Nutrient deficiencies

Critics of a purely plant-based diet argue that certain essential and physiologically important nutrients occur exclusively or predominantly in animal products.

Particular emphasis is placed on Vitamin B12, which is not present in significant amounts in unprocessed plant foods.

In addition, other vitamins are mentioned that allegedly occur only in animal foods in their active or natural form, including Vitamin D3 (cholecalciferol), Retinol (active form of Vitamin A), Riboflavin (Vitamin B2), and Pyridoxine (Vitamin B6).

Various minerals and trace elements are also said to be obtained primarily from animal products, particularly heme iron, zinc, iodine, selenium, and calcium.

In the area of protein, it is often argued that plant foods do not provide complete proteins because they allegedly do not contain all essential amino acids in sufficient quantities. Among those mentioned are lysine, methionine, tryptophan, leucine, isoleucine, valine, threonine, phenylalanine, and histidine.

Furthermore, long-chain omega-3 fatty acids such as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are considered almost exclusively animal-derived nutrients, primarily found in fatty fish.

In addition, various other substances are cited which, although not classified as essential, are said to play important physiological roles and to occur mainly in animal products. These include creatine, carnitine, carnosine, taurine, choline, coenzyme Q10, alpha-lipoic acid, creatinine, and conjugated linoleic acid (CLA).

From this wide range of supposedly non-plant-based nutrients, it is concluded that a vegan diet is structurally incomplete and cannot adequately meet human nutritional requirements. Animal products are therefore presented as a natural, evolutionarily established, and complete source of nutrients, whereas a purely plant-based diet is said to exhibit systematic deficiencies.

The argument lists a number of substances that are allegedly absent from plant-based foods. It is helpful to make a clear distinction here: some nutrients are essential, others are precursors, and still others are synthesized by the body and are therefore not essential. This argument deliberately does not address the issue of bioavailability (that is treated separately).

Vitamin B12 is important for blood formation, the nervous system, and cell division. In practice, it is the only nutrient that cannot be reliably covered on a vegan diet without fortified foods or supplements. Vegan supply is ensured through B12 supplements (e.g., cyanocobalamin or methylcobalamin) or fortified products such as plant milks and breakfast cereals. It should also be noted that animal products are rich in B12 largely because farm animals themselves receive supplements or fortified feed.

Vitamin D3 (cholecalciferol) is important for bone metabolism, immune function, and muscle health. Strictly speaking, it is not a purely dietary nutrient, as the body can synthesize vitamin D through sunlight exposure. In practice, adequate supply is often an issue regardless of dietary pattern. A vegan supply is possible through sun exposure, vegan vitamin D supplements (D3 from lichen or D2), and in some cases fortified foods. Vitamin D deficiency is not exclusively a vegan issue.

Retinol (active form of Vitamin A) is important for vision, immune function, and skin health. Retinol itself occurs in animal foods, but plant foods provide precursors (carotenoids) from which the body produces vitamin A. Vegan sources include carrots, sweet potatoes, pumpkin, spinach, kale, and red bell peppers.

Riboflavin (Vitamin B2) supports energy metabolism and cellular protection. It is essential and also found in plant foods. Good vegan sources include almonds, mushrooms, oats, whole grains, legumes, and fortified plant milks.

Pyridoxine (Vitamin B6) is important for nerve function and protein metabolism. It is essential and readily available from plant sources such as chickpeas, bananas, potatoes, whole grains, nuts, and seeds.

Heme iron occurs only in animal foods, but iron itself is essential and also present in plant foods. Good vegan sources include lentils, beans, chickpeas, tofu, pumpkin seeds, sesame, oats, and whole grains.

Zinc is essential for immune function, wound healing, and enzymatic processes. Vegan sources include legumes, whole grains, nuts, seeds (e.g., pumpkin seeds, sesame), and oats.

Iodine is essential for thyroid hormone production. On a vegan diet, supply is most reliably achieved through iodized salt; seaweed can also contribute, though controlled dosing is advisable.

Selenium is essential and important for thyroid function and antioxidant systems. Vegan sources vary by region; Brazil nuts are commonly mentioned, as well as whole grains, legumes, and nuts.

Calcium is essential for bones, muscles, and cellular signaling. Vegan sources include kale, broccoli, pak choi, sesame (tahini), almonds, fortified plant milks, and calcium-rich mineral water.

Regarding protein, it is often claimed that plant foods are incomplete. In reality, all essential amino acids are present in plant foods. The essential amino acids lysine, methionine, tryptophan, leucine, isoleucine, valine, threonine, phenylalanine, and histidine can be covered through a varied selection of foods. Practical vegan protein sources include soy (tofu, tempeh, soy yogurt), lentils, beans, chickpeas, seitan, quinoa, oats, nuts, and seeds.

EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are important omega-3 fatty acids, among other roles in inflammation regulation and brain function. They are mainly found in fish, but a direct vegan source exists in algae oil. Additionally, flaxseeds, chia seeds, walnuts, and rapeseed oil provide the precursor ALA.

Many of the other substances mentioned are not essential because the body can synthesize them or because there is no mandatory dietary requirement. These include creatine, carnitine, carnosine, and taurine. Although commonly found in animal foods, they are generally not considered nutritionally indispensable due to endogenous synthesis.

Choline may be relevant for cell membranes and neurotransmitter production. Vegan sources include soybeans, legumes, broccoli, cauliflower, whole grains, nuts, and seeds.

Coenzyme Q10 and alpha-lipoic acid are synthesized by the body and also occur in small amounts in plant foods. Creatinine is not a nutrient but a metabolic byproduct. Conjugated linoleic acid (CLA) is not an essential nutrient.

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