Plant-based diet benefits & risks

In this Article (Index)

• Vegan, Vegetarian or Omnivore?
• Effects of a Vegetarian/Vegan Diet
• Summary of the Pros and Cons of a Plant-Based Diet
• It has a Positive Effect on the Gut Microbiota
• Protein: Low and inadequate intake
• Similar Saturated Fat levels
• It is High in Fiber
• Vitamin B12 deficiency in vegan/vegetarian diets
• Vitamin D: risk of deficiency
• Iron, heme, and non-heme
• Omega-3 and omega-6 fatty acids
• Health Effects of a Plant-Based Diet
• Low Calcium levels
• Less Weight Gain
• Cholesterol levels
• Blood Pressure
• Cardiovascular disease
• Bone Health
• Diabetes
• Cancer
• Gastrointestinal disease
• Overall Death Rate
• A Balanced Omnivore Diet

Vegan, Vegetarian or Omnivore?

On our website when we mention a balanced diet, which includes plant-based foods (fruits, vegetables, pulses, whole grains, nuts, seeds, and healthy oils), we don't mean going 100% vegan, or vegetarian, or lacto-ovo-vegetarian, we mean eating an omnivore diet, a wholesome diet low in processed foods, high in natural foods, with fewer added sugars, saturated fats, low in sodium, red meat and processed meat, but including poultry, fish, and seafood.

This article looks into the pros and cons of vegan and vegetarian diets compared to animal-based ones, and concludes with an omnivore diet, with moderate amounts of animal protein, and a diverse source of healthy nutrients following the Dietary Guidelines for Americans, the Mediterranean diet, and the DASH diet.

Vegetarians and Vegans

Vegans do not eat any animal-sourced foods or by-products. Lacto-ovo-vegetarians do not consume meat (flesh of animals) yet they eat eggs and dairy products.

Roughly 2.2% of American adults claim they are vegetarian, and 0.5% state they are vegan.

66% of vegetarians are women, so 2.9% of American women and 1.5% of men are vegetarian.

Following a vegetarian or vegan diet isn't easy; most of those who try these diets revert to an omnivore one. For every current vegan or vegetarian, five persons were vegan or vegetarian in the past. Meaning that roughly 1 in 10 Americans have or are trying to eat a plant-based diet. (6)

Plant-based diets have become popular for several reasons, they are supposed to have a positive effect on human health, and also reduce the environmental impact of producing food (rearing animals to slaughter them has a higher impact on the environment and climate change than growing plants). There are also moral reasons, objecting to treating animals as things (breeding and killing sentient beings). Here we will only analyze the health aspects.

Effects of a Vegetarian/Vegan Diet

Summary of the Pros and Cons of a Plant-Based Diet

The fact that plant-based foods don't contain added sugars and additives, are low in saturated fats, and contain fiber, phytochemicals, natural vitamins, and minerals, should contribute to some beneficial health effects. On the other hand, the low-quality protein, and potentially low intake of certain trace elements like calcium, iodine, iron, and vitamins (B12, D) imply health risks.

People who eat a plant-based diet are usually thinner (lower BMI - Body Mass Index) and have improved cholesterol and blood pressure levels than those who eat meat. These factors should improve their cardiovascular health, and reduce the risk for diabetes.

The downside is that vegans and vegetarians have lower bone mineral density, with a higher risk for bone fractures, they also have a higher risk of stroke, mainly hemorrhagic stroke.

Typical Diet

The typical diet has high levels of refined carbohydrates, added sugars, Omega-6 (ω-6) fatty acids, saturated fats, and processed foods, and is low on dietary fiber.

Plant-based diets are rich in dietary fiber, phytochemicals, vitamin C, vitamin E, magnesium, boron, and relatively low intakes of protein, saturated fat, Omega-3 (ω-3) fatty acids, retinol, vitamin B12, heme iron, calcium, iodine, and zinc. (2)

The following sections will look into each of these factors.

