Iodine and plant-based diets: a narrative review and calculation of iodine content

Vegan and omnivore diets in relation to nutrient intake and greenhouse gas emissions in Iceland

Plant-rich diets have gained recognition for their environmental sustainability. However, relatively few studies have compared dietary habits of vegans and omnivores in terms of compliance with nutritional recommendations and dietary greenhouse gas (GHG) emissions, which this study aimed to assess. We used data on 651 omnivores and 68 vegans from the Icelandic National Dietary Survey (2019-2021) and a comparable survey on vegans (2022-2023), respectively. The median dietary GHG emissions was substantially lower among vegans than omnivores (2.6 vs. 5.3 kg CO2-eq/day). Compared to omnivores, vegans had a proportionally higher intake of energy from carbohydrates (48% vs. 39%) but a lower intake from fat (35% vs. 40%) and proteins (12% vs. 18%). More vegans compared to omnivores fell within the dietary recommendations for fiber (74% vs. 8%) and saturated fat (56% vs. 7%) while vegans were less likely to have protein intake in line with the recommended ≥ 0.83 g/kg body weight (52% vs. 79%). Despite frequent use of dietary food supplements among vegans (97%) and omnivores (72%) the prevalence of those reaching the recommended intake of iodine, calcium and vitamin D, was low (40-60%) in both groups. In conclusion, vegans were overall more compliant with macronutrient recommendations and had substantially lower dietary GHG emissions compared to omnivores. In terms of meeting dietary recommendations, room for improvements was observed in both groups.

Modern challenges of iodine nutrition: vegan and vegetarian diets

Vegetarian diets are gaining popularity worldwide, especially among women and in the younger part of the population, rising some concerns for the risk of inadequate iodine requirements if the diet is not correctly planned. Indeed, subjects under vegetarian dietary regimens, mainly the vegan ones, are at risk of developing both iodine deficiency and excess, due to lack of animal-derived foods on the one hand, and to the use of vegan alternatives (such as seaweed) and over-the-counter supplements on the other hand. Women in childbearing age and children are particularly vulnerable to the adverse thyroid consequences. Thus, this paper aims to provide some practical information to achieve adequate iodine intake and avoid adverse effects on thyroid in this population.

Risk of hypothyroidism in meat-eaters, fish-eaters, and vegetarians: a population-based prospective study

BACKGROUND

Plant-based diets are gaining popularity due to their well-documented cardiometabolic benefits and environmental sustainability. However, these diets are often lower in specific micronutrients such as iodine, raising concerns about their potential impact on thyroid health. Therefore, we examined the associations between plant-based diets and the risk of hypothyroidism.

METHODS

We analysed data from the UK (United Kingdom) Biobank cohort. Multivariable Cox proportional hazards regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) for incident hypothyroidism across vegans, vegetarians, pescatarians, poultry-eaters, low meat-eaters, and high meat-eaters aged 40-69 years. Ancillary to this, we carried out logistic regression analyses to evaluate associations between the diet groups and prevalent hypothyroidism according to International Classification of Diseases (ICD) codes at baseline.

RESULTS

We included 466,362 individuals from the UK Biobank, of which 220,514 followed a high meat, 221,554 a low meat, 5242 a poultry-based, 10,598 a pescatarian, 8057 a vegetarian, and 397 a vegan diet. During a median SD (Standard Deviation) follow-up of 12.7 (± 3.2) years, 10,831 participants developed hypothyroidism. In multivariable Cox regression models without adjustment for body mass index (BMI), none of the diets were significantly associated with the risk of hypothyroidism. However, there was a tendency for a higher risk of hypothyroidism among vegetarians compared to people following a high meat diet (HR = 1.13, 95% CI 0.98-1.30). After controlling for BMI, a potential collider, the association for vegetarians (HR = 1.23, 95% CI 1.07-1.42) became stronger and statistically significant. Furthermore, we observed a positive association between low meat-eaters (OR = 1.05, 95% CI 1.03-1.08), poultry-eaters (OR = 1.15, 95% CI 1.04-1.28), pescatarians (OR = 1.10, 95% CI 1.01-1.19) and vegetarian (OR = 1.26, 95% CI 1.15-1.38) with hypothyroidism prevalence.

