Vegan Diets


Examples:  Raw Food Diet, Neal Barnard, T Colin Campbell, John McDougall, Caldwell Esselstyn.  Among the reasons one might choose to become a vegan, is the belief that a diet free of animal foods is best for the body. Take a closer look at the health effects of this way of eating.

STRATEGY:   Elimination of all animal foods, including dairy products, eggs, gelatin, and honey.

FOODS:         All foods except animal foods are allowed.


Lower cholesterol levels
Lower IGF-1 levels (see below)
Lower body weight
People with dairy, egg, or specific meat/seafood sensitivities will feel better on a vegan diet.


Vitamin B6 deficiency
Vitamin B12 deficiency
Iron and other mineral deficiencies
Omega-3 fatty acid deficiency


Watch my 20-minute video presentation entitled “Little Shop of Horrors: The Risks and Benefits of Eating Vegetables” given at the 2012 Ancestral Health Symposium at Harvard University.

Approximately 1% of Americans report eating a vegan diet, and the popularity of this diet is rising. A vegan diet is very different from a lacto-ovo-vegetarian diet in that it contains no animal foods of any kind. While we know from thousands of years of recorded history that people can thrive for many decades eating anything from a lacto-ovo-vegetarian diet to a nearly 100% carnivorous diet, I am not aware of any examples in human history of a culture which has subsisted on a vegan diet from childhood through death.

Are vegan diets healthier?

Vegan diets, like all diets, can vary widely in quality, depending on food choices. However, it is certainly more challenging to eat junk food as a vegan, because so many junk foods contains dairy, egg, gelatin, or other ingredients that are derived from animals. For example, most fast food, many candies, and most commercially available brands of white bread are not suitable for vegans.

A vegan whose diet is based on whole foods and is careful to get enough protein, vitamins, minerals, and omega-3 fatty acids, is eating a much healthier diet than an omnivore who eats junk food all day long and doesn’t pay attention to the composition of his or her diet.  However, just because a particular food contains no meat, dairy, or eggs, doesn’t necessarily mean that it is healthy. Vegan-friendly candies, cakes, cookies, chips, and ice cream substitutes, are available, which are loaded with refined carbohydrates and are very poor in nutritional value. Some varieties of these types of foods may be high in artificial ingredients, as well.

In order to understand whether vegan diets are healthier than diets that contain animal foods, we would need to compare 100% plant food diets to similar diets containing animal foods. Ideally, both diets would contain roughly the same amount of calories, fat, protein and carbohydrate, so that the main difference between the two diets would be the presence or absence of animal foods.  Ideally, both groups of people would have similar lifestyles with respect to things like smoking and exercise.  Unfortunately, I am not aware of any studies of vegan diets which have been designed that way. Studies of vegan diets suffer from the same confusing limitations that studies of most diets do:

1) Most studies have been epidemiological studies, and therefore cannot prove that the reason why vegan diets are healthier is because they are free of animal foods;

2) Vegans, as a group, in most studies, not only avoid animal foods; they also tend to drink less alcohol, eat fewer calories, eat less fat, eat more fiber, and weigh less than omnivores. Most studies do not properly control for these variables. Therefore, while vegans appear healthier in some respects than omnivores, it may or may not be due to their avoidance of animal foods.

3) Epidemiological studies of vegans have not taken refined carbohydrate consumption into consideration as a potential risk factor for disease, therefore we do not know if vegans eat less refined carbohydrate than other people do.

4) The clinical trials (experiments) that have been conducted comparing the health effects of a plant-based diet to an omnivorous diet not only removed animal foods from the diet; they also removed most fat and refined carbohydrate, as well, comparing a low-fat, low-refined-carbohydrate vegan diet to an omnivore diet higher in fat and refined carbohydrate. Therefore there is no way to know whether the vegan study groups improved because they avoided animal foods, ate less fat, or ate less refined carbohydrate.

Can vegan diets help with weight loss?

Clinical studies have shown that vegan diets containing the same number of calories as meat-based diets do not lead to more weight loss, therefore simply avoiding meat, if you are eating the same number of calories as an omnivore, is unlikely to help you lose weight..

However, many epidemiological studies of vegans do find that they tend to weigh less than the general population.   We can only speculate about why this is.  Studies of vegans find that they tend to, on average, eat  more fiber, less saturated fat, and fewer calories than omnivores.  Whether any of these differences is responsible for the observation that vegans tend to weigh less than others is unknown.  Other possibilities that have not been explored in research studies include:

  • differences in refined carbohydrate intake
  • differences in whole food vs. processed/junk food intake
  • differences in exercise habits and alcohol intake

Do vegan diets improve cholesterol levels?

On the whole, studies suggest that vegan diets can lower cholesterol levels by between 10 and 35 percent.

Since cholesterol comes only from animal foods, vegan diets are, by definition, cholesterol-free. Even though cholesterol is a vital component of every human cell, vegans do not need to worry about not getting enough cholesterol, because the body can make all the cholesterol it needs from non-animal foods. In fact, it is even possible for strict vegans to to develop high cholesterol levels, because cholesterol is primarily created in the liver, not absorbed from the diet (see cholesterol).

