This article was written by one of our contributors; registered dietitian and gut health specialist – Kaitlin Colucci.
A vegan diet is defined as one that eliminates all animal foods and products such as meat, fish, shellfish, insects, dairy, eggs and honey. It is a plant-based diet which is rich in fruits, vegetables, wholegrains, nuts, seeds, beans and pulses, as well as other plant-based sources of protein such as tofu, tempeh, or meat alternative products.
It is now well known that a diet rich in plant diversity can increase the diversity of the gut microbiota (1) – the trillions of bacteria that live inside the large intestine. This is important as a more diverse gut microbiome is associated with better gut health. Research suggests that having a wide variety of microbes in our gut makes our microbiome more capable and resilient (2). A diverse microbiome can function better than a microbiome with only a few kinds of bacteria because if one microbe is unable to fulfil its function, another is available to step in.
What’s so great about plant foods?
Plant based foods are rich in dietary fibre. Fibre cannot be broken down by the body and so passes through the digestive tract undigested, until it reaches the large intestine. Here, the gut bacteria attempt to break down fibre through a process known as fermentation.
High fibre intake also encourages the growth of species that ferment fibre into metabolites known as short-chain fatty acids (SCFAs), most commonly acetate, propionate, and butyrate. SCFAs have a myriad of benefits to the body including improved immunity, blood–brain barrier integrity (3), can have a protective role against types of disease such as type 2 diabetes and inflammatory bowel disease (4), and can help regulate the function of the intestine, as well as brain, and other organs in the body. An increased level of SCFAs positively correlates with the consumption of fruits, vegetables, and legumes in those who follow a plant-based diet (5).
Another benefit of some plant foods to the gut microbiome is their rich polyphenol (special plant compounds) content. Foods such as blueberries, green tea, coffee, red wine, and olives can increase the number of Bifidobacterium and Lactobacillus in the gut, which are beneficial as they provide anti-pathogenic and anti-inflammatory effects and cardiovascular protection (6).
However, it is important to make gradual changes to your diet as any sudden increase in fibre may cause bloating and/or constipation or diarrhoea. In fact, one study found that a short-term but sudden increase in fibre intake resulted in a slight but significant decrease in gut microbiota diversity (7). This reduction in diversity might be the result of a rapid dietary change resulting in a temporary disruption to the microbial composition.
So is a vegan diet the answer to better gut health?
Adopting a vegan diet does not necessarily equal greater dietary variety. In a large clinical trial that compared those who ate a vegan diet, to those who ate a diet including animal products, it confirmed that the gut microbiota diversity was in fact associated with a greater number of overall plants in the diet versus reporting to follow a vegan diet. In fact, individuals who consumed more than 30 types of plants per week (this includes herbs and spices too) had a greater abundance of gut bacteria compared to those who ate less than 10 plants per week (1). What does this mean? Deciding to follow a vegan or plant-based diet must come with careful consideration of increasing total intake of plant-based foods and does not automatically equal a healthier diet if relying on meat and dairy alternative products all the time.
Whether you decide to follow a fully vegan diet or lean towards a more plant-based diet with occasional animal products, eating more plants means an increase in dietary fibre, particularly non-digestible carbohydrates found in a variety of plant-based foods, otherwise known as FODMAPs – fermentable, oligosaccharides, disaccharides, monosaccharides, and polyols.
FODMAPs pass straight through to the large intestine where they are fermented by gut bacteria. This fermentation process produces gas which is a normal part of digestion. However, in those with a hypersensitive intestine, such as those with a functional bowel disorder like irritable bowel syndrome (IBS) this gas production can lead to gut symptoms such as bloating, abdominal pain, diarrhoea, or constipation.
What can I eat if I have IBS and want to follow a vegan diet?
If you have IBS, following a vegan diet can appear challenging, as many plant-based protein sources are naturally high in FODMAPs such as beans and pulses. To make sure your diet is nourishing and nutritionally balanced, you will need to be organised and plan to ensure you get enough protein and nutrients every day.
As always, it is best to work with a dietitian if you suffer from IBS and are trialling a vegan diet. A dietitian will help to ensure that you meet all your nutrient requirements, in particular:
- Vitamin B12
- Omega 3
Aim to have 3-4 portions per day to obtain all essential amino acids.
