The momentum behind a move to plant-based and vegan diets for the good of the planet is commendable, but risks worsening an already low intake of an essential nutrient involved in brain health, warns a nutritionist in the online journal BMJ Nutrition, Prevention & Health.
To make matters worse, the UK government has failed to recommend or monitor dietary levels of this nutrient – choline – found predominantly in animal foods, says Dr. Emma Derbyshire, of Nutritional Insight, a consultancy specialising in nutrition and biomedical science.
Choline is an essential dietary nutrient, but the amount produced by the liver is not enough to meet the requirements of the human body.
Choline is critical to brain health, particularly during fetal development.
It also influences liver function, with shortfalls linked to irregularities in blood fat metabolism as well as excess free radical cellular damage, writes Dr. Derbyshire.
The primary sources of dietary choline are found in beef, eggs, dairy products, fish, and chicken, with much lower levels found in nuts, beans, and cruciferous vegetables, such as broccoli.
In 1998, recognising the importance of choline, the US Institute of Medicine recommended minimum daily intakes.
These range from 425 mg/day for women to 550 mg/day for men, and 450 mg/day and 550 mg/day for pregnant and breastfeeding women, respectively, because of the critical role the nutrient has in fetal development.
In 2016, the European Food Safety Authority published similar daily requirements. Yet national dietary surveys in North America, Australia, and Europe show that habitual choline intake, on average, falls short of these recommendations.
“This is….concerning given that current trends appear to be towards meat reduction and plant-based diets,” says Dr. Derbyshire.
She commends the first report (EAT-Lancet) to compile a healthy food plan based on promoting environmental sustainability, but suggests that the restricted intakes of whole milk, eggs and animal protein it recommends could affect choline intake.
And she is at a loss to understand why choline does not feature in UK dietary guidance or national population monitoring data.
“Choline is presently excluded from UK food composition databases, major dietary surveys, and dietary guidelines,” she adds.
It may be time for the UK government’s independent Scientific Advisory Committee on Nutrition to reverse this, she suggests, particularly given the mounting evidence on the importance of choline to human health and growing concerns about the sustainability of the planet’s food production.
“More needs to be done to educate healthcare professionals and consumers about the importance of a choline-rich diet, and how to achieve this,” she writes.
“If choline is not obtained in the levels needed from dietary sources per se then supplementation strategies will be required, especially in relation to key stages of the life cycle, such as pregnancy, when choline intakes are critical to infant development,” she concludes.
More information: Editorial: Could we be overlooking a potential choline crisis in the United Kingdom? DOI: 10.1136/bmjnph-2019-000037
Provided by British Medical Journal
Might vegan diets be healthy?
Many nutritionists claim that vegan diets can be healthy; the American Dietetic Association (ADA), for example, has argued that ‘appropriately planned … vegan diets … are appropriate for individuals during all stages of the life cycle’ (ADA 2009, 1266). To address this question in detail, however, it is necessary to focus on those dietary components that have frequently been suspected to be deficient in vegan diets. The components that deserve special scrutiny are: protein, calcium, vitamin B12, vitamin D, essential fatty acids, zinc, iodine, and iron.
Peas, lentils, and beans are good sources of protein that are readily available and relatively easy to grow in many parts of the world. It is important that vegans consume protein foods that contain the full range of essential amino acids overall; although there is no need for the full range of essential amino acids to be part of every meal (ADA 2009, 1268; McEvoy and Woodside 2010, 87), it is clear that we do need all essential amino acids to be healthy, which is why diets that rely on a very limited range of protein sources must be avoided. Although concern has been expressed over some populations that rely heavily on staples with limited quantities of protein, such as taro, cassava, and yams, Millward (1999, 259) has argued that ‘cereal-based diets, especially those based on wheat and maize, supply protein levels considerably above the requirement level’. However, there is no evidence to suggest that those who consume relatively small quantities of cereals are likely to have deficiencies, provided that they consume other foods that contain significant quantities of protein. Overall, there is no evidence to suggest that vegans who eat a good range of plant foods are likely to lack in protein (Messina et al. 2004).
