A plant-based diet may reduce the risk of cancer, heart disease and premature death due to cardiovascular disease, according to a new “umbrella” review of dozens of studies on health impacts of vegan and vegetarian diets. The findings were published in the journal PLOS One.

Vegetarian diets avoid animal meat. Vegan diets do not include any food derived from animals, including dairy products, which are allowed in vegetarian diets.

The research, led by researchers at the University of Bologna in Italy, included analysis of 48 previous studies published between 2000 and 2023, finding that vegetarian and vegan diets are “significantly associated” with better cholesterol profile, blood sugar control, healthier blood pressure readings and body weight, less inflammation, and lower risk of ischemic heart disease and gastrointestinal and prostate cancers. The vegetarian diet is also linked to less cardiovascular disease-related deaths.

The researchers found no difference based on diet in whether pregnant women develop gestational diabetes and hypertension.

“This research shows, in general, that a plant-based diet can be beneficial and taking small steps in that direction can make a difference,” review co-author Matthew Landry, assistant professor of population health and disease prevention at University of California, Irvine, told NBC News.

In the same NBC article, however, Dr. Walter Willett, professor of epidemiology and nutrition at Harvard’s T. H. Chan School of Public Health, made the point that not everyone who eats a plant-based diet eats the same foods. “A vegetarian diet could be based primarily on refined starches and sugars, which we see to be the worst dietary pattern,” said Willett, who was not involved in the new research.

The researchers warn that broad recommendations on adopting a vegan or vegetarian diet should wait until remaining gaps in knowledge are filled in. And they note that plant-based diets “may introduce vitamin and mineral deficiencies for some people.”

The researchers said they decided to do the review because, overall, the impact of such diets have not been clear.

Food for thought

Others say there’s no downside to a healthy plant-based diet. But the healthy part is important.

“From my perspective as a dietitian, a healthy plant-based diet — either vegetarian or vegan — can really meet just about all your vitamin and mineral needs,” Landry said.

A news release on the study said that “a diet that is poor in plant products and rich in meat, refined grains, sugar and salt is associated with higher risk of death. Reducing consumption of animal-based products in favor of plant-based products has been suggested to lower the risk of cardiovascular disease and cancer.”

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It’s well known that fruits and vegetables are high in antioxidants and help reduce inflammation, which may help explain benefits of a plant-based diet that numerous studies have found. Fruits and vegetables are also high in fiber, which is important for lowering bad cholesterol and which reduces the risk of gastrointestinal cancers like colorectal cancer. Grains and nuts also have health benefits.

Red meat, which is a staple of the average American’s diet, contains saturated fats, which are not good for people.

The Academy of Nutrition and Dietetics has stated that “appropriately planned vegetarian, including vegan, diets are healthful, nutritionally adequate and may provide health benefits for the prevention and treatment of certain diseases. These diets are appropriate for all stages of the life cycle, including pregnancy, lactation, infancy, childhood, adolescence, older adulthood and for athletes.”

The academy further notes that plant-based diets are “more environmentally sustainable than diets rich in animal products.” But the nutrition experts also note that “vegans need reliable sources of vitamin B12, such as fortified foods or supplements.”

Among limitations, the authors of the new study noted that participants in the studies reviewed were very similar in terms of sample size, demography, geographic origin, dietary patterns and lifestyle factors that could help account for findings without being identified as potentially responsible for findings.

The researchers conclude, however, that the study shows “how a vegetarian diet can be beneficial to human health and be one of the effective preventive strategies for the two most impactful chronic diseases on human health in the 21st century.”