CONCLUSIONS

In the present study, we found a moderately higher risk of hypothyroidism among vegetarians, after controlling for BMI, a potential collider. This slightly higher risk of hypothyroidism among vegetarians requires further investigation, taking iodine status and thyroid hormone levels into account.

Planetary health diet, mediterranean diet and micronutrient intake adequacy in the Seguimiento Universidad de Navarra (SUN) cohort

PURPOSE

Our study aimed to investigate and compare the association between adherence to a priori Planetary Health Diet Index and two well-known Mediterranean indices, the Mediterranean Diet Score (MDS) and the Mediterranean Adherence Screener (MEDAS), and micronutrient intake adequacy.

METHODS

We assessed 18,259 Spanish university graduates at baseline who participated in the SUN cohort using a validated semi-quantitative food frequency questionnaire. Inadequate intake of Zn, I, Se, Fe, Ca, P, Mg, Cr, K, vitamins B1, B2, B3, B6, B12, C, A, D, E, and folic acid was evaluated using the estimated average requirement (EAR) cut-point approach and the probabilistic approach. Logistic regression analyses were conducted to estimate the probability of failing to meet EAR for either ≥ 3 or ≥ 6 micronutrients.

RESULTS

Participants with higher adherence to the Planetary Health Diet had a lower risk of overall inadequacy, while the Mediterranean Diet (MedDiet) showed even greater nutritional adequacy. The adjusted Odds Ratio (OR) for failing to meet ≥ 3 EAR was 0·24 (95% CI 0·21 - 0·27) for the Planetary Health Diet Index, whereas it was substantially lower for MEDAS with OR = 0·12, 95% CI 0·11 - 0·13, and for MDS with OR = 0·09, 95% CI 0·08 - 0·10, always for the comparison of the fourth v. first quartile and using the probabilistic approach method.

CONCLUSION

In this Mediterranean cohort, better adherence to both the Planetary Health Diet and the MedDiet (with a stronger inverse association) showed lower risk of micronutrient inadequacy.

Nutrient Intakes in Vegans, Lacto-Ovo-Vegetarians, Orthodox Fasters, and Omnivores in Russia: A Cross-Sectional Study

In Eastern Europe, the number of vegetarians is growing, and the number of people adhering to Christian Lents is traditionally high. However, data on the nutritional value of plant-based diets in this part of the world are limited. The aim of this study was to compare the nutritional intakes of three groups with different plant-based patterns with that of omnivores in Russia, Moscow region. The nutrient intakes of 46 vegans, 49 lacto-ovo-vegetarians, 42 people who adhered to Orthodox Great Lent, and 48 omnivores were assessed. The food frequency questionnaire method was used for data collection and analysis. The differences in absolute and calorie adjusted nutrient intakes between the groups were analysed. Additionally, a pairwise comparison of the general plant-based group (combined of the vegan, lacto-ovo-vegetarian, and Great Lent samples) and the omnivorous groups was conducted. Vegan diet was the most favourable in micronutrient composition. The intake of many micronutrients increased when switching to a more plant-based diet from a more animal-based one. The opposite association was observed only for selenium and vitamins D and B12. Fasting people consumed more iodine and n-3 polyunsaturated fatty acids; however, after the calorie content was standardized, the omnivores caught up with them. The omnivores had the largest list of dietary inadequacies: they significantly more often than all other groups had inadequate intake of cholesterol (excessive), fibre, potassium, magnesium, iron, and vitamins B1, B6, B9, and E (insufficient). Inadequate intake of polyunsaturated fatty acids, calcium, iodine, chromium, molybdenum, and zinc; or vitamins B2, PP, H, B12, and D was observed rather often in all the studied groups. Although, the vegan diet was richer in most micronutrients, plant products often contain substances that reduce the bioavailability of various nutrients, which can partially affect their status in the body, and, thus, may increase the need in them in vegetarians and fasters.

Variation in milk‑iodine concentration around the world: a systematic review and meta-analysis of the difference between season and dairy-production system

Iodine is essential for thyroid hormone production. Milk and dairy products are important sources of iodine in many countries. We aimed to review systematically the variation in milk‑iodine concentration between countries, seasons and farming practice. We searched online food composition tables and published literature for data since 2006. Milk‑iodine concentration was available for 34 countries (from 66 sources) and ranged from 5.5 to 49.9 μg/100 g (median 17.3 μg/100 g). Meta-analyses identified that iodine concentration is significantly higher in: (i) winter than summer milk (mean difference 5.97 μg/100 g; p = 0.001), and (ii) in conventional than in organic milk (mean difference 6.00 μg/100 g; p < 0.0001). Sub-group analysis showed that the difference between organic and conventional milk was only significant in summer (p = 0.0003). The seasonal variation in milk‑iodine concentration may affect iodine intake and status so should be considered in dietary surveys, and when assessing population iodine status.

