A unique study done with 22 pairs of twins was used to evaluate the health effects of following a vegan diet. By using twins this study was able to eliminate factors that can complicate the evaluation of the findings that occur in other studies. Generally speaking researchers have to take into account the many differences that can occur between subjects who are participants in their studies. That would include the age of the participants, their ethnicity and a whole number of other details which are varied between all of the study participants. By using pairs of twins this study was able to compare the effect on the diet of one twin compared to the other twin who is the same on all other respects , except that one twin followed a vegan diet while the other twin did not.

This study was able to document clearly that the effect of the vegan diet was to lower the levels of “bad cholesterol” called LDL Cholesterol, lower insulin levels, and produce weight loss although the participants were not told to eat any differently (other than vegan or non-vegan) or attempt to lose weight during the study.

Both groups were provided with the food they would eat. During the first four weeks of the study both groups had prepared meals delivered to them for 3 meals per day-breakfast, lunch, and dinner. They were also given strict instructions regarding allowable snacks. They were provided a healthy diet containing whole grains, vegetables, fruits, legumes, nuts, and seeds. Processed foods were strictly avoided in their balanced diet, which provided a variety of food groups. The only difference in their diets was that one twin consumed meat, while the other twin ate a strictly plant-based diet. Subjects on the plant diet did lose some weight during the study, and researcher Dr Matthew Landry explained. “Although weight loss was not discouraged, our diet design did not include a prescribed energy restriction and was not intended to be a weight loss study. Participants were told to eat until they were satiated throughout the study.”

 Those twins placed on the vegan diet had lower insulin levels , decreased weight, and reduced levels of a protein associated with heart disease and stroke.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10027313/

With the results analyzed Stamford University researcher Christopher Gardner said ,”Based on these results and thinking about longevity, most of us would benefit from going to a more plant-based diet.”https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2812392?resultClick=3 

A vegan diet is higher in fiber, vitamins, minerals, and phytonutrients. It is important to note, however, that certain  nutrients can be limited in a vegan diet such as vitamin B_{12 which is primarily found in animal products.} Also iron and calcium intake may be inadequte.^15,16 These may need to be supplemented by many vegans to avoid deficiencies that can develop otherwise.

There are some factors that complicate the study of vegan diets: most studies^17,18 are epidemiologic surveys. There have not been many clinical studies.^{19,20   In doing an} epidemiologic study the subjects are asked to self report their dietary pattern and some who describe themselves as vegans may not be following what would be in line with the strict definition of a vegan diet.²¹ Also some vegans may eat poorly in terms of excess sugars and other unhealthy items. The study we have quoted was a carefully designed one, with strict dietary controls to scientifically compare the cardiometabolic effects of a healthy vegan diet with a healthy omnivorous diet, to evaluate the differences.  Also this study using identical twins removed the difference in genes, and other differences like ethnicity between subjects, which complicates the evaluation of other studies.

For their study, researchers recruited 22 pairs of healthy identical twins – to control for genetic, upbringing and lifestyle differences – and divided the twins into two groups.

Researcher Dr Gardner states lightheartedly, “Not only did this study provide a groundbreaking way to assert that a vegan diet is healthier than the conventional omnivore diet, but the twins were also a riot to work with. They dressed the same, they talked the same and they had a banter between them that you could have only if you spent an inordinate amount of time together.”

The twins who ate the vegan diet had the greatest improvement. They lowered their fasting insulin by 20 percent, and also lowered their levels of low-density lipoprotein cholesterol (LDL-C) “bad cholesterol” as well.

The optimum level for  LDL-Cholesterol is less than 100 mg/DL. Before the experiment the average  was 118.5 mg/dL for the omnivores, which dropped slightly to 116.1. In the vegan group, it went from above the recommended 100 level – 110.7, down to 95.5 mg/dL.

The researchers wrote, “We designed this study as a ‘free-living’ study; thus, the behavior of following a vegan diet may induce the physiological changes we observed. However, the biological mechanisms cannot be determined to be causally from solely the vegan diet alone because of confounding variables (weight loss, decrease in caloric intake, and increase in vegetable intake).”

The study did find the expected drop in vitamin B12 during vegan dieting, but during the short time period of the study, it had not yet become significant. This further outlines the benefit of Vit B12 supplementation https://doi.org/10.1016/j.clnu.2020.11.035   as the best way for many vegans to make sure they do not become deficient in Vit B12, which is so important to maintaining good health.

Although a vegan diet is not an easy one or even the most desirous for many or most people, it can’t be denied that it may be a very healthy option especially for those with the conditions research has shown are so beneficially affected such as its ability to create weight loss, and lowering the risks of diabetes and heart problems  and reducing blood pressure.  And these clearly work for different ethnic groups. Additionally Dr Garner explains, “A vegan diet can confer additional benefits such as increased gut bacteria and the reduction of telomere loss, which slows aging in the body. But “what’s more important than going strictly vegan is including more plant-based foods into your diet.”

See this research published in JAMA Network Open.