In the following sections we will detail its positive and negative effects on nutrients:

• It has a Positive Effect on the Gut Microbiota
• Protein: Low and inadequate intake
• Similar Saturated Fat levels
• It is High in Fiber
• Vitamin B12 deficiency in vegan/vegetarian diets
• Vitamin D: risk of deficiency
• Iron, heme, and non-heme
• Omega-3 and omega-6 fatty acids

It has a Positive Effect on the Gut Microbiota

Plant-based diets promote a more diverse and stable gut microbiome. Its fiber content promotes the growth of many bacterial strains (Ruminococcus, E. rectale, and Roseburia) and reduces the growth of pathogenic ones (Clostridium and Enterococcus), so do the plant's polyphenols increasing the populations of Bifidobacterium and Lactobacillus which have anti-inflammatory and heart-protecting effects.

Fiber fosters the growth of bacteria that ferment it and produce metabolites known as short-chain fatty acids (SCFAs) like acetate, propionate, and butyrate. SCFAs improve immunity, reinforce the gut barrier, and provide energy. (1)

Protein: Low and inadequate intake

The EPIC-Oxford study (European Prospective Investigation into Cancer and Nutrition Oxford cohort) is a cohort of 65,000 men and women living in the UK that was established in the 1990s (2). It revealed that plant-based diets were much lower in protein than diets that included fish or meat: The average protein energy intake was 17.2% (meat-eaters), 15.5% (fish-eaters), 14.0% (vegetarians), and 13.1% (vegans). Those with inadequate levels of protein intake were higher in the plant-based groups than in the meat and fish eaters (9.8% vegetarian men, 6.0% vegetarian women, 16.5% vegan men, 8.1% vegan women vs. less than 5% among meat and fish eaters). (2)

A 2023 study (5) recorded the food intake of 40 Danish vegans for 3 days, to investigate the protein and amino acid composition of their diet. It found that 60% of the subjects met the protein intake recommendations, 18% didn't meet them on any of the 3 days, and 7% met them on only one of the days. For specific amino acids, those who met the recommendations every day, were: 50% for lysine, 67.5% for sulfur-containing amino acids, and 70% for valine and leucine.

Combining both protein levels and intake of essential amino acids, less than half of the participants met the recommendations on all three days (47.5%).

Animal proteins have a better "Digestible Indispensable Amino Acid Score" or DIAAS, which measures protein quality. The DIAAS score for plant proteins is lower than animal proteins due to an unbalanced amino acid composition and lower digestibility. Vegans should combine different yet complementary sources of plant-based protein to ensure a balanced amino acid composition.

The subjects ate grain, oats, seeds, nuts, and peanut butter which are all low in lysine. Furthermore, lysine helps absorb calcium and can impact bone health and the synthesis of collagen. Lentils, tofu, pumpkin seeds, almonds, and quinoa are rich in lysine but were not part of the diet.

They also consumed legumes, mainly chickpeas consumed as hummus or falafel, and soy products (yogurt and milk). These are low in sulfur-containing amino acids like taurine, methionine, and cysteine, critical for maintaining neural health. Consuming quinoa, hemp, amaranth, and buckwheat could increase the intake of sulfur-containing amino acids.

In conclusion, our study showed that many vegan diets in the present survey failed to meet the daily protein intake requirements, both on single days and on all three days. Furthermore, the diets were particularly limited by the essential amino acids lysine, the sulphur-containing amino acids, leucine and valine. This could be ascribed to the fact that the diet was relatively uniform and only a limited number of protein sources were consumed during a day. Aaslyng, M.D., Dam, A.B., Petersen, I.L. et al., (2023)(5)

Similar Saturated Fat levels

The saturated fats intake reported by the EPIC-Oxford study, as a percentage of the total energy intake, was: 10.4%, 9.4%, 9.5%, and 6.9% in meat-eaters, fish-eaters, vegetarians, and vegans respectively. Vegetarians eat 50% more cheese (which is rich in saturated fats) than the flesh-eaters, and this makes their saturated fat intake similar to those eating fish or meat. (2)

It is High in Fiber

Plants and vegetables and unrefined plant-based foods (not refined flours, starches, or carbs) are rich in dietary fiber: 21.7g/day (meat-eaters), 24.9g/day (fish-eaters), 25.6g/day (vegetarians), and 28.9g/day (vegans). (2)

Vitamin B12 deficiency in vegan/vegetarian diets

Plants can't produce vitamin B12, so their content is nil. Animal-based diets, on the other hand, contain this vitamin because it is produced by bacteria in the gut of animals like cows, sheep, goats, deer, etc. and it accumulates in their tissue.

