A study in 22 pairs of identical twins found that a vegan diet may be superior to an omnivorous diet in boosting cardiovascular health.
The researchers instructed one twin to follow an omnivorous diet and the other a vegan diet for eight weeks. Paper It was published Nov. 30 in the Journal of the American Medical Association.
For the first four weeks, the twins were served ready meals. For the last four, they prepared their own meals with the help of a registered dietitian. They were asked to record all foods consumed during the study period.
Both diets were healthy, consisting of a variety of vegetables, legumes, fruits, and whole grains. The only difference was the presence of meat products (chicken, fish, eggs, dairy products and cheese) in the omnivorous diet.
At the end of the trial period, the twin on the vegan diet had lower levels of low-density lipoprotein cholesterol (LDL-C), called “bad” cholesterol because it can clog arteries.
In general, a healthy LDL-C level is below 100 milligrams per deciliter. At the beginning of the trial, the average level of vegans was 110.7 and omnivores was 118.5. At the end of the trial, the vegans’ level dropped to 95.5 and the omnivores’ level dropped to 116.1. When asked about the difference between baseline cholesterol levels in the two groups, study author Christopher Gardner said it was due to chance.
Researchers also found that vegan participants had lower fasting insulin levels than their carnivore counterparts at the end of the trial and lost an average of 4.2 pounds more.
Tips for using twins
Studies tracking the benefits of veganism can be complicated by confounding factors related to the participant’s social environment or genetics. The fact that the study was conducted on identical twins was largely controlled for this.
In addition to keeping most variables the same except for the inclusion of animal products in the omnivorous diet, the experiment also controlled for the fact that not all vegan diets are necessarily healthy.
“Vegan diets are defined by what is excluded rather than what is consumed. There are good and bad vegan diets,” said Tom Sanders, professor of nutrition and dietetics at King’s College London, who was not involved in the research. “For example, a poor vegan diet would be one that lacks vitamin B12 and is high in fat, salt and sugar.”
The study accounted for this by closely monitoring what participants ate, adding rigor that could not be explained if the diet was not controlled.
Nutritional satisfaction is lower among vegans
However, the study had some complications. For starters, the sample size was small. The researchers also noted that vegans’ overall nutritional intake is about 200 calories per day less than that of omnivores.
“This may explain the non-significant reduction in weight and perhaps at least partly explain the reduction in LDL cholesterol,” said Duane Mellor, a registered dietitian and senior lecturer at Aston University who was not involved in the research.
This may be due to lower nutritional satisfaction among vegans, Mellor said. This is outlined in the study’s supplementary materials.
“Participants consuming a vegan diet reported the greatest decrease in diet satisfaction when eating out (restaurant) at weeks 4 and 8 relative to baseline,” the study said. “Among participants in the omnivore diet arm, diet satisfaction either increased at weeks 4 and 8 or was maintained at levels reported at baseline.”
When asked about these criticisms, main author Christopher Gardner, professor of nutritional studies at Stanford University in the US, told DW that the calorie deficit was not due to the design of the study, but rather because the vegan participants did not consume all the nutrients. They were served meals for the first four weeks. He said that all groups were given the same amount of calories, while those in the vegan group ate less.
“Vegan diets are very restrictive,” Gardner said in his statement published on the X platform. “I assume those on a vegan diet might be hungry for fish, eggs, yogurt, or meat. But those were restricted. They weren’t. I’m hungry for more vegetables and beans.”
Outside researcher Mellor said the reported satisfaction levels showed that if people adopted a healthier diet, “this should be based on their own preferences and not on a particular dietary approach or other nutritional approach favored by health professionals or online influencers.”
When asked about the real-world application of this study, given vegans’ dissatisfaction with the diet, Gardner agreed that “if satisfaction with the diet is low, that suggests that it would be difficult to maintain this type of diet.”
“Over time, someone may revert to the type of diet they are more accustomed to and familiar with,” he told DW. “It would be great to do these studies for a year, 5 years, 10 years. Then we would be more confident about sustainability. Realistically, most people are only willing to participate in a nutrition intervention study for a few months.”
However, intriguingly, the researchers found that the vast majority (91%) of twins given the vegan diet said they planned to continue the habits they learned in the trial in their normal lives, unlike twins given the meat diet. – Dieting (67%).
Edited by: Sushmitha Ramakrishnan