Nutritional Considerations of Plant-Based Diets for People With Food Allergy

Plant-based diets (PBD) have been reported throughout history, but are increasingly common in current times, likely in part due to considerable emphasis on climate change and human health and wellness. Many dietary organisations around the world endorse well-planned, nutritionally adequate PBD, which exclude some or all forms of animal-based foods. However, special attention must be given to patients who follow PBD and also have food allergy (FA), as avoidance may increase the risk of developing nutritional deficiencies, including poor growth in children, weight loss in adults and vitamin and mineral deficiencies. Given the increasing prevalence of both PBD and food allergen avoidance diets, healthcare providers are likely to counsel patients with FA who also follow a PBD. In this review, an overview of PBD in patients with FA is provided, including recent trends, macro- and micronutrient needs, and growth for children and weight gain considerations for adults. With regard to a PBD, special attention should be given to ensure adequate fat and protein intake and improving the bioavailability of several minerals such as iron, zinc, iodine, calcium and magnesium, and vitamins such as A, B2, B12 and D. Although the collective data on growth amongst children following a PBD are varied in outcome and may be influenced in part by the type of PBD, growth must be regularly monitored and in adults weight gain assessed as part of any clinical assessment in those people with FA.

Micronutrient intake and status in young vegans, lacto-ovo-vegetarians, pescatarians, flexitarians, and omnivores

PURPOSE

Whether youth who follow plant-based diets in Nordic countries meet their dietary needs for micronutrients remains unclear. This study aims to evaluate micronutrient intake and status in Norwegian youth following vegan, lacto-ovo-vegetarian, pescatarian, flexitarian and omnivore diets.

METHODS

Cross-sectional design, with healthy 16-to-24-year-olds (n = 165). Participants were asked to complete a questionnaire and four 24-hour dietary recalls. Dried blood spots (DBS) and spot-urine samples were collected for analysis of methyl malonic acid (MMA) (n = 65), haemoglobin (Hb) (n = 164) and urinary iodine concentration (UIC) (n = 163).

RESULTS

Vegans reported highest habitual supplement usage of multivitamin (58%), B12 (90%) and macroalgae consumption (32%), while flexitarians reported highest habitual usage of omega-3 supplements (56%). For daily supplement usage, vegans reported highest use of multivitamins (42%), B12 (79%), iodine (37%) and iron (63%). Increased risk of inadequate intake (energy-adjusted) were found for vitamin D (60% within lacto-ovo-vegetarians), selenium (70% within lacto-ovo-vegetarians, 65% within omnivores), and iodine (63% within vegans). Median MMA levels suggest low risk of insufficient B12 status across all groups (MMA 0.04‒0.37µmol/l) and 2% had MMA levels indicating possible B12 deficiency and 8% had elevated levels. Median Hb levels indicated low risk of anemia across all groups (≥ 12.0 females, ≥ 13.0 g/dl males), though 7% had Hb values indicating risk of mild anemia and 4% risk of moderate anemia. The median UIC indicates mild iodine deficiency in all groups (UIC < 100 µg/l), except vegans, who were moderately iodine deficient (UIC < 50 µg/l).

CONCLUSIONS

Our study indicated that the participating youth had low risk of inadequate intake of most micronutrients, partly due to high supplement usage. However, for iodine, vitamin D, and selenium higher risk of inadequate intake was found. UIC corroborated the low iodine intake among vegans. Thus, we suggest iodine status of youth in Norway should be monitored, especially among young fertile women who omits dietary iodine sources, until a mandatory iodine fortification program is implemented. Furthermore, we suggest that food education on how to secure sufficient nutrients from food in general should be provided to the Norwegian youth population, especially how to secure adequate intake of vitamin D, selenium and iodine.

Animal board invited review: Dietary transition from animal to plant-derived foods: Are there risks to health?

