Plant-Based Diets: Potential Health Risks And Dangers

A plant-based diet is often touted as a way to improve health and manage weight, but it is not without its dangers. While it can help lower the risk of heart disease, type 2 diabetes, and certain cancers, it may also increase the risk of stroke. A plant-based diet can also lead to nutritional deficiencies, such as vitamin B12, iron, zinc, calcium, and omega-3 fatty acids, which are more abundant in animal-derived foods. This can result in health issues like cognitive problems, hair loss, weak bones, muscle wasting, skin rashes, hypothyroidism, and anemia. Additionally, plant-based diets can cause digestive issues, such as gas and bloating, especially if the transition is abrupt.

Nutritional deficiencies

Protein

Protein intake is often lower in people following plant-based diets compared to meat-eaters. However, this is usually well within recommended intake levels.

Vitamins and Minerals

Vitamins B12, D, and iodine, as well as calcium, iron, and zinc, may not be sufficient in plant-based diets as these are low, lacking, or have a low bioavailability in plant foods.

Vitamin B12 is only present in animal foods, and vegans rely on regular use of fortified foods or supplements.

Vitamin D is naturally present in fatty fish, eggs, meat, and mushrooms treated with UV light, and vegans are at risk of inadequate intake.

Calcium intake is often lower in vegans compared to vegetarians and meat-eaters, and one-third of studies reported intakes below the recommended amount for all dietary patterns.

Iron and zinc absorption from plant-based diets can be reduced due to the higher amount of phytate and fiber.

Iodine content is usually higher in animal-based foods, and vegans are at risk of inadequate iodine intake.

Fatty Acids

Plant-based diets are often lower in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are mainly present in fish and seafood.

Fiber, Polyunsaturated Fatty Acids, and Folate

On the other hand, plant-based diets are often higher in fiber, polyunsaturated fatty acids (PUFA), and folate.

Energy

Energy intake is usually similar across dietary patterns.

Increased risk of stroke

While a plant-based diet is often associated with a reduced risk of heart disease, some studies have found a link between such diets and an increased risk of stroke, specifically hemorrhagic stroke. Hemorrhagic stroke is caused by a ruptured blood vessel in the brain, leading to blood spillage. This type of stroke can be deadlier than ischemic strokes caused by blood clots.

A study published in the UK-based BMJ analysed 48,188 people in their 40s with no history of heart disease or stroke. The study found that vegetarians experienced a 20% higher risk of stroke than meat-eaters. However, it is important to note that the overall risk was small, equating to three extra cases per 1,000 people over ten years.

There are several possible explanations for the increased risk of stroke among vegetarians. One theory suggests that it may be due to low blood levels of total cholesterol. Another possibility is that vegetarian diets may be deficient in certain essential nutrients, such as vitamin B-12, vitamin D, and other B vitamins like folic acid and B-6, which can increase the risk of stroke.

However, it is worth noting that the BMJ study had some limitations. For example, it was an observational study, which means it may not have accounted for all relevant factors. Additionally, the study population may not have been representative of other genetic backgrounds or obesity rates. Further research is needed to confirm the association between plant-based diets and increased stroke risk and to understand the underlying mechanisms.

Higher rates of depression and anxiety

Following a strictly plant-based diet may lead to higher rates of depression and anxiety. A study found that the mean depressive symptom score for participants following an omnivore dietary pattern was 16.27, which is above the cut-off criterion score of 16, indicating possible experiences of depressive symptoms. In contrast, the mean depressive symptom scores for those following a vegetarian dietary pattern and vegan dietary pattern were below the criterion cut-offs.

Another study found that vegetarians and vegans had increased depressive symptoms compared to their omnivore counterparts. However, other studies demonstrate lower symptoms of depression in plant-based diet samples than in omnivore samples.

A study that surveyed 219 vegans and vegetarians aged 18 to 44 years found that a high-quality plant-based diet was associated with reduced depressive symptoms, and a low-quality plant-based diet was associated with increased depressive symptoms.

A cross-sectional multicentric community trial found that an unhealthy plant-based dietary index is associated with a higher risk of depression and anxiety, while a plant-based dietary index and a healthy plant-based dietary index were not associated with depression and anxiety.

Mechanisms of Action

Protective effects of fruits and vegetables

Plant foods are high in antioxidants and phytochemicals, which generally help to repair damage and decrease inflammation in brain cells. In addition, plant foods can help restore balance to neurotransmitters.

Harmful effects of animal foods

A type of fat found only in animals, arachidonic acid, serves as a precursor to inflammatory chemicals in our bodies. By eating foods high in arachidonic acid, such as chicken, eggs, and other animal products, we set off a cascade of chemical reactions in our body that lead to an increase in inflammatory mediators circulating in the bloodstream. When inflammation reaches the brain, subsequent feelings of anxiety, stress, hopelessness, and depression arise.

