Vegetarian and Vegan Diets: The Evidence.

First, the different types.

• Vegetarian may or may not include egg and dairy products.
• Lacto-ovo-vegetarian includes eggs and dairy products.
• Lacto-vegetarian includes dairy products, but not eggs.
• Ovo-vegetarian includes eggs and egg products, but no dairy.
• Vegan excludes egg and dairy products, and may exclude honey.
• Raw vegan is based on fruits, nuts, vegetables, seeds, legumes, and sprouted grains. The amount of uncooked food varies from 75% to 100%.

Still with me? Good. Now the important part. I am going to cover the benefits, then the risks, and then I will give you an overall conclusion. I will also explain how the risks can be reduced or prevented.

The benefits.

• Decreased risk of ischaemic heart disease, also known as coronary artery disease. This disease is responsible for a major number of deaths worldwide. In the UK alone it is responsible for around 63,000 deaths each year, an average of 170 people a day (British Heart Foundation, 2026). Vegetarians and vegans are at reduced risk (Melina et al, 2016; Raj et al, 2025).
• Decreased risk of type 2 diabetes. People with diabetes have high levels of blood sugar. Type 2 diabetes is where the body's cells stop responding to insulin, which plays a vital role in regulating blood sugar. It can also be where the body does not produce enough insulin. Type 1 is where the body does not produce any insulin at all. Diabetes is a serious condition that can have deadly implications, not to mention the risk of limb amputation due to reduced blood circulation. Plant-based diets are associated with a lower risk (Melina et al, 2016; Raj et al, 2025).
• Decreased risk of certain cancers. Yep, sorry to break the news. Vegetarian diets carry less of an overall cancer risk, and a particularly lower risk of gastrointestinal cancer. Sorry, my fellow meat eaters. The research has found this to be true, at least so far (Melina et al, 2016; Raj et al, 2025).
• Decreased risk of diverticular disease. This condition affects your large bowel. It happens when small pouches, called diverticula, develop in the lining of your bowel and protrude through the bowel wall. In some people this causes symptoms such as stomach pain, though many people have none. British research following nearly 47,000 people found vegetarians had a 31% lower risk (Crowe et al, 2011).
• Decreased risk of eye cataracts. Cataracts occur when changes in the lens of the eye cause it to become less transparent, resulting in cloudy vision. In the same British cohort, vegetarians and vegans had around a 26% lower risk than meat eaters (Appleby et al, 2011).
• Lower body weight. Those who consume high levels of meat will often carry more saturated fat in their diet, and vegetarians tend to have lower body mass indices than meat eaters (Melina et al, 2016; Raj et al, 2025).
• Lower cholesterol. Vegetarian diets tend to produce less low-density lipoprotein cholesterol, the bad cholesterol that likes to clog up our arteries (Melina et al, 2016; Raj et al, 2025).
• Better blood sugar control. Veggie diets are associated with better serum glucose control, which is how well the body regulates blood sugar (Melina et al, 2016; Raj et al, 2025).

Now I want to stress this: these benefits only hold when a vegetarian diet is planned properly. Eating poorly could leave you with a deficiency that makes you sick, tired, and malnourished.

The risks.

• Veggies who miss out on iron are vulnerable to anaemia. More on that in a minute.
• Vegans need continuous sources of vitamin B-12. The bad news is that B-12 is not a reliable component of plant foods, meaning intake for vegans can only be met through fortified foods and supplements. Vegetarians have a bit more room, as they can find it in cheese, eggs, milk, and yoghurt (Melina et al, 2016).

Omega-3 (EPA and DHA)

Vegan diets are typically low in the long-chain fatty acids EPA and DHA, which matter for development and maintenance of the brain, retina, and cell membranes, and which favourably affect pregnancy outcomes and the risk of cardiovascular and other chronic diseases. The long-term effects of reduced EPA and DHA intake are currently not fully understood. Despite this, vegetarian and vegan children do not appear to experience impairment in visual or mental development (Melina et al, 2016).