Animal-derived foods (ADFs) are a very varied group of foods, but many are nutrient rich and contain higher quality protein than provided by plant-derived foods such that a simple replacement of ADF protein is likely to lead to a reduction in overall protein quality. In addition, many ADFs are richer in some nutrients than plant-based foods (e.g. Fe, Ca) and these often have a higher bioavailability. ADFs also provide nutrients that plants cannot supply (e.g. vitamin B12) and some provide beneficial health functionality (e.g. hypotensive) which is not explained by traditional nutrition. However, there remains a good health reason to increase the proportion of plant-derived food in many diets to increase the intake of dietary fibre which is often consumed at very sub-optimal levels. It seems logical that the increased plant-derived foods should replace the ADFs that have the least benefit, the greatest risk to health and the highest environmental impact. Processed meat fits these characteristics and should be an initial target for replacement with plant-based based protein-rich foods that additionally provide the necessary nutrients and have high-quality dietary fibre. Processed meat covers a wide range of products including several traditional foods (e.g. sausages) which will make decisions on food replacement challenging. There is therefore an urgent need for research to better define the relative health risks associated with the range of processed meat-based foods. The aim of this review is to examine the evidence on the benefits and risks of this dietary transition including the absolute necessity to consider initial nutrient status before the replacement of ADFs is considered.

Thyroid function and iodine intake: global recommendations and relevant dietary trends

Iodine is a micronutrient that is essential for thyroid hormone production. Adequate iodine intake is especially important during pregnancy and early life, when brain development is dependent on thyroid hormones. Iodine intake recommendations vary around the world, but most recommendations generally reflect the increased requirements during pregnancy and lactation, although adequate iodine intake before pregnancy is also important. Tremendous progress has been made in improving iodine intake across the world over the past 30 years, mainly through salt-iodization programmes. However, in countries without strong iodine fortification programmes, and with shifts in dietary patterns, a need has arisen for health organizations, governments and clinicians to ensure that adequate iodine is consumed by everyone in the population. For example, in countries in which adequate iodine intake depends on individual food choice, particularly of iodine-rich milk and dairy products, intake can be highly variable and is also vulnerable to changing dietary patterns. In this Review, iodine is considered in the wider context of the increasing prevalence of overweight and obesity, the dietary trends for salt restriction for cardiovascular health and the increasing uptake of plant-based diets.

Analysis of the Nutritional Composition of Ready-to-Use Meat Alternatives in Belgium

BACKGROUND

The interest in meat alternatives has increased over the years as people embrace more varied food choices because of different reasons. This study aims to analyse the nutritional composition of ready-to-use meat alternatives and compare them with meat (products).

METHODS

Nutritional composition values were collected in 2022 of all ready-to-use meat alternatives in Belgian supermarkets, as well as their animal-based counterparts. A one-sample t-test was performed to test the nutritional composition of ready-to-use meat alternatives against norm values, while an independent samples t-test was used to make the comparison with meat.

RESULTS

Minced meat and pieces/strips/cubes scored favourably on all norm values. Cheeseburgers/schnitzels, nut/seed burgers and sausages contained more than 10 g/100 g total fat. The saturated fat and salt content was lower than the norm value in each category. Legume burgers/falafel contained less than 10 g/100 g protein. Vegetarian/vegan minced meat and bacon contained fewer calories, total and saturated fat, and more fibre compared to their animal-based counterparts.

CONCLUSIONS

Minced meat and pieces/strips/cubes came out as the most favourable categories regarding nutritional composition norm values. Vegetarian/vegan steak came out the least favourable compared to steak, while vegetarian/vegan minced meat and vegetarian/vegan bacon came out the most favourable compared to their animal-based counterparts.

"Climate-friendly" diets from an allergy point of view

Since the EAT-Lancet Commission's call for a change in diet towards more plant-based foods, especially protein sources, this so called "Planetary Health Diet (PHD)" has been widely discussed. While for some the reduction in animal foods is not enough and vegan diets are advocated to save the climate, others are sounding the alarm that the reduction is too drastic and that the PHD makes it impossible to provide a diet that meets our needs (of essential nutrients). In addition to climate aspects, health benefits often cited to justify the PHD do not take into account that vegetarians/vegans differ from the general population by far more factors than the reduction or elimination of animal foods. Also not sufficiently discussed is the fact that a diet which excludes or severely restricts animal foods is also associated with health risks if critical nutrients are not adequately covered. Moreover, the challenge of meeting protein requirements is underestimated by many. The food industry has responded to the trend towards more plant-based foods by massively expanding the range of highly processed or ultra-processed vegan foods. These - vegan or not vegan - are suspected of being partly responsible for the development of non-communicable diseases. In addition to general criticism regarding the usefulness of advertising the PHD, the replacement of animal protein sources with plant-based sources notably harbors a number of additional relevant risks for allergy sufferers so that the latter should be classified as an unfavorable target group for the implementation of the PHD recommendations.

