A plant-based diet is a powerful way to achieve good health. It can help lower the risk of heart disease, type 2 diabetes, obesity, and other health conditions. Plant-based diets are also rich in dietary fiber and provide all the necessary protein, fats, carbohydrates, vitamins, and minerals for optimal health. However, there are certain nutrients that individuals following these diets may not get enough of, such as calcium, iron, vitamin B-12, and omega-3 fatty acids. With careful planning and the inclusion of dietary supplements, these limitations can be overcome, and individuals can experience the full benefits of this approach to eating.

What other nutrients are affected during a plant-based diet?

Iron: Non-heme iron from plants is not absorbed as efficiently by the body as heme iron from meat

Iron is an essential element for most forms of life, and it is a key component in the human body's metabolic processes, including DNA synthesis, electron transport, and oxygen transport. The body's iron levels are controlled by absorption, and it is estimated that only 3-6% of dietary iron is absorbed by the intestine.

There are two types of absorbable dietary iron: heme and non-heme iron. Heme iron, derived from animal sources such as meat, seafood, and poultry, is more easily absorbed by the body (15-35%) and contributes significantly to our total absorbed iron. On the other hand, non-heme iron, which comes from plants and iron-fortified foods, is less efficiently absorbed. This is because non-heme iron must be converted from ferric (Fe3+) to ferrous (Fe2+) iron before it can be transported and absorbed by the body.

The body's ability to absorb non-heme iron can be further inhibited by certain compounds found in plant-based diets, such as phytates, polyphenols, and oxalic acid. These compounds have a dose-dependent effect on iron absorption, reducing its availability in the human gastrointestinal tract.

However, the absorption of non-heme iron can be enhanced by including vitamin C in the diet. Ascorbic acid forms a chelate with ferric iron in the stomach, which remains soluble in the duodenum, thus improving absorption.

While heme iron is more efficiently absorbed, it is important to note that it comprises only about half of the iron in meat, with the rest being non-heme iron. Therefore, a balanced diet that includes a variety of plant-based and animal-based sources of iron can help ensure adequate iron intake and absorption.

Calcium: Vegans are observed to consume less calcium than vegetarians and omnivores

Calcium is the most common mineral found in the body and is essential for many bodily functions, such as muscle movement, including the heart. It also plays a role in muscle contraction, blood clotting, nerve signalling, and regulating blood pressure. The body cannot produce calcium on its own, so it must be obtained through diet.

Vegan diets are often found to be lacking in calcium, which is primarily found in dairy products. Research has shown that vegans tend to consume less calcium than vegetarians and omnivores. This is because many non-dairy foods that contain calcium, such as vegetables, have very low levels of calcium compared to dairy products. Furthermore, some vegetables contain substances that block the body's ability to absorb calcium. For example, spinach, which is high in calcium, also contains oxalic acid, which prevents the body from absorbing 95% of the calcium it provides.

To get the recommended daily amount of calcium without consuming dairy, one would need to eat a large volume of vegetables. For instance, a person would need to eat 20 servings of broccoli or 10 servings of kale per day to get the same amount of calcium as a cup of milk. This is why experts say that vegans are likely to be calcium deficient.

However, there are some plant-based sources of calcium that can fit into a well-balanced vegan diet. These include soybeans and soy products like tofu, tempeh, and soy milk; leafy greens like spinach, turnip greens, kale, and collard greens; certain seeds and nuts, especially almonds, Brazil nuts, chia seeds, and sesame seeds; seaweed; beans and lentils; and some fruits, such as figs, oranges, kiwis, apricots, and papaya. In addition, some processed foods and drinks are fortified with calcium, including certain cereals, plant-based yogurts, and plant-based milk alternatives.

It is important for vegans to monitor their calcium status and include a wide variety of calcium sources in their diet. If necessary, vegans can also take calcium supplements to ensure they are getting enough of this vital mineral.

Vitamin B12: Found in animal products, so vegans need to supplement their diet with B12-fortified foods

Vitamin B12, also known as cobalamin, is an essential nutrient for humans. It is a vital component in the synthesis of blood cells and brain nerve tissue, and it also plays a crucial role in the formation of DNA. A deficiency in vitamin B12 can lead to adverse health effects, such as fatigue, weakness, tingling sensations in the hands and feet, depression, and memory impairment.

Vitamin B12 is naturally found in animal products, including meat, eggs, and dairy. As a result, vegans, and to a lesser extent, vegetarians, are at a higher risk of vitamin B12 deficiency since they exclude some or all of these products from their diets. It is important to note that vitamin B12 is not produced by plants, and while some plant-based sources like shiitake mushrooms and certain algae products do contain small amounts of vitamin B12, their bioavailability may vary.

To ensure adequate vitamin B12 intake, it is recommended that vegans and vegetarians include B12-fortified foods in their diets. This can include vitamin B12-fortified breakfast cereals, plant-based milk alternatives, and nutritional yeast. Additionally, taking a daily vitamin B12 supplement can help prevent a B12 deficiency.

