People who follow a plant-based diet may have a lower risk of heart disease and cancer, as well as lower odds of developing several risk factors that contribute to these medical problems, a new study suggests.

For the study, scientists examined results from 48 research reviews published over two decades that explored the health effects of vegan or vegetarian diets. A vegan diet is a type of vegetarian diet that excludes all forms of meat, eggs, dairy, and other animal products, such as honey or gelatin.

They were also both tied to a reduced risk of prostate cancer and gastrointestinal cancers like colon cancer. Vegetarian diets were also connected to a lower risk of dying from cardiovascular disease

In addition, both diets were associated with decreased odds of developing several risk factors that can contribute to heart disease and cancer, such as obesity, high cholesterol, elevated blood pressure, and inflammation.

The foods vegetarians and vegans choose to consume — as well as the animal-based foods they avoid — can both contribute to better health, says senior study author Federica Guaraldi, MD, PhD, of the Institute of Neurological Sciences in Bologna, Italy.

“People adopting vegetarian or vegan diets consume more food such as vegetables and whole foods containing high levels of vitamins, minerals and other substances with antioxidant and anti-inflammatory effects, while reducing the pro-oxidant and pro-inflammatory effect of substances included in the meat and processed food,” Dr. Guaraldi says.

Study Only Examined Strictly Vegetarian and Vegan Diets

The analysis only included people who strictly followed vegetarian or vegan diets — not people who consume plant-based meals some of the time. It also looked at all forms of animal protein the same way, making it impossible to determine from the findings whether avoiding specific foods like red meat, poultry, or fish might have the most health benefits.

In addition, the study wasn’t designed to prove whether or how a vegetarian or vegan diet might directly improve health and longevity. And, because each of the smaller studies included in the analysis measured the health benefits of plant-based diets differently, scientists were unable to calculate exactly how much plant-based diets might reduce the odds of developing heart disease, cancer, or the risk factors that can contribute to these conditions.

Beyond this, not all vegetarian and vegan diets are equally nutritious, says study co-author Davide Gori, MD, PhD, of the department of biomedical and neuromotor sciences at the University of Bologna in Italy.

“We must consider the fact that even vegetarian or vegan diets that emphasize consumption of unhealthy plant foods, such as fruit juices, refined grains, potato chips, and even sodas might have detrimental effects on the body,” Dr. Gori says.

Fiber-Rich Fruits and Vegetables Offer Multiple Health Benefits

One reason eating lots of fruits and vegetables may help lower the risk of chronic diseases is because these foods are packed with fiber, which isn’t a nutrient found in animal-based foods, says Micaela Karlsen, PhD, MSPH, who serves as the senior director of research at the American College of Lifestyle Medicine.

“Eating foods packed with fiber helps slow digestion, keeps blood sugar from spiking and crashing, and helps people feel full,” says Dr. Karlsen, who wasn’t involved in the new study. “This means people tend to eat a little bit less over the long-term and this helps prevent weight gain. In addition, fiber helps to clean out the digestive tract and seems to be related to having lower cholesterol.”

All of these effects of fiber help reduce cancer and heart disease risk, Karlsen says. At the same time, avoiding meat is helpful because saturated fat and animal protein tends to increase risk for cancer and atherosclerosis, or hardening of the arteries that contributes to heart disease.

“So when people eat vegan or vegetarian diets, they are not only getting lots of whole plant foods, they are avoiding the foods that tend to cause problems,” Karlsen says.

While the study didn’t focus on which types of animal protein is best to limit or avoid, Karlsen says there’s one group to cut out first: red and processed meats like steak, hamburgers, hot dogs, and deli meat.

“When you’re ready to eliminate animal foods, definitely eliminate red meat and processed meat first. Those meats have been shown to have the strongest association with cardiovascular disease and cancer,” Karlsen says.

You Don’t Have to Be Vegan to Get the Benefits of Plant-Focused Eating

Even though the study only focuses on people who followed exclusively vegetarian or vegan diets, it is possible to see health benefits from adding more plant-based meals to your diet while continuing to consume animal proteins, Karlsen says.

“The most important thing to start with is an intention to add in more whole, plant-based foods. This will help crowd out other foods, because you’ll feel full,” Karlsen advises. “If you eat meat, you could leave the meat until last and see if you really feel like you need to eat more.”