Impact of iodine supply in infancy and childhood

PURPOSE OF REVIEW

To assess the most relevant articles on the impact of iodine supply in at-risk populations, namely infants and young children, pregnant and lactating women.

RECENT FINDINGS

The 2022 Iodine Global Network Annual Report confirmed the dramatic decrease of severe iodine deficiency over the last 30 years, thanks to universal iodine iodization. However, mild to moderate deficiency is still present in many countries, where recent data showed a decrease of iodine intake and an impairment of iodine status. Unfortunately, there is yet no validated biomarker to classify the iodine status at the individual level. Available data show that there is no clear evidence to link mild-to-moderate iodine deficiency to adverse health outcomes in pregnant and lactating women as well as in infants and children. The description of a negative impact of maternal iodine excess on neurodevelopment of infants is of concern.

SUMMARY

Optimization of salt iodization (e.g. careful increase in iodine concentration in salt, use by food industry in processed foods) combined with targeted, personalized supplementation under medical supervision if needed (e.g. low intake of iodine rich foods, vegan diet) seems currently preferable to blanket supplementation.

Unacceptable use of substandard metrics in policy decisions which mandate large reductions in animal-source foods

Many recent very influential reports, including those from the Global Burden of Disease (GBD) Risk Factor Collaborators, the EAT-Lancet Commission on Food, Planet, Health, and the Lancet Countdown on Health and Climate Change, have recommended dramatic reductions or total exclusion of animal-source foods, particularly ruminant products (red meat and dairy), from the human diet. They strongly suggest that these dietary shifts will not only benefit planetary health but also human health. However, as detailed in this perspective, there are grounds for considerable concern in regard to the quality and transparency of the input data, the validity of the assumptions, and the appropriateness of the statistical modelling, used in the calculation of the global health estimates, which underpin the claimed human health benefits. The lessor bioavailability of protein and key micronutrients from plant-source foods versus animal-source foods was not adequately recognised nor addressed in any of these reports. Furthermore, assessments of bias and certainty were either limited or absent. Despite many of these errors and limitations being publically acknowledged by the GBD and the EAT-Lancet authors, no corrections have been applied to the published papers. As a consequence, these reports continue to erroneously influence food policy decisions and international dietary guidelines, such as the World Wildlife Fund's Livewell Diet, and the Nordic Nutrition Recommendations 2023.

Vegan Diets for Children: A Narrative Review of Position Papers Published by Relevant Associations

The scientific discourse on vegan diets for children and adolescents primarily involves referencing position statement papers from different scientific and professional organizations, including paediatric associations. Over the past two decades, specialized associations have issued official statements and published position papers about adopting well-designed vegan diets during crucial life stages, including pregnancy and lactation, infancy, and childhood. A subset of these associations firmly supports the notion that a well-designed vegan diet can indeed be healthy and support normal growth and development during particularly delicate life stages, emphasizing careful planning, vitamin B12 supplementation, and regular supervised medical and dietetics oversight. In contrast, specific paediatric associations caution against vegan diets for children and adolescents, citing potential harm and the lack of adequate substantiation. These criticisms in position papers frequently point to lower-quality studies and/or outdated studies. Additionally, concerns extend to comparing vegan and omnivorous diets, considering public health issues such as obesity and early stages of cardiovascular disease as well as the risk of prediabetes and type 2 diabetes. Notably, some scepticism stems from studies where children's adherence to a well-designed vegan diet is incomplete. Scientific rigor suggests performing a comparable assessment of omnivorous and vegan diets. This narrative review highlights the need for a comprehensive, up-to-date literature review to inform balanced perspectives on vegan diets for children and adolescents. Researchers and decision-makers should aim to actively improve the design and consistent implementation of both diet types.