Is a vegetarian diet good for health?

Vegetarianism is a growing trend with around 10% of Europeans[1] and 4% of Americans consuming a vegetarian diet, 1.6% of which are following the more restrictive vegan diet. Popularity is expected to increase over the next decade both in the west and globally[1][2].

A vegetarian diet can be described as a diet which excludes meat, fish, or poultry. However, there are variations, with some vegetarians consuming dairy products and/or eggs, others follow a more restrictive vegan diet which excludes all animal products[3].

There are many reasons people choose to become a vegetarian, including religious and philosophical beliefs, environmental sustainability, animal welfare, media, popularity and perceived health benefits[4]. But how ‘healthy’ is a vegetarian or vegan diet compared to a non-vegetarian diet?

Studies show a reduction in the risk of obesity, type 2 diabetes, hypertension, heart disease and some cancers amongst those following a vegetarian diet. This is thought to be due to the increased intake of antioxidants such as vitamin C, vitamin E, carotenoids, health-promoting phytochemicals and a reduction in cholesterol and saturated fat associated with heart disease[5][6].

However, evidence is based on the average diet of well-educated vegetarians living in western countries and may not apply to the general population. Studies of vegetarians compared to health conscious non-vegetarians from the same population show little difference in rates of mortality[7], suggesting health benefits are more likely to be from a generally healthier lifestyle, increase in fruit and vegetable consumption and reduction in saturated fats.

Vegetarian diets can be unhealthy if animal products are not substituted with comparable alternatives. Some plant based sources of nutrients are more difficult for the body to absorb, this is further confounded by the high fibre content characteristic of a vegetarian diet, which is known to inhibit nutrient absorption[8].

Vegetarians, particularly vegans may have lower intakes of quality protein, iron, calcium, zinc, riboflavin, omega 3 fatty acids and vitamins D and B12[3][7]. Despite potential deficiencies, a well planned and varied vegetarian or vegan diet can deliver all the nutrients required for health, growth and physical activity[9].

Protein

Protein is required for growth, repair and immune function, proteins are made up of amino acids, few plant based proteins contain all 8 essential amino acids. Studies show adequate intake of essential amino acids in a vegetarian diet, however those on a vegan diet (particularly women) are at risk of deficiency. It’s recommended to combine different sources of protein to ensure adequate intake. Consuming pulses and grains or pulses and nuts/seeds over the course of the day can aid amino acid balance. Products made from soya are considered to be a good source of protein, comparable to some animal derived proteins[21] [22].

Due to reduced absorption of proteins from plant sources it’s recommended to increase protein intake compared to a non-vegetarian diet.

 

 

Vitamin B12

Vitamin B12 is required for the production of red blood cells, protein synthesis, maintenance and repair of muscle tissue and the central nervous system. There is no reliable source of vitamin B12 from plant based sources, those who exclude foods from animal sources are at risk of B12 deficiency[12]. Inadequate intakes of vitamin B12 can lead to anaemia associated with reduced oxygen transport[4] and irreversible neurological impairment which is not always obvious, signs have been known to take between 5 and 30 years to manifest [12].

Studies show up to 86% of vegetarian adults are deficient in B12, older vegetarians (>60ys) are at higher risk due to reduced nutrient absorption with age[13]. A systematic review of 43 studies investigating the association of B12 with cognitive function found B12 deficiency to be associated with an increased risk of Alzheimer’s disease, vascular dementia and Parkinson’s disease. Vegetarianism was considered an independent factor increasing the risk of cognitive impairment[14]. B12 supplementation and fortified foods have been shown to prevent deficiencies[12]. Some soya products and breakfast cereals are fortified with B12.

Iron

Iron is required by the body for energy metabolism, immune health, red blood cell and antioxidant function. Due to the lower absorption of iron from plant sources (non-haem iron), vegetarians are particularly at risk of iron deficiency anaemia, leading to physical exhaustion[4].

