Vegan diets: health benefits and risks
Previously, we have referred to a definition of vegan diet by what is eliminated. However, a vegan diet can also be described as rich in a wide variety of foods: whole grains, legumes, vegetables, fruits, nuts, seeds, vegetable fats, herbs and spices [
3]. The high amount of macro- and micronutrients, as well as a wide variety of carbohydrate types seems to enhance the development of a diverse intestinal flora [
12,
13], of increasing interest in disease prevention [
14]. Benefits of, and reasons for adopting a vegan diet range widely, and include animal welfare [
15], health benefits [
15‐
17], personal well-being [
15], improvement of disease symptoms [
18], increased meat prices [
19] and environmental concerns [
20,
21].
Recently, vegan diets were found to be an effective means of prevention and treatment of cardiometabolic disease [
22,
23], with a decreased risk up to 40% of associated diseases. Moreover, the risk of metabolic syndrome and type 2 diabetes may be decreased by 50%, and, if well planned, can assist in reversing atherosclerosis, and reducing blood lipids and blood pressure. These health benefits may result, in part, from the observation that, compared to non-vegans, those following a vegan diet have a lower body mass index (BMI) and waist circumference. But there are some exceptions. In a recent meta-analysis, compared to a typical Taiwanese diet, vegan diets are not associated with improved cardiometabolic outcomes or lower BMI [
23,
24].
However, potential vegan diet pitfalls exist, particularly amongst children. Young children may benefit from a variety of plant-based proteins during small and frequent meals to allow for consumption of a large volume of foods [
3]. Whereas many of guidelines support vegan diets for infants and children [
2,
12,
13,
25,
26], there are some exceptions to these guidelines [
27].
Vegan diets and macronutrient deficiencies
Much of the literature on vegan diets and nutritional outcomes is based on adult populations [
14,
22,
28‐
33]. Less is known about vegan diets amongst infants and children. Thus, these age groups need to be carefully and routinely monitored, if following a vegan diet [
34]. Infants and children have higher energy and nutrient needs, which may be difficult to achieve on a restricted diet. Recent data support that children to age 3 years following a vegan diet consume adequate energy intake, but compared to omnivore children, significantly more carbohydrates (and fibre) and significantly less protein [
35].
Protein requirements in vegan diets are met mainly through vegetables, tofu, beans, whole grains, nuts and seeds. In order to achieve sufficient amounts of essential amino acids, daily varied consumption is recommended [
36]. As the above-mentioned foods often contain considerable amounts of fibre and anti-nutritional factors, i.e. substances that prevent optimal absorption of specific nutrients, protein intakes are recommended to be increased by 10% during periods in life when protein needs are higher. Two of these periods are infancy and childhood [
3]. Protein needs can be met in a well-planned vegan diet, provided that the caloric need is met. For this reason, vegan protein-rich alternatives with less fibre, such as tofu and seitan, may be preferable since these foods usually result in high satiety and might support appropriate protein intake [
37,
38]. First results from a Swedish trial of infants randomized to a diet with decreased protein intake, compared to a traditional Nordic diet has, thus far, shown no group differences in growth or iron status at 9 months of age [
39]. Forthcoming results will glean further insight into the role of decreased protein intake, compared to a traditional Nordic diet, on anthropometric outcomes, metabolic and inflammatory biomarkers, as well as the gut microbiome [
40].
These data notwithstanding, there are case reports of alarming nutritional deficiencies as a consequence in what has, sometimes been described as vegan diets. However, critical review of these reports can lead to the conclusion that these children often have very restricted vegan diets with limited caloric intake [
41], or very limited food choices, for example extensive use of unfortified plant-based beverages [
42]. In extreme situations, these restrictions may contribute to protein-calorie malnutrition [
42], or kwashiorkor, in which the child consumes adequate calories but inadequate protein [
43] as well as inadequate micronutrients [
42]. Notably, these diets cannot be considered well-planned vegan diets, and any conclusions regarding vegan diets for children based solely on these reports are misleading [
3].
Special nutritional considerations in food allergic individuals
An important reminder on the role of the allergy team is to help identify the specific foods to be eliminated from the diet and preventing further avoidance expanding to whole food groups which limits the diet unnecessarily. For example, cooked vegetables and fruits, as well as roasted nuts may sometimes be consumed by those with oral pollen related food syndrome (or oral allergy syndrome) due to birch-, mugwort- or other pollen allergies. Likewise, patients with soy allergy may tolerate other beans and/or lentils within the wide pulse family. Additionally, vegan patients with allergy to peanuts and tree nuts may consider other nuts and seeds as good alternatives. Professional advice is warranted to assist patients and prevent the unnecessary exclusion of important sources of protein and nutrients in a vegan diet [
96,
97].
