Study Finds Certain Vegetarian Diets Significantly Lower Risk of Cancer, Heart Disease, and Mortality

A study reveals that specific vegetarian diets can greatly reduce the risk of cancer, heart disease, and mortality. This research underscores the health benefits of plant-based eating, suggesting that such diets can enhance overall health and increase life expectancy.

CNN - According to a new “umbrella” analysis of over 20 years of research, following a vegan, vegetarian, or lacto-ovo vegetarian diet significantly lowers the overall risk of developing cancer, heart disease, and dying prematurely from cardiovascular disease.

An umbrella review examines existing meta-analyses of numerous studies, offering a comprehensive overview of current research on a topic.

In addition to reducing cardiovascular risk factors such as blood pressure and cholesterol, the umbrella analysis identified a “protective effect” for specific cancers, including liver, colon, pancreas, lung, prostate, bladder, melanoma, kidney, and non-Hodgkin lymphoma, according to lead author Dr. Angelo Capodici, a graduate student in health science, technology, and management at Scuola Superiore Sant’Anna in Pisa, Italy.

Vegetarians do not eat any animal flesh, while lacto-ovo vegetarians allow dairy products and eggs but exclude all meat, poultry, and fish. Veganism, the strictest form of vegetarianism, excludes all meat, poultry, seafood, and animal by-products such as gelatin.

However, the study authors noted that the protective benefits of these diets could be undermined by poor dietary choices.

"Diets that emphasize consumption of unhealthy plant foods, such as fruit juices, refined grains, potato chips, and even sodas, might counter the positives of a plant-based diet for health," said study coauthor Dr. Federica Guaraldi, medical director of the pituitary unit at the IRCCS Institute of Neurological Sciences of Bologna in Italy.

Fruit juices, which are “full of sugars or sweeteners,” Guaraldi added, “were recently demonstrated to have a detrimental impact on metabolism as much as or even more than white sugar.”

Results may be influenced by other lifestyle factors

Researchers have long known that people who follow plant-based diets often live healthier lives, engaging in regular exercise and avoiding sugar-sweetened foods and beverages, refined grains, snacks, alcohol, and tobacco, according to the study.

“What is attributed to diet here may be in part due to other lifestyle practices,” said Dr. David Katz, a specialist in preventive and lifestyle medicine who founded the nonprofit True Health Initiative, a global coalition of experts dedicated to evidence-based lifestyle medicine. He was not involved in the study.

“That is a minor concern, however,” Katz said in an email. “The net effect of plant-predominant dietary patterns is clearly favorable to crucial health outcomes even if some of the observed benefits are attributable to other lifestyle practices.”

In fact, adopting a plant-based diet, even without additional exercise, could still yield health benefits. A November study on twins by Christopher Gardner, a coauthor of the umbrella analysis published in PLOS One, found that healthy twins who ate a vegan diet for eight weeks had lower "bad" low-density lipoprotein (LDL) cholesterol, better blood sugar levels, and greater weight loss than their siblings who ate a diet of meat and vegetables. Gardner is a research professor of medicine at the Stanford Prevention Research Center in Palo Alto, California.

“There was a 10% to 15% drop in LDL cholesterol, a 25% drop in insulin, and a 3% drop in body weight in just eight weeks, all by eating real food without animal products,” Gardner told CNN at the time.

One reason for these improvements may be the nutritional boost provided by plants, which are high in vitamins, minerals, and other substances with antioxidant and anti-inflammatory effects. Additionally, plant-based diets reduce the inflammatory impact of meat and processed foods, the authors noted.

“Plants have more fiber (animal foods have zero), less saturated fat, and zero cholesterol (all animal foods have cholesterol),” Gardner said in an email. “An entirely separate category is phytochemicals (literally, ‘plant chemicals’) such as antioxidants. By definition, there are no phytochemicals in animal foods.”

No meat, poultry, or seafood, but dairy and eggs are allowed

The new review analyzed 48 meta-analyses that investigated the impact of vegetarian or vegan diets on the development of cancer, cardiovascular disease, and early death.

“We analyzed reviews considering vegan and vegetarian diets that completely exclude meat, poultry, and seafood,” said study coauthor Dr. Davide Gori, an associate professor of biomedical and neuromotor sciences at the University of Bologna in Italy.

“To be more precise regarding vegetarian diets, we included lacto-vegetarian (allowing certain dairy products such as yogurt, cheese, and milk), ovo-vegetarian (allowing whole eggs, egg whites, and egg-containing foods such as mayonnaise, egg noodles, and certain baked goods), and lacto-ovo-vegetarian diets,” Gori said in an email.

However, vegetarian diets that limit but do not completely exclude certain types of meat and fish, such as pesco- or pollo-vegetarian diets, were excluded, he added.

The review found that eating these plant-based diets reduced the risk of cardiovascular disease, diabetes, and inflammation by affecting risk factors such as body mass index, fasting glucose, other measures of blood sugar control, and both systolic (top) and diastolic (bottom) blood pressure measurements.

The diets also significantly lowered total cholesterol, LDL cholesterol, and "C-reactive protein—an index of inflammation that is typically higher in cardiovascular and metabolic diseases," Gori said. Metabolic disease includes symptoms such as obesity, high blood pressure, and poor control of cholesterol and blood sugars, which can all lead to type 2 diabetes, heart disease, and stroke.

However, there was no observed benefit in eating plants for pregnant women, an "intriguing finding" that requires further research, said Guaraldi of the IRCCS Institute of Neurological Sciences. It’s possible that pregnancy hormones might affect the results, and "we cannot rule out that participants took supplements during the study period that could have altered the impact of diet on the considered parameters."

‍Special considerations of plant-based diets

Because certain vitamins and minerals are more easily found and absorbed from meat, dairy, or fish, vegetarians and vegans must take extra precautions to include these nutrients in their diets, experts say.

Unless the diet is carefully optimized, additional sources of B12, calcium, iron, zinc, iodine, and vitamin D may be needed to avoid deficiencies, according to the Mayo Clinic.

“Strictly vegan diets can be deficient in vitamin B12,” Gardner said. “This is easily resolved by consuming foods fortified with B12, as the recommended daily allowance for B12 is lower than for any other vitamin or mineral.

“Iron is another nutrient that is harder to get from a fully vegan diet,” Gardner added. “Many plant foods are relatively high in iron, such as beans and legumes. Again, supplements can be helpful.”

Protein can also be a challenge, but good sources in plants include legumes like lentils, chickpeas, and beans, as well as nuts, seeds, whole grains, and soy products such as edamame, tempeh, and tofu.

Processed meat substitutes are options as well, but experts warn they can be high in sodium due to processing, so it’s important to read labels carefully.

Source: CNN‍