Vegetarian & Vegan Diets Explained

Health Advice

Article by: Consultant Dietitian Charity Chin

Vegetarian diets focus on plants-derived foods that include fruits, vegetables, legumes (dried beans, peas, lentils), whole grains, seeds, and nuts and excludes some or all foods derived from animals [1]. There are many reasons that people choose to follow a vegetarian or vegan diet, for some people it may be due to environmental concerns, humanitarian and ethical values, religious practices, avoiding hormones used in animal foods/products, or may be due to overall health considerations [1, 2].

When people think about vegetarian diets, they usually think about a diet that doesn’t include meat, poultry, or fish. But vegetarian diets vary in what foods they include and exclude. Within the broad category of vegetarian diets, there are several common subcategories, for example:

  • Vegan diets: exclude meat, poultry, fish, eggs, and dairy products and foods that contain these products [1]
  • Lacto-vegetarian diets: exclude meat, fish, poultry, and eggs, as well as foods that contain them, but include dairy products, such as milk, cheese, yogurt, and butter [1]
  • Lacto-ovo vegetarian diets: exclude meat, fish, and poultry, but include dairy and egg products [1]
  • Ovo-vegetarian diets: exclude meat, poultry, seafood, and dairy products, but include eggs and egg products [1]

Benefits of Vegetarian Diet

The purpose of following a vegetarian diet varies for each individual but one of the reasons is health benefits. The health benefits include reducing the risk of heart disease, obesity, hypertension, diabetes, and some cancers. According to the Academy of Nutrition and Dietetics, vegetarian and vegan diets are “healthful, nutritionally adequate, and may provide health benefits for the prevention and treatment of certain diseases” when patients and clients meet their daily nutritional needs [1].

Generally, vegetarians exhibit healthier dietary intake and lower body fat compared to non-vegetarians. Evidence indicates that the low intake of saturated fat and high consumption of dietary fiber and phytonutrient-rich foods, characteristic of vegetarian diets, result in lower total cholesterol and low-density lipoprotein cholesterol levels. This dietary pattern also improves glucose control, contributing to the prevention, reduction, and treatment of chronic diseases such as heart disease, stroke, weight management issues, type 2 diabetes, and metabolic syndrome. [4, 6, 7].

Vegetarian Diet Considerations

Vegetarian or vegan diets often feature processed foods, which may contain high levels of calories, sugar, fat, and sodium. Because of dietary restrictions, obtaining all necessary nutrients can be challenging. Here are some nutrients to be mindful of:

Calcium and Vitamin D deficiency

Most sources are from milk and dairy foods. To get them through plant-based foods, vegetarians/vegans need to consume sufficient quantities of dark green vegetables such as turnip and collard greens, kale, and broccoli, or other sources including rice and oat drinks, milk and dairy alternatives, fortified unsweetened soy, and fortified foods. [2, 5].

Vitamin B-12 deficiency

In nature, this vitamin is primarily found in animal products. It is present in very small amounts in fermented foods such as nori (seaweed), spirulina, and nutritional yeast. Those who follow a vegan diet should take a vitamin B12 supplement or consume fortified foods such as fortified yeast extracts (Marmite), breakfast cereal, fortified soy products, or fortified nutritional yeast. [5]

Protein deficiency

Due to the differences in amino acid composition in the protein sources, vegetarians’ and vegans’ protein needs may be slightly higher compared to non-vegans. It is important for vegetarians and vegans to include protein-rich foods such as beans, peas, lentils, nuts and seeds, and soy products such as tofu, tempeh, and edamame in their diets to meet the daily protein requirements. [2]

Omega-3 fatty acids EPA and DHA deficiency

These are significantly lower in vegetarians and generally absent in vegans compared with non-vegetarians because they are found mainly in fish and other seafood. Alpha-Linolenic Acid (ALA) is found mainly in plants and can convert to EPA and DHA. However, the conversion process is inefficient in humans. [9] Omega-3 fatty acids are essential fatty acids that the body is unable to produce and must be obtained from food. To raise the overall levels of omega-3 fatty acids in vegetarian or vegan diets, one should consume plant sources like flaxseed, flax oil, chia seeds, soybean oil, and walnuts. [3, 9]