Compared to non-food allergic children, allergic children consume significantly less calcium and protein, and are more likely to have diets that are deficient in essential fatty acids [
98]. These nutritional inadequacies are associated with other concomitant micronutrient deficiencies [
99], have direct impacts on bone mineral density and physical growth [
99], and may impair learning [
100]. Such differences also appear to exist between children with different types of allergy, suggesting that the food to which a child is allergic, and thus must eliminate from his or her diet, also needs to be considered. For example, children with cow’s milk allergy had significantly lower calcium intakes than children with non-cow’s milk food allergy [
101]. Importantly, any food allergy (not limited to only cow’s milk allergy) in childhood may predict non-significant differences in calcium intake in adolescence [
102]. Likewise, in observational studies, both zinc [
71] and iodine deficiencies [
103,
104] have been noted for cow’s milk allergic children, even if the child was taking a vitamin/mineral supplement [
105].
The few previous studies on the associations between anthropometry and food allergy have been cross-sectional [
106,
107] and thus report on anthropometrical differences between children with or without food allergies, rather than growth
. Nonetheless, these studies provide evidence that both height and weight are negatively impacted by the presence of food allergy. For example, American children with food allergies were found to be significantly shorter and lighter, but not different in terms of body mass index (BMI; (weight (kg)/height (metres
2))) [
108], than non-food allergic peers. Notably, many of these differences were attenuated upon consideration to type of health insurance, and also varied by age group [
106]. Likewise, British researchers reported that both underweight and short-for-age affected approximately 10% of food allergic children, compared to World Health Organization standards [
107]. These differences became even more pronounced amongst children with multiple food allergies.
Whereas the above studies provide evidence that children with food allergy are more likely to be underweight, in at least one study, British researchers found that children with food allergy were significantly more likely to be overweight or obese than their non-allergic peers [
107]. For children with food allergy and who follow a vegan diet, the risks of overweight and obesity are likely to be low, provided that they follow a well-planned, nutrient rich diet. However, this British study provides evidence that overweight and obesity can nonetheless occur.
Even in the absence of nutrient deficiencies, height, weight, weight-for-age, and weight-for-height may be lower by as much as two standard deviations [
107]. Lumbar spine bone mineral density is also significantly lower in children with cow’s milk allergy compared to children with non-cow’s milk food allergy [
101]. Such differences are indicative of moderate malnutrition, and are thus clinically relevant issues that warrant immediate attention [
107]. These previous studies were performed in high-income countries, but which lack national school meal programs or, in some cases, widely subsidised prescriptions for allergic children.
Finally, vegan diets have been associated with a higher odds of atopic dermatitis [
109]. Thus, food allergic individuals following a vegan diet ought to be cautioned about this possibility. In contrast, patients with asthma who followed a vegan diet for 1 year had dramatically improved clinical biomarkers [
110].
Given the restrictions associated with a plant-based diet, even greater attention is warranted when those following a vegan diet also have additional restrictions resulting from food allergy. Recently, American authors reported that people with asthma, another allergic disease but which does not mandate dietary restrictions, commonly turned to YouTube for information on vegan diets [
111]. However, such information was frequently deemed to be of poor quality [
111].
In light of the above-described concerns, it is unsurprising that numerous nutrition and dietetic societies advise that vegan diets should only be used under appropriate medical or dietetic supervision with expertise in food allergy. Moreover, parents should understand the serious consequences of failing to follow advice regarding supplementation of the diet [
9]. These guidelines reflect a shift from a decade ago, when total avoidance of a vegan diet in infants and young children was recommended [
112]. Failure to follow dietary advice may compromise both nutrition and growth. These conditions become even more important when the diet is further limited by food allergy.
Soy, peanuts, tree nuts and wheat are three of the six most usual foods IgE-mediated food allergies [
113] and soy the second most common eliciting food in non-IgE mediated food allergies [
114,
115] further restricting the choices for vegans. Special attention has to be paid to the amount, as well the quality of the protein in the vegan diet [
3,
5,
38,
114,
116].
Of additional concern is the volume of food (i.e. portion size) needed to achieve recommended/appropriate levels of energy and nutrients [
3,
5,
38,
114,
116]. As such, one cannot dismiss the possibility that children with food allergy and who have allergic conditions face particular challenges meeting their nutrient and energy demands through a vegan diet.
