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Eating a vegan, vegetarian, or lacto-ovo vegetarian diet significantly reduces the overall risk of developing cancer, heart disease and premature death, a recent "umbrella" analysis spanning more than 20 years of research suggests.

An umbrella review consolidates existing meta-analyses of numerous studies, providing a comprehensive overview of current research on a particular topic.

Lead author Dr. Angelo Capodici, a graduate student in health science, technology, and management at Scuola Superiore Sant'Anna in Pisa, Italy, has noted a "protective effect" for specific cancers, including liver, colon, pancreas, lung, prostate, bladder, melanoma, kidney and non-Hodgkin lymphoma.

While vegetarians avoid all animal flesh, lacto-ovo vegetarians include dairy products and eggs while excluding meat, poultry and fish. Veganism, the strictest form of vegetarianism, prohibits any food products derived from animals, including gelatin.

However, the beneficial impact of these diets could be undermined by poor dietary choices, cautioned study co-author Dr. Federica Guaraldi, medical director of the pituitary unit at the IRCCS Institute of Neurological Sciences of Bologna in Italy. Consumption of unhealthy plant foods like fruit juices, refined grains, potato chips and sodas might offset the health benefits of a plant-based diet.

The study underscored the influence of other lifestyle factors, such as regular exercise and avoidance of sugar-sweetened foods and beverages, refined grains, snacks, alcohol, and tobacco, which are often associated with plant-based diets.

Dr. David Katz, founder of the nonprofit True Health Initiative, highlighted the overall favorable impact of plant-predominant dietary patterns on crucial health outcomes, even if some benefits may stem from other lifestyle practices.

"What is attributed to diet here may be in part due to other lifestyle practices," Katz said in an email according to CNN. "That is a minor concern, however. The 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."

In a separate study, healthy twins who adopted a vegan diet for eight weeks experienced significant improvements in cholesterol levels, blood sugar control, and weight loss compared to siblings consuming a meat-based diet, according to Christopher Gardner, 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.

The nutritional richness of plants, characterized by high levels of vitamins, minerals, antioxidants, and anti-inflammatory substances, may contribute to these health benefits according to Gardner.

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

The review, analyzing 48 meta-analyses, found a significant reduction in cardiovascular disease, diabetes and inflammation associated with plant-based diets, affecting factors such as body mass index, blood glucose levels, blood pressure and cholesterol.

While plant-based diets offer numerous health benefits, individuals must ensure adequate intake of essential nutrients such as vitamin B12, calcium, iron, zinc, iodine and vitamin D to prevent deficiencies. Good sources of protein in plant-based diets include legumes, nuts, seeds, whole grains and soy products.