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Is a vegetarians diet adequate?

Today I will focus on various aspects of a vegetarian diet. From a sustainability standpoint, there is widespread support for a reduction in meat consumption with one of the main issues in meat production and processing being the amount of greenhouse gas (GHG) emissions produced. However, there are thought to be issues regarding the adequacy and potential problems of diets with no meat.
The main nutrients I will focus on will be protein, iron, zinc and vitamin B12 which are the main nutrients found in red meat.

Protein and vegetarian diets:

It is thought by both consumers and health professionals that protein needs are difficult to meet on a vegetarian diet.

Amino acids are the building blocks of protein. Protein foods which have a large amount of essential amino acids are usually of higher quality. These essential amino acids are usually in foods from animal origins. However, a few plant based protein sources are considered to be of higher quality too. These include soy, grains, quinoa and amaranth. The latest evidence suggests that a combination of vegetable proteins can provide enough amino acids of good quality to meet physiological needs.

Vegetarians should include a variety of protein rich foods each day including:

  • Legumes (soybeans, chickpeas, lentils, kidney beans, split peas and baked beans

  • Whole grains (brown rice, buckwheat, polenta, quinoa and amaranth)

  • Soy products(soy milk, soy yoghurt, tofu)

  • Nuts and seeds

While vegetarian diets do contain generally lower quality protein that diets containing meat. There is increasing evidence that plant based protein may, in fact, be one of the reasons vegetarians have a generally lower risk of being overweight and having chronic disease as a result of the decreases in saturated fat intake which also accompanies animal based products.

Iron and vegetarian diets:

Iron is an essential nutrient for haemoglobin and transportation of oxygen around the body. There are two main types of Iron. Haem Iron (predominantly in animal products) and non-haem iron.

Plant foods (cereals, breads, dry beans, dark leafy green vegetables, dried fruits, nuts and seeds) contain only non-haem iron. Haem iron has been shown to have a much more uniformed and effective absorption in the body and as a result Iron deficiency is thought to be of concern in vegetarian populations.

Non haem iron bioavailability is influenced by various dietary components that either enhance or inhibit its absorption. Therefore, it is wise that those who follow a vegetarian diet are aware of the most efficient ways to obtain dietary Iron.

INHIBITORS

The greatest inhibitor of non-haem iron absorption is an antioxidant called phytate, usually found in legumes, nuts, wholegrain cereals and unprocessed bran (many of which are also sources of dietary iron for vegetarians. Processing removes much of the phytate, but also removes Iron in the food. Soaking legumes, grains and seeds is a great way to reduce phytate levels while leaving iron leaves intact. .

Other inhibitors of Iron absorption include polyphenol containing beverages (tea, herbal tea, coffee, cocoa and red wine)

Calcium has also been shown to inhibit both haem and non-haem iron.

ENHANCERS

The most significant enhancer or iron absorption is Vitamin C (both synthetic and dietary, ~50mg of vitamin C per meal) and can enhance absorption up to sixfold in those who have low iron stores.

Other organic acids (citric, malic and lactic acid) as well as vitamin A and beta-carotene mostly found in citrus fruits and vegetables, have also been shown to enhance non-haem Iron absorption.

So, are vegetarians at risk of Iron deficiency?

Surprisingly, vegetarian and vegan diets generally contain just as much or more iron than a omnivorous diet. However, compared with meat-eaters vegetarians often have lower serum ferritin levels (a main predictor in iron deficiency). Although still within the normal reference ranges.

Vegetarians may reduce their risk of low iron levels by incorporating foods rich in components which enhance, such as Vitamin C and other organic acids with every meal.

Therefore, a well planned vegetarian diet can provide adequate amounts of non-haem iron if a wide variety of plant foods are regularly consumed. Vegetarian diets are typically rich in vitamin C and other factors as a result of high fruit and vegetables, that facilitate non haem iron absorption

Zinc and vegetarian diets:

Zinc is an trace mineral with antioxidant properties and is essential in many aspects of metabolism in the body.

Special attention needs to be attributed to zinc in a vegetarian diet as vegetarian sources of zinc often contain phytate and other inhibitors of zinc absorption. Therefore it is thought that the vegetarian and vegan population may be at risk of zinc deficiency.

Although lean red meat provides the highest concentration of zinc, wholegrain breads and cereals, rolled oats, brown rice, nuts, seeds, legumes, tofu, soy products and fortified cereals and juices are important sources of zinc for vegetarian.

Similarly to Iron, the absorption of zinc is inhibited by phytates and enhanced by sulphur containing amino acids found in a range of seeds, nuts and grains as well as citric acids found in citrus fruits. Higher levels of dietary protein will also bind zinc to assist with absorption.

With good planning vegetarians can consume enough zinc from legumes, wholegrain products and frequent intake of nuts, seeds, fruits and vegetables. Interestingly, recent studies have shown, as phytate or other dietary inhibitors typically decreased zinc absorption, there is normally a compensatory improved efficiency of absorption and excretion of zinc in this population. Therefore, vegetarians appear to be at no greater risk of zinc deficiency than non-vegetarians.

Vitamin B12 and vegetarian diets:

Vitamin B12 is an essential vitamin required for DNA synthesis and maintaining nerve integrity. It is found almost exclusively in animal-based products including red meats, poultry, sea food, milk, cheese and eggs. Therefore Vitamin B12 deficiency is a potential concern for anyone significantly restricting animal based foods.

Lacto-ovo-vegetarians (vegetarians including products derived from animal sources) will have a reliable source of vitamin B12 in their diet, provided they consume adequate amount of dairy products and eggs, although their intake is likely to be lower than meat eaters. Vitamin B12 fortified foods are more necessary for those who follow a vegan diet.

Foods fortified with Vitamin B12 in Australia include soy milks, yeast spread (vegemite, promite) and vegetarian meat alternatives ( soy based burgers and sausages).

Summary:

  1. Vegetable proteins can provide enough high good quality to meet physiological protein needs

  2. A well planned vegetarian diet including foods which enhance non-haem iron absorption can provide adequate amounts of non-haem iron to prevent deficiencies

  3. Due to compensatory efficiency of absorption and excretion of zinc in this population. Vegetarians are at no greater risk of zinc deficiency than non-vegetarians.

  4. All vegans and lacta-ovo-vegetarians who don’t consume dairy products or eggs should incorporate a vitamin B12 supplement along with vitamin B12 fortified foods.

Russell Nassim (APD)

References:

Marsh KA, Munn EA & Baines SK 2012 ‘Protein and Vegetarian diets’ The Medical journal of Australia, Volume 1, Supplement 2, pp 7-10.

Saunders AV, Craig WJ, Baines SK & Posen JS 2012 ‘Iron and Vegetarian diets’ The Medical journal of Australia, Volume 1, Supplement 2, pp 11-16.

Saunders AV, Craig WJ & Baines SK 2012 ‘Zinc and Vegetarian diets’ The Medical journal of Australia, Volume 1, Supplement 2, pp 17-21.

Zeuschner CL, Hoskin BD, Marsh KA, Saunders AV, Reid MA & Ramsay MR 2012 ‘Vitamin B12 and Vegetarian diets’ The Medical journal of Australia, Volume 1, Supplement 2, pp 27-32

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Accredited Practicing Dietitian  Accredited Nutritionist 

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