• Fortified breakfast cereals: Fortified cereals are a good source of vitamin B12, as they have high bioavailability, meaning the body can easily absorb the vitamin.
• Plant-based milk alternatives: Non-dairy milk alternatives, such as soy, oat, or almond milk, are often fortified with vitamin B12 and can be a good way for vegans to get their daily intake.
• Nutritional yeast: This is a popular choice for vegans and vegetarians as it has a cheesy, nutty flavor and can be easily added to various dishes. Nutritional yeast is typically fortified with vitamin B12, providing a significant amount of the daily value in small quantities.
• Seaweed and algae: Seaweed, commonly used in Asian cuisine, is a natural source of vitamin B12. However, the amount of vitamin B12 can vary depending on the type and batch of seaweed.
• Shiitake mushrooms: While these mushrooms contain vitamin B12, the amount is relatively low, and they may need to be supplemented with other sources.

In addition to including B12-fortified foods, it is recommended that individuals on plant-based diets monitor their vitamin B12 levels and seek expert advice when transitioning to a vegan diet, especially for those who are pregnant, planning to become pregnant, or older than 60 years of age.

Omega-3 fatty acids: Plant-based diets provide alpha-linolenic acid (ALA), which the body converts to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), but the conversion is inefficient

Omega-3 fatty acids are essential fats that have numerous health benefits, including maintaining heart and brain health, kidney function, eye health, and skin health. There are three main types of omega-3 fatty acids: EPA, DHA, and ALA. While EPA and DHA are mostly found in animal foods like fatty fish, ALA is the most common omega-3 fat and is predominantly found in plants.

Plant-based diets provide alpha-linolenic acid (ALA), which the body can convert into eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, this conversion process is inefficient in humans, with only a small percentage of ALA being converted into EPA and even less into DHA. On average, only 1-10% of ALA is converted into EPA, and 0.5-5% into DHA. This conversion rate depends on having adequate levels of other nutrients such as copper, calcium, magnesium, zinc, iron, and vitamins B6 and B7, which may be lacking in a vegetarian or vegan diet. Additionally, certain omega-6 fatty acids compete for the same enzymes needed for this conversion process, and the high amount of omega-6 in the modern diet may further reduce the conversion of ALA to EPA and DHA.

Despite the inefficient conversion, individuals following plant-based diets are not necessarily deficient in these longer-chain omega-3s. In fact, one study found that women following vegan diets had significantly more long-chain omega-3 fats in their blood compared to fish eaters, meat eaters, and ovo-lacto-vegetarians. This suggests that even with zero intake of long-chain omega-3s (EPA and DHA) and a lower intake of plant-derived ALA, vegan participants were able to convert robust amounts of shorter-chain fatty acids into these long-chain fatty acids.

Most people following plant-based diets have no problem getting enough omega-3s in their diet, and one study found that people who follow vegan diets have intakes above the recommended amounts for omega-3 fats. However, the likelihood of having lower EPA and DHA levels among vegans is higher, but this does not extend to any known clinical relevance. Researchers note the advantage of a vegan diet for heart health compared to a non-vegan diet. Additionally, a plant-based diet that includes whole, plant-based foods may result in a more desirable ratio of omega-6 to omega-3 fatty acids, reducing excess inflammation in the body.

Vitamin D: Found in animal products, though the body can also produce it through sun exposure

Vitamin D is essential for maintaining optimal health, and while humans derive most of it from sunlight exposure, it can also be obtained through diet. Vitamin D, also known as cholecalciferol (vitamin D3), is naturally present in certain animal products and plays a crucial role in regulating calcium and phosphorus metabolism, ensuring normal mineralisation of bones.

Vitamin D is predominantly found in animal-based foods such as fish, meat, offal, eggs, and dairy products. However, the vitamin D content varies significantly among these food sources. Fish, especially fish liver, contains the highest levels of vitamin D, ranging from <2 µg/kg to 477 µg/kg. Offal, such as liver and kidney, also provides substantial amounts, with kidney containing the highest concentration among these meats. The vitamin D content in muscle meat, including beef, pork, lamb, veal, and poultry, is generally much lower, ranging from 0.0 µg/kg to 23.0 µg/kg. Egg yolks contain moderate amounts of vitamin D, with concentrations ranging from 32.5 µg/kg to 55.8 µg/kg.

It is important to note that milk and dairy products are typically low in vitamin D if they are not fortified. Butter is an exception due to its high-fat content, which can result in higher vitamin D levels. Additionally, the vitamin D content in animal products can be influenced by factors such as animal supplementation, sunlight exposure, seasons, and geographical location.

While vitamin D is naturally present in animal products, it is essential to recognise that a plant-based diet can still provide adequate vitamin D through sun exposure. However, with the shift towards indoor activities in modern Western lifestyles, sun exposure may not always be sufficient for optimal vitamin D production. As a result, dietary intake becomes crucial, and vitamin D supplements or fortified foods may be necessary to meet the recommended daily intake.

In summary, while vitamin D is found in animal products, it is also produced by the body through sun exposure. The amount of sun exposure required can vary depending on individual factors and geographical location. A plant-based diet does not directly provide vitamin D from food sources, but it does not necessarily lead to a deficiency as sunlight can be a significant contributor to overall vitamin D levels. However, in cases where sun exposure is limited, supplements or fortified foods may be necessary to ensure adequate vitamin D intake.

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