Aim to use alternative protein foods such as tofu, tempeh, Quorn, soya mince, nuts, and seeds more regularly in your diet. However, the following foods may be suitable:
Tinned and thoroughly rinsed legumes contain fewer FODMAPs compared to those boiled from dry.
The following are classed as low FODMAP:
- ¼ cup (2tbsp) tinned chickpeas
- ¼ cup (2tbsp) tinned butterbeans
- ¼ cup (2tbsp) tinned adzuki beans
- ½ cup (4tbsp) tinned lentils
- 1 cup (8tbsp) tinned kidney beans
As well as these foods, many plant grains contain protein such as quinoa, teff and millet so there’s no need to sacrifice your protein intake.
|65g uncooked teff||12.8g protein|
|175g cooked millet||6.0g protein|
|100g cooked quinoa||4.4g protein|
|40g raw oats||4.2g protein|
|30g rice protein isolate||23.0g protein|
What doesn’t count?
Jackfruit and dairy alternatives are often highlighted as a replacement for a non-vegan food item.
Jackfruit is low in protein and if processed, can be high in fat and salt. Adults should eat no more than 6g salt per day which is approx.1 tsp. A typical glass of almond milk is just about 2% almonds and contains almost no protein (0.1g per 100ml). Soya milk is a good dairy alternative in terms of protein content.
Vitamin D keeps our bones healthy by helping to control the amount of calcium and phosphate in our bodies. It also appears to keep our muscles healthy too.
Vitamin D is mostly made in our skin when we expose our skin to direct sunlight. Some foods contain small amounts of vitamin D, but nowhere near enough to reach the recommended intake of 10mcg per day.
Therefore, it is recommended to take a 10 micrograms (mcg) Vitamin D supplement between the months of October – March.
When choosing a supplement, be aware that some types of vitamin D are not vegan-friendly. Vitamin D2 is always suitable for vegans, but vitamin D3 can be derived from an animal source such as sheep’s wool or lichen (a vegan friendly source).
Calcium is a nutrient that helps keep our bones and teeth strong. In the UK, the recommended intake for adults is 700 milligrams (mg) per day.
Calcium-set tofu and calcium-fortified foods are particularly good sources of calcium. For example:
- 400ml of calcium-fortified plant milk provides around two thirds of an adult’s recommended daily intake of calcium
- 100g of calcium-set tofu (uncooked) provides around half
Other plant-based sources of calcium include:
|food||calcium content (mg)|
|100g uncooked firm calcium-set tofu||350|
|200ml calcium-fortified plant milk||240|
|125g calcium-fortified soya yogurt||150|
|80g cooked kale||120|
|1 tbsp chia seeds||69|
Iron deficiency is the most common nutrient deficiency in the world. The good news is there are lots of plant foods containing good amounts of this mineral.
For adults in the UK, recommended daily iron intakes are 14.8mg for women and 8.7mg for men. Women need more iron than men to make up for the amount of iron they lose during their menstrual period.
Good sources of iron include:
|food||iron content (mg)|
|30g pumpkin seeds||3.0|
|100g uncooked firm calcium-set tofu||2.7|
|30g hulled hemp seeds||2.4|
|30g chia seeds||2.3|
|150g cooked quinoa||2.2|
There are lots of factors that affect the amount of iron that your body absorbs from your diet.
If you are eating a food rich in iron, add a good source of vitamin C to help your body absorb the iron, such as pepper, broccoli, kiwi fruits, oranges, strawberries, or grapefruit.
Avoid drinking tea or coffee with meals as this can make it difficult for your body to absorb iron.
Our bodies need zinc for lots of different functions, including fighting infection and growth.
For adults in the UK, recommended daily zinc intakes are 7mg for women and 9.5mg for men. These recommendations are based on the assumption that zinc losses are higher in men, taking into account losses via skin, hair and semen.
Good sources of zinc include tofu, walnuts, chia seeds, ground linseeds, hemp seeds, pumpkin seeds and quinoa. These foods provide protein and iron too.
It is essential that all vegan diets contain a reliable source of vitamin B12. Deficiency of vitamin B12 can cause anaemia and nervous system damage. Vitamin B12 is made by micro-organisms and isn’t produced by plants. Fortified foods and supplements are the only proven reliable source for vegans. Vitamin B12 is added to some alternatives to milk products, vegan spreads, nutritional yeast flakes, yeast extracts and breakfast cereals.
