Written by Lizzie Davies

Lizzie is a final year student dietitian at King’s College London. Her current interests in dietetics include women’s health and cystic fibrosis. In her spare time, she loves to bake and cook, and volunteers in the charity sector. Find her on Instagram @lizziedietetics.

 

The onset of the new year is prime time for targeting of diet and health related advertisements, aligning perfectly with new year’s resolutions. Many people find that these messages inspire them to make changes for their health. Unfortunately, though, this also leaves the door open for misinformation and health claims often from little evidence base. Healthcare professionals have a responsibility to educate patients on the evidence base of claims that they see online, and to provide them the information and resources needed to make decisions for their health.

You Are What You Eat- A Twin Experiment  

As mentioned, this time of year is perfect for advertising nutrition-based information, so it is no surprise that Netflix’s latest nutrition-based documentary ‘You are What You Eat, a twin experiment’ has spent a number of the days in the Netflix top 10. This 4-part documentary follows the Stanford Twin Study (1) in which 22 sets of identical twins are each randomised to follow a vegan diet, or a ‘healthy’ omnivorous diet for 8 weeks, basing the food around whole grains, fruits and vegetables, limited sugars and refined grains. The primary outcome for the study was difference in low-density lipoprotein concentration from start to end and the secondary outcomes were changes in several cardiometabolic measures, plasma vitamin B12 level and body weight. The main findings of the study were that the twins randomized to a vegan diet had significant decreases in LDL-cholesterol concentration, fasting insulin and body weight at the study end point compared to their omnivorous counterparts.

Whilst the study itself may be credible, the Netflix documentary is more controversial. ‘You are what you eat’ is not merely a storyline of the Stanford Twin Study, but also provides information around the health benefits of veganism and the environmental impacts and health implications of the meat and dairy industry. Navigating through the wealth of information that this documentary throws at you in between the much shorter clips of the study is difficult, even for someone with good nutritional knowledge. This documentary is very captivating, with the twins selected making for very good television, but the main problem lies with the one-sided argument of veganism.

When navigating these types of documentaries, an important aspect is who funded them? In this case, it was funded by an organisation that supports the Oceanic Preservation Society, who’s aim is preserving the planet. There is evidence that veganism is the most sustainable diet for our planet (2), thus it is unsurprising that the vegan diet is heavily pushed in this documentary.

 

The Claims and The Evidence

Nutritional research is notoriously difficult to conduct due to the differences in how people react to different foods and dietary patterns. Studying identical twins is ideal for research in which a nutritional intervention takes place, as it takes away a big confounder, genetics.

Vegan diets have been rising in popularity, due to perceived health and environmental benefits (3). Mainstream campaigns like ‘Veganuary’ have also promoted veganism since 2014, with many media outlets and supermarket chains getting on board with promotion. There is good research that a well-planned and balanced vegan diet can promote certain aspects of health and reduce the risk of several risks associated with metabolic syndrome like hyperglycaemia, hyperlipidaemia, high blood pressure and overweight and obesity (4, 5).This is a big aspect of what this documentary discusses whilst regularly comparing to the risks of consuming meat and dairy products. It is true that there are several health risks of a diet high in red and processed meats including colorectal cancer and cardiovascular risk, (6-8). The evidence base of dairy risk is more controversial, with some data even suggesting that full fat dairy consumption may be protective against metabolic syndrome (9, 10), but the documentary failed to provide any insight to this or discuss the many benefits of dairy in the diet (good source of calcium, protein, vitamin D etc). Providing no insight into this can cause confusion, as dairy is recommended in the UK dietary guidelines (Eatwell Guide) and is a food group that many people rely on.

Whilst there is lots of credible evidence on the benefits of vegan diets, this documentary fails to provide the other side of the argument. Vegan diets are criticised for their tendency to promote lower intake or even deficiencies in vitamin B12, B2, B3, D, iodine, iron and calcium amongst others (11, 12). The risks are also greater in certain groups including the frail elderly, adolescents, and pregnant and breastfeeding women (5). It is therefore important that people are aware of these risks, and therefore proper planning is imperative to a balanced vegan diet.

Some twins in the study found it difficult to consume their caloric goals whilst on the vegan diet, which can be a common struggle due to the nature of plant-based foods being less energy dense and thus vegan diets can often lead to weight loss. One scene in the documentary briefly showed what a balanced vegan meal would look like, especially in terms of having to consume a greater volume of food to eat the recommended amount of protein. Whilst this could have been a good opportunity for them to explain the differences between a vegan and omnivorous diet and help people transition between the two in terms of getting the right balance of nutrients, they seemed to skim through this part and could leave the viewer feeling more confused. This seems to be a theme throughout, with a lack of practical advice for someone wishing to try following a vegan diet.

Lastly, despite the Stanford twin study comparing a vegan diet to a ‘healthy’ omnivore diet, this documentary fails to make much reference to this in discussions, only focusing on the effects of the ‘standard American diet’ (13) which is different to the one the study compares against. Amongst the evidence provided for the health benefits of vegan diets, it fails to make any reference or comparison to other highly researched diets that are omnivorous in nature, such as the Mediterranean diet, which have demonstrated positive results for non-communicable diseases like cardiovascular disease, diabetes and high blood pressure (14-16). Therefore, a major weakness of this documentary is presenting people with a one-sided argument that gives no other option but to become vegan.

