In the long-running debate on whether a meat-free or meat-filled diet promotes better health, a new study is giving weight to the benefits of a meat-free diet.

Researchers at Stanford University examined the health of 22 sets of identical twin adults to see how they fared when one twin ate a vegan, or animal product-free diet, while the other twin ate an omnivorous, or animal- and plant-filled diet over two months.

The study, published Nov. 30 in the journal JAMA Network Open, looked specifically at the twins’ cardiovascular health, including cholesterol levels, sugar levels, insulin levels and body weight.

After eight weeks following their respective diets, the twin siblings who ate a vegan diet had lost more weight, reduced their LDL, or “bad” cholesterol, and experienced lower insulin levels, according to the study’s findings.

“The findings from this trial suggest that a healthy plant-based diet offers a significant protective cardiometabolic advantage compared with a healthy omnivorous diet,” the study’s authors wrote.

Two people sitting at a table together and having lunch at home.
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The study’s findings build on previous research showing that plant-based diets are better than non-plant-based diets when it comes to cardiovascular health.

A study published last year found that eating a plant-based diet can add years to your life. For that study, researchers in Norway used computer models to compare a typical Western diet — heavy on animal-based proteins, dairy and sugar — with a more ideal plant-based diet that’s heavy on fruits, vegetables, beans and grains, and light on animal-based proteins.

According to the computer models, a 20-year-old who went all in on the plant-based diet could add 10 years to their life. An 80-year-old who started a plant-based diet could add three years to their life expectancy, according to the study, published in February 2022 in PLOS Medicine.

What makes the Stanford study different is its use of twins who have the same genetic makeup and contributing environmental factors, according to the study’s authors.

“Because identical twins have nearly identical DNA and many shared experiences (eg, upbringing, geographic region growing up, and similar exposure to other variables), observed differences in health outcomes after adoption of different dietary patterns can largely be attributed to the diet itself,” the authors wrote.

A plant-based diet is a way of eating that consists mostly or entirely of foods derived from plants, including vegetables, grains, nuts, seeds, legumes and fruits.

Plant-based diets typically consist of eating few to no animal foods and are different from vegan diets, which eliminate all animal foods and products, and vegetarian diets, which eliminate all meat, fish and poultry.

Plant-based diets also often emphasize whole foods.