Absorption can be influenced by other foods, consuming promotors such as vitamin C found in orange juice or fermented foods such as miso and pickles can enhance absorption, whereas inhibitors such as dietary fibre and polyphenols in tea and coffee reduce absorption[15].

Some studies suggest potential iron overload and risks to health following supplementation. Supplements should be used with caution and only after deficiency has been confirmed by a doctor[15]. Good sources of iron include fortified breakfast cereals, lentils, cashew nuts, almonds, green vegetables and dried fruits[4].

Calcium

Calcium is needed for the growth, repair and maintenance of bones and ensures muscle contraction, energy metabolism and nerve function. Calcium intakes are generally low in vegetarians, especially females who are avoiding dairy products[4].

Studies show no difference in bone density between vegetarian and non-vegetarian subjects. However, studies on women following a long-term vegan diet show a reduction in bone density and therefore increased risk of fracture and breaks compared to non-vegetarians. Reduced protein intake is believed to be a factor, however calcium deficiency is considered to be the main culprit[16][17][18]. Calcium supplementation or consumption of calcium fortified foods is recommended for women avoiding dairy products.

Good dietary sources of calcium include tofu, tahini, dark leafy greens, seaweeds, almonds, hazelnuts and sesame seeds[16].

Vitamin D

Vitamin D is required for regulation of calcium, deficiency can result in decreased bone mass density and increased risk of break or fracture. Vitamin D from non-animal sources is less bioavailable than animal derived vitamin D, for those following a vegetarian (particularly a vegan diet), who also limit exposure to the sun, it’s recommended to consume vitamin D fortified foods or supplements[16]. Some soya products and breakfast cereals are fortified with vitamin D.

Zinc

Zinc is required for immune function, protein synthesis and blood cell formation. In a non-vegetarian diet 50-60% is from meat and dairy products[16]. Despite concern of zinc deficiency, studies show no deficiency symptoms in those following a vegetarian or vegan diet[3][16].

Good sources of Zinc include whole grains, legumes, and soy products[16].

Riboflavin

Riboflavin is required for energy metabolism, for vegetarians excluding both dairy and soy products intake is likely to be low. Requirements increase in physically active subjects, with deficiency impairing sports performance, particularly aerobic and endurance activities. Vegan athletes should consider increasing riboflavin consumption to avoid a negative effect on performance. Good sources of Riboflavin include yeast extract, wheatgerm, fortified breakfast cereals, almonds, pumpkin, sunflower, sesame seeds, avocado and seaweed[4].

Omega 3

Omega 3 is required for heart health, brain and eye function, inflammation response and immune function. Studies show vegan and vegetarian diets to be low in Omega 3 due to reduced absorption of plant based Omega 3 in the body[4][16].

Those on a vegetarian diet are advised to consume plant foods naturally rich in Omega 3, such as flaxseed, linseed, walnuts, canola oil, soya products, pumpkin seeds and products containing seaweed. Vegan based microalgae supplements are also available[16].

Energy

Energy intake among vegetarians is typically lower than non-vegetarians, this is partly due to an increased consumption of fibre and complex carbohydrates which can be quite ‘bulky’ and filling without providing energy[4].

Research suggests that vegetarian diets can achieve adequate energy, however adolescents and young athletes, particularly those on a vegan diet may struggle to support energy requirements for high levels of physical activity plus healthy growth[20]. Energy dense foods such as nuts, nut spreads, pulses, dried fruit, soya cheese, vegetable oils and margarines are recommended.

It is important to note that vegetarianism is a self-induced dietary restriction, in some venerable groups vegetarianism can be used as a mask for an eating disorder[19]. If dietary restrictions are resulting in excessive weight loss, it is recommended to work with your Doctor or Nutritionist to ensure adequate energy intake to support good health.

Summary

Overall, evidence suggests a vegetarian diet to be good for health, similar to that of a comparable non-vegetarian diet[7]. Health benefits associated with a vegetarian diet are thought to be the result of a generally healthier lifestyle, increase in fruit and vegetable consumption and reduction in saturated fats.