The only source of vitamin B12 for vegans is foods that are fortified with this vitamin, or if they take supplements.

Vitamin B12 deficiency can damage the nervous system, and cause gastrointestinal problems and anemia.

lacto-ovo-vegetrians despite consuming dairy and eggs, have a lower intake of dietary vitamin B12 due to the low levels of this vitamin in eggs and unfortified milk. (4)

The EPIC-Oxford study took some blood samples to measure serum levels of vitamin B12 and reported 281 pmol/l in meat eaters, 182 pmol/l in vegetarians, and 122 pmol/l in vegans. Note that 52% of the vegans and 7% of the vegetarians were below the deficiency threshold of 118 pmol/l. (2)

Since vitamin B12 helps break down the amino acid homocysteine, low levels of this vitamin can lead to increased homocysteine levels, which increases the risk for heart disease, stroke, and dementia.

Vitamin D: risk of deficiency

Vitamin D is normally produced by the body when it is exposed to the sun, but there is a global deficiency of vitamin D influenced by lifestyle, geographic location (in more northern latitudes), the use of sunscreen, etc. So a dietary intake of vitamin D is necessary.
Most of the foods rich in vitamin D are animal-based (eggs, milk, beef, or fish) where it is present in the D3 form, which has a higher bioavailability than the D2 form found in plant-based foods. Vegans and strict vegetarians might be at risk of vitamin D deficiency. (4)

There is a link between Seasonal Affective Disorder or Winter Blues & Vitamin D, and many ways to counteract this disorder.

Iron, heme, and non-heme

The body can't synthesize iron so it obtains it from food or supplements. The heme iron found in animal-based foods (meat, poultry, seafood) is easily absorbed while the non-heme iron found in plant sources like beans, nuts, legumes, spinach, or dark chocolate has a lower bioavailability.

Plant polyphenols, oxalates, and fiber hinder the absorption of non-heme iron. So the uptake of non-heme iron is roughly half of that of heme iron.

It is possible that non-heme iron absorption increases when iron stores are low, like in vegetarians or vegans, and vitamin C, and organic acids found in plant-based foods promote iron absorption; "which might be why iron status is adequate in vegetarians and have no risk of iron deficiency anemia." (4)

Omega-3 and omega-6 fatty acids

Omega (ω) Fatty Acids are found in animal and plant-based foods. The vegan and vegetarian diets are high in omega-6 but low in omega-3 fatty acids. They also lack the two main omega-3 fatty acids: EPA and DHA which are found in oily fish like tuna, salmon, or sardines. (4)
This could entail some health risks as an imbalance of omega-6 to omega-3 increases the risk of cardiovascular disease, diabetes, cancer, and obesity.

Low Calcium levels

Dietary calcium is obtained mainly from milk and dairy products so vegans have a low calcium intake. The daily intakes measured in the EPIC-Oxford study were 1083 mg/day (meat-eaters), 1131 mg/day (fish-eaters), 1117 mg/day (vegetarians), and 848 mg/day (vegans), note that at the beginning of the study, vegans consumed roughly 600 mg/day (582 mg/day and 610 mg/day in women and men respectively), but it increased over the course over the 14-year study. The authors suggest that "the higher intakes in vegans... may be explained by more questions on the questionnaire, and greater availability in shops, for plant-based dairy replacements with calcium fortification." (2)

Many plant-based drinks and breakfast cereals are fortified with calcium. Calcium levels in vegetarians can be 25% lower than in omnivores. A healthy strategy for vegetarians is to choose plant-based foods rich in calcium, and that are high in bioavailability. Another factor to consider is calcium uptake. Calcium absorption varies with age, pregnancy, lactation, and the food we eat.

