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Explaining Vegetarian / Vegan Diets

Written by: Consultant Dietitian Charity Chin

Vegetarian diets focus on plant-derived foods including fruits, vegetables, legumes (such as dried beans, peas, lentils), whole grains, seeds, and nuts, and exclude some or all foods derived from animals [1]. There are many reasons people choose to follow a vegetarian or vegan diet. For some, it may be due to environmental concerns, humanitarian and ethical values, religious practices, avoidance of hormones in animal products, or overall health considerations [1, 2].

When people think about vegetarian diets, they often imagine a diet that excludes meat, poultry, and fish. However, vegetarian diets vary in terms of what foods they include and exclude. Common subcategories include:

  • Vegan diets: Exclude meat, poultry, fish, eggs, dairy products, and any food containing these products [1].

  • Lacto-vegetarian diets: Exclude meat, fish, poultry, and eggs (including products 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 a Vegetarian Diet

People follow a vegetarian diet for various reasons, but one common motivation is the potential health benefits. These include reducing the risk of heart disease, obesity, hypertension, diabetes, and certain 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 nutritional needs are properly met [1].

Vegetarians generally demonstrate healthier dietary patterns and lower body fat compared to non-vegetarians. Their diets, which are typically lower in saturated fats and higher in dietary fiber and phytonutrients, contribute to lower total cholesterol, lower LDL cholesterol, and improved glucose control. These factors help prevent, reduce, and manage chronic diseases such as heart failure, stroke, obesity, type 2 diabetes, and metabolic syndrome [4, 6, 7].

Considerations for a Vegetarian Diet

While vegetarian and vegan diets offer many benefits, they can also pose nutritional challenges if not well planned. Processed vegetarian foods may be high in calories, sugar, fat, and sodium. Additionally, restrictive diets can make it harder to obtain all essential nutrients. Key nutrients to monitor include:

  • Calcium & Vitamin D: Often lacking due to limited intake of dairy products. Vegetarians and vegans can obtain these nutrients from dark green vegetables (e.g., turnip greens, collard greens, kale, broccoli), fortified plant-based drinks (e.g., rice, oat, soy), and fortified foods [2, 5].

  • Vitamin B12: Naturally found in animal products and only in trace amounts in fermented plant foods like nori (seaweed), spirulina, and nutritional yeast. Vegans should consume B12-fortified foods (e.g., yeast extracts like Marmite, fortified cereals, soy products, nutritional yeast) or take a B12 supplement [5].

  • Protein: Because plant-based proteins may lack some essential amino acids, vegetarians and vegans may require slightly higher protein intake. Key sources include beans, lentils, peas, nuts, seeds, tofu, tempeh, and edamame [2].

  • Omega-3 Fatty Acids (EPA and DHA): Found mostly in fish, and often low in vegetarian and vegan diets. ALA (from flaxseeds, chia seeds, walnuts, soybean oil) can convert to EPA and DHA, though the process is inefficient. Supplementation or regular intake of ALA-rich foods is important [3, 9].

  • Iron & Zinc: Absorption is hindered by phytates found in whole grains, legumes, and nuts. Other inhibitors include calcium supplements, coffee, tea, and soy protein [6, 11]. Enhancing iron absorption with vitamin C and incorporating foods like dried fruits, dark leafy greens, fortified cereals, and soaking/sprouting legumes and grains can help. Zinc bioavailability is also improved through fermented foods like tempeh, miso, and yeast-leavened bread [1, 5, 6].

  • Iodine: Low in plant-based diets due to low iodine content in soil and limited seafood intake. Sources include sea vegetables (nori, kelp, kombu, wakame), iodized salt, and fortified cereals or breads [4, 10].

Who Is a Vegetarian Diet Suitable For?

Vegetarian and vegan diets are suitable for people of all ages, including during pregnancy, provided that the diet is well-planned to ensure adequate nutrient intake. It’s essential to assess each individual’s food preferences and lifestyle to help them meet nutritional needs, achieve energy balance, and include a wide variety of plant-based foods.

Those following vegetarian or vegan diets should pay special attention to nutrients like protein, iron, calcium, vitamin D, omega-3 fatty acids, zinc, iodine, and vitamin B12 to maintain long-term health and well-being.

Reference List

  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. Nih.gov.
  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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Explaining Vegetarian / Vegan Diets
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