Omnivores often claim it is impossible to stay healthy on a vegetarian (or vegan) diet. This is not true in general, but still it is not completely unsubstantiated. We will first discuss misleading arguments used by “carnivores” and then similarly misleading arguments used by vegetarians. Note: because many people consider this kind of discussion controversial, this article is based on reliable large-scale human studies; you can find numbered references at the end of the article.
Carnivorous fallacy: Vegetarian nutrition cannot provide enough protein
A common misconception is that one cannot get enough protein from a vegan or vegetarian diet. However, there are good vegan sources of protein, such as legumes, tofu, seitan, tempeh, and many others. Vegetarians can furthermore eat eggs and dairy products, which are again a source of protein. Diets that include the aforementioned foods shouldn’t have a problem in reaching the recommended daily intake of about 60g of protein for an average person.
There was a concern that isoflavones in soy may cause hormonal imbalance and lead to a lower quality of sperm in men or a greater risk of breast cancer in women. However, these worries were dismissed by recent meta-analyses.
Also, even though soy is known to be a common allergen, soy allergy probably affects no more than 0.1% of the population (there are actually more people born with more than 10 fingers than there are people allergic to soybeans). In these rare cases, obtaining enough protein from a vegetarian diet may prove problematic, and the affected person must follow a carefully constructed diet. However, for the majority of us, soy can even have some beneficial effects, such as improvement of memory in aging individuals.
What is important to note is that while vegans generally consume enough protein if they consume legumes, whole grains, soy products and other protein-rich products, most omnivores in western countries consume much more protein than their body requires, and this causes unnecessary stress on kidneys and has been (at least in the case of some animal proteins) linked to a higher incidence of cancer.
Nevertheless, physically active people (such as athletes) require higher than average protein intake; if they are vegetarian, using a whey protein powder supplement is a healthy alternative (as it may actually also lower the risk of cancer), or they can use a soy protein powder if they are vegan (both can be used also for cooking as flour substitutes).
Carnivorous fallacy: Vegetarians don’t consume enough iron
Another common argument is that vegetarians cannot get enough iron, because the main source of it is meat. While it is true that meat usually contains much more iron than vegetables per unit weight, many vegetable sources contain much more iron than meat per calorie which means, strictly speaking, that a vegetarian diet often contains even more iron than that of omnivores; however, the iron form found in vegetarian diet is less bioavailable (it cannot be absorbed as well as the heme iron present in meat), so the blood iron levels in vegetarians are generally slightly lower than in omnivores.
Nevertheless, it has been shown that the incidence of iron deficiency (i.e. iron levels low enough to causes any physiological problems) is virtually the same in vegetarians and in omnivores, and, in fact, iron has been shown to be carcinogenic in larger doses, so there doesn’t seem to be any benefit from getting greater quantities than necessary from food.
Carnivorous fallacy: Dairy is important for strong bones
A common argument against veganism is that without dairy, one wouldn’t be getting enough calcium, which would lead to osteoporosis. However, studies have shown that veganism doesn’t lead to lower bone mineral density if enough calcium-rich foods (such as almonds, figs, carobs, and others) or fortified foods are consumed.
However, it has been shown that vegans who are calcium deficient have a higher risk of fractures[10'], and, of course, vegans are more likely to be calcium deficient than the general population.
Once one gets enough calcium (and the necessary level appears to be below what is generally recommended by some authorities), there seems to be no benefit from taking even more. On the contrary, the higher your calcium intake is, the more likely you will develop osteoporosis later in your life.
A possible explanation is that each cell in the human body can divide only a certain number of times. Having to process larger amounts of calcium means the cells must be replaced more often, which may cause your bone cells to age faster than the rest of your body.
Furthermore, cheese and other dairy products contain large amounts of saturated fats. This kind of fat has some detrimental effects on human health when consumed in larger quantities; most importantly, it increases the risk of cancer.
Nevertheless, it should be noted here that the label “vegetable oil” doesn’t necessarily mean “good oil”. There are two commonly used types of vegetable oils—palm oil and coconut oil—which also contain great proportion of saturated fats.
Fact: Red meat and processed meat cause cancer
Finally, there is an overwhelming amount of evidence that eating red meat and processed meat significantly increases the risk of cancer, vascular diseases and diabetes (processed meat means meat that is not sold raw, e.g. sausages, bacon, salami etc.).
For example, one meta-study from 2010, which included over 1.2 million individuals, concluded that eating just 50g of processed meat per day (which is only a fraction of what most people consume) was associated with 42% higher risk of heart disease and a 19% higher risk of type 2 diabetes.
Red meat seems to contain compounds that become carcinogenic during cooking. For example, one study found that regularly eating grilled or well done red meat increases the risk of cancer by more than 50%.
Vegetarian fallacy: Meat is inherently wrong and there is no reason to eat it
It should be noted that although meat may have many detrimental effects on human health, there are several nutrients found in meat that have also very beneficial effects.
The most important of these is vitamin B12 which must be taken as a supplement (or in fortified foods) by both vegans and vegetarians because long term B12 deficiency can lead to impaired cognitive function, and there is no reliable natural plant source of it. It can take several years before the B12 stores in the body become depleted, and this is probably the reason why some vegetarians and vegans start to feel unwell after several years on a meat-free diet, and their problems magically disappear after they start eating meat again.
Furthermore, red meat is the largest natural source of creatine and carnosine; two compounds that are not essential, but at appropriate dosages can have beneficial effects on cognition and life span. While many would argue that “you should eat meat to be smart and live long”, it is actually much healthier to avoid the detrimental effects of red meat consumption and simply take advantage of these compounds by taking them as supplements.
Vegetarian fallacy: Poultry and fish are as bad as any other meat
To end our discussion on meat consumption, there is one fact that should be noted. Poultry and fish have not been mentioned yet. There are also some risks associated with eating poultry and fish, but these are not inherent properties of the meats themselves.
About 50% of poultry meat (in the U.S.) is contaminated with dangerous bacteria, and improper cooking of meat is the most common source of bacterial gastrointestinal illnesses. The risk can be completely eliminated if the meat is cooked properly.
Sea fish are often contaminated with mercury and other toxic compounds (due to pollution in water), which in long term can lead to very serious health issues. However, the amount of contaminants depends on the species and the habitat of a particular fish, and some fish don’t contain any dangerous chemicals at all.
If the factors mentioned above are eliminated, it seems that eating unprocessed poultry and fish in small amounts is completely healthy (I am not aware of any single study linking these to any kind of disease). Note that the vitamin B12 content in fish and poultry is also quite low, so B12 supplementation for poultry-and-fish-only eaters is also advisable.