Protein is the macronutrient of concern in this unique population. But, many plant-based, protein rich foods are also common allergens. Soy-based formulas are a common alternative to cow’s milk formulas, for both vegan infants and those with cow’s milk allergy. However, soy-based formulas should not be prescribed to prevent the development of food allergy [
117,
118]. Likewise, soy formula is not recommended for infants aged < 6 months, due to concerns of lower rates of absorption of minerals and trace elements due to the phytate content in soy [
119]. Nuts are also a key source of protein and fat, but must be avoided by those with a nut allergy. Likewise, almond milk, a common plant-based alternative to cow’s milk, must be avoided by those with almond allergy. Yet, almond milk is richer in calcium and fat, yet low in calories compared to other plant-based milks [
120]. For vegans with a nut allergy, nut avoidance can be particularly difficult [
121]. It is recommended that specific nuts to which an individual is not allergic should be introduced. However, caution is warranted with pre-packed snacks with precautionary allergen labelling [
122].
Some groups have greater energy and nutrient demand. For infants, children and athletes who follow a vegan diet and also have food allergy, caution is warranted to ensure optimal intakes. Achieving greater intake may be challenging due to the portion size needed to achieve recommended/appropriate levels of energy and nutrients [
3]. The challenge is higher for infants and children who generally have higher needs due to growth [
107,
123], as well as in certain atopy, e.g. atopic dermatitis [
124]. Recently, biologically negligible, but statistically significant differences in resting energy expenditure, anthropometry, and dietary intake in an Italian study of 30 children with food allergy matched to 31 healthy children were described [
124]. In contrast, others have reported that sustained intestinal or skin inflammation due to allergies [
125,
126] and avoidance diets [
127‐
129] may contribute to impaired growth.
The above examples highlight the complexity of managing cross-reactions for those with food allergy, while limiting avoidance to only those foods that elicit symptoms. People with cross-reactions due to birch pollen allergy (i.e. those who test negative for the storage proteins Ara h 1, 2, 3 and 9 and positive for Ara h 8 for peanut and / or negative tests for Cora 8, 9 and 14 storage proteins and positive for Cor a 1 hazelnuts) are more likely to have non-life-threatening reactions [
130]. When possible, it would be beneficial to test for reactivity to food components, rather than only food-specific IgE [
130]. In the absence of the availability of such testing, SPT may be of some benefit only if patients complain of allergic type symptoms to both food types. Otherwise, patients may be encouraged to consume soy, lentils and chickpeas carefully (at first exposure) or
ad libidum (if testing is negative, and/or if they are asymptomatic when consuming these foods). As these food types represent a major calorie- and protein source for those following a vegan diet, the elimination of these food types is strongly cautioned unless the peanut allergic patient has a confirmed allergy to soy, lentils and/or chickpeas.
In cases where a vegan patient is allergic to soy, the dietitian is encouraged to review common sources of soy in the diet, both in obvious forms, such as tofu and soy-based beverages, as well as in processed foods, which commonly contain soy lecithin. These patients should be considered particularly vulnerable for protein deficiencies, given than soy is a common, widely available and generally palatable source of protein in the vegan diet. True soy allergies, as confirmed by OFC, are uncommon [
131]. Clinical experience suggests that many patients with soy allergy may tolerate soy lecithin, likely due to low antigenicity of the proteins in soy lecithin and soy oil [
132]. The need of avoidance of soy lecithin seems to be reduced to a couple of case reports on children with severe soy allergy reacting to soy lecithin in medication [
133,
134]. Further complicating the understanding of soy allergy is evidence that children may develop tolerance to soy, not so to peanut [
135]. Taken together, these findings underline the importance of a careful diagnosis, and, when prudent, re-evaluation of soy allergy. Thus, the decision to include or exclude soy lecithin should be taken on case-by-case basis.
Patients with peanut and tree nut allergies, are less likely to achieve clinical tolerance than patients allergic to milk or egg [
5,
136]. Pea protein is an increasingly widely available vegan protein, and may be a suitable alternative to soy. However, pea allergies have been documented [
137], most commonly amongst those with allergies to other legumes.
Patients who are also allergic to wheat pose a challenge in that they are unable to consume wheat protein alternatives, including seitan, as well as more widely available vegan alternatives, such as wheat-based pastas or breads. These foods represent protein-, calorie- and convenience losses to the patient. Alternatives to consider are bean- and lentil-based pastas, as well as legumes in their original forms.
Pain noir, or buckwheat, is a common staple in parts of Asia and northern France, and is commonly found in noodles, and flour mixes originating from these regions, as well as many gluten free flour mixes in these regions and beyond. Buckwheat is botanically related to grasses, rather than wheat, and thus can be consumed freely by wheat allergy sufferers. However, cross-reactivity between buckwheat and peanut has been demonstrated [
138].