Plant phytates and oxalates inhibit calcium in plant-based foods. Choosing fortified soy-based products (low in inhibitors and high in calcium) will ensure optimal absorption.

Adequate vitamin D levels help the body absorb calcium. While sodium, caffeine, and phosphoric acid in sodas have the opposite effect, promoting calcium excretion. (4)

Health Effects of a Plant-Based Diet

The following sections will look into the positive and negative health effects of a plant-based diet.

• Less Weight Gain
• Cholesterol levels
• Blood Pressure
• Cardiovascular disease
• Bone Health
• Diabetes
• Cancer
• Gastrointestinal disease
• Overall Death Rate

Less Weight Gain

At the beginning of the EPIC-Oxford study, the BMI (Body Mass Index) of vegans and vegetarians was 2 kg/m² and 2 kg/m² lower than those of meat-eaters, respectively. Showing that they started out thinner.
Over the first five years, meat-eaters and vegetarians gained 400 g per year vs. 300 g per year in vegans, who put on weight at a slower rate.
Yes, unfortunately, we all put on weight as we age as shown by a 2013 study (3) that reviewed data involving almost 125,000 men and women over four years and found that: everyone gains weight over the years.

Being overweight increases the risk of diseases linked to obesity in meat-eaters, but being underweight, for vegans, also entails risks.

Cholesterol

Vegans had a lower level of low-density lipoprotein (LDL), or "bad" cholesterol than meat-eaters. With vegetarians lying in between both groups. (2)

Blood Pressure

Blood pressure was lowest in vegans, influenced by their lower BMI, while meat-eaters and vegetarians had very similar levels. (2)

Cardiovascular Disease

The EPIC-Oxford study reported that the risk for ischemic heart disease was 23% lower in vegans, and 22% in vegans plus vegetarians compared to meat-eaters. The low LDL cholesterol levels and blood pressure values are the likely cause of this lower risk. (2)

Surprisingly, the risk of stroke in vegetarians was 17% higher than in meat-eaters. Similar results were reported by other studies and the cause is unknown, but very likely caused by far too low LDL cholesterol levels or the low intake of animal protein. Low vitamin B12 levels could play a role too. Further research is necessary to clarify this point.

Bone Health

The UK Biobank data shows that the BMD t-score, which compares bone mineral density with that of a young adult (-1 or higher indicates healthy bones, -1 to -2.5 indicates osteopenia, and below -2.5 is a sign of osteoporosis) is lower in vegans: -0.77 vs. -0.61 in vegetarians and -0.55 in meat eaters.
The authors propose that lower intakes of vitamin D, calcium, or protein may be the cause of a worse score. (2)

Vegetarians had a 9% higher risk of bone fracture at any site than meat-eaters, for vegans, the risk was 43% higher. It was 25% higher for hip fracturex in vegetarians and 131% more in vegans. The vitamin D and calcium intakes play a role in this hazard. (2)

More Health Pros and Cons of a Plant-Based Diet

Diabetes

The EPIC-Oxford study reported that " vegetarians and vegans in this population have a substantially lower risk of diabetes than meat-eaters, which appears to be largely or entirely due to their lower BMI." (2)

Cancer

Vegans had an 18% lower risk for any type of cancer compared to meat-eaters, for vegetarians the risk was reduced by 10%. For stomach cancer and hematological cancers, the risk reduction was 62% and 36% in vegetarians. (2)

Gastrointestinal diseases

Compared with meat-eaters, the risk of diverticular disease was 27% lower in vegetarians and 72% lower in vegans (2)

Overall Deat Rate

Despite the influence of disease, "In comparison with regular meat-eaters, all-cause mortality did not differ in vegetarians... or in vegans." The authors suggest that other factors besides diet influence long-term health; they mention, alcohol intake, smoking, and socio-economic factors which affect behavior and lifestyle choices. (2)

A Balanced Omnivore Diet

The Best of Both Worlds

Plant-based diets like vegan or vegetarian offer health benefits, but also have their own health risks. Lack of heme iron, and calcium, the deficit of vitamin B12 and vitamin D, an unhealthy ratio of omega-6 to omega-9 fatty acids, and a low intake of protein with an inadequate mix of amino acids all pose potential health risks.

