Twin research: evidence towards the cardiometabolic benefits of a vegan diet

Aim

This study aimed to compare the impact of a vegan or omnivorous dietary pattern on cardiometabolic outcomes.

This was done through recruitment of identical twins to take part in an 8-week dietary intervention.

Method

The study was a randomised trial on a population of identical twins (n=44), allocated to a ‘healthy vegan’ or ‘healthy omnivorous’ diet plan.

In the first four-weeks, the diet was provided through a meal delivery service, then from week 5-8 the participants prepared their own foods within their allocated dietary pattern.

The primary outcome measure from baseline to 8-weeks was reduction in low density lipoprotein cholesterol (LDL-C).

Changes in other cardiometabolic measures like insulin and fasting triglycerides were also measured as secondary outcome contributing to cardiometabolic risk.

Key findings

Both groups improved from their baseline physiological metrics when measured at the end of the 8-week trial period, however, clinical significance was only met for measures in the vegan diet group.

Mean LDL-C was significantly reduced in the vegan dietary intervention group (p=0.02)

LDL-C is the category of cholesterol associated with negative cardiometabolic outcomes like heart disease and stroke. The healthy range is under 100mg/dL:

• The twins following the vegan diet modestly reduced LDL-C to within the healthy range, from 110.7 mg/dL to 95.5 mg/dL. o This compared to a non-significant reduction from 118.5 mg/dL to 116.1 mg/dL in the omnivore group.

• A majority of the improvement in LDL-C was observed after only 4-weeks of the trial period when meals were being provided to the participants.

• Because the participants already had healthy LDL-C levels at baseline, it can be speculated this change could be greater when applied to other populations with higher baseline levels.

Other secondary outcomes linked to metabolic syndrome were also beneficially impacted by the vegan diet intervention

• Significant differences were found for fasting insulin reduction of ~20% (p=0.03) and body weight of 1.9kg lost (p=0.01).

• Both of these have impacts on long-term health conditions like type 2 diabetes and cardiovascular disease.

• There was no significant difference in B12 decline between either of the two groups: likely linked to the study duration, cobalamin is present in longer-term stores in the body.

It should be noted also that the vegan diet group had lower intake of protein as a percentage of calories and lower dietary satisfaction. This may be due to the discrepancy between their normal, typically omnivorous, diets and the vegan diet provided. The vegan group also naturally consumed ~200kcal/day less than the omnivorous group despite this not being intrinsic to the study design.

Conclusion

There is a cardiometabolic advantage of a vegan diet over an omnivore diet in this study population, especially in the primary outcome measure of LDL-C. Future research could corroborate these findings with a larger sample size and longer study duration. Clinicians should consider this study and the evidence base in which it sits when recommending plant-based dietary patterns.

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