Veganism and Vegetarianism: The Science and Philosophy of Plant-Based Nutrition

Nutritionists have long heralded a diet rich in fruits, vegetables, whole grains, and lean proteins as the foundation for a lean, strong body and optimal health. Much to the discontent of vegans and vegetarians, this has always included animal products, such as lean meat, poultry, seafood, and low-fat dairy products like milk, eggs, and cheese.

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But two schools of nutritional (as well as ethical and environmental) thought support a plant-based diet that eliminates many or all animal products: veganism and vegetarianism.
While some view a plant-based diet as eating almost all plants, along with some animal products (vegetarianism), others view a plant-based diet as one that is void of all animal products (veganism). As such, the term plant-based diet is often used interchangeably to mean vegan or vegetarian. The term many dietary experts use to describe a health promoting diet that consists of whole, unprocessed foods is “Whole Food Plant Based,” or simply WFPB.  This term is used to describe a plant-based diet that is truly healthy, in recognition of the fact that a diet that is simply vegan or vegetarian may not necessarily always be healthy. 

According to Vegetarian Times, 7.3 million Americans are vegetarians, and nearly 23 million more follow a vegetarian-inclined diet. About 1 million people in the U.S. identify as vegans.

The Science that Supports the Philosophy of a Plant-Based Diet

Numerous studies have shown that plant-based nutrition has significant health benefits that include:

  • Healthier weight
  • Lower risk of cancer and diabetes
  • Longer life
  • Better cardiovascular health/reversal or prevention of heart disease
  • Lower cholesterol
  • Lower blood sugar
  • Lower blood pressure
  • Fewer medications
  • Improved symptoms of rheumatoid arthritis

For example, a 2009 article published by the American Journal of Clinical Nutrition reported that vegetarians typically enjoy a lower risk of cardiovascular disease, obesity, Type 2 diabetes, and some cancers than omnivores.
Other findings published in the American Journal of Clinical Nutrition article included:

  • Vegan diets increase the intake of protective nutrients and phytochemicals and minimize the intake of dietary factors related to a number of chronic diseases.
  • Vegans (compared to omnivores) consume greater quantities of fruit and vegetables, which are associated with lower blood cholesterol, lower incidences of stroke, and lower risk of mortality from stroke and heart disease.
  • Vegans consume more whole grains, soy, and nuts, all of which provide significant cardiovascular protection.
  • Vegans consumer more legumes, fruits, vegetables, tomatoes, allium vegetables, fiber, and vitamin C than omnivores, all of which are protective against cancer of the lung, mouth, esophagus, stomach, and prostate.
  • Because red meat and processed meat consumption are associated with an increased risk of esophageal, liver, lung, and colorectal cancers (ranging from 20 to 60 percent), this risk to vegans is greatly reduced.
  • Vegans tend to have a high intake of tofu and other soy products, which are suggested to have a beneficial effect on bone health in postmenopausal women.

A Closer Look at The Vegan and Vegetarian Approaches to Nutrition and Dietetics

Veganism and vegetarianism are fundamentally different approaches to nutrition, but both represent a decided way of life. Although both veganism and vegetarianism support a plant-based diet, there are a number of significant differences between these two schools of nutritional thought:


Veganism is not just a way of eating for many people, it is a way of living. Many vegans choose a vegan lifestyle—not just a vegan diet—based on ethical, moral, religious, or even environmental reasons.

According to The Vegan Society, veganism “seeks to exclude, as far as is possible and practical, all forms of exploitation of, and cruelty to, animals for food, clothing, or any other purpose.”  According to the Vegan Society, all vegans share a common conviction to eat a plant-based diet that is void of all animal products and by-products, including dairy, eggs, and honey, and to eliminate purchasing or wearing animal products (such as leather, wool, or silk, or cosmetics/soaps derived from animal products) or products tested on animals.

Sources of Protein, Calcium, and Vitamins/Minerals in the Vegan Diet

From a solely nutrition perspective, veganism should include a varied diet of fruits, vegetables, leafy greens, whole grain products, nuts, seed, and legumes. Any type of animal product or food made or derived from animal products is eliminated.
According to the Vegetarian Resource Group, vegans should be able to meet their protein needs as long as they maintain their caloric intake. Sources of protein for vegans include:

  • Almonds
  • Broccoli
  • Chickpeas
  • Kale
  • Lentils
  • Peanut butter
  • Peas
  • Potatoes
  • Rice
  • Soy milk
  • Spinach
  • Tofu
  • Whole wheat bread

Vegan diets are naturally free of cholesterol and are generally low in fat. These diets are therefore often followed to reduce the risk of major chronic diseases, such as heart disease and cancer. Many vegan diets consist of small amounts of fats found in foods like avocado, coconut, nut butters, nuts, and seed butters.