To get the full benefit, vegans should do one of the following:
- Eat fortified foods two or three times a day to get at least 3 mcg of vitamin B12 a day
- OR Take one vitamin B12 supplement daily providing at least 10 mcg.
- OR Take a weekly vitamin B12 supplement providing at least 2000 mcg.
This might seem like a lot of vitamin B12 in comparison to the daily intake of 1.5mcg recommended for adults in the UK. However, your body absorbs vitamin B12 more efficiently in frequent small amounts, so the less frequently you consume it, the more you need.
Your body uses iodine to make thyroid hormones. These hormones control how fast cells work. In the UK, the recommended iodine intake for adults is 140 mcg per day. Every vegan needs a reliable source of iodine in their diet. However, it is important to avoid too much iodine because this can lead to thyroid disorders.
Seaweed – although seaweed is a rich source of iodine, there are several reasons why it may not be the best option. The iodine content of seaweed is variable, and sometimes too high. Some types may be contaminated.
Iodised salt – public health authorities recommend that we cut down on salt, so this is also not a good option.
Non-seaweed supplement – arguably the most reliable way of meeting your body’s need for iodine.
Plant milk fortified with iodine – identify this type of product by looking for the potassium iodide in the list of ingredients.
Omega-3 & Omega-6
Omega-3 & Omega-6 are classed as essential fatty acids because our bodies cannot make them. These fatty acids affect our immune system, brain, nerves and eyes.
The essential omega-3 fatty acid is called alpha-linolenic acid (ALA). The essential omega-6 fatty acid is called linoleic acid (LA).
If you are eating a varied and balanced diet, it is likely that you are consuming good sources of LA on a regular basis. These include hemp seeds, pumpkin seeds, sunflower seeds, and walnuts. However, eating enough ALA may require more planning.
The following foods are good sources of Omega-3:
- 1 tbsp chia seeds or ground linseeds
- 2 tbsp hemp seeds
- 6 walnut halves
- Use vegetable (rapeseed) oil as your main cooking oil
Although there are no specific recommendations for Omega-3 and Omega-6 intake in the UK, try to include the foods listed above in your diet daily.
Take home message
Can you follow a vegan diet if you suffer from gut related problems? YES! But do you need to follow a vegan diet to cure your gut? NO! Although plant-based foods increase your gut microbe diversity, you can still increase your plant intake whilst consuming dairy and animal products, so the choice is yours!
(1) McDonald, D., Hyde, E., Debelius, J., Morton, J., Gonzalez, A., Ackermann, G., et al. (2018) American Gut: an Open Platform for Citizen Science Microbiome Research. eCollection. May 15;3(3):e00031-18.
(2) Lozupone, C. A., Stombaugh, J.I., Gordon, J.I., Jansson, J.K., Knight, R. (2013) Diversity, stability and resilience of the human gut microbiota. Nature. Sep 13; 489(7415): 220-230.
3) Erny D, Hrabě de Angelis AL, Prinz M. Communicating systems in the body: how microbiota and microglia cooperate. Immunology. (2017) 150:7–15. 10.1111/imm.12645
(4) Koh A, De Vadder F, Kovatcheva-Datchary P, Bäckhed F. From dietary fiber to host physiology: short-chain fatty acids as key bacterial metabolites. Cell. (2016) 165:1332–45. 10.1016/j.cell.2016.05.041
(5) De Filippis F, Pellegrini N, Vannini L, Jeffery IB, La Storia A, Laghi L, et al. . High-level adherence to a Mediterranean diet beneficially impacts the gut microbiota and associated metabolome. Gut. (2016) 65:1812–21. 10.1136/gutjnl-2015-309957
(6) Singh RK, Chang H-W, Yan D, Lee KM, Ucmak D, Wong K, et al. . Influence of diet on the gut microbiome and implications for human health. J Transl Med. (2017) 15:73. 10.1186/s12967-017-1175-y
(7) Scott KP, Duncan SH, Flint HJ. Dietary fibre and the gut microbiota. Nutr Bull. (2008). 33: 201–211. 10.1111/j.1467-3010.2008.00706.x