To ensure a ‘healthy’ vegetarian (particularly vegan) diet, you must have knowledge of what constitutes a nutritionally adequate diet and accessibility to nutrient rich and fortified foods[16]. Meals should be from a variety of food sources and well planned to ensure no nutritional deficiencies. Those on a vegan diet should consider supplementation with vitamin B12 to avoid potential neurological impairment[12].

References

[1] Rizzo G, Laganà AS, Rapisarda AM, La Ferrera GM, Buscema M, Rossetti P, Nigro A, Muscia V, Valenti G, Sapia F, Sarpietro G, Zigarelli M, Vitale SG (2016) Vitamin B12 among Vegetarians: Status, Assessment and Supplementation. Nutrients 8(12) E767.

[2] Craig WJ (2009) Health effects of vegan diets. Am J Clin Nutr 89(5):1627S-1633S.

[3] American Dietetic Association, Dieticians of Canada (2003) Position of the American Dietetic Association and Dieticians of Canada vegetarian diets. Can J Diet Pract 64:62-81.


[4] Lanham-New SA, Stear SJ, Shirreffs SM, Collins AL, (2011): Sports and Exercise Nutrition: The Nutrition Society.

 

[5] Key TJ, Fraser GE, Thorogood M, Appleby PN, Beral V, Reeves G, Burr ML, Chang-Claude J, Frentzel-Beyme R, Kuzma JW, Mann J, McPherson K (1999) Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am. S. Clin. Nutr 70(3):516s-524s

[6] Craig W.J. (2010) Nutrition concerns and health effects of vegetarian diets. Nutr Clin Pract. 25:613–620.

[7] Key TJ, Appleby PN, Rosell MS. (2006) Health effects of vegetarian and vegan diets. Proc Nutr Soc 65(1):35-41.

[8] Institute of Medicine (2005) Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients), National Academies; Washington, DC, USA.

[9] Nieman DC (1999), Physical fitness and vegetarian diets; is there a relation? Am J Clin Nutr, 70:570S-575S.

[10] Pawlak R., Lester S.E., Babatunde T (2014). The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: A review of literature. Eur. J. Clin. Nutr. 68:541–548.

[11] Waldvogel-Abramowskia, S. Waeberb, G. Gassnerc, C. Buserd, A. Beat, M. Freyc, B. Favrate, JD, Tissota. (2014) Physiology of Iron Metabolism. Transfus Med Hemother 41: 213–221.

[12] Allen L.H (2009) How common is vitamin B-12 deficiency? Am. J. Clin. Nutr. 89:S693–S696.

[13] Pawlak R, Lester SE, Babatunde T. (2014) The prevalence of cobalamin deficiency among vegetarians assessed by serum vitamin B12: a review of literature. Eur J Clin Nutr. 68(5):541-8.

[14] Moore E, Mander A, Ames D, Carne R, Sanders K, Watters D (2012) Cognitive impairment and vitamin B12: a review.Int Psychogeriatr 24(4):541-56.

[15] Craig WJ (2010) Nutrition concerns and health effects of vegetarian diets. Nutr Clin Pract. 25(6):613-20.

[16] Craig WJ (2009) Health effects of vegan diets. J Clin Nutr 89:1627S–33S.

[17]. Chiu JF, Lan SJ, Yang CY (1997) Long-term vegetarian diet and bone mineral density in postmenopausal Taiwanese women. Calcif Tissue, 60:245–9.

[18]. Lau EMC, Kwok T, Woo J, Ho SC. (1998) Bone mineral density in Chinese elderly female vegetarians, vegans, lacto-ovegetarians and omnivores. Eur J Clin Nutr, 52:60–4.

[19] Berning JR, Maughan RJ (2014) The Vegetarian Athlete.The Encyclopaedia of Sports Medicine: An IOC Medical Commission Publications, Sports Nutrition. West Sussux, UK: Wiley; P382–391.

[20] Garner DM (2004) Eating Disorder Inventory. Professional Manual Psychological Assessment Resources, Incorporated.

 

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