The pitfalls of a vegetarian or vegan diet

Updated: Jul 18, 2019

You may have recently decided to change your diet to a vegetarian or vegan plant-based diet, due to environmental, ethical, and/or health concerns. Or you may have been eating this way for many years.

Research shows that a plant-based diet, when followed correctly, can be very effective for weight loss (1), improve bacterial diversity in the gut (2), and can also reduce the risk of diabetes, heart disease, and rheumatoid arthritis (3,4).

However, unsuccessful vegan or vegetarian diets can quickly result in nutrient deficiencies and suboptimal health, so it is important that you understand what nutrients are missing.

This may involve increasing your protein intake, and ensuring that you are getting adequate complete proteins in the diet. Or it also may involve supplementing accordingly, in order to maintain good health over the long term.

While a plant-based diet is high in protective, antioxidant phytonutrients, fibre, and many other vitamins and minerals, we know that a vegan diet is lacking in vitamin B12. It can also be prone to deficiencies in omega-3 long chain fatty acids EPA and DHA, iron, zinc, calcium, vitamin K2, as well as vitamins A and D.

In order to stay healthy, vegans need to ensure an adequate supply of protein and healthy fats. Some plant foods contain all of the essential amino acids, and these include quinoa, amaranth and soybeans. Flaxseeds, hemp seeds, and chia seeds are plant proteins that also contain short chain ALA omega 3 fats, however, they are not so well converted in the body to the long chain fats that the brain requires (EPA and DHA), and this conversion may only be around 10% efficient.

Vegetarians typically include eggs and dairy, and pescatarians will include fish, thus bulking up their protein and vitamin B12 intake.

Amino acids are the ‘building blocks’ of protein, and there are 22 in total. There are nine ‘essential’ amino acids that the body relies on for effective functioning, and they are called essential because they must come from the diet as the body does not make them. These include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

As the body doesn’t store amino acids, it needs a daily supply of these essential building blocks.

Non-essential amino acids can be synthesised by the body, and these include alanine, asparagine, arginine, glutamine, tyrosine, cysteine, glycine proline, serine, aspartate, and ornithine. So while the body does make them, we can also get them from the diet.

Some telltale signs that you are not getting enough protein include food cravings, low blood sugar levels, poor immunity, poor sleep, low mood, muscle or joint pain, and poor hair, skin and nails.

So while you may be reducing your carbon footprint, it’s important to be aware of your body’s nutrient requirements. If you are feeling at all unwell on a vegetarian or vegan diet it is recommended to seek advice from a BANT registered nutritional therapist to ensure you are meeting those requirements.


1. Turner-McGrievy, G.M. et al., 2015. Comparative effectiveness of plant-based diets for weight loss: A randomized controlled trial of five different diets. Nutrition.

2. Barnard, N.D. et al., 2009. A low-fat vegan diet and a conventional diabetes diet in the treatment of type 2 diabetes: A randomized, controlled, 74-wk clinical trial. In American Journal of Clinical Nutrition.

3. Barnard, N.D. et al., 2006. A low-fat vegan diet improves glycemic control and cardiovascular risk factors in a randomized clinical trial in individuals with type 2 diabetes. Diabetes Care.

4. McDougall, J. et al., 2002. Effects of a Very Low-Fat, Vegan Diet in Subjects with Rheumatoid Arthritis. The Journal of Alternative and Complementary Medicine.

  • Black Facebook Icon


Site design © 2017 Designed by Aquila Dunford Wood.