According to the Vegetarian Society, vegetarians are people who do not eat the products or byproducts of animal slaughter.

Vegetarians do not consume:

• meat, such as beef, pork, and game
• poultry, such as chicken, turkey, and duck
• fish and shellfish
• insects
• rennet, gelatin, and other types of animal protein
• stock or fats that derive from animal slaughter

However, many vegetarians do consume byproducts that do not involve the slaughter of animals. These include:

• eggs
• dairy products, such as milk, cheese, and yogurt
• honey

Vegetarians typically consume a range of fruits, vegetables, nuts, seeds, grains, and pulses, as well as “meat substitutes” that derive from these food types.

Vegetarianism is generally less strict than veganism, so there are several well-known variations of the vegetarian diet. These include:

• Lacto-ovo-vegetarian. People who follow this diet avoid all types of meat and fish but do consume dairy products and eggs.
• Lacto-vegetarian. People on this diet do not eat any meat, fish, or eggs but do consume dairy products.
• Ovo-vegetarian. Individuals following this diet do not eat any meat, fish, or dairy products but do consume eggs.
• Pescatarian. Those who follow this diet avoid all meats except fish and other types of seafood. However, this does not meet the traditional definition of vegetarianism, and many people refer to the pescatarian diet as being semi-vegetarian or flexitarian.

Veganism is a stricter form of vegetarianism. Vegans avoid consuming or using any animal products or byproducts. The Vegan Society define veganism as “a way of living, which seeks to exclude, as far as is possible and practicable, all forms of exploitation of and cruelty to animals for food, clothing, or any other purpose.”

Vegans strictly avoid consuming any foods or beverages that contain:

• meat
• poultry
• fish and shellfish
• eggs
• dairy products
• honey
• insects
• rennet, gelatin, and other types of animal protein
• stock or fats that derive from animals

Strict vegans also extend these principles beyond their diet and will try, where possible, to avoid any product that directly or indirectly involves the human use of animals. These products can include:

• leather goods
• wool
• silk
• beeswax
• soaps, candles, and other products that contain animal fats, such as tallow
• latex products that contain casein, which comes from milk proteins
• cosmetics or other products that manufacturers test on animals

Many vegetarians also apply some of these principles to their lifestyle, for example, by avoiding leather goods and products that involve animal testing.

Scientific research suggests that vegetarian and vegan diets may offer several health benefits.

A 2017 studyTrusted Source examined the effectiveness of a plant-based diet in 49 adults who were overweight or had obesity and also had at least one of the following conditions:

• type 2 diabetes
• ischemic heart disease
• high blood pressure
• high cholesterol levels

The researchers randomly assigned participants to either normal diet and care or a low fat, plant based diet program comprising low fat whole foods, which did not involve calorie counting or mandatory regular exercise. The intervention also included two 2-hour sessions each week, which provided the participants with cooking training and education by doctors. The nonintervention group did not attend any of these sessions.

At the 6-month and 12-month follow-ups, participants in the diet group had significant reductions in body mass index (BMI) and cholesterol levels compared with those in the normal care group.

A 2017 systematic review and meta-analysisTrusted Source found evidence to suggest that plant based diets can help lower levels of total cholesterol, low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol. The researchers did not analyze how the changes in cholesterol influenced heart disease outcomes.

Another 2016 observational studyTrusted Source found that vegetarians living in South Asia and America were less likely to develop obesity than nonvegetarians.

A 2019 reviewTrusted Source cites evidence suggesting that plant-based diets may offer a number of cardiovascular health benefits for endurance athletes. These benefits include:

• lower cholesterol levels
• improved blood pressure and blood flow
• better blood sugar control
• a lower risk and even reversal of atherosclerosis
• reduced oxidative stress and inflammation

A 2019 study also found an association between a healthful plant based diet and a lower risk of developing chronic kidney disease. Interestingly, those who followed an unhealthful plant based diet with a higher proportion of sugar-sweetened foods and refined grains had a significantly higher risk of chronic kidney disease.