Lily has shared with FEMAIL Food&Drink how exactly these deficiencies could pose a danger to your health, and how you can make sure you consume essential vitamins while still following a vegan diet.
Lily says this vitamin is important for the formation of blood as well as brain function.
She explained: "Deficiencies can result in fatigue, megaloblastic anaemia, early dementia, increased risk of heart disease, nerve dysfunction, forgetfulness, lack of coordination, and psychiatric disorders, as well as the possible development of neurological disorders in babies of breast-feeding mothers.
"This nutrient is only found in animal products (apart from some types of algae), and so it has been shown that as many as 92 per cent of vegans are deficient in this critical vitamin."
But there is a way to consume the vitamin while still being a vegan.
Lily advises vegans to eat plenty of nori seaweed and tempeh - a fermented form of soy that can be fried, grilled or steamed to replace meat - as well as taking a vitamin B12 supplement.
Heme iron
"Heme iron is a specific type of iron, which is only found in meat and fish and is absorbed at a much greater rate than plant-based non-heme iron," says Lily.
She said vegans must eat a lot of iron-rich food such as legume, quinoa, tofu, pumpkin seeds, and dark, green leafy vegetables.
She also recommends taking a vitamin C supplement at mealtimes to help with the absorption of iron.
Omega 3 fats
"These fats are primarily found in oily fish and are essential for both brain and heart health," says Lily.
"They also play a positive role in depression and anxiety, as well as inflammatory conditions, and line every cell within the body. So, if you really want glowing skin and shiny hair, then you need these oils."
Lily says that comparatively, plant-based food has small amounts of omega 3 oils, so you would need to eat a lot of omega 3-rich vegan foods in order to get the same amount that you get from oily fish.
Lily recommends eating flax seeds, flax seed oil, chia seeds, chia seed oil and walnuts everyday if you're embarking on a vegan diet.
High quality protein
"Vegan diets can often be low in high quality protein," says Lily.
"Protein is an essential dietary component, and it is literally the building blocks of the body. Protein is vital to make muscles, organs and even hair, skin and nails. It is also essential for our immune system, as well manufacturing hormones and neurotransmitters such as serotonin."
But Lily says there is a way vegans can make sure they eat plenty of protein if they include at least one of these ingredients in every meal and snack: tofu, tempeh, beans, lentils, chickpeas, peas, quinoa, nuts, seeds and protein powder.
Vitamin d3
"Food sources of vitamin D come from fish and egg yolks, meaning that vegans may be at a greater risk for a low vitamin D status," says Lily.
But she says that vegans can get all the vitamin D they need if they spend enough time in the sunshine and eat plenty of vitamin D-fortified foods.
THE BENEFITS OF GOING VEGAN
There may be risks, but Lily and Jane Land, the founder of Veganuary - the annual drive for people to try veganism in January - says there are plenty of benefits too.
Weight loss
"There is ample research to suggest that vegan diets can be effective for weight loss," says Lily.
"In one study, those following a vegan diet lost 2.52kg more weight than those following an omnivore or vegetarian diet. But the most interesting aspect of the study was that the vegan diets lead to a greater weight loss than the calorie-controlled diet, despite the vegan groups eating until they were full.
"It is likely that this effect is down to the rich fibre content of vegan diets. Fibre can delay stomach emptying, which balances blood sugar and delays feelings of hunger."
Reduced risk of cancer
Jane says: "Vegan diets tend to be higher in fibre, which decreases the risk of colorectal cancer. In 2015, the World Health Organisation classified the consumption of red meat as carcinogenic to humans. This association was observed mainly for colorectal cancer, but associations were also seen for pancreatic cancer and prostate cancer."
Lower risk of heart disease
"High blood pressure is a significant risk factor for heart disease," says Jane. "In 2012, a cross sectional study in Public Health Nutrition compared the blood pressure of non-vegetarians, semi vegetarians, pescatarians, and vegans. The results showed that vegans had the lowest risk for high blood pressure."
Reduced risk of arthritis
"Studies have shown that arthritis suffers who are following a vegan diet may experience less joint pain and swelling," says Lily.
Less likely to die
Jane says: "A recent study conducted by experts at the prestigious Oxford University's Oxford Martin School have found that by 2050, widespread adoption of plant-based diets would avert 8.1 million premature human deaths every year."