Fruits and vegetables that contain relatively large amounts of potassium and magnesium decrease bone calcium resorption, whereas diets that include relatively large amounts of nuts and grains increase such resorption by producing a high renal acid load, mainly caused by residues of sulfates and phosphates (ADA 2009, 1269). Green leafy vegetables that are low in oxalate, including broccoli, kale, spring greens, and cabbage, tend to be high in calcium, as well as in vitamin K, another important contributor to bone health (Messina and Mangels 2001, 663). The study of the Oxford-cohort of the European Prospective Investigation into Cancer and Nutrition (the ‘Oxford-EPIC cohort’) found that adult vegans who consume more than 525 mg of calcium per day do not show higher fracture rates than omnivores (P. Appleby et al. 2007). There is no evidence that well-planned vegan diets fail to provide sufficient calcium, but there is evidence that diets that include adequate amounts of calcium and vitamin D are protective of bone health (Tang et al. 2007).
No plant foods are known to produce vitamin B12, or cobalamin, but those who eat plants inadvertently eat B12 as this vitamin is produced by micro-organisms (particularly Pseudomonas denitrificans and Propionibacterium shermanii) who live in symbiosis with many plants. The presence of vitamin B12 is essential for cell growth, and crucial for a healthy nervous system. Vitamin B12 deficiency leads to elevated plasma homocysteine (Hcy) concentrations (hyperhomocysteinaemia), a risk factor for neurological disorders and cardio-vascular problems, including pernicious anaemia and haematological disease (megaloblastic anaemia with demyelination of the central nervous system) (McEvoy and Woodside 2010, 90; Waldmann et al. 2005). Whereas our intestinal bacteria can synthesise B12, it is generally assumed that we should also consume products containing B12 (Li 2011).
Some studies have found that some vegans had inadequate intakes of B12, where particular concerns have been raised over the B12 status of older people due to their limited absorption capacity and of pregnant women due to their higher demands (Majchrzak et al. 2006; Waldmann et al. 2005; Donaldson 2000; ADA 2009; Piccoli et al. 2015). This is not a reason to eat flesh, as B12 binds with the protein in animal foods, impeding absorption, which is precisely why older people are better off with vegan sources of B12 (Norris and Messina 2011, 31). Since the haematological symptoms of vitamin B12 deficiency may go undetected for a long time due to a high consumption of foods containing folate (folic acid), of which many vegans consume rather a lot through the consumption of things like oranges, green leafy vegetables, and beans, vegans must be very careful to ensure that their consumption of B12 is sufficient (ADA 2009, 1269). Many products, including cereals and yeast extracts, now exist that have been fortified with B12 produced through industrial fermentation of bacteria. In his assessment of the evidence, Sanders (1999, 267) has written that, provided that ‘these foods are consumed regularly, the hazard of vitamin B12 deficiency is easily avoided’.
Norris and Messina (2011, 32) usefully point out that the human body only absorbs a tiny amount of B12 every time the vitamin is consumed, which is why they recommend the adoption of any one of these strategies for optimal consumption: 1/ two daily servings of fortified foods, providing 1.5 to 2.5 micrograms each; 2/ one daily supplement of at least 25 micrograms; 3/ one supplement of 1,000 micrograms twice weekly.
Inadequate levels of vitamin D have long been known to contribute to bone problems such as rickets, but more recently have also been found to contribute to a range of other conditions, including fibromyalgia, rheumatoid arthritis, multiple sclerosis, depression, cancer, hypertension, and diabetes (Norris and Messina 2011, 47). Adequate exposure to sunlight can provide the body with all the vitamin D it needs, but overexposure must be avoided as ultraviolet irradiation is a significant contributor to skin cancer. Those people who are not regularly exposed to sunlight, as well as those whose bodies are limited in the uptake of vitamin D, such as older and dark skinned people, must therefore consume products that have been fortified with vitamin D or take supplements (Craig 2009, 1629S; Stacey et al. 2005, 1444; Holick 2007). Vitamin D3 (cholecalciferol), used as a supplement, is usually derived from lanolin (sheep’s wool) or fish oil, and is also found in some lichen and extracted from them by some companies, but the consumption of vitamin D2 (ergocalciferol)—produced from the ultraviolet irradiation of ergosterol from yeast—has been shown to be as effective in providing the human body with vitamin D (Holick et al. 2008).