Iron

Iron is an integral component of blood. If we do not have enough, our body cannot make enough oxygen-carrying red blood cells, and this causes iron-deficiency anaemia. Vegetarians generally consume as much iron as omnivores, or even slightly more. Despite similar intakes, the iron stores of vegetarians are typically below those of non-vegetarians.

So why could this be?

• Iron is found in food in two forms, heme and non-heme. Heme iron makes up about 40% of the iron in meat, poultry, and fish, and it is well absorbed.
• Non-heme iron makes up the other 60% of the iron in animal tissue and all of the iron in non-meat sources such as fruits, vegetables, grains, and nuts, and this form is less well absorbed. However, non-heme iron absorption can be up to ten times greater in iron-deficient individuals than in iron-replete ones (Lynch et al, 1989). This means we can compensate for low iron intake by ramping up absorption, literally many times over, and pull in more non-heme iron. Over time the body adapts to lower intakes and even reduces the amount of iron it loses.
• In one study, total iron absorption increased significantly, by roughly 40% (from 0.12 to 0.17 mg per day), after 10 weeks of consuming a low-bioavailability diet (Hunt & Roughead, 2000).

Zinc

Zinc is found in cells throughout the body and is needed for the immune system to work properly. It also plays a role in cell division, cell growth, wound healing, and the breakdown of carbohydrates, and is needed for the senses of smell and taste.

• Compared with non-vegetarians, studies show adult vegetarians have zinc intakes that are similar or slightly below omnivores, with serum zinc concentrations that were lower but still within the normal range. There do not appear to be any adverse health effects in adult vegetarians attributable to lower zinc intakes (Melina et al, 2016).
• Zinc sources for vegetarians include soy products, legumes, grains, cheese, seeds, and nuts. Organic acids such as citric acid can enhance zinc absorption to some degree.

Iodine

Iodine is a mineral important for a variety of functions, including growth, metabolism, reproduction, nerve and muscle function, regulation of body temperature, and blood cell production.

• Plant-based diets may be low in iodine, and vegans who do not consume key vegan sources such as iodised salt or sea vegetables may be at risk of deficiency. The iodine content of sea vegetables varies widely and some may contain substantial amounts. Intakes should not exceed the Tolerable Upper Intake Level of 1,100 micrograms per day for adults (Institute of Medicine, 2001). Vegan women of childbearing age who do not use iodised salt should supplement with 150 micrograms a day of iodine (Melina et al, 2016). Sea salt, kosher salt, and salty seasonings such as tamari are generally not iodised. Dairy products may contain iodine, although amounts vary considerably.

Calcium

Your body uses 99% of its calcium to keep bones and teeth strong. The remaining 1% plays a key role in cell signalling, blood clotting, muscle contraction, and nerve function.

• Lacto-ovo-vegetarians, whose diet includes eggs and dairy, typically meet or exceed calcium recommendations, while calcium intakes of vegans vary widely and may fall below recommendations. Absorption from high-oxalate vegetables (oxalate being a salt or ester of oxalic acid), such as spinach, beet greens, and Swiss chard, may be as low as 5%, so these are not good calcium sources despite their high calcium content. Absorption from low-oxalate vegetables such as kale, turnip greens, Chinese cabbage, and bok choy is about 50%. Absorption from calcium-set tofu and most fortified plant milks is similar to cow's milk, at roughly 30%. Other plant foods, such as white beans, almonds, tahini, figs, and oranges, provide moderate amounts of calcium with somewhat lower absorption, around 20% (Weaver et al, 1999).

Vitamin D

The major role of vitamin D is to maintain normal levels of calcium and phosphorus in the blood. It also helps the body absorb calcium, which forms and maintains strong bones.

• Status depends on sunlight exposure and intake of vitamin D-fortified foods or supplements. Foods fortified with vitamin D include cow's milk, some non-dairy milks, fruit juices, breakfast cereals, and margarines. Eggs may also provide some. Interestingly, mushrooms treated with ultraviolet light can be significant sources (Melina et al, 2016). If sun exposure and fortified foods are insufficient, supplements are recommended, especially for older adults. Experts recommend daily intakes of vitamin D of 1,000 to 2,000 international units a day.

