Possible Deficiencies in a Vegetarian Diet

There are many benefits to a vegetarian diet and some nutritional concerns and possible deficiencies associated with strict vegetarian diets. Vegetarian diets in general are not unhealthy. Eating a wide range of different types of vegetarian foods is recommended.

As with many types of diets, it is possible to develop a habit of eating the same or similar foods, perhaps because they are the most easily available or the most appealing. In the cases of vegetarians and vegans, experts have recommended ensuring sufficient intake of the following:

Nutrients that are sometimes deficient in vegetarian diets




Sufficient protein intake is probably the most commonly mentioned 'deficiency' in vegetarian diets.

Although it would be possible to develop a protein deficiency due to an unplanned vegetarian diet e.g. by following a typical 'western diet' but simply omitting all meat and fish products, that is not how real long-term vegetarians eat.

To understand the nutritional significance of concern about protein intake it helps to bear in mind that:

  • Proteins are large molecules sometimes described as "building blocks" essential for growth.
  • Proteins are broken-down by the digestive system into amino acids (which can be absorbed into the blood). This is can also be expressed in terms of proteins 'containing' amino acids.
  • Different types of proteins are available in a wide range of animal and non-animal food sources e.g. meat, fish, eggs, pulses and beans. In this context "different types of proteins" means large molecules that contain different amino acids.
  • Given that proteins are broken-down into amino acids, the nutritional concern is really about sufficient intake of all of the essential amino acids, that is the amino acid (molecules) that need to be included in human diets because those particular molecules are not made (some books say 'synthesized' rather than 'made') within the human body itself.
  • Amino acids are used by the body to build and repair structures of the human body including various types of tissues. The same or similar processes apply to many other animals so it is not surprising that animal flesh (meat) includes proteins formed from many of the same amino acids that are used to build and repair human tissues - often in approximately the same proportions as required by humans.
    Therefore meat products are good sources of essential amino acids in the form of the animal proteins. However, meat products are not the only sources of protein (amino acids).
  • The complication with non-meat proteins is that, individually, they do not necessarily include ideal relative proportions of the amino acids needed to make animal proteins as found in meats and as formed within the human body to grow and maintain healthy tissues. This means that a good vegetarian diet should include different types of non-meat proteins that, collectively, supply sufficient quantities of all of the essential amino acids needed for human growth and maintenance of healthy tissues.
  • For example, consider the amino acids typically present in grains e.g. corn and legumes e.g. beans:

Amino Acids in corn
and other grains:

Essential Amino Acids
listed in alphabetical order

Amino Acids in beans
and other legumes:







Why is it needed?

Proteins are essential for growth, especially for infants, children and body-builders, and for maintenance and repair of body tissues. A person's diet should provide both the essential amino acids and sufficient amino acid nitrogen to enable the body to synthesize the non-essential amino acids it requires ("non-essential" means not essential within the diet because the body can make these particular biochemicals itself - given the necessary starting materials).

What are proteins?


Vitamin B12

The main sources of vitamin B12 are meat, fish, eggs and dairy products. Vegetarians who eat dairy products such as milk and cheese and / or eat eggs can easily include sufficient vitamin B12 in their diets. However, vegans (who do not eat eggs or dairy products) may choose to give particular attention to ensuring that they consume sufficient vitamin B12. Only a limited range of vegan foods include this vitamin which is available in wheatgerm and in beer. Vegetarians and/or vegans concerned about their intake of B12 may choose to take appropriate supplements.

Why is it needed?

Vitamin B12 is important for the healthy functioning of many processes within the body, including growth, preventing anaemia, maintaining the nervous system, synthesizing nucleic acids, production of certain hormones and the action of some enzymes (that catalyze certain chemical reactions within the body).

More about vitamin B12.



Iron is an important mineral of which sufficient dietary intake is essential for good health.

There is sometimes concern about vegetarians receiving enough iron in their diets because many of the main sources of iron are animal products (including meats esp. liver and fish e.g. sardines and tuna). However, iron is also present in many green leafy vegetables and other plant sources such as dried fruits, parsley and watercress. Dietary iron exists in two forms:

  • Haem iron - from meat products ; rapidly absorbed by the human body.
  • Non-haem iron - from vegetables and cereals ; absorbed by the human body slowly.

Vegetarians and vegans can usually ensure that their need for dietary iron is met by consuming enough foods containing iron. Some people e.g. some menstruating women, pregnant women, and people who consume significant quantities of antinutrients such as coffee and tea that can reduce absorption of dietary iron, take iron supplements. However, it is often recommended that iron supplementation is best taken as part of a multivitamin / multimineral supplement and/or with expert supervision - due to possible adverse effects of an overdose of iron, which can be fatal.

Why is it needed?

The mineral iron is needed for production and maintenance of red blood cells (erythrocytes). It is also important for maintaining energy levels and a healthy immune system (incl. fighting infections) and is especially important in pregnancy.



Calcium is an important mineral of which sufficient dietary intake is essential for good health.

There is sometimes concern about vegans receiving enough calcium in their diets, especially if the hulls of the grains and legumes they eat have been removed e.g. by food processing techniques. Vegetarians can easily receive their dietary requirement for calcium in dairy products such as milk, cheese, ice-cream, etc..

Another consideration is the possible reduction in the bioavailability of dietary calcium when consumed as part of a high fibre diet. There are many reasons why the higher proportion of dietary fibre in vegetarian and vegan diets is considered an advantage - i.e., a benefit of vegetarian diets. However, the phytate in dietary fibre can reduce the bioavailability of calcium. Phytate is a salt or ester of phytic acid that is present in plants, esp. cereal grains, and can form insoluble complexes with minerals such as calcium, zinc and iron, thereby interfering with the ability of the body to absorb those nutrients. This is effect is not of concern for vegetarians and vegans specifically but is useful to be aware of, together with other considerations re. absorption of calcium, e.g. the importance of sufficient vitamin D - see below.

Why is it needed?

The mineral calcium is important for healthy teeth and bones (incl. reducing risk of osteoporosis). It is also necessary for muscle contraction, blood clotting, transmission of nerve impulses, cardiac function and a healthy immune system.


Vitamin D

Vitamin D is common in milk and dairy products and so is consumed in adequate quantities by many vegetarians, but not vegans. Fortunately the human body produces vitamin D itself - provided that the skin is exposed to sufficient sunlight. This is one of many reasons why an active outdoor lifestyle can be healthy while spending all of one's time indoors, e.g. during dark cold winters, is not beneficial.

Some vegans might benefit from vitamin D supplements if they are unable to spend enough time in sunlight e.g. due to illness, accident, or the season & their location, or if they do spend time outside but with their skin covered e.g. for medical or religious reasons. However, ingestion of excessive amounts of vitamin D can lead to toxic reactions so expert supervision of vitamin D supplementation is often recommended.

Why is it needed?

Vitamin D is important for controlling the body's absorption of calcium and hence for the development of healthy teeth and bones and for blood clotting.

See also carbohydrates, types of sugar, dietary fibre, fatty acids, fats, proteins
and dietary needs for different life stages.

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