Plasma 25-hydroxyvitamin D concentrations were measured in 2,107 participants of the Oxford-EPIC cohort, showing that vegans had lower concentrations of vitamin D, particularly during the winter months (Crowe et al. 2010). Whereas most participants in this study had concentrations that were deemed to be adequate, it is nevertheless very important to recognise that many people who live far away from the equator and who do not expose themselves frequently to sunlight (because of spending much time indoors and clothing) fail to meet recommended levels. This may be why Craig (2009, 1630S) has expressed the view that a daily supplement of 5–10 micrograms of vitamin D would be ‘highly desirable for elderly vegans’; however, some recent studies suggest that a higher dosage may be required to maintain optimal blood levels, which is why Norris and Messina (2011, 47) recommend 25 micrograms or 1,000 International Units (IUs) daily for people who do not benefit from adequate sun exposure.
Essential fatty acids
Omega-3 (or n-3) and omega-6 (or n-6) fatty acids are widely regarded to be beneficial for human health. The two most important ones of these are two short-chain polyunsaturated fatty acids: α-linolenic acid (ALA), which the body can use to create other fats within the n-3 fatty acid family, and linoleic acid (LA), which the body can use to create other fats within the n-6 fatty acid family. These two fatty acids are called ‘essential’ because they cannot be synthesised by the human body, but are required for healthy functioning. They must therefore be supplied by our diets. Enzymes in our bodies convert these short-chain fatty acids to long-chain n-3 and n-6 polyunsaturated fatty acids. ALA is converted (incidentally, not only by humans, but also by many other animals, including fish) to eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid, with stearidonic acid (SDA) as an intermediate in the pathway; LA is converted to arachidonic acid (Saunders et al. 2012a).
The palaeolithic diets that were adopted by hunter-gatherers are estimated to have had an n-6:n-3 ratio of 1:1 to 2:1. Many people who live today, by contrast, overconsume LA (C. Williams and Burge 2006). The n-6:n-3 ratio of typical Western diets has been estimated to be around 15:1 to 17:1 (O’Neill 2010, 200). This is a serious problem, as overconsumption of LA impairs ALA conversion. Many people also underconsume ALA, which may cause deficiencies in the particularly important EPA and DHA (B. Davis and Kris-Etherton 2003). High intakes of trans-fatty acids, alcohol, and caffeine, as well as imbalanced diets and illness in general, may produce the same deficiencies in EPA and DHA. Such deficiencies are believed to cause cardio-vascular disease and cancer, as well as exacerbated pain associated with a range of conditions (Simopoulos 2002; von Schacky 2009; Christophersen and Haug 2011). They may also cause cognitive decline, age-related macular degeneration, and depression (Saunders et al. 2012a, 24S).
A clear message emerges from this. Vegans must make sure to consume adequate amounts of ALA, and avoid high consumption of products that inhibit the conversion of ALA, including products that contain relatively large quantities of LA. Accordingly, a recent study recommends that at least one unit of n-3 be consumed for every four units of n-6 (Saunders et al. 2012a, 24S). The authors of the study also recommend an ALA intake of 2.6 g/day for men and 1.6 g/day for women, whilst recommending the following daily intakes for infants and children: 0.5 g at 0–6 months; 0.5 g at 7–12 months; 1 g for children aged 1–3; 1.6 g for children aged 4–8; 2 g for boys aged 9–13; 2.4 g for boys aged 14–18; and 1.6 g for girls aged 9–18 (Saunders et al. 2012a, 24S). The main reason for the gender differences relates to the fact that males tend to convert ALA less efficiently (Childs et al. 2008).
