Plain language summary
Heart disease and cancer are complex diseases, with poor diet thought to play a role in their development. The adoption of a plant-based diet has been suggested to reduce the risk of cancer and heart disease; however, controversy surrounds this due to concerns over differences between plant-based diets, potential vitamin and mineral deficiencies, and what diets like these mean at critical life stages such as pregnancy. This review aimed to assess the effects of plant-based on the development of heart disease and cancer in adults and pregnant women. The results showed that vegetarian and vegan diets were associated with a lower risk for heart disease and cancer, and had beneficial effects on blood lipid levels, blood sugar levels, body weight, and inflammation. Vegetarian diets were associated with lower mortality due to heart disease. However, plant-based diets varied between the studies making it difficult to determine the optimal diet. It was concluded that plant-based diets may reduce the risk of heart disease, cancer, and death due to heart disease. However, due to the difference in the diets studies, the risks associated with diets which restrict one food group and nutrients, and individual needs, plant-based diets should not be broadly recommended. This study could be used by healthcare professionals to understand the benefits of a plant-based diet. However, the recommendation of these diets should be done on an individual basis and potentially vitamin levels need to be monitored.
Expert Review
Conflicts of interest:
None
Take Home Message:
- A plant-based diet may help to reduce the risk of CVD and cancer, and their associated morbidities.
- However, the results of this umbrella review should be read with caution due to the low strength of evidence and the myriad of confounding factors that cloud interpretation.
- Risks for macro- and micronutrient deficiencies of fully plant-based diets cannot be ignored.
- Registered nutritional therapists and registered nutritionists are ideally placed to mitigate these risks with proper education, particularly essential in the case of those wishing to consume a fully plant-based diet where no dairy, eggs or fish are consumed.
Evidence Category:
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X
A: Meta-analyses, position-stands, randomized-controlled trials (RCTs)
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B: Systematic reviews including RCTs of limited number
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C: Non-randomized trials, observational studies, narrative reviews
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D: Case-reports, evidence-based clinical findings
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E: Opinion piece, other
Summary Review:
Introduction
Cardiovascular diseases (CVD) and cancer are leading causes of morbidity and mortality worldwide. This umbrella review sought to synthesise evidence from existing systematic reviews and meta-analyses describing the effect of plant-based diets on the incidence of CVD and cancer, and related morbidities globally.
Methods
- Study design: umbrella review (review of reviews)
- Eligible article types: reviews, systematic reviews and meta-analyses reporting on the effect of vegetarian and vegan diets (“animal-free” and “animal product free”) compared to consumption of omnivorous diets, on health parameters associated with CVD, metabolic disorders, cancer, or their associated morbidities.
- Data were extracted and relevant meta-analyses reported. No further meta-analyses were performed in the present review.
- AMSTAR-R rating was applied to assess the quality of included articles and describe the strength of the evidence collated.
Results*
- From an initial search yield of 2502 articles, 49 were included in the final analysis.
- Vegetarian and vegan diets appeared to reduce/improve: Total and LDL cholesterol; Fasting glucose and HbA1c; Bodyweight/BMI; Inflammation
- Other indices including HDL cholesterol, triglycerides, and blood pressure were inconclusive.
- General results from three meta-analyses suggested favourable outcomes for cancer, though when analyses were stratified by cancer type, results were inconsistent.
- Though some studies scored well in the AMSTAR-R rating for some points, reporting was poor elsewhere.
Conclusion
- Plant-based or vegetarian and vegan diets may afford some protection against CVD and cancer, and their associated morbidities.
- An overall low quality of the included publications was accorded, which lowered the strength of evidence and reduced external validity of findings.
- The findings may be further affected by the potential risks in nutrient imbalance caused by restrictive dietary regimens.
*Due to the extensive data reporting and limited space in this review, readers are invited to consult the paper for specific data from meta-analyses on the indices described above.
Clinical practice applications:
- Nutritional therapists may consider a plant-based approach in cases of CVD or associated morbidities to help augment care but should exercise caution if recommending completely plant-based, as the evidence presented by this umbrella review is of low strength or inconclusive.
- Applications of plant based diets in cancer are inconclusive to date.
- Therapists should take care to provide sufficient education on mitigating risks of nutrient deficiency in both partially (vegetarian) and fully (vegan) plant-based diets
Considerations for future research:
- Future studies could assess the impact of increasing the amount of vegetables in omnivorous or fish-based diets compared to vegetarian or full plant-based diets in relation to CVD and cancer incidence.
Abstract
CONTEXT Cardiovascular diseases (CVDs) and cancer are the two main leading causes of death and disability worldwide. Suboptimal diet, poor in vegetables, fruits, legumes and whole grain, and rich in processed and red meat, refined grains, and added sugars, is a primary modifiable risk factor. Based on health, economic and ethical concerns, plant-based diets have progressively widespread worldwide. OBJECTIVE This umbrella review aims at assessing the impact of animal-free and animal-products-free diets (A/APFDs) on the risk factors associated with the development of cardiometabolic diseases, cancer and their related mortalities. DATA SOURCES PubMed and Scopus were searched for reviews, systematic reviews, and meta-analyses published from 1st January 2000 to 31st June 2023, written in English and involving human subjects of all ages. Primary studies and reviews/meta-analyses based on interventional trials which used A/APFDs as a therapy for people with metabolic diseases were excluded. DATA EXTRACTION The umbrella review approach was applied for data extraction and analysis. The revised AMSTAR-R 11-item tool was applied to assess the quality of reviews/meta-analyses. RESULTS Overall, vegetarian and vegan diets are significantly associated with better lipid profile, glycemic control, body weight/BMI, inflammation, and lower risk of ischemic heart disease and cancer. Vegetarian diet is also associated with lower mortality from CVDs. On the other hand, no difference in the risk of developing gestational diabetes and hypertension were reported in pregnant women following vegetarian diets. Study quality was average. A key limitation is represented by the high heterogeneity of the study population in terms of sample size, demography, geographical origin, dietary patterns, and other lifestyle confounders. CONCLUSIONS Plant-based diets appear beneficial in reducing cardiometabolic risk factors, as well as CVDs, cancer risk and mortality. However, caution should be paid before broadly suggesting the adoption of A/AFPDs since the strength-of-evidence of study results is significantly limited by the large study heterogeneity alongside the potential risks associated with potentially restrictive regimens.
Methodological quality
Jadad score
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Not applicable
Allocation concealment
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Not applicable