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Vegan/Vegetarian Diet Pros and Cons

For some, a vegan or vegetarian diet seems undesirable; but for those interested, is avoiding meat really that much healthier than the typical omnivorous diet? The following is a review of the negative and positive effects of vegan and vegetarian diets. First of all, to define the difference between the two, a vegetarian diet excludes meat, but may still include animal products or fish, whereas a vegan diet is primarily plant based, excluding meat, dairy, fish, eggs and all other animal products, including honey in some cases. A vegetarian diet has sub-groups, including lacto-vegetarian (including dairy but not eggs), ovo-vegetarian (including eggs but not dairy) and pesco-vegetarian (including fish but not eggs or dairy. One can also combine these, such as an ovo-pesco-vegetarian.Listed are some reasons why a vegetarian or vegan diet, if properly balanced, can be beneficial:

  • Potential decreased risk for disease: In comparison to a non-vegetarian, omnivorous diet, a vegan diet is associated with healthier atherosclerosis risk profiles and decreased occurrence and mortality from ischemic heart disease, stroke, diabetes mellitus, high blood pressure, metabolic syndrome and high cholesterol

  • Associated with increased antioxidants

  • Associated with increased self-control: In some cases, vegans and vegetarians have are more aware of what they are eating and its benefit for them and/or the environment, depending on their motive

  • Without animal products, the diet allows more room for plant-based fats, therefore less saturated fat intake and increased mono- and poly-unsaturated fat intake

  • Associated with decreased sodium intake

  • Associated with consumption of fewer calories

  • Associated with higher fiber intake

  • Associated with healthier intestinal microbial profiles (gut flora)

If properly balanced, vegetarian and vegan diets can result in lower body mass index, lower blood pressure and decreased risks for arteriosclerosis, coronary heart disease, type 2 diabetes, poor intestinal microbiota and metabolic syndrome. However, if not balanced, vegan and vegetarian diets may prompt risks for vitamin B-12, iron and calcium deficiencies, though a vitamin B-12 supplement and a good knowledge of vegan food combinations for proper nutrients is more advantageous than copious prescription drugs for illnesses associated with common dietary habits. In a study comparing a vegan, vegetarian, semi-vegetarian, pesco-vegetarian (vegetarians who consume fish) and omnivorous diets, vegan diets contained the fewest calories, better fat intake profiles, the lowest protein intake and the highest dietary fiber intake. The omnivorous diet was rated lowest and the vegan diet was rated highest for the Healthy Eating Index 2010 values and the Mediterranean Diet Score, partly because of its high fruit and vegetable intake, low sodium and low saturated fat intakes. It should be noted that the omnivore diets observed in this study may not have included diets of those who were concerned with eating healthy, as many of those adhering to vegetarian and vegan diets are.

Intestinal Health

Intestinal microbial profiles analyze the gut, or gastrointestinal, microbiota (also known as gut flora), which is the community of microorganisms that live in our digestive tracts. These microorganisms are necessary for digestion and immunity, but they can include good and bad bacteria. While good bacteria improve digestion, immunity and the manufacturing of vitamins, bad bacteria can result in mental, skin and digestive issues, among other problems. In analysis of intestinal microbial profiles, vegans had less pathobionts, organisms associated with chronic inflammatory conditions, and more protective organisms than omnivores. Also, vegans had less of the intestinal microbiota that converts dietary L-carnitine, found in red meat, to proatherosclerotic TMAO, which is associated with increased risk for cardiovascular issues. So, the intestinal microbial profiles among vegans, as well as many vegetarians, contribute toward less inflammation than those consuming omnivorous diets, indicating more good intestinal bacteria.

