Are we getting enough nutrients?
A diet as described above contains ample amounts of dietary fibres and sufficient protein. Several plant-based proteins, such as soy protein, have a dietary protein quality that is equal to that of protein from animal sources (17). Amino acids from legumes and cereal products complement each other, which means that protein quality is rarely a problem in a diet that contains protein from different plant sources. However, legumes and cereal products do not need to be consumed in the same meal, as was previously thought (17).
Protein quality is rarely a problem in a diet that contains protein from different plant sources
People who follow a vegetarian or vegan diet often have a higher intake of unsaturated fat and a lower intake of saturated fat than others (18). However, special attention must be paid to the intake of long-chain polyunsaturated omega-3 fatty acids. The long-chain omega-3 fatty acid docosahexaenoic acid (DHA) is necessary for, inter alia, the growth and development of the brain and nervous system in foetuses and infants. An adequate DHA intake is therefore particularly important for pregnant women, breastfeeding mothers, and young children. In a traditional diet, common sources of this fatty acid are fish, seafood, cod liver oil and eggs. In a vegetarian or vegan diet, long-chain omega-3 fatty acids can be added in the form of algae oil capsules or liquid oil (1). The short-chain omega-3 fatty acid alpha-linolenic acid, which is found in plants, can be converted to DHA in the body to some extent. Good sources of alpha-linolenic acid include flaxseed and flaxseed oil, walnuts, and pumpkin seeds. However, the conversion rate varies considerably and can be influenced by genetic factors, gender, health, age, and diet (6, 19).
Without supplements or fortified products, it can also be difficult to achieve a sufficient intake of certain vitamins and minerals, such as vitamin B12, iodine and vitamin D (5, 19). An adequate intake of vitamin B12 and iodine during pregnancy and while breastfeeding is essential for normal development of the brain and nervous system in the foetus and breastfed infant. In adults, long-term subclinical vitamin B12 deficiency is associated with, inter alia, dementia (5). A supplement containing various vitamins and minerals, including vitamin B12, vitamin D and iodine, is therefore recommended for vegetarians and vegans (1). The different supplements have slightly different content of nutrients.
A supplement containing various vitamins and minerals, including vitamin B12, vitamin D and iodine, is therefore recommended for vegetarians and vegans
In some supplements, the vitamin B12 content is higher than the recommended intake. The usual mechanism of uptake for this vitamin, via intrinsic factor, is normally saturated at about half the recommended intake of a meal. To increase the uptake, supplements or fortified products can therefore be consumed in two different meals. Another uptake mechanism is via passive diffusion, with approximately a 1 % uptake of higher doses (20). This is the reason why some supplements have a much higher vitamin B12 content than the daily requirement (4). This vitamin has low toxicity, and taking more than the recommended dose is not considered a risk.
Marine plants such as seaweed and kelp have a high iodine content, and some types have dangerously high amounts of iodine. It is therefore important to know the iodine content and adjust the intake accordingly if marine plants are to be used to meet a person's iodine requirement. Dietary supplements are often a safer alternative in terms of iodine (1, 21). Many plant-based drinks are fortified with calcium and various vitamins, including vitamin B12, and those fortified with calcium contain as much calcium as cows' milk. About a half-litre of plant-based drinks fortified with calcium per day, together with calcium-rich foods such as green vegetables and almonds, will provide a sufficient intake. It should be noted that organic plant-based drinks do not contain added vitamins or minerals.