In a recent study published in the Nutrition, Metabolism and Cardiovascular Diseases Journal, researchers conducted a comprehensive review to compare the impacts of vegetarian and non-vegetarian diets on the outcomes of major cardiometabolic and other non-communicable diseases.
Study: A comprehensive review of healthy effects of vegetarian diets. Image Credit: Elena.Katkova/Shutterstock.com
The opinions about the association between meat consumption and health have been divided, with diets low in or devoid of animal food sources being considered low in nutritional content, resulting in essential nutrient deficiencies.
Emerging research supports contrasting opinions that plant-based diets meet the regular nutritional requirements and provide various health benefits, such as lowering the risks of multiple diseases.
However, the term ‘vegetarian’ is used loosely to encompass various dietary patterns such as vegan, ovo-vegetarian, lacto-vegetarian, lacto-ovo-vegetarian, and semi-vegetarian.
Vegetarian diets also range from the Western patterns of vegetarianism mentioned above to dietary patterns based on ethnicities, such as Buddhist or Asian diets, where the availability of animal food sources or socio-economical or cultural factors influences the diet.
This wide range of variations in vegetarian diets has resulted in contrasting results among studies that examine the relationship between vegetarian diets and health benefits.
Individuals in developing countries generally follow a more balanced and well-developed vegetarian diet in comparison to those in developing countries where access to food is dependent on socioeconomic factors.
About the study
In the present study, the researchers conducted a comprehensive review of research that examined various vegetarian diets and their effects on outcomes related to health, including the risks of various non-communicable diseases.
Studies examining various types of vegetarian diets, from Western vegetarian dietary patterns to vegetarian diets influenced by religious beliefs, were reviewed.
The non-communicable diseases examined in the review broadly included cardiovascular, cerebrovascular, cardiometabolic diseases, obesity, hypertension, dyslipidemia, metabolic syndrome, and type 2 diabetes.
Observational studies and randomized controlled trials that compared the effects of vegetarian diets with those of non-vegetarian or omnivore diets were included.
Furthermore, for each category of non-communicable diseases, the researchers conducted a thorough literature search using a wide range of keywords associated with the disease.
The review included cohort studies, randomized controlled trials, longitudinal studies, and prospective cohort studies that reported on the comparative effects of vegetarian and non-vegetarian diets in the context of disease risk.
The results reported that while it appears that following vegetarian diets may help in reducing the risk of cardiometabolic diseases, the non-uniformity of the findings due to the cultural and ethnic differences in the approach to vegetarianism, as well as due to differences in methodology across the studies makes it difficult to form definitive inferences.
Several cohort studies in the review reported that following a vegetarian diet compared to a non-vegetarian diet was advantageous in lowering the risk of incidence and mortality associated with obesity, overweight, and ischemic heart disease.
Vegetarian diets were also linked to a lower risk of hypertension and positively affected plasma parameters and type 2 diabetes risk.
Furthermore, while cohort studies reported mixed results on the effects of vegetarian diets on metabolic syndromes, randomized controlled trials reported that vegetarian diets, especially those involving low-fat foods, improved glycemic control and resulted in higher weight loss compared to non-vegetarian diets.
One randomized controlled study also reported improvements in coronary atherosclerosis associated with vegetarian diets. In contrast, most randomized controlled studies reported a lowering of blood pressure and low-density lipoprotein-cholesterol levels, albeit with an accompanied lowering of high-density lipoprotein levels.
The researchers also discussed the possible mechanisms that explain the association between vegetarian diets and the reduced risk of many non-communicable diseases.
They believe that while the health benefits of vegetarian diets might sometimes be specific for certain diseases, often, the etiopathogenetic mechanisms of many diseases are shared, and the impact of vegetarian diets in lowering the risks of such diseases is through more generalized mechanisms.
The low to no animal food content of vegetarian diets results in a lower intake of saturated fats and reduces the detrimental effects of excess animal proteins and heme-irons.
Furthermore, the high fiber, polyunsaturated fatty acid, complex carbohydrate, and micronutrient content of plant-based diets also improve conditions such as type 2 diabetes, hypercholesteremia, and overweight.
Whole plant food consumption has also been encouraged due to its benefits in decreasing oxidative stress and inflammation and improving insulin sensitivity and endothelial function.
Overall, the review covered a comprehensive set of studies that compared the impacts of vegetarian and non-vegetarian diets on overall human health and in lowering the risk of many non-communicable diseases.
Although many studies have reported that vegetarian diets have various beneficial effects on human health and are believed to lower the incidence and mortality risks of major non-communicable diseases, the methodologies and classifications of vegetarian diets continue to be too non-uniform to form definitive inferences on the subject.