Protein/Deficiency Concerns

Whether or not a vegan diet can provide sufficient protein is a common and valid concern when adhering to a vegan diet. Amino acids are the organic compounds of which proteins are made. Of the 20 amino acids that can make protein, our bodies produce all but nine of them. So, these nine amino acids, known as essential amino acids, must be consumed. Essential amino acids include leucine, isoleucine, valine, lysine, threonine, tryptophan, methionine, phenylalanine, and histidine. Foods considered to be complete protein sources are those that contain the nine essential amino acids in near equal amounts. If not eating eggs, soy, dairy or other food with complete proteins, one needs to learn which complementary foods must be eaten together to get them. Protein is often a big concern among athletes. For physically active individuals, obtaining sufficient protein, iron and creatinine to perform at high intensities, maintain proper hormone levels and maintain muscle growth may pose a challenge when adhering to a vegan diet. For athletes and women, it may be advisable to add eggs and/or salmon to ensure they absorb sufficient iron, protein and amino acids. Often, those consuming a vegan diet may have to increase their plant-based protein consumption, because plant-based sources are not as bioavailable (easily absorbed by our bodies for use) as animal protein sources. However, laboratory and field studies have provided sufficient evidence supporting that a well-planned vegan diet can meet the recommended dietary needs for competitive athletes.

In addition to adequate protein, other concerns when consuming a vegan or vegetarian diet include:

  • Hyperhomocysteinemia: a high homocysteine (amino acid found in blood plasma) level that could contribute to blood clots or arterial damage

  • Anaemia: low red blood cells (hemoglobin)

  • Insufficient creatine in muscle

  • Menstrual disruption, especially among physically active women

  • Increased risk for low bone density (osteopenia) or osteoporosis

  • Plant-based protein sources are less bioavailable (easy to absorb) that animal protein sources

  • Plant-based protein sources, except for soy, do not contain complete proteins

  • Regular soy intake is associated with decreased sperm production in men and decreased fertility in women

Though an ovo-lactovegetarian diet is associated with several benefits, a strict vegan diet raises concern for B-12, iron and calcium deficiency. Vitamin B-12 deficiency is common among vegans who do not consume dairy and/or egg products. Though vitamin B-12 deficiency may be alleviated partly by consuming dairy and eggs, it is still prevalent among lact-ovo-vegetarians as well. Vitamin B-12 deficiency is associated with increased risk for impaired arterial endothelial function, neurological disorders (including brain degeneration), pernicious anemia (large, oval-shaped red blood cells and fatigue. Early predictors of vitamin B-12 deficiency include unusual fatigue and digestive problems. This being said, it is important vegans and vegetarians carefully monitor their vitamin B-12 profiles. Sufficient iron and calcium is another concern among vegans. Because of insufficient calcium intake, vegans have a higher risk for bone fractures than omnivores, pesco-vegetarians and vegetarians, except for vegans averaging 525 mg of calcium per day. As far as iron intake, sufficient dietary iron does not necessarily indicate sufficiency among vegans, because plant-based iron is less bioavailable (easy to absorb). These deficiencies can be avoided with adequate supplementation and a well-balanced vegan diet; but consider that supplements are also less bioavailable (easy to absorb) than food sources.


If considering or already eating a vegetarian or vegan diet, checking with one’s doctor is advised, including regular blood work to check for deficiencies. If beginning a vegetarian or vegan diet, allow time to adjust and realize complete protein sources, like eggs and dairy, may be needed. Ensure the diet includes enough plant protein, vitamin B12 and eat iron-rich plant sources with foods high in vitamin C, to increase iron absorption. Because a good vegan diet includes more fiber than most diets, it important to stay hydrated, as soluble fiber needs water to move through body systems properly and insoluble fiber retains a lot of water from the intestines. Anyone attempting a vegan or vegetarian diet should be aware of the risks for vitamin deficiencies and probable need for more calories to ensure absorbency of adequate nutrients. Many people do not regulate their dietary needs, whether adhering to a vegan, vegetarian or omnivorous diet, in which case consequences exists for all of them; however an omnivore diet poses less threat for deficiencies, because it includes all the major food groups. Any diet excluding one or more of the major food groups, fruits, vegetables, grains, dairy and protein foods, is at increased risk for deficiencies and associated health problems.


Brown, J. E. (2017). Nutrition Through the Lifecycle. Boston, MA: Cengage Learning.

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