and maintaining a healthy plant-based lifestyle in this article.

Lack of satisfaction was also reported among the vegan group. Again, this makes me ask the question, exactly what they were eating? Were they adding a can of beans to rice and calling it a day just to meet their legume and starch requirements? Or did they use the beans and rice to create a delicious fulfilling perfectly seasoned plant-based burger smashed in between two whole grain buns with all their favorite fixings, like pickles, onion, tomato, avocado, and a delicious plant-based sauce? Because the latter can be incredibly satisfying, but based on the reports stating lack of time to prepare meals, I’m guessing that the meals may not have been prepared in a way that was super delicious to them. (Check out Grillable Beet Burger and Hearty Lentil Burgers for super satisfying and nourishing plant goodness!)

Also, the protein intake of the vegan group was much lower than the omnivore group. This is another valuable takeaway from the study. Yes, Americans following the standard American diet get too much protein, especially from meat. But something I see often is that, when shifting from meat to plant-based eating, many people aren't sure what to add in place of meat, making it very possible to get insufficient protein. This can lead to dissatisfaction with the diet and, long-term, can be detrimental to health (after all, protein is essential!). Ensuring enough plant-based protein from both nutritional and satisfaction perspectives is key in making this diet sustainable. Get a list of 47 protein-packed plant-based foods here.

Other key takeaways

Iron Intake

Iron intake was higher in the vegan group compared to the omnivore group. This correlates with research showing that vegans are at no higher risk of iron deficiency anemia compared to meat eaters. Bottom line is that you can get sufficient iron on a plant-based diet and increase the absorption exponentially when you pair high iron foods with high vitamin C and vitamin A foods, as well as alliums (onion, garlic, leeks and shallots). Luckily, these foods naturally pair well together (beans + salsa in tacos, legume pasta + tomato sauce, or whole grain bowl with beans + a variety of veggies like broccoli, onions and peppers).

Fasting Insulin

Fasting insulin was significantly lower in the vegan group despite their carbohydrate intake increasing from an average of 45% to 51% of intake. Their dietary fat intake also decreased from 39% to 36%. What was different from their baseline diet was that they consumed carbohydrates from whole grains, vegetables, and fruits during the study rather than processed foods that were consumed before the study. The lower fasting insulin levels may reflect that the type of carbohydrate matters.

Vitamin B12

B12 intake was significantly lower in the vegan group, but their B12 serum levels were not low. A couple of points here:

• methylmalonic acid (MMA) is a better measure of B12 status than serum B12 (and it looks like the researchers measured serum B12).

• B12 stores take 2 years+ to deplete so you wouldn’t see a change in just 8 weeks.

• The significant drop in B12 intake confirms the need to take a B12 supplement on a vegan diet to prevent stores from getting low over time.

And before any naysayers say “see you need to supplement on a vegan diet, therefore a plant-based diet not good for you” … B12 used to be plentiful in our soil. Before large-scale farming and pesticide use, humans and animals received their vitamin B12 from food grown in soil. But due to soil desertification and mineral depletion, B12 is no longer found in most of the soil where food is grown. Cows are also supplemented with vitamin B12 so why not just go directly to the supplemental source?

TMAO

When we eat certain foods, like meat, dairy, eggs, and fish, a compound called trimethylamine (TMA) is formed in our gut. It's then sent to our liver, which creates Trimethylamine-N-oxide (TMAO). Research is finding that TMAO may have a big impact on the development of chronic disease and overall health. In fact, it's now being used in some medical facilities as a biomarker to help prevent heart disease.

With regard to the vegan vs omnivore research study, TMAO was significantly reduced in the vegan group when outliers were removed. This is not a surprise as other studies show that substituting plant-based protein for meat, fish, and egg protein can lower TMAO levels. It would be interesting to see the long-term effects of this as high TMAO is associated with adverse cardiovascular outcomes and risk of death.

PHEW! That was a lot. Bottom line about this study from a plant-based dietitian perspective:

1. The population was small and it was short term. It would be nice to follow up with these individuals to see if they continued to follow their respective diets and how the outcomes measured continue to be affected.

2. As a plant-based dietitian and recipe developer, I would have like to have seen exactly what the vegans were eating and would like to know if the meals prepared at home were delicious or just made to fulfill the study's needs nutritional needs. :P

3. The small, short-term study validates the need for B12 supplementation and shows that iron can be sufficient on a plant-based diet when meals are balanced and variety is consumed.

4. Protein is important! Plant-based health educators may want to consider emphasizing the importance of plant-based protein with each meal to help with satisfaction, sustainability, and to preserve lean body mass when clients or patients are transitioning from an omnivore diet to a plant-based diet.

5. As a dietitian, I personally love to lead with nutrition education and why plant-based foods are important from a nutritional perspective. But from a consumer perspective, it seems that taste and convenience reign over nutrition. Therefore, focusing on taste and easy convenient meals may be more effective in facilitating change with consumers with an understanding by the plant-based dietitian that the dishes are also nutritionally complete.

6. The results showing lower LDL, lower insulin levels and weight loss are in alignment with other research showing that lower calorie, fiber- and phytochemical-rich diets can support better health outcomes.

7. Dear filmmakers – next time please have a dietitian weigh in!

Did you see "You Are What You Eat" and what were your thoughts?