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Nutrition
The vegetarian diet: Is it healthy?
Written by
Robbie Puddick
Medically reviewed by
Fiona Moncrieff
9 min read
Last updated December 2024
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Is a vegetarian diet healthy? Yes, but there are downsides
A vegetarian diet can be considered a healthy eating pattern. In many observational studies, well-planned vegetarian diets have been associated with a lower risk of heart disease and better health outcomes than meat-eaters, including lower cholesterol levels and blood pressure.
However, much of this research is confounded by what is known as ‘healthy user bias’.
Vegetarians are more health-focused and tend to exercise more, smoke and drink less, and lead healthier lifestyles than the typical omnivore (meat eater). So it’s difficult to say that the health benefits are down to diet or overall lifestyle.
When research has compared health-conscious vegetarians to omnivores, the ‘advantage’ of vegetarian diets largely disappears.
Vegetarians are also more at risk of deficiencies in B12 and iron and are more likely to have lower bone mineral density and an increased risk of fractures.
However, this isn’t to say you can’t be healthy as a vegetarian; there’s enough research suggesting that if you’re able to get all the nutrients your body needs and your diet is based on whole foods, it promotes good health outcomes and reduces your risk of chronic diseases.
But vegetarians might need to pay a bit more attention to ensure they’re getting enough of certain nutrients to promote optimum health than non-vegetarians.
What is a vegetarian diet?
Vegetarian diets have been around for millennia. Ancient religions such as Hinduism and Sikhism are predominantly vegetarian, with some sectors of those religions eating a largely plant-exclusive diet where they might occasionally consume eggs or dairy.
In modern Western culture, many people that follow a vegetarian diet tend to be motivated by ethical and environmental concerns around animal agriculture.
Many will also be motivated by health, particularly heart health, and vegetarians’ diet quality tends to be higher than meat-eaters.
A higher intake of plant-based whole foods such as fruits, vegetables, nuts and seeds will likely lead to health improvements, including benefits to the gut microbiome.
However, research suggests that vegetarians are more at risk of certain deficiencies, such as B12 and iron, and an increased risk of fracture than meat and fish eaters as they typically consume fewer essential amino acids in animal foods.
There are many different forms of a vegetarian diet, with some vegetarians avoiding only the flesh of the animals (meat) and others avoiding eggs or dairy as well.
Predominantly, the term vegetarian (or veggie) refers to individuals who base their diets on plant-based foods such as whole grains like quinoa and brown rice, lentils, legumes, chickpeas, nuts, seeds, and vegetables. Vegetarian diets are typically low-fat, particularly saturated fat and higher in carbohydrates compared to omnivorous diets.
They’re predominantly plant-based diets as they don’t eat the flesh of animals but, different to vegan diets, consume some animal products such as eggs or dairy foods.
The three main types of vegetarian diets:
- Lacto-Ovo vegetarian: consumes dairy and eggs but no meat
- Lacto-vegetarian: consumes dairy but not eggs or meat
- Ovo-vegetarian: consumes eggs but not dairy or meat
To simplify things in this guide, we’ll use the blanket term ‘vegetarian’ to encompass all vegetarian-style diets. (Unless there’s a specific need to identify the individual styles if we’re talking about the risk of certain deficiencies.)
At Second Nature, you’d be supported by a registered nutritionist and dietitian and have access to over 200 plant-based recipes to ensure you’re maximising your health on a vegetarian diet.
Click here to here to join plant-based eaters, like Sarah, on their journey to improved health. Otherwise, keep reading as we analyse three lines of evidence assessing the vegetarian diet.
1) The vegetarian diet can have modest effects on weight loss
Considering high body fat is associated with various chronic diseases such as type 2 diabetes, heart disease, and some cancers, maintaining a healthy weight is crucial to a healthy lifestyle.
Observational research suggests vegetarians have a lower risk of developing obesity than omnivores. However, as discussed above, this is typically determined by overall diet quality and lifestyle.
Still, randomised controlled trials have suggested that vegetarian diets can have a modest effect on weight loss compared to healthy diets that include meat.
