One of my first assignments as a nutritional-therapy student was to compare the advantages of a vegan diet over those of an animal-based diet. While some of the lecturers made very compelling arguments in favor of meat, I, having personally become a vegan for health reasons, was determined to fight my corner and dig up as much scientific evidence as I could.
Although there is so much more left to say, here is a condensed version of what I found:
Protein
Protein comes from the Greek word “proteios,” meaning “of prime importance,” and since the 19th century has become interchangeable with animal-based products. This has led to a confused belief that protein is meat.
Protein is essential for building amino acids in the body, which are needed to make enzymes and hormones, as well as assist tissue repair and growth. While some amino acids can be made in the body, nine are required from the diet. A complete, high quality protein contains all nine, whereas an incomplete protein only contains a few. Most complete proteins are found in animal sources and incomplete typically in plants. However, if different plant proteins are combined, the amino acids complement each other and make a complete protein, a process called mutual supplementation.
Therefore, if a vegan diet is balanced, amino acids won’t be a problem.
Additionally, studies have shown that very high protein diets actually have adverse effects on health, as protein alters how carcinogens are detoxified in the liver.
Fat
Another macronutrient that differs across plant and omnivore diets is fat. Early research has shown that saturated fat results in high blood cholesterol, potentially leading to cardiovascular disease. In general, meat-eaters obtain a higher proportion of energy from saturated fat than vegans, with meat products contributing to 22% of saturated fat intake, compared to the 5–8% of saturates that vegans consume.
On the other hand, animal-based diets contain omega-3 and 6, which are important in perceptual, sensory, motor, and cognitive systems; have protective properties for cardiovascular health; and are involved in behavior management and mood control. 
Although the vegan diet can provide omega-6, levels of omega-3 are generally lower due to lack of fish oils. Again, with careful planning, plant-based eaters can obtain omega-3 from certain sources such as chia seeds, walnuts, and flax seeds.
Vegans on average also have lower cholesterol, blood pressure, and lower BMI’s, which may protect against heart disease and high blood lipids, as well as a reduction in obesity risk.
Carbohydrates
Carbohydrates are another macronutrient important in achieving optimal health. It’s suggested that carbohydrates should make up a third of the daily intake of food, with these being complex and unrefined. Compared with meat-based diets, vegans on average have a higher intake of carbohydrates, and fiber is especially high. Dietary fiber reduces the risk of developing a range of diseases including heart disease, stroke, obesity, gastrointestinal disorders, and bowel cancers.
A big argument against eating grains and legumes however, is the “anti-nutrient” content. Grains and legumes contain phytates, tannin, oxalate, and polyphenols, and can affect the absorption of other nutrients. For example, tannins inhibit protein digestibility and phytates reduce the absorption of minerals, which suggests a big disadvantage for a purely plant-based diet. However, studies have shown that preparation and cooking methods can alter this completely. Protein digestibility is improved by up to 93% from boiling and 105% using a pressure cooker in five different legumes studied; thermal processing improves absorption of thaimin, niacin, carotenoids, vitamin B6, and folate; pounding of cereals enhances zinc, iron, and calcium absorption; soaking reduces phytate content of grains by 50% and fermentation reduced this further to 90%, as well as improving vitamin B content and protein digestibility and quality. So while the vegan diet can contain a large portion of anti-nutrients, cooking methods can change this significantly.
Also, while some studies have shown that vegans may have lower intakes of certain minerals such as zinc, blood plasma measurements don’t differ in comparison to meat eaters. It’s therefore thought that compensatory mechanisms occur with a long-term vegan diet. So while mineral intake may be lower in comparison to an animal-based diet, the body can adapt to ensure optimal health is still achieved.
Micronutrients (vitamins and minerals)
Looking at micronutrients, meat and animal products are a good source of iron, vitamin A, vitamin B12, vitamin D, and calcium, which is postulated to be lacking in the vegan diet.
Vitamin A
Vitamin A is essential for the development and growth of tissues, vision, and healthy skin, and is found in two different forms: the first is retinol (found from animal sources) and the second is beta-carotene (found in orange and yellow vegetables and fruits). While the vegan diet is lower in retinol, it is compensated for by the higher carotenoids.
Vitamin B12
Vitamin B12 is not generally found in plant foods, and so fortified foods or dietary supplements are the main source (it is yet to be established whether tempeh and seaweed contain vitamin B12). Studies have shown that blood plasma concentrations and intake of B12 is higher in meat eaters than vegans, and in some vegans, deficiency has been reported. Vitamin B12 deficiency can lead to psychiatric and neurological symptoms including psychosis, mood and motor disturbances, dementia, and difficulty concentrating. Therefore supplementation may be necessary here. Interestingly it is thought that years ago this would not have been a problem, as the soil contained many more nutrients and beneficial bacteria than there are today.
Vitamin D and Calcium
Another vitamin that vegans may be at a disadvantage with is vitamin D, with vegans showing the lowest intake across various diets. Vitamin D is required for calcium absorption and bone health, and while it can easily be obtained through the skin via the sun in 15–20 minutes, it is also found in animal and fortified foods. Vitamin D also works in conjunction with calcium, in which vegans also have a lower intake of.
However, although there may be a vitamin D deficiency in vegans, in a prospective study, bone loss or incidence of fractures did not differ from non-vegans, and although calcium was lower, there was no difference in bone mineral density either. Additionally, magnesium, potassium, and vitamin K are involved in bone health, in which vegan diets provide adequate amounts. A plant-based diet is also generally more alkaline, which may have protective effects especially in bone health, in comparison to a meat-based diet, which can create a more acid ash in the body, in turn resulting in calcium being excreted. Therefore, while on the surface calcium and vitamin D intake may appear lower in a plant-based diet, there does not appear to be any adverse consequences.
Iron
One of the main nutrients that seems more advantageously found in an animal-based diet is iron. The absorption is higher in animal sources as it’s in the form of heme, in comparison to the non-heme form in plant-based sources. However, while an animal-based diet may seem to be at an advantage, an excess of heme can actually cause problems, with a risk of high iron intake leading to heart disease and some cancers.
Larger scale studies
While the above highlights advantages and disadvantages of certain nutrients across both diets, studies looking at certain nutrition-related diseases are of interest.
The China Study was one example of a longitudinal study in which illnesses like heart disease, diabetes, autoimmune diseases, and some cancers significantly correlated with the intake of animal protein and showed that plant-based diets could reverse some of the effects.
Studies looking at seventh-day Adventists who mostly follow a vegetarian diet also show a 50% lower risk of developing certain types of cancers, strokes, diabetes, and heart disease. One study in particular demonstrated that on average, males within this group lived 7.3 extra years and females lived an extra 4.4 years in comparison to other people living in the same region.
To conclude…
In conclusion, there are definitely health benefits and disadvantages to each diet in terms of specific nutrients, with adaptations taking place in the body to compensate for some potential problems, particularly in the vegan diet. Large-scale studies also demonstrate protection against a range of diseases when consuming plant-based diets, which is why I particularly removed meat and dairy from my life.
Interestingly for me, I was happily able to dispel myths about why my way of eating would lead me to deficiencies and ill- health, and I now feel confident that science can back me up.
I personally supplement B12, but other than that, soaking grains and legumes, consuming large amounts of leafy greens, and including my vegan sources of omega-3 sets me up to combat any problems.
