Eating a vegan, vegetarian or lacto-ovo vegetarian diet significantly reduces the overall risk of developing cancer, heart disease and dying early from cardiovascular disease, according to a new 鈥渦mbrella鈥� analysis of more than 20 years of research.
An umbrella review looks at existing metanalyses of large numbers of studies, providing a high-level view of existing research on a topic.
In addition to lowering cardiovascular risk factors such as blood pressure and cholesterol, the umbrella analysis found a 鈥減rotective effect鈥� for specific cancers, including 鈥渓iver, colon, pancreas, lung, prostate, bladder, melanoma, kidney and non-Hodgkin lymphoma,鈥� said lead author Dr. Angelo Capodici, a graduate student in health science, technology and management at Scuola Superiore Sant鈥橝nna in Pisa, Italy.
Vegetarians don鈥檛 eat any animal flesh, while the lacto-ovo version of vegetarianism allows dairy products and eggs while excluding all meat, poultry and fish. Veganism, the stricter form of vegetarianism, bans any food products made from meat, poultry and seafood as well as any animal by-products such as gelatin.
However, the protective nature of the diets could be sabotaged if poor dietary choices were made, the study authors said via email.
鈥淒iets that emphasize consumption of unhealthy plant foods, such as fruit juices, refined grains, potato chips, and even sodas鈥� 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 鈥渇ull of sugars or sweetener,鈥� Guaraldi said, 鈥�(were) recently demonstrated to have detrimental impact on metabolism as much as or even more than white sugar.鈥�
Results may be affected by other lifestyle factors
Researchers have long known that people who follow plant-based diets often live healthier lives full of exercise and an avoidance of sugar-sweetened foods and beverages, refined grains, snacks, alcohol and tobacco, the study said.
鈥淲hat is attributed to diet here may be in part due to other lifestyle practices,鈥� 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.
鈥淭hat is a minor concern, however,鈥� Katz said in an email. 鈥淭he net effect of plant-predominant dietary patterns is clearly favorable to crucial health outcomes even if some of the observed benefit is attributable to other lifestyle practices.鈥�
In fact, adopting a plant-based diet, even without additional exercise, could still yield health benefits, according to a November study on twins by Christopher Gardner, one of the coauthors of the umbrella analysis published Wednesday in the journal PLOS One.
In the 2023 study, healthy twins who ate a vegan diet for eight weeks had lower 鈥渂ad鈥� low-density lipoprotein, or LDL, cholesterol, better blood sugar levels and greater weight loss than siblings who ate a diet of meat and vegetables, according to Gardner, a research professor of medicine at the Stanford Prevention Research Center in Palo Alto, California.
鈥淭here was a 10 per cent to 15 per cent drop in LDL cholesterol, a 25 per cent drop in insulin, and a 3 per cent drop in body weight in just eight weeks, all by eating real food without animal products,鈥� Gardner told CNN at the time.
One reason for that may be the nutritional boost that plants provide, including high levels of vitamins, minerals and other substances with antioxidant and anti-inflammatory effects, while also reducing the inflammatory impact of meat and processed food, the authors said.
鈥淧lants have more fiber (animal foods have zero), less saturated fat and zero cholesterol (all animal foods have cholesterol),鈥� Gardner said in an email. 鈥淎n entirely separate category is phytochemicals (literally, 鈥榩lant chemicals鈥�) such as antioxidants. By definition there are no phytochemicals in animal foods.鈥�
No meat, poultry or seafood, but dairy and eggs are OK
The new review analyzed 48 metanalyses that had investigated the impact of eating a vegetarian or vegan diet on the development of cancer, cardiovascular disease and early death.
鈥淲e analyzed reviews considering vegan and vegetarian diets that completely exclude(ed) meat, poultry and seafood,鈥� said study coauthor Dr. Davide Gori, an associate professor of biomedical and neuromotor sciences at the University of Bologna in Italy.
鈥淭o be more precise regarding vegetarian diets, 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 were included,鈥� Gori said in an email.
However, vegetarian diets limiting but not completely excluding certain types of meat and fish, such as pesco- or pollo-vegetarian diets, were excluded, he said.
The review found 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 and other measures of blood sugar control, and the systolic (top) and diastolic (bottom) measurements of blood pressure.
The diets also significantly lowered total cholesterol, LDL cholesterol, and 鈥淐-reactive protein 鈥� an index of inflammation that is typically higher in cardiovascular and metabolic disease,鈥� Gori said. Metabolic disease is a constellation of symptoms such as obesity, high blood pressure and poor control of cholesterol and blood sugars that can all lead to type 2 diabetes, heart disease and stroke.
However, there was no benefit in eating plants for pregnant women, an 鈥渋ntriguing finding鈥� that needs further research, said Guaraldi of the IRCCS Institute of Neurological Sciences. It鈥檚 also possible that the hormones of pregnancy might affect findings, and 鈥渨e cannot rule out that participants have taken supplements during the study period that could have altered the impact of diet on the considered parameters.鈥�
Special considerations of plant-based diets
Because certain vitamin and minerals are more easily found and absorbed from meat, dairy or fish, vegetarians and vegans must take extra precautions to add those into 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 a deficiency, according to the Mayo Clinic.
鈥淪trictly vegan diets can be deficient in vitamin B12,鈥� Gardner said. 鈥淭his is easily resolved by consuming foods fortified with (vitamin) B12 鈥� easy to do because the recommended daily allowance for B12 is lower than any other vitamin or mineral.
鈥淚ron is another nutrient that is harder to get from a fully vegan diet,鈥� Gardner added. 鈥淢any plant foods are relatively high in iron (beans/legumes). Again, supplements can be helpful.鈥�
Protein is also a challenge, but good sources in plants include legumes such as lentils, chickpeas and beans, nuts, seeds, whole grains and soy products such as edamame, tempeh and tofu.
Processed meat substitutes are options as well, experts say, but due to the processing can be packed with sodium, so read labels carefully.