There are numerous epidemiological studies demonstrating that vegans tend to have lower total cholesterol levels and lower LDL (so-called “bad cholesterol”) levels. However, they also tend to have lower HDL (so-called “good cholesterol”) levels. In epidemiological studies it is impossible to be certain that levels were lower because of vegan diet, as opposed to some other lifestyle difference, however, the trend is very clear.

There have also been a number of human clinical trials that show a vegan diet can lower cholesterol levels, unfortunately most of them were designed in such a way that factors other than animal food avoidance (avoidance of refined carbohydrate, or reduction in fat, for example) could have been responsible for the reduction.

Do vegan diets treat or prevent heart disease?

Vegans tend to eat more fiber, have lower LDL cholesterol levels, and weigh less than omnivores, and these factors are all associated with lower risk for heart disease. However, vegans also tend to have lower HDL cholesterol levels, higher levels of homocysteine, and may have higher triglyceride levels in some cases, and these are all associated with higher risk for heart disease. While numerous studies find that vegetarians are at lower risk for heart disease than the general population, there is no data I am aware of that answers the question of whether vegans are at lower or higher risk than the general population.

Former President Clinton credits the nutritional advice of Professor T Colin Campbell for his successful weight loss and improved heart health. Prof Campbell is a very well known proponent of a vegan diet. As is the case with other plant-based diet advocates, Professor Campbell does not simply recommend the elimination of animal foods; he also recommends limiting fat to 10% of calories, avoiding all processed foods, and avoiding refined carbohydrates. Therefore, it is impossible to know whether the potential health benefits of his approach are due to the lack of animal foods, the lack of refined carbohydrates, the lack of processed foods, and/or the reduction in fat.

Do vegan diets improve blood sugar control?

Blood sugar control is primarily about dietary carbohydrate, not about meat, so if a vegan eats a diet low in refined and high glycemic index carbohydrate, or eats a low carbohydrate diet, his or her blood sugar control will improve.

Dr. Neal Barnard has authored numerous scientific articles about the benefits of low-fat, plant-based diets for controlling diabetes or for losing weight. In a study published in 2009, he compared diabetics eating a low-fat vegan diet to patients eating the standard diet recommended by the American Diabetes Association (ADA). The vegan group lost the same amount of weight as the ADA diet group did, but the vegan group had lower cholesterol and lower blood sugar values. However, the vegan group was also told to “favor low glycemic index foods”. Therefore, it is impossible to know whether the potential benefits of his diet were due to the fact that it was low-fat, that it was vegan, or that it had a low glycemic index.

Do vegan diets treat or prevent cancer?

The quality of evidence is generally poor on this topic. In practice, it would be very difficult to design a human experiment that could answer this question. The majority of epidemiological studies find no difference in cancer rates between vegans and omnivores.  However, vegans do tend to have lower levels of IGF-1, a growth hormone that is associated with cancer. The two dietary factors most closely linked to IGF-1 levels are dairy products and refined carbohydrates. Since vegans do not eat dairy products, (and may also eat less refined carbohydrate?), the fact that vegans enrolled in these studies tend to have lower levels of this growth factor makes sense.

Do vegan diets improve digestive health?

Constipation and the general health of the digestive tract are primarily about digestibility. When foods are easily broken down and absorbed, they tend not to cause constipation. Dairy products, and all plant foods except for fruits, are somewhat difficult to digest and absorb, whereas meat and fat are relatively easy to digest and absorb. Since vegan diets are based on plant foods, and since most omnivores also eat lots of plant foods, digestive issues can be problematic for both groups. In my clinical experience I have worked with vegetarian and vegan patients who have severe constipation as well as with meat-eaters who have severe constipation. However, some people do notice that they have less trouble with constipation if they eat a high-fiber diet. Fiber does not necessarily help with constipation (see: fiber) —it depends on your individual chemistry and on what else you are eating. Vegan diets may or may not be higher in fiber than meat-based diets—it depends on food choices.

Do vegans live longer?

All we have are epidemiological observations to attempt to answer this question, but these do not show any difference in mortality between vegans and omnivores.

Do vegans get enough protein?

Protein deficiency is actually uncommon, and is easily avoided by counting protein grams. We used to think that vegans had to eat special combinations of plant foods at every meal to make sure they were getting all nine essential amino acids their bodies needed. We now know that the body can hold on to amino acids for several hours, so, as long as vegans are getting all nine essential amino acids in their diet at some point every day, they don’t have to worry about eating them simultaneously at every meal.  However, vegans must be careful to eat a variety of plant protein sources in order to obtain all necessary amino acids.  If rice, corn, wheat, or cassava is the SOLE source of dietary protein, essential amino acid requirements will not be satisfied.

Some sources indicate that vegans may require 25% more protein per day than vegetarians and carnivores, because plant proteins are more difficult to digest and absorb than animal proteins.

