Assez d’études pour conclure ?

Bien qu’une alimentation largement végétalisée ait montré de potentiels bienfaits, les études sur le végétarisme et le végétalisme sont-elles suffisantes pour conclure à l’innocuité des ces alimentations et pour en évaluer les avantages ou les risques, pour tous et sur toute une durée de vie ?
Un certain nombre de publication, parfois par des pionniers des alimentations végétales (Key, Appleby…), soulignent la rareté des études existantes, leur faible qualité, leur durée insuffisante, le faible niveau de preuve, l’hétérogénité des résultats, les risques de biais, d’erreurs dans l’évaluation des aliments effectivement consommés, la faiblesse des échantillons, et réclament des études prospectives d’ampleur, de qualité et de durée suffisante.

Although a largely vegetarian diet has shown potential benefits, are the studies on vegetarianism and veganism sufficient to conclude that these diets are safe and to evaluate the benefits or risks, for everyone and over a lifetime?
A number of publications, sometimes by pioneers of plant-based diets (Key, Appleby…), underline the scarcity of existing studies, their low quality, their insufficient duration, the low level of evidence, the heterogeneity of the results, the risks of bias, of errors in the evaluation of the foods actually consumed, the weakness of the samples, and call for prospective studies of sufficient size, quality and duration.

Do Vegetarian Diets Provide Adequate Nutrient Intake during Complementary Feeding? A Systematic Review [Texte]
Simeone et al.
Nutrients, 2022

Based on current evidence, vegetarian and vegan diets during the complementary feeding period have not been shown to be safe, and the current best evidence suggests that the risk of critical micronutrient deficiencies or insufficiencies and growth retardation is high: they may result in significantly different outcomes in neuropsychological development and growth when compared with a healthy omnivorous diet such as the Mediterranean Diet.

Plant-based diets and long-term health: findings from the EPIC-Oxford study [Texte]
Key et al.
Proceedings of the nutrition society, 2021

Overall, the health of people following plant-based diets appears to be generally good, with advantages but also some risks, and the extent to which the risks may be mitigated by optimal food choices, fortification and supplementation is not yet known.
[…] the number of vegans in the study is too small (about 2500 vegans) to give accurate relative risk estimates, and that as with other epidemiological studies the measurements of dietary and other factors are subject to error.
[…] Further research is required, and it would be ideal to recruit a large new cohort including tens of thousands of vegans, with the best available methods to measure diet, to eventually provide reliable evidence on their long-term health.

A Systematic Review of the Association Between Vegan Diets and Risk of Cardiovascular Disease [Texte]
Kaiser et al.
Journal of Nutrition, 2021

Using the Grading of Recommendations Assessment, Development and Evaluation approach, evidence was deemed to be of low to very low strength/quality.
[…] Among the Western populations studied, evidence weakly demonstrates associations between vegan diets and risk of CVDs, with the direction of associations varying with the specific CVD outcome tested. However, more high-quality research on this topic is needed.

Meta-analysis of effect of vegetarian diet on ischemic heart disease and all-cause mortality [Texte]
Jabri et al.
American Journal of Preventive Cardiology, 2021

A vegetarian diet, compared with a non-vegetarian diet, was associated with a reduced risk of ischemic heart disease mortality, whereas it had no effect on all-cause and cerebrovascular mortality. However, the results are to be considered with caution considering the low certainty of evidence.

Vegetarian and Vegan Weaning of the Infant: How Common and How Evidence-Based? A Population-Based Survey and Narrative Review [Texte]
Baldassare et al.
Environmental research and public health, 2020

To date, consistent findings to support both the safety and feasibility of alternative weaning methods are still lacking.

Systematic review and meta-analysis of the associations of vegan and vegetarian diets with inflammatory biomarkers [Texte]
Menzel et al.
Nature scientific reports, 2020

Despite strong associations between CRP and a vegan or vegetarian diet were seen, further research is needed, as most inflammatory biomarkers were investigated only in single studies so far.

The effects of plant-based diets on the body and the brain: a systematic review [Texte]
Medawar et al.
Translational psychiatry, 2019

putative effects of plant-based diets on brain health and cognitive functions as well as the underlying mechanisms remain largely unexplored and new studies need to address these questions.

Vegetarian diets in childhood and adolescence.
Position paper of the nutrition committee, German Society for Paediatric and Adolescent Medicine (DGKJ)

Rudloff et al.
Molecular and cellular paediatrics, 2019

Whether the corresponding health benefits in vegetarians outweigh the risks of nutrient deficiencies has not been fully clarified.

Effects of vegan complementary feeding on the health of children from 6 to 24
months of age : literature review [Abstract]

Diaz & Yadira
Pontificia Universidad Javeriana, 2019

Conclusion: The scarce literature available on the subject, the heterogeneity of the studies and the biases that may occur in the sample populations, do not allow to conclude the benefits and risks that vegan diets may present in the health and nutritional status of Children from 6 to 24 months old.

