Although people worldwide follow plant-based diets for various reasons—cultural, ethical, environmental, and religious—there are also plenty of health reasons to do so. Studies show that vegetarians have lower total blood cholesterol, low-density lipoprotein levels, and blood pressure, all of which reduce their cardiovascular risks; indeed, research suggests that vegetarians have a lower risk of obesity, heart disease, hypertension, cancer, type 2 diabetes, and mortality than those consuming a typical western diet. Vegetarians also tend to have a higher intake of nutrients including vitamins C and E, magnesium, potassium, folate, antioxidants, and phytochemicals.

According to the 2010 Dietary Guidelines for Americans, “In prospective studies of adults, compared to non-vegetarian eating patterns, vegetarian-style eating patterns have been associated with improved health outcomes—lower levels of obesity, a reduced risk of cardiovascular disease, and lower total mortality." Affirming the nutritional and health benefits of plant-rich diets, the 2015 Dietary Guidelines for Americans include the Healthy Vegetarian Eating Pattern that provides recommendations for those who follow a vegetarian pattern.

The Vegetarian Pattern is similar to the Healthy U.S.-Style Pattern (see chapter 2), but is higher in calcium and fiber and lower in vitamin D. Also, the Vegetarian Pattern increases consumption of soy products, legumes, nuts and seeds, and whole grains and eliminates meats, poultry, and seafood.

To reflect the habits of most U.S. vegetarians, dairy foods and eggs are included, but a vegan variation is provided. Echoing earlier Guidelines, the 2015 edition cites reduced risk of cardiovascular disease, lower rates of obesity and lower total mortality associated with vegetarian-style eating patterns.

How and why plant-based diets are beneficial is an area of active research. A plant-based diet may benefit mortality because of general patterns of lower body weight, decreased consumption of processed (smoked, salted, cured) meat, and an increased consumption of plant foods. For example, a diet rich in meat may be at the expense of fruits and vegetables and the fiber and other biologically active nutrients they contain. Some processed meats contain carcinogenic (cancer-causing) compounds formed during cooking or produced during processing to preserve color or flavor.