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Possible Deficiencies in a Vegetarian Diet

Although there are many benefits to a vegetarian diet, there are also some nutritional concerns and possible deficiencies associated with strict vegetarian diets. This does not mean that vegetarian diets are not healthy, just that it is a good idea to eat a wide range of different types of vegetarian foods.

Regardless of personal criteria concerning foods and diet, it is possible to fall into the habit of repeatedly eating the same types of foods - either because they are the most easily available, or because they are the most appealing. In the cases of vegetarians and vegans, experts in diet and nutrition recommend attention to ensuring sufficient intake of the following:

Nutrients that are sometimes deficient in vegetarian diets

 

Nutrient

 

1.

Protein

Sufficient protein intake is probably the most commonly mentioned "deficiency" in vegetarian diets.
However, 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:


leucine

methionine
phenylalanine
threonine
tryptophan
valine

isoleucine
leucine
lysine
methionine
phenylalanine
threonine
tryptophan
valine

isoleucine
leucine
lysine

phenylalanine
threonine

valine

2.

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.

3.

Iron

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.

4.

Calcium

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.

5.

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 may 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.

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

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