Plant foods that are high in omega-3 fatty acids include chia, flax, canola (rapeseed), hemp, walnuts, perilla, and olive oil (Saunders et al. 2012a; O’Neill 2010, 201). Blackcurrant seed oil, derived from the seeds of Ribes nigrum, is rich not only in omega-3 fatty acids, but also in SDA, and the same applies to oil derived from plants belonging to the Echium genus, a collection of species within the Boraginaceae family (Li 2011). Genetically engineered soybeans that contain SDA have also been recommended (Saunders et al. 2012a), but their inclusion within a diet would depend on their acceptability, a debate that I touched upon briefly in section 2.11 and that I shall not engage with any further here. To ensure adequate consumption of ALA, Norris and Messina (2011, 89) recommend that adults consume three to four daily servings from this list: ‘1 teaspoon canola oil, 1/4 teaspoon flaxseed oil, 2/3 teaspoon hempseed oil, 1 teaspoon walnut oil, 2 teaspoons ground English walnuts or 2 walnut halves, 1 teaspoon ground flaxseeds, 1/2 cup cooked soybeans, 1 cup firm tofu, 1 cup tempeh, 2 tablespoons soynuts’.
People with increased needs (for example pregnant and lactating women) and people with compromised conversion rates (for example people with diabetes or hypertension, and older people) may also benefit from consuming limited amounts of DHA- and—where available—EPA-fortified foods and DHA-supplements derived from microalgae (which can retro-convert to EPA inside the human body), as well as from consuming brown algae (kelp) oils (Saunders et al. 2012a; ADA 2009, 1268, 1271; Craig 2009, 1629S; Geppert et al. 2005). Norris and Messina (2011, 58, 55) write that vegans over the age of 60 ‘should consider’ a daily DHA (or a combination of DHA and EPA) supplement of 200 to 300 milligrams, a supplement dose that they are also ‘inclined to recommend’ at a frequency of every two to three days for those who are younger.
Although it may be unlikely to happen, overconsumption of DHA-rich products must be avoided, as this may raise total and low density lipoprotein (LDL) cholesterol, cause prolonged bleeding, and reduce immunity (Craig 2009, 1629S; Geppert et al. 2005; Sanders et al. 2006).
Provided that it is present in the soil, many plant foods contain zinc. Plants that tend to be high in zinc are cereals and legumes. Unrefined whole grains provide higher concentrations than refined grains, as zinc can be found particularly within the outer layer of grains (Saunders et al. 2012b, 17S). Various ways to increase zinc uptake have been described, including soaking and sprouting beans, seeds, and grains, as well as leavening bread and consuming foods that contain citric acids (Lönnerdal 2000). Zinc absorption can be reduced by phytates (phytic acids), protein, and insoluble fibre, as well as by some minerals, including iron, calcium, and potassium (Li 2011). Whereas whole grains are higher in phytates than refined grains, the relative greater effect of phytates in the former is more than compensated for by the fact that whole grains are higher in zinc (Messina and Mangels 2001, 664). A study that compared 25 vegans with 20 omnivores found that the inhibitory effect of phytate failed to compromise zinc status as the bodies of people who take in little zinc appear to be able to increase zinc absorption and retention (Haddad et al. 1999).
As an aside, whereas it is good to be mindful that potassium may inhibit the absorption of zinc, it is nevertheless important to secure a sufficient intake of potassium as well. The following are listed as good sources of potassium by Norris and Messina (2011, 76): beet greens, spinach, Swiss chard, cooked tomatoes and tomato juice, bananas, sea vegetables, orange juice, and legumes.
Iodine deficiency affects more than two billion people. It is the leading cause of preventable mental retardation worldwide. Foetuses and breastfed children are particularly vulnerable as they depend on maternal iodine intake for thyroid hormone synthesis, which is essential for human neurological development. Thyroid iodine uptake is inhibited by perchlorate—an ubiquitous environmental contaminant—cigarette smoke, cruciferous vegetables (of the family Brassicaceae), and seaweeds of the genus Laminaria (including kombu) (Leung et al. 2011, e1304; Lightowler 2009, 433–434); there is also concern over the inhibitory effects of particular isoflavones found in soya and flaxseed. Both the underconsumption and the overconsumption of iodine can cause goitre (an enlargement of the thyroid gland) and hypothyroidism, but the latter can also cause hyperthyroidism (Norris and Messina 2011, 70–71). A small American study found, however, that in spite of the fact that a cohort of Boston-area vegans had relatively low urinary iodine levels, these low levels were not associated with thyroid dysfunction (Leung et al. 2011).