Iron and zinc deficiency

Phytate, found in whole grains, nuts, and legumes, inhibits the absorption of iron and zinc. [6, 11]. Other inhibitors of iron absorption include calcium supplements, coffee and tea (content polyphenols/tannins), and soy protein [6, 11]. To enhance the absorption of iron is to incorporate vitamin C, because vitamin C enables to counteract the effects of phytates, polyphenols, and calcium. To increase iron, increase the consumption of dried fruit, dark green vegetables (watercress, broccoli, spring greens), whole meal bread, fortified cereals with added iron [1, 5, 6]. By soaking and sprouting phytate-containing food such as beans, peas, lentils, grains, nuts, and seeds, it helps increase the zinc bioavailability for absorption. Other sources include yeast leavened whole grain bread, and fermented soy products such as tempeh and miso also may improve zinc bioavailability [1, 5, 6].

Iodine deficiency

Vegetarian diets may lead to higher iodine deficiency due to the exclusive consumption of plant-based foods, limited intake of fish or other seafood, and reduced use of iodized salt.[4]. Iodine content in food from plant origin is lower compared with animal sources due to a low iodine concentration in soil [4]. Dietary source for vegetarians is available from sea vegetables like seaweed (nori, kelp, kombu, wakame), table salts that contain “iodized”, and to a lesser extent in fortified foods like breads, cereals, and milk [10].

Vegetarian Diet’s Ideal Target Population

People of all ages, from young to old, can adopt vegetarian or vegan diets successfully by planning accordingly to ensure they receive essential nutrients for health and strength. Assessing acceptable foods helps individuals meet nutritional needs, achieve energy balance, ensure nutritional adequacy, and promote the use of a variety of plant-derived foods. Therefore, those opting for vegetarian or vegan diets must include a wide variety of foods and focus on protein, iron, calcium, vitamin D, omega-3, zinc, iodine, and vitamin B12 to meet their nutritional requirements.


  1. Nutrition Care Manual. Academy of Nutrition and Dietetics. 2018
  2. Becoming A Vegetarian. Harvard Health Publishing Harvard Medical School. 2020.
  3. Omega-3 fatty acids.
  4. Krajcovicová-Kudlácková M, Bucková K, Klimes I, Seboková E. Iodine deficiency in vegetarians and vegans. Ann Nutr Metab. 2003;47(5):183–5.
  5. Melina V, Craig W, Levin S. Position of the Academy of Nutrition and Dietetics: Vegetarian diets. J Acad Nutr Diet [Internet]. 2016;116(12):1970–80.
  6. Walczyk T, Muthayya S, Wegmüller R, Thankachan P, Sierksma A, Frenken LGJ, et al. Inhibition of iron absorption by calcium is modest in an iron-fortified, casein- and whey-based drink in Indian children and is easily compensated for by addition of ascorbic acid. J Nutr. 2014;144(11):1703–9.
  7. Kahleova H, Levin S, Barnard ND. Vegetarian dietary patterns and cardiovascular disease. Prog Cardiovasc Dis. 2018;61(1):54–61.
  8. Leitzmann C. Vegetarian diets: What are the advantages? In: Forum of Nutrition. S. Karger AG; 2005. p. 147–56.
  9. Greupner T, Kutzner L, Nolte F, Strangmann A, Kohrs H, Hahn A, et al. Effects of a 12-week high-α-linolenic acid intervention on EPA and DHA concentrations in red blood cells and plasma oxylipin pattern in subjects with a low EPA and DHA status. Food Funct. 2018;9(3):1587–600.
  10. Iodine. The Nutrition Source. Harvard School of Public Health. 2021.
  11. Maares M, Haase H. A guide to human zinc absorption: General overview and recent advances of in vitro intestinal models. Nutrients. 2020;12(3):762.

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