However, since oil is highly refined and consists of only fat with no fiber or other nutrients from the food it was originally derived, many vegan doctors do not recommend the consumption of oils of any kind, including extra virgin olive oil and coconut oil which have been promoted as healthy in recent years. Dr. John McDougall is among those that recommend a completely oil-free diet free of any high-fat foods, including nuts, nut butters and other high-fat foods that have historically been a staple of the vegan diet. Dr. McDougall has found that vegetables alone contain enough natural fat to support a healthy diet, a view that has been echoed in the British Medical Journal.

Another prominent pioneer of the oil-free diet, Dr. Caldwell Esselstyn, has identified that both mono unsaturated and saturated fat contained in oils are harmful to the endothelium lining of the artery, and that consuming oils of any kind can provide a gateway to vascular disease. According to leading thinkers in the field, this goes for oils containing omega-3 and 6 fatty acids, vegetable oils, olive oil, coconut oil and canola oil.

Vitamin D is not naturally found in a vegan diet; however, vegans can ensure they get adequate amounts of Vitamin D through exposure to sunlight and through vitamin D-fortified soy milk and rice milk.

Vegans can get the required calcium in their diet through a number of food sources, including:

  • Almonds/almond butter
  • Bok choy
  • Calcium-fortified soy milk and orange juice
  • Dark green vegetables (collard greens, kale, broccoli)
  • Soybeans
  • Tofu (made with calcium sulfate)

Many plant-based foods are excellent sources of iron for vegans:

  • Bok choy
  • Chick peas
  • Dark green vegetables
  • Dried beans
  • Kidney beans
  • Lentils
  • Millet
  • Prune juice
  • Soybeans
  • Watermelon

Still, rather than eating for specific nutrients, the dominant vegan model is one that involves eating a varied diet of healthy food that consists of enough calories. The only consistent and absolute recommendation from most dietary experts is that vegans supplement B-12.


Vegetarianism is generally defined as a diet free of meat, fish, and poultry. Unlike veganism, vegetarianism includes the consumption of some animal products and by products. However, depending on dietetic needs or personal choices, vegetarians may include and/or exclude certain types of foods. Therefore, vegetarians may fall into a number of different classifications:

  • Lacto-Vegetarian: Excludes meat, eggs, seafood, and poultry but includes dairy products
  • Ovo-Vegetarian: Excludes meat, seafood, poultry, and dairy products but includes eggs
  • Lacto-Ovo Vegetarian: Excludes meat, seafood, and poultry but includes eggs and dairy products
  • Semi-Vegetarian/Flexitarian: Excludes red meat but includes chicken and fish with plant foods, dairy products, and eggs
  • Pescatarian: Excludes meat, poultry, dairy and eggs but includes fish
  • Pollotarian: Excludes meat, diary, and fish but includes poultry

Sources of Protein, Calcium, and Vitamins/Minerals in the Vegetarian Diet

Vegetarians can ensure they receive adequate nutrition by eating a varied diet. Although they do not receive protein through meat, poultry, and seafood sources, they can get plenty of protein in their diet from a variety of sources, such as:

  • Legumes
  • Lentils
  • Nuts and seeds
  • Soy products
  • Whole grain products
  • Dairy products: Vegetarians can meet their protein needs through foods such as milk, cheese, eggs, and cottage cheese.

Vegetarians can get the recommended amount of calcium and Vitamin D in their diet through the following sources:

  • Calcium-fortified juices, cereals, soy milk, and tofu
  • Dark green vegetables (turnips, collard greens, kale, and broccoli)
  • Milk/dairy foods

Sources of iron and zinc in the vegetarian diet include:

  • Dairy products (milk, yogurt)
  • Eggs
  • Fruits/dried fruits
  • Leafy green vegetables
  • Nuts and seeds

All-In Plant-Based Diets for Vegans and Vegetarians vs Generally Plant-Based Diets

A plant-based diet includes many plant foods in their whole, unprocessed form. This includes vegetables, fruits, beans, lentils, nuts, seeds, whole grains, and small amounts of healthy fats. It may also include small amounts of animal products, but people that identify as vegans and vegetarians would insist that this would never include meat.

The Mediterranean and Asian regions have long followed plant-based diets. Despite the differences in total fat, all include large amounts of fruits, legumes, vegetables, whole grains, and nuts, and smaller amounts of red meats and refined grains. It is believed that these generally plant-based diets have contributed to greater longevity and lower incidences of coronary artery disease among these populations.

According to an article in Permanente Journal, a healthy, plant-based diet aims to maximize nutrient-dense plant foods while minimizing animal foods, oils, and processed foods. Some physicians recommend allowing animal products, such as eggs and skim milk, in a plant-based diet, while others recommend completely avoiding all animal-based products.

According to the Permanente Journal article, plant-based diets are not always “all or nothing” diets, but instead are often adjusted based on an individual’s specific health needs. For example, stricter forms of plant-based diets with little or no animal products often benefit individuals with advanced coronary heart disease, while a generally plant-based diet low in sodium may be ideal for those with hypertension.