To study the cardiovascular effects of a vegan diet, medical experts turned to an unusual test subject: twins.
Researchers assigned different diets to 22 pairs of identical twins. One twin ate a vegan diet for eight weeks while the other followed a diet that included meat. At the end of the study, the twins on the vegan diet had improved their so-called "bad" cholesterol concentration and fasting insulin levels better than their omnivorous siblings. They also lost an average 4 pounds.
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The twins provided researchers with a unique experiment control. Genetic differences can often complicate test results, but studying identical twins eliminated that factor. The twins also grew up in the same household, and reported similar lifestyles, limiting other potential complications.
On average, the twins who went vegan saw significant decreases in their low-density lipoprotein cholesterol, known as the "bad" cholesterol, and fasting insulin compared to their siblings who ate meat. High levels of fasting insulin put a person at greater risk of developing diabetes. The vegan twins also saw greater decreases in their levels of triglycerides, glucose, high-density lipoprotein cholesterol and vitamin B12, but these were not statistically significant.
"Based on these results and thinking about longevity, most of us would benefit from going to a more plant-based diet," said co-author Christopher Gardner, a professor of medicine at Stanford University.
According to Gardner, the vegan diet helped participants do the three most important things for improving heart health: increase dietary fiber, reduce saturated fats and lose weight.
"What's more important than going strictly vegan is including more plant-based foods into your diet," he said.
The study, published in the Journal of the American Medical Association, adds to research that has found a vegan diet helps people lose weight, lower cholesterol levels, reduce cardiovascular risks and lower blood sugar levels.
There are several types of vegan diets, but they all seek to eliminate animal products from one's diet, including dairy, eggs and honey. That's more strict than a vegetarian diet, which excludes meat, poultry and fish. Other diets, including the Mediterranean diet, stress plant-based foods without eliminating meat products.
Subjects for the experiment were drawn from the Stanford Twin Registry, a database of fraternal and identical twins open to participating in research. The researchers only included twins without cardiovascular disease. Most were women (77%) and the average age was 39.6.
During the first four weeks, researchers provided meals tailored to each diet through a delivery service. For the final four weeks, participants prepared their own food. Blood was drawn and analyzed at the start of the trial, halfway through and at the end. The subjects also were weighed at these times.
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