There is concern that vegans may not get enough sulfur in their diet due to lower levels of certain amino acids which provide sulfur to the body. Sulfur is necessary for a variety of important cellular functions, including antioxidant activity and vitamin function. However, there are plant foods that are high in sulfur, including the cruciferous vegetables and vegetables in the onion/garlic family; therefore, eating more of these (if you can tolerate them) may be helpful.

Vitamin deficiencies in vegans

Vitamin B12 is only found in animal foods, therefore B12 deficiency may occur, and is more common in vegans than vegetarians. Potential consequences of B12 deficiency include anemia, fatigue, difficulty concentrating, and depression. B12 deficiency is easily remedied with supplements.

The form of Vitamin B6 that is found in most plant foods (pyridoxine) is less bioavailable than the forms found in animal foods, therefore vegans may have lower than normal levels of B6.  Severe deficiencies are uncommon, but symptoms of significant B6 deficiency include mouth ulcers and neurological symptoms, including irritability and depression. Unfortunately standard B6 supplements are also in the pyridoxine form, so it probably makes more sense to simply increase the amount of B6-rich plant foods, such as bananas and spinach.

Vitamin D deficiency is more common in vegans than vegetarians, because the only other dietary source of Vitamin D other than sunlight exposure is animal foods. Vitamin D is available in supplement form. Potential consequences of vitamin D deficiency include rickets (soft bones) and muscle weakness.

Mineral deficiencies in vegans

Deficiencies of minerals occur more often in vegans.

Plant foods are naturally high in “anti-nutrients”, like cellulose, phytates and tannins that interfere with the absorption of minerals. Iron, zinc and calcium deficiencies are most common. Omnivores who eat lots of plant foods are also at risk for these deficiencies.

Iron deficiency is best known for causing mild anemia and fatigue, but iron is also required for proper function of the brain, and deficiency can cause memory and other cognitive problems, particularly in the very young.

Iron deficiency is common in vegans; probably because plant sources of iron are harder to absorb.  Vegetable iron (or “non-heme” iron), is 8 times less available to the body than “heme” iron, the form of iron found in meat.  Heme iron is available in supplement form, but it comes from animal sources.

Taking iron supplements to correct the deficiency is not always as helpful as we wish it were.  Traditional (non-heme) iron supplements are just as hard to absorb as plant food sources of iron, and in addition, can be irritating to the gastrointestinal tract (constipation is a common side effect). If you do take non-heme iron supplements, you may experience few gastrointestinal side effects if you take them less often.  You actually only need to take them 2-3 times per week, because intestinal cells can only absorb so much before they become saturated with iron and stop taking any more in. Avoid taking calcium supplements with iron supplements because calcium interferes with iron absorption.  Taking vitamin C supplements can improve iron absorption from supplements as well as from plant foods.

Zinc deficiency can increase susceptibility to infection and skin problems.  If you need supplemental zinc, use small doses, as zinc cannot only cause nausea, it can also cause copper deficiency.

Vegans also seem to be at higher risk for bone fractures than vegetarians and omnivores, perhaps because their intake of bioavailable protein, Vitamin D and calcium is lower than in others.  If you need supplemental calcium, choose calcium citrate over other forms, as it is easier to absorb.

How do vegans get omega-3 fatty acids?

Most fats that are naturally found in plant foods tend to be very high in omega-6 fatty acids and are essentially devoid of omega-3 fatty acids.  This can lead to an unhealthy imbalance in the omega-3 to omega-6 ratio.

To lower omega-6 levels, it may be helpful for vegans to emphasize fats from coconut (only about 2% of the fat in coconut is omega-6), and olive oil (about 10% omega-6) and limit oils from seeds, nuts, legumes, and grains, which tend to be high in omega-6 (usually 50% or higher).

Essential omega-3 fatty acid levels can be low in vegans. Of the three essential omega-3 polyunsaturated fatty acids—ALA, DHA, and EPA, only ALA is found in traditional plant foods, such a flaxseed and walnuts. Unfortunately, only a very small amount of ALA (about 5%) can be converted to DHA, so dietary deficiencies of DHA can occur. Omega-3 fatty acid supplements are now available from (vegan) microalgae sources. The health consequences of low omega-3 fatty acid status are poorly understood.


While many vegans tend to weigh less and have lower cholesterol levels (including lower levels of HDL, the so-called “good cholesterol”) than others, it is unclear if these trends are due to the lack of animal foods in their diet or due to other lifestyle factors, such as lower fat intake, lower caloric intake, lower protein intake, and/or lower intake of processed foods.

A vegan diet must be very carefully planned to avoid vital nutrient deficiencies.

Vegans are at significantly higher risk for a variety of vitamin deficiencies, including vitamins B6, B12, and D, therefore supplementation may be necessary.

Vegans are at higher risk for mineral deficiencies, including iron, calcium, and zinc, therefore supplementation may be necessary.

Vegans are at higher risk for omega-3 fatty acid deficiencies, therefore supplementation may be necessary.

To read a complete, detailed article about how vegan diets affect the brain and mental health, including a full description of all potential deficiencies, please see my post Your Brain On Plants: Micronutrients and Mental Health.

To read about other popular diets, visit the Diets page.

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Last Modified: Jan 5, 2018