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The Nutritional Advantages and Disadvantages of Vegetarian or Vegan Diets

This month our Sussex health expert talks about the nutritional advantages and disadvantages of becoming vegetarian or vegan, and what you can do to make sure you stay in optimal health.

the nutritional advantages and disadvantages of becoming vegetarian or vegan

The “up” side

There are many well-researched advantages of a vegetarian or vegan diet to health in general.

One of the most significant shifts in the modern Western diet is a massive increase in how much protein and starch we consume, which causes a constant tendency towards tissue acidity. Tissue acidity has many negative effects on general wellbeing – decreased energy output, altered bowel function, decreased mineral and vitamin absorption potential, dysbiosis – as well as increasing the long-term risk of inflammation and associated degenerative diseases. In contrast, a balanced vegetarian diet has a much greater intake of fruit and vegetables, fibre, complex carbohydrates and good-quality fats, all of which have obvious health benefits.

Vegetarians and vegans have a much lower risk of developing heart disease. A vegetarian diet has been shown to be effective in reducing cholesterol levels and reducing the risk of atherosclerosis. This is most likely due to:

  1. the absence of red meat which contains high levels of fat and puts huge demands on the digestive system, and
  2. a high intake of fibre and complex carbohydrates.

the nutritional advantages and disadvantages of becoming vegetarian or vegan

Vegetarians generally have lower blood pressure and lower incidence of hypertension. Whilst dietary levels of sodium do not significantly differ, the vegetarian diet contains more potassium, complex carbohydrate, fibre, calcium, magnesium and vitamin C; all of which contribute to better heart function and circulation. Plant-based diets are also linked to better regulation of blood sugar levels.

The vegetarian diet is associated with lower incidence of breast disease. A Western diet leads to lower gut flora diversity and productivity. High intake of red meat and processed starch slows bowel transit time and reduces the number of bowel movements. The micro-organisms in our faeces are able to re-synthesise oestrogen from previously excreted oestrogen. Therefore, the longer our faeces stay in our bowel, the more oestrogen our bodies will reabsorb, leading to toxic levels and increased risk of oestrogen-dependent diseases such as fibrocystic breast disease.

A vegetarian diet has been shown to be protective against gallstone formation. This is most likely due to the increased fibre content of the vegetarian diet. Additionally, animal proteins have been shown to increase the formation of gallstones; whilst vegetable proteins, like soy, are preventive against gallstone formation.

Vegetarian and vegan diets are associated with lower risk of osteoporosis. Although bone mass in vegetarians does not differ greatly from meat eaters in the third to fifth decades, there are significant differences in later decades; indicating that the decreased incidence of osteoporosis in vegetarians is not due to increased initial bone mass, but rather decreased bone loss in later life. The most important factor is probably the lowered intake of protein and phosphorus, both of which increase excretion of calcium in the urine and lead to tissue acidity.

A vegan diet, excluding all meat, fish, eggs and dairy products has been shown to have significant benefits for asthma sufferers. This is probably due to the absence of polyunsaturated fats found only in animal fats which would otherwise lead to the production of pro-inflammatory compounds called leukotrienes. Leukotrienes are potent stimulators of airway constriction.

the nutritional advantages and disadvantages of becoming vegetarian or vegan

The “down” side

However, on the other side of the coin, it is essential to understand the specific dietary needs of a vegetarian, even more so of a vegan.

The human body requires eight essential amino acids (the building blocks of protein), from which all other amino acids can be derived in the presence of various micronutrients. These eight amino acids are present in all meat, fish, eggs, poultry, dairy products and soya. Plant foods, however, are low or devoid of one or more essential amino acids, so must be eaten in groups in order to complete the group of eight. Hence the need to combine foods e.g. rice with beans, bread with peanut butter, lentils with potato, and so on. Furthermore, the amino acids in vegetables are less stable and degrade more easily in the storage and preparation of food; so that the freshness of the food and method of cooking become more critical.

