June 23, 2024

Vegetarian and vegan diets may lower risk of heart disease and cancer, review finds

A plant-based diet is associated with a reduced risk of heart disease, cancer and death, according to a large-scale review published Wednesday. 

The research, which appears in the journal PLOS ONE, analyzed the results of nearly 50 studies published from 2000 to 2023.

The studies examined the health effects of either vegetarian diets or vegan regimens, which restrict any food derived from animals, including dairy.

A clear consensus emerged: Both eating patterns were associated with a lower risk of cancer and ischemic heart disease (heart problems caused by narrowed arteries). In particular, the diets seemed to reduce the risk of prostate cancer and gastrointestinal cancers like colon cancer. Vegetarian diets were also linked to a lower risk of dying from cardiovascular disease.

In addition, plant-based diets were associated with a reduction in risk factors for heart disease and cancer, including high body weight, inflammation and LDL or “bad” cholesterol. 

“This research shows, in general, that a plant-based diet can be beneficial, and taking small steps in that direction can make a difference,” said Matthew Landry, one of the review’s authors and an assistant professor of population health and disease prevention at the University of California, Irvine.

“You don’t have to go completely vegan to see some of these benefits,” he added. “Even reducing a day or two per week of animal-based consumption can have benefits over time.”

However, Dr. Walter Willett, a professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health, pointed out that not everyone who follows a plant-based diet eats the same foods, so levels of healthiness still vary.

“A vegetarian diet could be based primarily on refined starches and sugar, which we see to be the worst dietary pattern,” Willett, who was not involved in the new research, said in an email. 

A healthy plant-based diet, he said, should consist mostly of whole grains, fruits, vegetables, nuts, soy, beans and non-hydrogenated plant oils. 

Why are plant-based diets so healthy?

Researchers are still investigating the mechanisms through which plant-based diets lower the risk of disease. 

Some of it may have to do with preventing obesity, which is linked to heart disease and certain cancers. But the benefits likely extend beyond that, Landry said. 

“Some of it is independent of weight. Even when weight is maintained or doesn’t change, we still see reductions in some of these other clinical health outcomes, especially when it relates to cardiovascular disease,” he said.

One possible reason is that many fruits and vegetables are high in anti-inflammatory nutrients and antioxidants, which can reduce plaque buildup in the arteries.

Plant-based diets also tend to be high in fiber, which helps lower bad cholesterol, said Brie Turner-McGrievy, a professor of health promotion, education and behavior at the University of South Carolina. She published a study in 2014 which found that plant-based diets can reduce risk factors for heart disease, stroke and Type 2 diabetes. The research was included in the new review.

“Soluble fiber that’s found in things like beans and oats is really a powerful tool to help lower LDL cholesterol levels,” she said.

Turner-McGrievy noted, though, that much of that benefit can only be achieved through eating whole foods: “It’s not like you can take a fiber supplement and hope to have these same outcomes.”

Another benefit of a plant-based diet may come simply from the absence of meat, she said. People who are vegan tend to consume less saturated fat than meat eaters. 

“It’s just really hard to lower your saturated fat intake if you’re consuming animal-based foods,” Turner-McGrievy said. “Cheese, for example, is the No. 1 source of saturated fat in the diet.”

Processed meat products such as bacon or salami are also known to raise the risk of cancer, according to the World Health Organization. The agency considers red meat in general to be a “probable human carcinogen.”

Is a vegan or vegetarian diet right for everyone?

According to the Academy of Nutrition and Dietetics, vegetarian and vegan diets are adequate and healthy at all stages of life, including pregnancy, childhood and older adulthood. 

But the new review stopped short of recommending plant-based diets for everyone. 

“During pregnancy, it’s not recommended based on the data that we have to use a strict vegetarian diet,” said Dr. Federica Guaraldi, one of the review’s authors and an endocrinologist at the IRCCS Institute of Neurological Sciences of Bologna in Italy. 

Guaraldi and her co-authors found that the plant-based regimens studied didn’t lower the risk of gestational diabetes or hypertension in pregnant women. One study included in the review suggested that pregnant women who followed a vegetarian diet had lower levels of zinc — which is important for children’s growth, development and immune function than those who ate meat. Another study in the review found that vegetarian mothers had an increased risk of delivering babies with low birthweights. 

The review’s authors also cautioned that plant-based diets might lead to vitamin B12 deficiencies in the general population. Landry said that can be addressed by taking a B12 supplement.  

“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,” he said.