A vegan diet improves heart health, according to a study of identical twins

It’s known that eating less meat improves cardiovascular health¹. Vegan diets are generally higher in fibre and lower in bad cholesterol - both of which are good for our health².

However, it’s often difficult for researchers to compare vegan and non-vegan diets in studies because of other factors that may influence the results - like people’s genetic differences and their lifestyle choices.

A study involving 22 pairs of identical twins by Stanford Medicine researchers suggests that a vegan diet is indeed healthier than a non-vegan diet. By using twins, the researchers were able to control for genetics and limit other factors, as the siblings grew up in the same households and had similar lifestyles.

Between May and July 2022, the twins were given diets to stick to - one sibling was allocated a vegan diet and the other was given a non-vegan diet.

Both vegan and non-vegan diets were healthy and contained vegetables, fruits and wholegrains, while avoiding sugars. The vegan diet was entirely plant-based, included no meat or animal products such as eggs or milk. The omnivore diet included chicken, fish, eggs, cheese, dairy and other animal-sourced foods.

During the first four weeks, a meal service delivered breakfasts, lunches and dinners. For the remaining four weeks, they made their own meals.

Vegan diet benefits

At three time points - at the beginning of the trial, at four weeks and at eight weeks - the researchers weighed the participants and tested their blood.

All of those who took part showed the most improvement over the first four weeks of the diet change. Both the vegans and non-vegans benefited from the healthy diet plans and ended up with lower levels of bad cholesterol - known as low-density lipoprotein cholesterol.

However, those following a vegan diet had significantly lower low-density lipoprotein cholesterol levels, insulin and body weight - all of which are associated with improved cardiovascular health. The vegans also lost an average of 4.2 more pounds than the omnivores.

The researchers have attributed the health benefits to three key factors. The vegans - and to a lesser extent, non-vegans - cut back on saturated fats, ate more dietary fibre and lost weight.

Although the study had a small sample size of just 44 participants, the results suggest it’s possible to improve your health in just two months by switching to a vegan diet, or eating more vegan meals.

Christopher Gardner, the director of nutrition studies at the Stanford Prevention Research Centre, said the study provided a groundbreaking way to assert that a vegan diet is healthier than the conventional omnivore diet.

"Based on these results and thinking about longevity, most of us would benefit from going to a more plant-based diet," Gardner said. "What's more important than going strictly vegan is including more plant-based foods into your diet. Luckily, having fun with vegan multicultural foods like Indian masala, Asian stir-fry and African lentil-based dishes can be a great first step."

However, it's important to note that this study doesn't show the long-term health implications of following a vegan diet. Also, vegans may need to take vitamin supplements - for example, iron supplements - so it's important to speak to your doctor if you're worried about your diet or are making big changes.

Further reading

1. Satija et al: Plant-based diets and cardiovascular health.

2. Clarys et al: Comparison of nutritional quality of the vegan, vegetarian, semi-vegetarian, pesco-vegetarian and omnivorous diet.

3. Landry et al: Cardiometabolic Effects of omnivorous vs vegan diets in identical twins.