Provided that they have access to adequate nutrition, vegans should not suffer from iodine deficiencies. Iodine can be provided through plants grown on iodine-rich soil, the consumption of seaweed, and the consumption of iodised salt. As levels of iodine in seaweed vary considerably and are therefore unreliable, and as the overconsumption of salt must be avoided, Norris and Messina (2011, 72, 89) recommend the use of supplements as their favourite strategy, where their recommendation for adults is that they take supplements of 75 to 150 micrograms three to four days per week in order to meet a recommended daily allowance of 150 micrograms, whereas lower levels of 90 micrograms daily are recommended for very small children and higher levels of up to 290 micrograms daily for lactating women. They also recommend one quarter of a teaspoon of iodised salt per day as an alternative to supplementation. The development of a global strategy to ensure routine, adequate iodisation of foods which are commonly used that guards at the same time against excess intake of iodine, which negatively affects the thyroid gland (Lightowler 2009, 431), would seem to be appropriate in view of the scale of the problem of iodine deficiency. Some localities have already developed guidelines; in the USA, for example, vegan pregnant and lactating women have been recommended to supplement their diets with 150 micrograms of iodine daily (Leung et al. 2011, e1303).
Foods contain iron in two forms: haem iron and non-haem iron. Vegan foods only contain the latter, which is less easily absorbed by the body. Whereas iron deficiency can be a problem for vegans, it is more likely to be a problem for omnivores who consume large quantities of milk than for diet-conscious vegans. Good vegan sources of iron are dried fruit, sea vegetables, leafy green vegetables, and beans (Norris and Messina 2011, 64, 70). Vegans who consume a good range of fruit and vegetables in addition to foods that contain relatively large amounts of iron are unlikely to be affected by a deficiency as many fruits and vegetables contain large quantities of vitamin C, as well as other organic acids, which enhances iron absorption. Retinol, carotenes, and alcohol have also been reported to increase iron absorption, whereas inhibitors include oxalates, phytates, and calcium, as well as the polyphenolics that are present in tea, some herbal ‘teas’, coffee, and cocoa (Ma et al. 2005; Siener et al. 2006; Hallberg and Rossander 1982; Li 2011; McEvoy and Woodside 2010, 88; ADA 2009, 1268). It is for this reason that Norris and Messina (2011, 70) recommend that people who drink tea and coffee only do so between meals rather than with their meals. As low iron status is moderately common in premenopausal women, these women need to make sure that their diets include good sources of iron, together with vitamin C to aid absorption (Key et al. 2006, 37). At the same time, there is evidence of the human body’s ability to adapt to low iron intake by increasing absorption and decreasing losses (Hunt and Roughead 1999; Hunt and Roughead 2000).
The account presented above shows that vegan diets can fulfil all the nutritional requirements that are needed to support good health. Nutrients that present particular concerns are vitamin B12 and omega-3 fatty acids as few vegan foods that are currently used for human consumption contain these. Accordingly, vegans must make sure that they consume adequate portions of such foods. A nutrient that I have not mentioned, but that may be a concern, is selenium (Norris and Messina 2011, 76): as the selenium content of soil varies across the world, vegans must ensure that they do not restrict their diets to foods that are grown on soils that have low selenium levels. All in all, vegan diets can be adequate for all human beings, including children. Although small children with reduced stomach capacities may need to eat regularly and must ensure that they eat foods that are sufficiently high in energy density to provide sufficient calories, that are relatively easy to digest (for example by including cooked rather than raw foods), and that are not excessive in fibre (Messina and Mangels 2001, 662), many nutritionists adopt the view that vegan diets can be adequate for all human beings (Messina and Mangels 2001; Norris and Messina 2011; Van Winckel et al. 2011; ADA 1997).