If vegetarians are too relaxed about using alternative food sources for their amino acid intake, failing to use beans, pulses, peas and lentils, it can become quite easy for their protein metabolism to become depleted, leading to low energy levels. If this is the case, a multiple amino acid formula or high-quality protein powder should be supplemented into the diet. Vegan sources of protein-rich foods include legumes, tofu, seitan, edamame, quinoa, chia seeds.

the nutritional advantages and disadvantages of becoming vegetarian or vegan

Another common cause of energy deficiency in vegetarians is iron deficiency. Iron is found not only in meat, fish and eggs, but is also abundant in green leafy vegetables, nuts, cereals and beans. However, vegetable-source iron is much more difficult to absorb than meat-source iron; so that haemoglobin levels in vegetarians will always tend to be slightly lower. It is probably a good policy for vegetarians to supplement iron in an absorbable compound, such as glycinate or picolinate, for one week per month to maintain an adequate level. Iron will only cause constipation if given in an unabsorbable form, such as sulphate.

Vitamin B12 levels can also become low in vegetarians since the vegetarian sources e.g. seaweed, spirulina, and tempeh are not common food sources in the Western diet. This is further complicated by the fact that vitamin B12 deficiency is masked by folic acid; and folic acid levels are generally high in the vegetarian diet. A supplement of activated B12 (adenosyl-, hydroxy- or methyl-cobalamin forms) is therefore probably to be recommended on a cyclical basis of one week on – one week off; or two weeks on – two weeks off. A B12 supplement is almost certainly necessary in the vegan diet.

Vitamin A is found only in animal foods, but can be made from beta-carotene (abundant in many vegetables) in the presence of zinc. It is therefore important as a vegetarian that you have adequate intake of zinc but, given that this is now the most common mineral deficiency in the Western World, a cyclical supplementation of vitamin A (or zinc!) may be considered.

Vitamin B3 and B5 are other common deficiencies in the vegetarian diet as they tend to be in much higher concentrations in meat and fish sources.

It can be quite difficult for vegetarians to get an adequate source of omega 3 oils into their diet if they do not eat fish. Most people are very poorly informed about the difference between good fats and bad fats, exacerbated by poor media understanding and fad diets. Nuts and seeds provide an excellent source of oils and are essential in the vegetarian and vegan diet.

A daily intake of omega 3 oils, in the form of flax seed, linseed or algae-sourced EPA is to be recommended to all vegetarians and vegans.

Consider periodic blood testing to check levels of iron, B12 and zinc.

vegetarian or vegan

Dietary recommendations 

Having weighed up the nutritional advantages and disadvantages of becoming vegetarian or vegan, consider the following recommendations:

  • Ensure a correct combination of protein and carbohydrate sources to complete the range of amino acids
  • Recommend a regular intake of foods naturally high in iron and vitamin B12
  • Ensure a high intake of zinc as a food source or in supplement form
  • Ensure a daily intake of mixed seeds and nuts for vitamin B3 intake
  • Ensure a daily intake of untreated cereal e.g. buckwheat or granary bread for vitamin B5 intake
  • Add a dietary supplement of omega 3 oil e.g. flax seed oil or algae-based EPA
  • Ensure the fruit and vegetables eaten are fresh. Prepare vegetables by breaking rather than cutting wherever possible (which better preserves the micronutrients and enzymes), and steam in preference to any other mode of cooking.
  • Vegan sources of minerals are often high in compounds that prevent absorption. These “phytates” can be denatured by steaming or boiling.
  • Aim to “eat the colours of the rainbow” on a daily basis as this covers the full spectrum of nutrients the body needs for optimum health. Focus more heavily on those that grow above the ground.


Sussex health

Nutritional supplement options

  • A combination of essential Amino Acid formula
  • Iron in an absorbable form on a cyclical basis
  • B12 on a cyclical basis
  • Vitamin B3 if required
  • Vitamin B5 if required
  • Zinc
  • Omega 3 oil
  • Vitamin A as required
  • Additionally for vegans: choline, biotin, vitamin D and vitamin K

vegetarian or vegan

Article contributed by Dr Tracy S Gates, DO, DIBAK, L.C.P.H., Consultant, Pure Bio Ltd. Copyright © Pure Bio Ltd 2023. All rights reserved. Pure Bio Ltd are a leading UK supplier of the highest quality PURE nutritional supplements, based in Horsham, West Sussex. Proud Winners of Southern Enterprise Awards, Best Nationwide Hypoallergenic Nutritional Supplements Distributor 2022.

Visit  for all your nutritional supplement needs.

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