A 3-month trial investigated the impact of a low-calorie vegetarian diet to a Mediterranean diet on weight loss and other markers of cardiovascular health in omnivores at baseline.
The study showed that both groups lost a similar amount of weight, with the vegetarian diet group averaging 1.88kg and the Mediterranean diet averaging 1.77kg.
Interestingly, only the Mediterranean diet improved levels of triglycerides and a pro-inflammatory cytokine called Il17. Both are considered risk factors for cardiovascular disease.
Similarly, a meta-analysis of randomised controlled trials found that the vegetarian diet was more effective at promoting weight loss than diets containing meat.
However, most studies in this analysis compared a healthy vegetarian diet to control diets that are typically the standard American diet – a diet that’s very high in ultra-processed foods and low in dietary quality that also contains meat.
So while the vegetarian diet can promote weight loss compared to unhealthy diets containing meat, it doesn’t seem more effective at promoting weight loss than healthy omnivorous diets.
Key points:
- Observational research suggests a positive association between vegetarian diets and body weight.
- Randomised controlled trials also show a modest effect on weight.
- While vegetarian diets show a positive effect on weight loss compared to unhealthy diets containing meat, it doesn’t seem more effective than healthy omnivorous diets.
2) Potential deficiencies
Many people will likely enjoy a honeymoon period after transitioning to a vegetarian diet. Your health will likely improve with a reduction in ultra-processed foods and an increased intake of fruits and vegetables.
However, certain nutrients are challenging to obtain from plant foods, and some can only be found in animal foods, such as vitamin B12 or K2.
These deficiencies will take time to develop. For example, the liver can store enough B12 for up to 3-5 years before deficiency becomes clinically apparent.
Vitamin B12
Also known as cobalamin, vitamin B12 is essential for the function and development of the central nervous system, ensuring healthy red blood cell formation, and DNA synthesis.
While eggs and dairy are rich sources of B12, research has suggested that vegetarians are more at risk of developing B12 deficiency than omnivores.
A study from Germany assessed the nutrient status and bone health of vegetarians and omnivores in 122 individuals.
It showed that vegetarians’ average blood levels of B12 were 57% lower compared to omnivores, and 66% of vegetarians had vitamin B12 levels below the recommended threshold, indicating deficiency.
However, it’s been observed that a higher intake of foods containing B12 and supplementation can help avoid B12 deficiencies.
A study in German children comparing nutrient status among vegan, vegetarian, and omnivores suggested no difference between the three groups in B12 levels; 39% of vegetarians in the study reported taking B12 supplements regularly.
It’s recommended that vegetarians should consider taking a B12 supplement if eggs and dairy aren’t consumed in a high enough volume to maintain adequate levels of B12.
It’s also recommended to check whether your dairy replacements, like soy milk or other soy products, are fortified with B12.
Vitamin K2
K2 is an essential nutrient that has roles in our cardiovascular system, is a potent anti-inflammatory, and works with vitamin D to promote good bone health.
Insufficient intake of K2 could lead to an increased risk of cardiovascular disease, fractures, and bone conditions such as osteoporosis (a condition of excess bone breakdown).
K2 is primarily found in animal products, particularly fermented foods such as yoghurt and cheeses.
K2 can be found in some fermented plant foods. A Japanese dish of fermented soybeans known as natto, for example, is the richest source of a type of K2 called MK-7. MK-7 is the most bio-available form of K2 and has the most health-promoting benefits.
However, fermented plant foods aren’t readily available to everyone and aren’t typically consumed in a high enough volume to promote K2 levels in the blood.
It’s therefore recommended that vegetarians regularly consume fermented dairy products, while Ovo-vegetarians should consume a K2-MK7 supplement if fermented plant foods aren’t regularly consumed.
Iron
Iron is an essential mineral that has key roles in many biological processes in the body, from blood transport to energy metabolism.
Iron is rich in many plant foods, mainly green leafy vegetables such as spinach and kale. The issue comes, however, in the bioavailability (how much your body can absorb and use).
The form of iron found in plant foods is known as non-heme iron, which is not as readily absorbed by the gut. Plants also contain anti-nutrients such as phytates and oxalates, inhibiting iron absorption.
