Vegan and vegetarian diets are certainly trendy, with more people than ever before making the switch. While some people are choosing to go plant-based for environmental reasons, others are adopting these diets because of their health benefits.

It's hardly surprising, given studies have linked vegetarian and vegan diets to a lower body mass index (BMI) and a lower risk of certain diseases – including cancer, type 2 diabetes, and heart disease.

But while plant-based diets may have many health benefits, they can, without some planning, also result in nutrient deficiencies. In fact, one survey suggests around 28 percent of vegans and 13 percent of vegetarians show one or more nutrient deficiencies. This is because many plant-based diets don't contain high levels of certain nutrients, such as vitamin B12, omega-3 fatty acids, iodine, calcium, selenium, iron and zinc.

Research shows that veganism in particular is linked with significantly low intakes of vitamin B12 and calcium – especially in people who aren't taking any vitamin supplements. Intakes of selenium, zinc, vitamin D and iodine are also low in this group.

While vegetarian diets may contain slightly higher levels of amino acids, B12, calcium and protein compared to vegan diets, intake may still be lower than when following an omnivorous diet.

Proper planning

Vitamins and minerals are important for good health. For example, vitamin B12 is important for brain function and producing red blood cells. But our body doesn't naturally produce many important vitamins and minerals (including vitamin B12, iron, selenium, and iodine) which is why it's essential to get them from the foods we eat.

But not getting enough of these important vitamins and minerals can lead to deficiencies. These can have a range of side effects, including excessive tiredness and brain fog. If left untreated, over time, this can lead to serious nervous, skeletal and blood disorders.

If you're someone who's thinking of making the switch to a vegetarian or vegan diet, here are a few things to consider to avoid vitamin deficiencies:

• Seek expert advice. To help you plan your diet to ensure that it contains all the essential nutrients you need, especially if you're transitioning from a vegetarian diet to a vegan diet, if you are or may become pregnant, or if you're older than 60 years of age.
• Focus on your nutrients. Aim to pick plant-based food products that have been fortified with important vitamins and minerals, or foods that naturally contain high amounts of important nutrients. For example, Brazil nuts are rich in selenium, while seaweed is a good source of vitamin B12 and iodine.
• Eat a varied diet. This is especially important when it comes to the plant-based proteins you eat to ensure you get all the essential amino acids from your diet. Some foods that contain these include lentils, pulses, beans, soy, tofu, nuts and seeds.
• Pair certain nutrients. Certain nutrients can help others be better absorbed into the body. For example, vitamin C can increase iron absorption. Vitamin B12 supplements should also be taken with food to help the body absorb it more easily.
• Keep an eye on your health. If you start experiencing fatigue, memory problems, or even low mood, it might be a sign of a vitamin deficiency. Be sure to consult a doctor before taking any supplements to be sure you're taking the right ones.

If you need to use a vitamin supplement, be sure to look for supplements that are labelled GMP certified, as these will contain proper nutrition. But long-term supplement use may have its downsides, such as being costly or interacting with certain drugs.

There is also a danger of over-supplementation, which can lead to an accumulation of certain unmetabolized nutrients in our body. It's currently unknown how common this is and what the long-term effects might be. For all of these reasons, it's important to consult a GP before taking any supplements.

A well-planned, plant-based diet can be good for both your health and the planet. But it's important to keep an eye on what foods and nutrients you might be eating to avoid deficiencies of essential nutrients.

--Martin Warren, Chief Scientific Officer and Group Leader, Synthetic Biology and Biosynthetic Pathways, Quadram Institute; Kourosh Ahmadi, Reader in Precision Nutrition, University of Surrey; Liangzi Zhang, Research scientist, Food Composition and Dietary Assessment, Quadram Institute, and Maria Traka, Research Leader, Personalised Nutrition and Gut Microbiome, Quadram Institute