Is a vegetarian diet safe to follow during pregnancy? A systematic review and meta-analysis of observational studies [Abstract]
Tan et al.
Critical studies in food science and nutrition, 2019

 Given the high heterogeneity of the included studies, lack of high-quality evidence, and limited studies included for each category, we failed to reach conclusive results regarding the risks of hypospadias, intrauterine growth retardation, maternal anemia, and gestational diabetes mellitus.[…] Asian vegetarian mothers presented increased risks to deliver babies with LBW than those of omnivores. Large-scale prospective studies focusing on pre- and/or early gestational nutrition will help clarify the correlation between vegetarian diet and various pregnancy outcomes.

Alimentation végétarienne et ­végane chez les enfants et ­adolescents [Texte]
Bieri et al.
Forum médical suisse, 2018

Pour conclure, il convient de mentionner qu’il y a un besoin urgent de clarification et de recherche sur les conséquences à long terme d’une alimentation végétarienne ou végane chez les enfants. Il n’existe jusqu’à présent guère de données sur les répercussions métaboliques, les bénéfices, mais aussi les risques à long terme d’un régime sans viande durant l’enfance

Vegetarian Diets in Children? – An Assessment from Pediatrics and Nutrition Science [Abstract]
Kersting et al, 2018

Vegetarian diets as the lacto-ovo-vegetarian diet (exclusion of meat, fish) and the vegan diet (exclusion of all food groups of animal origin) need to be evaluated for their potential to safely meet the high and specific requirements for growth and development. In this regard, high-quality studies are needed.

Is vegetarianism healthy for children? [Page]
Nathan Cofnas.
Critical review of food science and nutrition, 2018.

The present paper argues that the Academy of Nutrition and Dietetics ignores or gives short shrift to direct and indirect evidence that vegetarianism may be associated with serious risks for brain and body development in fetuses and children. Regular supplementation with iron, zinc, and B12 will not mitigate all of these risks. Consequently, we cannot say decisively that vegetarianism or veganism is safe for children.

Vegetarian, vegan diets and multiple health outcomes: A systematic review withmeta-analysis of observational studies [PDF]
Monica Dinu et al.
Critica reiews in food science and nutrition, 2017

data obtained from cross-sectional studies need to be interpreted with caution because of the moderate-to-high risk of bias reported in the vast majority of these studies, and also because of the high degree of heterogeneity evidenced in our overall analysis.
[…]reinforcing the hypothesis that the studies coming from Adventist cohorts present a low degree of generalizability when compared to other cohort
[…]we could not analyze an important datum such as the duration of adherence to the vegetarian or to the vegan pattern in the different cohorts. Indeed, only one study explicated this finding that is extremely relevant for understanding the relationship with mortality and incidence of disease. In addition, the definition of the control group, i.e., those following an omnivorous diet was not really well-defined, including in some cases subjects consuming a high intake of meat and meat products and in other cases subjects with a reduced consumption of meat and derivatives. A final potential weakness is the accuracy of the assessment of vegetarian and vegan status. There are several slight differences in the population of vegetarians throughout the world, and the possibility that some studies could have included vegetarians and vegan altogether cannot be ruled.
[…]vegan diet seems to be associated with a lower rate of cancer incidence, but this result must be interpreted with caution, because of the very small sample size and the low number of studies evaluating this aspect

Vegetarian diets in children: a systematic review [PDF]
Schürman et al.
European journal of nutrition, 2017

Due to the study heterogeneity, the small samples, the bias towards upper social classes, and the scarcity of recent studies, the existing data do not allow us to draw firm conclusions on health benefits or risks of present-day vegetarian type diets on the nutritional or health status of children and adolescents in industrialized countries.

The long-term health of vegetarians and vegans [PDF]
Appleby & Key
Proceedings of the nutrition society, 2016

Much more research is needed, particularly on the long-term health of vegans.
[…] More data are needed, for example on stroke and sub-types of stroke, bone health and diseases and conditions not yet studied, as well as for vegetarians and others with a low intake of animal products in non-western populations. For vegans, the current data are insufficient to draw any strong conclusions and much more research is required.

The National Osteoporosis Foundation’s position statement on peak bone mass development and lifestyle factors: a systematic review and implementation recommendations [Texte]
Weaver et al.
Osteoporosis international, 2016

To our knowledge, there are no long-term prospective studies of vegetarian children with bone outcomes. Few studies have examined the influences of vegetarian dietary patterns on bone

Vegan–vegetarian diets in pregnancy: danger or panacea? A systematic narrative review [Abstract]
GB Piccoli et al.
BJOG, 2015

The evidence on vegan–vegetarian diets in pregnancy is heterogeneous and scant. The lack of randomised studies prevents us from distinguishing the effects of diet from confounding factors.


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