Protein

• Vegetarians and vegans typically meet or exceed protein requirements when caloric intake is adequate, meaning when you are eating enough of the right food (Melina et al, 2016).

Vitamin B-12

Vitamin B-12 is especially important for maintaining healthy nerve cells, and it helps in the production of DNA and RNA, the body's genetic material (NIH Office of Dietary Supplements, 2024).

• Supports healthy cell renewal. Your body constantly replaces old cells with new ones, and that process depends on DNA being copied correctly each time a cell divides. B-12 is essential for that copying. When you're short on it, cell division goes wrong, which is why a deficiency shows up as large, malformed red blood cells.
• It also works closely with vitamin B-9, also known as folate or folic acid, to help make red blood cells and to help iron work more effectively in the body (NIH Office of Dietary Supplements, 2024).
• B-12 plays a key role in how your body creates energy.
• Improves mood and outlook. Most of you have probably heard about the chemical, serotonin. Our brain uses serotonin to regulate our mood. If you aren't getting enough B-12, you may find yourself feeling down (Moore et al, 2012).
• Protects brain health. Researchers have noted Alzheimer's patients have much lower levels of B-12 than those of a similar age who have sharp, clear memory. In the same way B-12 helps protect nerve cells, it also helps to protect the myelin sheaths of brain cells that are often lacking in Alzheimer's patients (Moore et al, 2012).
• Protects the heart. One of its jobs is to help clear homocysteine. When homocysteine is permitted to roam through our blood, it damages our arteries which leads to inflammation and consequently, coronary artery disease (Esse et al, 2019).

One important correction on B-12 sources. You will often see spirulina, chlorella, and generic algae listed as vegan B-12 sources. They are not reliable: the B-12 they contain is largely made up of inactive analogues that look like B-12 but do not work like it in the body, and may even interfere with true B-12. Nori (purple laver) is more promising, and a 2024 trial found 5 grams a day improved B-12 status in vegetarians (Huang et al, 2024), but it is not yet something to rely on as your only source. The reliable vegan sources are fortified foods (fortified plant milks such as soy, almond, or coconut, and fortified cereals) and supplements. Fortified nutritional yeast, such as Bob's Red Mill, counts only if it is fortified with B-12. Vegetarians can additionally get B-12 from yoghurt, cheese, eggs, and milk.

• Bottom line: vegans must regularly consume reliable sources from supplements or fortified foods, or they will become deficient. This applies to all age groups (Melina et al, 2016). Vegetarians should also include B-12 sources deliberately. One cup of milk and one egg a day provides only about two-thirds of the Recommended Dietary Allowance.

The early warning signs of a serious B-12 deficiency are unusual fatigue, tingling in the fingers or toes, poor cognition, poor digestion, and, in small children, failure to develop properly. Less severe deficiency raises homocysteine, which is associated with inflammation of the blood vessels. This can restrict blood supply to tissues and the oxygen and glucose they need, which is why B-12 deficiency may also be a risk factor for coronary artery disease. People with little or no B-12 intake may feel healthy at first, but long-term deficiency can lead to complications including stroke, dementia, and poor bone health (NIH Office of Dietary Supplements, 2024; Esse et al, 2019).

Conclusion.

A well-planned vegetarian or vegan diet, as the Academy of Nutrition and Dietetics holds, is healthy and provides health benefits when planned properly, although more research is still needed on the long-term effects of a vegan diet (Melina et al, 2016; Raj et al, 2025). A poorly planned diet, whether vegan, vegetarian, or omnivore, is harmful. As a general rule, about two-thirds of our plate should come from vegetables, fruits, whole grains, and beans, and saturated fat should not make up more than 10% of the diet. Vegans in particular should make sure they are getting adequate B-12 and vitamin D for good long-term health.

So there you have it. When planned properly, vegan and vegetarian diets are not only healthy, they may also help prevent some diseases and provide real benefits. Just keep in mind that more research is needed on the long-term effects of vegan diets, particularly the long-term effects of B-12 deficiency and of the missing fatty acids, EPA and DHA.