Tryptophan and Serotonin

The brain uses the amino acid tryptophan to produce serotonin, a neurotransmitter largely responsible for feelings of happiness and well-being. While meats such as turkey also contain the amino acid, the body can have a difficult time converting it to serotonin. Competition from other amino acids prevents tryptophan from entering the brain, resulting in low serotonin production. A high-protein meal, thus, leads to more amino acids in the blood stream and more competition for tryptophan to enter the brain.

Carbohydrates

Scientists have found meals rich in carbohydrates promote an increase in insulin production, allowing muscle cells to absorb competing amino acids. This makes it easier for tryptophan to cross the blood-brain barrier, increasing serotonin levels in the brain. This may explain the association between depression and carbohydrate cravings.

Omega-3 fatty acids

While the anti-inflammatory effects of omega-3 fatty acids are valid, evidence supports that a diet free of fish and all animal products is optimal for mood improvement. Since a well-planned vegan diet contains alpha-linolenic acid (ALA), which the body is able to convert into EPA and DHA, there is no need to consume it from animal sources.

Difficulties meeting protein requirements

Protein is one of three macronutrients that our bodies use for energy, the other two being carbohydrates and fats. Proteins are made up of 20 individual building blocks called amino acids, 11 of which can be made in the body, while the remaining nine are termed "essential" and need to be obtained through diet.

While plant-based diets can provide all the necessary protein, fats, carbohydrates, vitamins, and minerals for optimal health, they do carry some risk of inadequate protein, vitamin, and mineral intake. However, these risks can be mitigated by choosing the right vegetarian foods and supplements when necessary.

According to Catherine Perez, a registered dietitian with a focus on vegan and plant-based nutrition, vegans and vegetarians should aim to eat 0.9 grams of protein per kilogram of their body weight each day. This slightly higher recommendation compared to the general population (0.8 grams per kilogram) accounts for differences in the digestibility of plant-based proteins due to their high fiber content.

• Eat a Wide Variety of Plant-Based Proteins: Many plant-based protein sources are lacking in one or more essential amino acids. By choosing different options throughout the day, you can ensure adequate intake of all essential amino acids. Include a variety of grains, beans, nuts, seeds, and soy in your diet.
• Choose Plant-Based Milks Fortified with Calcium and Vitamin D: These micronutrients are commonly found in dairy products, but they can also be obtained through plant-based sources.
• Sample Different Whole Grains, Beans, and Lentils: These foods provide a full package of complex carbohydrates, protein, iron, zinc, and B-vitamins.
• Sprinkle Nutritional Yeast on Your Meals: Nutritional yeast is a flavourful ingredient that is a great source of vitamin B12, which is typically obtained from meat.
• Include Nuts and Seeds: These are nutrient-dense options packed with healthy fats, protein, magnesium, and more.
• Opt for Soy-Based Foods: Soy is a complete protein, containing all nine essential amino acids. Examples include textured vegetable protein, black beans, pinto beans, kidney beans, and hemp seeds.
• Incorporate High-Protein Beverages: Include soy milk and pea protein milk in your diet.
• Try Tofu, Tempeh, and Seitan: These are highly digestible plant-based proteins that usually have slightly more protein compared to beans.
• Vegan Meats, Crumbles, and Sausages: These products can help boost your protein intake.

By following these guidelines and being mindful of your protein requirements, you can ensure that you meet your protein goals while following a plant-based diet.

Lack of vitamin B12

Vitamin B12 is an essential vitamin that plays a crucial role in maintaining nerve and blood cell health, as well as DNA synthesis. It is naturally found in animal products like meat, dairy, and eggs, but plant-based foods do not contain significant amounts of this vitamin. As a result, those following a vegan or vegetarian diet need to ensure they consume enough vitamin B12 through other sources or risk facing a deficiency.

The human body requires a small amount of vitamin B12, with an adult's daily intake recommended to be 2.4 mcg. However, it is challenging for vegans to meet this requirement through diet alone. Lacto-ovo-vegetarians can get sufficient vitamin B12 by consuming dairy products and eggs, but vegans primarily rely on fortified foods or supplements. Examples of fortified foods include nutritional yeast, certain breakfast cereals, and plant-based milk substitutes. Additionally, some natural foods like nori seaweed, a type of marine algae, contain small amounts of vitamin B12.

Vitamin B12 deficiency can lead to serious health issues such as pernicious anaemia, impaired brain function, neurological disorders, and an increased risk of developing Alzheimer's and heart disease. Deficiency in pregnant or breastfeeding women can also impact the health of their children, causing neurological disorders in infants.

To avoid vitamin B12 deficiency, it is recommended that individuals following a plant-based diet take a daily vitamin B12 supplement, consume vitamin B12-fortified foods, and regularly monitor their vitamin B12 levels through blood tests. Seeking expert advice when planning a plant-based diet is also encouraged, especially for those who are pregnant, planning to become pregnant, or over the age of 60.

Frequently asked questions