Plant-Based Diet: What Nutrients Are Missing?

A plant-based diet is a powerful way to achieve good health. However, it is important to be mindful of what you could potentially be limiting when restricting certain foods and/or food groups. Nutrients that are limited in a plant-based diet include calcium, vitamin B12, vitamin D, iodine, iron, zinc, and omega-3 fatty acids. Calcium, for example, is more readily available in dairy products than in plant sources. Similarly, vitamin B12 is only found in animal-based foods. In a plant-based diet, it is important to include fortified foods and/or supplements to ensure adequate intake of these limited nutrients.

Calcium

The general calcium recommendations are:

• Adults under 50 years: 1000 mg calcium daily
• Adults over 50 years: 1200 mg calcium daily
• Maximum: stay below 2000 mg/day from food and supplements combined

It is absolutely possible to obtain all calcium needs solely from food, without any animal products or direct supplementation. However, vegans have been found to show a lower calcium intake than vegetarians and omnivores. This is due to the limited bioavailability of calcium in plant-based diets.

The presence of oxalic acid, or oxalate, in many calcium-rich plant foods, particularly leafy greens, reduces calcium bioavailability as it binds to calcium to form oxalate, which is not very well absorbed by the gut. Spinach, beet greens, and Swiss chard are examples of foods with high oxalate content.

On the other hand, low-oxalate foods such as broccoli, bok choy, kale, and mustard greens are great sources of absorbable calcium. Fortified plant-based milk, tofu, and orange juice are also good options.

It is recommended to obtain calcium from food sources over supplements wherever possible. This is because food sources provide added benefits such as energy, fibre, vitamins, minerals, and antioxidants. If it's not possible to obtain the recommended amount of calcium from food, then supplements may be taken.

Vitamin B12

For those adhering to a plant-based diet, it is crucial to include dietary sources that are fortified with vitamin B12 or take a daily supplement. Fortified foods provide a convenient way to increase vitamin B12 intake. Some common fortified food products include breakfast cereals, plant-based milk alternatives (such as soy milk, almond milk, and rice milk), and meat alternatives made from plants. Additionally, nutritional yeast and yeast extracts, such as Marmite, are often fortified with vitamin B12.

It is worth noting that the body's ability to absorb vitamin B12 decreases with age, as the stomach's capacity to produce the necessary compounds for absorption declines over time. Therefore, it is recommended to consume vitamin B12-fortified foods in smaller quantities throughout the day to ensure adequate absorption.

By including these fortified foods or taking supplements, individuals following a plant-based diet can ensure they meet their vitamin B12 requirements and maintain their overall health and well-being.

Iodine

Dairy products are a main source of iodine in the diet because iodine is used as a disinfectant in many dairy farms. In the United States, Ireland, the UK, and most of Europe, the main source of iodine is from milk and milk products, followed by fish and meat. The high iodine content in milk is a result of iodine addition in cow feed and iodine-containing disinfectants used during milking.

Iodised salt policies have been implemented in various countries to eradicate iodine deficiency. However, recommendations to reduce salt intake to support heart health also mean reducing iodine intake. Most salt used in packaged foods is not iodised.

There is limited research investigating the bioavailability of iodine in plant-based diets, although it appears to be high. However, most literature papers investigating vegan diets highlight iodine as a nutrient at risk of inadequate intakes.

People on vegan diets have been found to fall short of this nutrient and may need a supplement. The recommended daily intake of iodine for adults is 140-150 mcg per day.

Zinc

Some studies suggest that vegans may need up to 50% more zinc than non-vegans, due to the lower bioavailability of zinc in plant-based diets. This means that vegans may need to consume about 16 milligrams per day, and women about 12 milligrams. It is possible to get this amount of zinc from a vegan diet, but it may require careful planning.

Some signs of zinc deficiency include impaired growth in infants and children, frequent infections, loss of appetite, reproductive problems, altered sense of taste and smell, poor wound healing, and changes in cognitive function.

Iron

The recommended dietary allowance (RDA) for iron varies depending on age and sex. For males assigned at birth (MAAB) and females assigned at birth (FAAB), the RDA is about 8–18 milligrams (mg) of iron per day. Children and adolescents may need more or less, depending on their age, and individual needs can vary. For people who are breastfeeding or pregnant, the requirement increases to 9–27 mg per day. Vegans need up to 1.8 times more iron than people who eat meat because non-heme iron from plants is not absorbed as well as heme iron from animal products. On average, vegan women need 32 milligrams of iron per day, while vegan men need 14 milligrams per day.

• Blackstrap molasses: Two tablespoons contain 7.2 milligrams of iron.
• Lentils: One cup contains 6.6 milligrams of iron.
• Tofu: Half a cup contains 6.6 milligrams of iron.
• Tempeh: One cup contains 4.5 milligrams of iron.
• Spinach: One cup of cooked spinach contains 6.4 milligrams of iron.
• Beans: Kidney beans, soybeans, and lima beans have the highest iron content.
• Swiss chard: One cup of cooked Swiss chard contains 4 milligrams of iron.

To increase the absorption of non-heme iron from plant sources, it is recommended to consume vitamin C-rich foods alongside iron-rich plant foods. Vitamin C binds to non-haem iron to form a chelate that is soluble and digestible within the small intestine. Examples of vitamin C-rich foods include bell peppers, broccoli, cabbage, Brussels sprouts, kiwi fruits, oranges, strawberries, pineapples, grapefruits, and orange juice. It is also beneficial to avoid drinking tea and coffee with meals and for at least an hour before or after, as they can reduce iron absorption.

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