The Good, The Bad and the Ugly

It is important to address the potentially hazardous statements that arise in conversations where phrases such as “milk is meant for baby cows” are used to justify the argument that dairy might not be inherently natural for humans, justified by the widespread prevalence of lactose intolerance. Moreover, there are scenes in throughout in which the mayor of New York discusses anecdotal experiences following an unexpected diagnosis of type 2 diabetes. After learning the alarming risks of his diagnosis, such as loss of sight, he looks back on his decision to forego taking prescribed diabetes medication and instead taking on a completely plant based vegan diet. He adds that when returning to the doctor his blood tests, including HbA1c, had greatly improved, claiming that his doctor was astounded by the results. This discussion has several issues as the mayor is not a credible scientific source, nor do they include any additional evidence for any of his claims. It is understandable how an influential and seemingly trustworthy figure promoting the decision to forego medication could be appealing to a vulnerable patient struggling with their diabetes diagnosis. However, promoting this could be harmful, especially if someone was to emulate this without medical supervision.

What Should we be Recommending?

So, when your patient with type 2 diabetes, heart disease or high blood pressure asks you what you think of a plant based or vegan diet, how do you approach this in the best way?

Unfortunately, nutrition research is rarely clear cut, and several things can be true at once when it comes to the benefits and risks of certain foods and diets. This makes it difficult for patients and healthcare professionals alike when navigating the evidence base and deciding what is best. Overall, vegan diets are not outwardly recommended over omnivorous diets in most guidance for the general population or in specific diseases. However, vegan diets spark interest in a lot of people, and it is possible to follow a healthy vegan diet with the right planning and preparation. Good resources for patients wanting to follow a vegan diet include:

• The Vegan Society
• The Vegan Eatwell Guide
• NHS website

 

References

1. Landry MJ, Ward CP, Cunanan KM, Durand LR, Perelman D, Robinson JL, et al. Cardiometabolic Effects of Omnivorous vs Vegan Diets in Identical Twins: A Randomized Clinical Trial. JAMA Network Open. 2023;6(11):e2344457-e.
2. Chai BC, van der Voort JR, Grofelnik K, Eliasdottir HG, Klöss I, Perez-Cueto FJA. Which Diet Has the Least Environmental Impact on Our Planet? A Systematic Review of Vegan, Vegetarian and Omnivorous Diets. Sustainability. 2019;11(15):4110.
3. Wang T, Masedunskas A, Willett WC, Fontana L. Vegetarian and vegan diets: benefits and drawbacks. Eur Heart J. 2023;44(36):3423-39.
4. Marrone G, Guerriero C, Palazzetti D, Lido P, Marolla A, Di Daniele F, et al. Vegan Diet Health Benefits in Metabolic Syndrome. Nutrients. 2021;13(3).
5. Pollakova D, Andreadi A, Pacifici F, Della-Morte D, Lauro D, Tubili C. The Impact of Vegan Diet in the Prevention and Treatment of Type 2 Diabetes: A Systematic Review. Nutrients. 2021;13(6).
6. Shi W, Huang X, Schooling CM, Zhao JV. Red meat consumption, cardiovascular diseases, and diabetes: a systematic review and meta-analysis. Eur Heart J. 2023;44(28):2626-35.
7. Chan DS, Lau R, Aune D, Vieira R, Greenwood DC, Kampman E, et al. Red and processed meat and colorectal cancer incidence: meta-analysis of prospective studies. PLoS One. 2011;6(6):e20456.
8. Turesky RJ. Mechanistic Evidence for Red Meat and Processed Meat Intake and Cancer Risk: A Follow-up on the International Agency for Research on Cancer Evaluation of 2015. Chimia (Aarau). 2018;72(10):718-24.
9. Houston M. The relationship of saturated fats and coronary heart disease: fa(c)t or fiction? A commentary. Ther Adv Cardiovasc Dis. 2018;12(2):33-7.
10. Unger AL, Torres-Gonzalez M, Kraft J. Dairy Fat Consumption and the Risk of Metabolic Syndrome: An Examination of the Saturated Fatty Acids in Dairy. Nutrients. 2019;11(9).
11. Bakaloudi DR, Halloran A, Rippin HL, Oikonomidou AC, Dardavesis TI, Williams J, et al. Intake and adequacy of the vegan diet. A systematic review of the evidence. Clin Nutr. 2021;40(5):3503-21.
12. Bali A, Naik R. The Impact of a Vegan Diet on Many Aspects of Health: The Overlooked Side of Veganism. Cureus. 2023;15(2):e35148.
13. Grotto D, Zied E. The Standard American Diet and its relationship to the health status of Americans. Nutr Clin Pract. 2010;25(6):603-12.
14. Esposito K, Maiorino MI, Bellastella G, Chiodini P, Panagiotakos D, Giugliano D. A journey into a Mediterranean diet and type 2 diabetes: a systematic review with meta-analyses. BMJ Open. 2015;5(8):e008222.
15. Velázquez-López L, Santiago-Díaz G, Nava-Hernández J, Muñoz-Torres AV, Medina-Bravo P, Torres-Tamayo M. Mediterranean-style diet reduces metabolic syndrome components in obese children and adolescents with obesity. BMC Pediatr. 2014;14:175.
16. Dayi T, Ozgoren M. Effects of the Mediterranean diet on the components of metabolic syndrome. J Prev Med Hyg. 2022;63(2 Suppl 3):E56-e64.