This section will look into omnivore diets that combine the benefits of both animal and plant-based diets.

A 2022 review (6) takes an evolutionary approach to diet, suggesting that for over two million years, humans and their hominin ancestors have consumed not only fruits, roots, nuts, and plants, but also meat, fish, seafood, and eggs. We are "genetically adapted to procure nutrients from both plant and animal sources."

It lists the negative consequences of a strict vegan diet that we have mentioned further up and suggests that "a more logical diet is a plant-forward omnivorous eating pattern that emphasizes generous consumption of natural, unprocessed foods predominantly from plants. To balance this diet, modest amounts of wholesome animal foods, such wild-caught fish/seafood, pasture-raised meat and eggs, and fermented unsweetened dairy should be consumed regularly."

Sticking to a vegan diet requires concentration, understanding the nutrients, and the effects of the diet, and planning supplementation to counteract any nutrient deficit.

A balanced diet that includes dairy products and meat is recommended by the American Dietary Guidelines.

Furthermore, there is no strong scientific evidence suggesting that eliminating all animal-based food from the diet is good for human health.

Rather than veganism, a plant-forward, omnivorous, whole-foods diet that emphasizes generous intake of natural, unprocessed foods predominantly from plants, ideally consumed at the start of the meal, is more compatible with evolutionary human biology. This diet should be rich in vegetables, nuts, seeds, avocados, olive oil, berries, and other fruits... James H. O'Keefe, Evan L. O'Keefe, Carl J. Lavie, Loren Cordain, (2022) (6)

A study (7) investigated the effects of an entirely plant-based vs a low-fat, reduced–animal product omnivorous diet on body weight and blood lipids in 159 African American adults at risk for cardiovascular disease (CVD). The trial which took place during 2019 and 2020 reported that "participants in both groups saw similar improvements in body weight and CVD risk factor outcomes... Both plant-based and low-fat omnivorous soul food diets produced modest weight loss and CVD risk-related improvements." Showing that a healthy omnivorous diet has positive health effects.

Research supports the notion that modest reductions in animal foods and increases in healthy plant-based foods can improve cardiovascular health benefits compared with a traditional Western Diet.

For instance, a healthy Mediterranean-style diet with lean beef "improved lipids and lipoproteins compared with a typical American dietary pattern." (8) Adding reasonable amounts of lean beef to a low saturated fat, Mediterranean-style diet didn't blunt its heart-protecting effects.

Another study found that not all plant-based foods are the same and that eating more quantity of "healthier plant foods is associated with substantially lower CHD [coronary heart disease] risk, whereas a plant-based diet ... that emphasizes less-healthy plant foods is associated with higher CHD risk." (9)

The healthy plant foods included whole grains, fruits, vegetables, nuts, legumes, healthy oils, tea, and coffee). Less-healthy plant foods included juices and sweetened beverages, refined grains, potatoes, fries, and sweets.

Closing Comments

Combine a Balanced Diet with an active healthy lifestyle

Adding plant-based food to your diet like fruit, vegetables, seeds, whole grain, healthy oils (olive oil), seeds and nuts, and non-beef meat (seafood and fish), lowering the intake of added sugars, saturated fats, beef, processed meat, saturated fats, processed foods, and refined carbohydrates will help you improve your health, reduce CVD risks, diabetes, obesity, and overall mortality.

But diet isn't all; making small changes in your lifestyle can improve your life quality. Add exercise, walking, cycling, swimming, going outdoors, immerse in nature, feel good, and enhance your well-being.