Observational research has suggested that vegetarians are at an increased risk of iron deficiency.
Similarly, a cross-sectional study of vegan, vegetarian, and omnivore children in Poland found that 18.3% of vegetarians had depleted iron stores, compared to 12.8% of omnivores.
In contrast, a study on German children showed that both vegan and vegetarian children had sufficient iron levels (although they were lower than omnivores), as their iron supplementation was high.
It’s also been shown that cooking and including vitamin C in meals can increase the absorption of non-heme iron. So alongside supplementation, there are simple and accessible ways of increasing iron status in vegetarians.
Omega-3 fatty acids
While there’s no official cut-off or diagnosis for omega-3s, good evidence suggests they provide multiple health benefits.
Vegetarians might consider taking an algae supplement to ensure they have a marine omega-3s EPA and DHA source. Plant-based foods like flaxseed, walnuts, and chia seeds can also boost some conversion of ALA into EPA and DHA.
Key points:
- Many people will experience improved health after transitioning to a vegetarian diet, despite lower intakes of certain nutrients.
- Some nutrient deficiencies take years to develop and become clinically apparent.
- Research has suggested that vegetarians are at increased risk of B12, K2, and iron deficiency.
- Paying close attention to ensure foods higher in these nutrients are consumed, and potentially using supplementation, should help avoid deficiencies.
- It’s recommended to see you GP if you’re concerned about nutrient deficiencies.
- Vegetarians should consider and omega-3 algae supplement to boost intake of EPA and DHA.
3) Bone health
Bone health is essential to maintaining the quality of life and independence. Falls, for example, are one of the most significant mortality predictors in adults over 65.
The relationship between falls and mortality can be attributed to lower bone mineral density and increased fracture risk, leading to further complications such as osteopenia (muscle wasting).
Bone health can be measured in three ways:
- Osteoporosis incidence
- Risk of fractures
- Bone mineral density
Research has shown that vegetarians are at a higher risk of developing fractures and having lower bone mineral density than meat and fish eaters, while evidence on osteoporosis is currently lacking.
To maintain adequate bone health, the body is constantly going through a process of bone remodelling known as ossification.
We require a few critical nutrients for bone remodelling: protein, calcium, vitamin D, vitamin B12, and vitamin K2.
As highlighted above, some of these nutrients and vitamins are more challenging to obtain on vegetarian diets.
However, research has suggested with proper planning; a vegetarian diet can support adequate bone remodelling and bone mineral density.
A trial investigated the impact of three different sources of protein on bone mineral density during weight loss in premenopausal women.
It found that Lacto-Ovo sources of protein, such as eggs and dairy, enabled women to maintain bone mineral density. At the same time, those consuming lean pork or chicken saw a decrease in bone mineral density during weight loss.
Therefore, it’s recommended to prioritise a higher intake of foods that contain these nutrients, particularly protein, and consider supplementation.
If you don’t have a background in nutrition, it can be difficult to know where to start and what foods to prioritise. Click here if you’d like a 7-day vegetarian meal plan developed by the nutritionists at Second Nature.
Key points:
- Bone health is essential to our longevity, particularly as we age and is typically measured by bone mineral density and fracture risk.
- Observational and cross-sectional studies have suggested that vegetarians are at increased risk of lower bone mineral density and fracture risk.
- B12, K2, and protein are key vitamins and nutrients to support bone remodelling and health.
- While more challenging to obtain on a vegetarian diet, research suggests that with proper planning adequate intake can be achieved.
Take home message
The vegetarian diet is a healthy way to eat. There’s sufficient research showing that vegetarians typically eat a diet of higher quality (more whole foods) than the typical meat eater and have a lower risk of early mortality than the general population.
However, like any diet that removes entire food groups, there’s always a risk of certain deficiencies, such as B12 or K2, or insufficient intake, such as protein and iron, which could have negative effects in the long term.
We’d recommend paying close attention to some of the nutrients and vitamins we’ve highlighted and seeing your GP for an annual check-up to ensure you’re providing your body with everything it needs to thrive.
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