Health Benefits and Nutritional Risks of Vegan Diets
While some people choose a vegan diet for religious or environmental reasons, others make this choice to improve their health. But is a vegan diet healthy?
Did you know that to compensate for lower iron absorption, the RDA for iron for vegetarians, including vegans, is 1.8 times higher than for those who eat meat.
The number of Americans eating a vegan diet has increased by over 500% in recent years; most surveys estimate that about 4% to 6% of the U.S. population identifies as vegan.  This dietary pattern excludes all animal products, including meat, fish, poultry, eggs, and dairy products such as milk, butter, and cheese; some vegans even exclude honey because it is made by bees. A vegan diet includes only foods of plant origin such as grains, vegetables, legumes, fruits, nuts, seeds, and plant oils. While some people choose a vegan diet for religious or environmental reasons, others make this choice to improve their health. But is a vegan diet healthy? Can this dietary pattern meet all your nutrient needs, or will it put you at risk of nutrient deficiencies?
Vegan dietary patterns offer an impressive list of health benefits. They are associated with a lower body mass index and hence a reduced risk of obesity when compared with diets that include animal products. Vegans have lower total serum cholesterol, LDL cholesterol, glucose, blood pressure, and levels of chronic inflammation compared with omnivores. These parameters are associated with a lower incidence of chronic diseases including cardiovascular disease (CVD), diabetes, hypertension, and certain types of cancer. [2,3] The health benefits of vegan diets are believed to be related to the nutrients and other dietary components that are plentiful in this dietary pattern as well as to those that are limited.
The most obvious difference between a vegan diet and a standard North American diet is the exclusion of meat and dairy. These foods are the only source of cholesterol and provide most of the saturated fat in the American diet. Cholesterol and saturated fat have long been tied to an increased risk of CVD.  Diets high in meat, particularly red meat, are associated with an increased risk of colon cancer. Recent evidence also suggests that there is an association between red meat intake and the development of type 2 diabetes.
Vegan diets are high in whole grains, legumes, nuts, vegetables, and fruits, making them high in fiber. Diets high in fiber have been shown to reduce the risk of colon cancer and other diseases of the digestive system. Fiber is believed to act by diluting the colon contents and speeding transit through the gut, both of which reduce the amount of contact between the colon epithelium and potentially cancer-causing substances in the feces. When fluid intake is adequate, diets high in fiber increase fecal bulk and lessen the pressure needed for defecation, reducing the risk of constipation, hemorrhoids, and diverticulosis. Fiber in the colon also causes changes in the intestinal microbiota that protect against the development of colon cancer and inflammatory bowel disease.
Diets high in fiber are also associated with a reduced risk of obesity and type 2 diabetes. This connection is related to differences in the caloric density of vegan compared with omnivorous diets and the effect of these diets on insulin sensitivity and the gut microbiome.  Vegan diets based on minimally-processed plant foods are high in water and fiber, which add volume to the diet, but few calories, lowering caloric density. Since people tend to consume the same volume of food at meals vegans feel full after consuming fewer calories than meat eaters. Vegan dietary patterns improve insulin sensitivity; increased insulin sensitivity reduces the risk of weight gain and the development of type 2 diabetes. The gut microbiome, which is affected by diet composition, influences energy balance; the predominant bacteria in the microbiome of vegans reduces the risk of weight gain by reducing both appetite and nutrient absorption.
The prevalence of fruits, vegetables, legumes, grains, and nuts makes vegan diets higher than omnivorous diets in antioxidants. This includes the antioxidant vitamins A (in the β-carotene form), C, and E, as well as phytochemicals that act as antioxidants. A higher intake of dietary antioxidants has been associated with a reduced incidence of diseases related to oxidative stress, including CVD, cancer, and diabetes.
Despite the positive health associations of eating a vegan diet, this dietary pattern doesn’t guarantee good health. Compared to omnivorous diets, vegan diets are associated with lower intakes of protein, long chain omega-3 fatty acids, vitamin B12, and several other vitamins and minerals. Protein intake is lower in vegan diets because plant foods are typically less concentrated sources of protein than animal products. In addition, the amino acid composition of animal proteins is a better match to that of human proteins than are plant proteins, so more plant protein is needed to meet protein needs. Nonetheless, adequate protein is rarely a problem in vegan diets that contain a variety of protein sources, such as legumes, grains, nuts, and seeds. The amino acids provided by legume proteins complement those in grain, nut, and seed proteins, hence providing a complete mix of the amino acids needed by the human body.
Intake of the long-chain omega-3 fatty acids DHA and EPA is low in most vegan diets because the primary source of these is fish. DHA and EPA have a number of regulatory roles that help protect against inflammatory and other chronic diseases. They can be synthesized in the body from the essential omega-3 fatty acid, α-linolenic acid, as long as intake of this fatty acid, found in foods such as canola oil, walnuts, and flaxseed, is adequate.
Vitamin B12 deficiency is a particular concern in vegan diets. This vitamin is not synthesized by plants or animals. It accumulates in the meat and milk of ruminants through a symbiotic relationship with the bacteria in ruminant stomachs, and in fish and shellfish who acquire it from plankton and pass it up the food chain. To get adequate vitamin B12, vegans need to take supplements or consume products fortified with this vitamin such as plant-based milks, breakfast cereals, and nutritional yeast.
Low intakes of calcium and vitamin D, which are needed for bone health, are a risk for vegans because they do not consume dairy products, the primary source of these nutrients in the North American diet. In one study vegans had a 30% greater risk of bone fracture than meat eaters, but this difference disappeared in vegans who consumed the recommended amounts of calcium.  Good vegan sources of calcium include high-calcium vegetables such as broccoli, kale, and Bok choy, as well as legumes and tofu processed with calcium. Calcium and vitamin D can also be found in fortified plant-based milks and breakfast cereals, and vitamin D can be synthesized in the skin with exposure to sunlight.
Although the amount of iron in vegan diets is comparable to or higher than that in diets containing animal products, vegans are more likely to have reduced iron stores than nonvegetarians.  This is likely because the absorption of iron from plant foods, such as leafy green vegetables and whole and enriched grains, is much lower than it is from meat. To compensate for lower iron absorption, the RDA for iron for vegetarians, including vegans, is 1.8 times higher than for those who eat meat. Zinc is lower in vegan than in omnivorous diets and, as with iron, the forms found in plant foods such as whole grains, wheat germ, legumes, and nuts, are less absorbable than those found in meat. Iodine is a nutrient of concern if iodized salt is not used because fish and dairy products, which are the primary sources of dietary iodine, are omitted from vegan diets.
Despite the potential risk for nutrient deficiencies, the Academy of Nutrition and Dietetics has determined that vegan diets can meet the nutritional needs of people of all ages and at all stages of the lifecycle, from infancy to late adulthood and during pregnancy and lactation.  The Academy recognizes that vegan diets can provide significant health benefits but suggest that to meet all nutrient needs these diets must be carefully planned. Simply taking animal products off your plate can result in a boring meal plan that does not provide enough of all the essential nutrients. But choosing a diet that relies heavily on highly processed vegan foods can exceed recommendations for added sugar, salt, and calories. For more information making healthy vegan choices see “How to Plan a Healthy Vegan Diet”.
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