Plant-based dietary patterns associated with reduced risk of all-cause mortality in diabetes subgroups: a prospective cohort study from the UK Biobank

Objective: To investigate the association between adherence to a plant-based dietary index (PDI), healthy-PDI and unhealthy-PDI with all-cause mortality in people with type 2 diabetes and to assess whether associations varied by diabetes subgroups. Research design and methods: We included 4,829 UK Biobank participants with type 2 diabetes and at least two 24-hour dietary recalls. We generated overall-PDI, healthy-PDI and unhealthy-PDI scores. Multivariable Cox regression estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for all-cause mortality, comparing the highest (T3) with the lowest tertile (T1) of adherence to PDI, healthy-PDI, and unhealthy-PDI. Interactions between PDI adherence and diabetes subgroups (age at diagnosis, HbA1c, waist circumference) were assessed by two-dimensional B-splines and by including product terms into the model. Results: During a mean follow-up of 11.3 years, 679 deaths occurred. Individuals with highest adherence to PDI, compared to those with lowest adherence, were at lower risk of all-cause mortality (T3 vs T1; HR 0.79 (95% CI 0.63; 0.99)) and similar direction was observed for healthy-PDI (0.82 (0.67; 1.02)), however the 95% CI included the null value. Unhealthy-PDI was associated with increased mortality risk (1.24 (1.00, 1.54)). The associations between PDI, healthy-PDI and unhealthy-PDI with all-cause mortality risk were more pronounced for those with poorer glycaemic control, higher waist circumference, diagnosed earlier in life, and with longer diabetes duration. Conclusions: Higher PDI adherence was associated with decreased, while higher unhealthy-PDI adherence with an increased mortality risk. There was an indication for differences in these association depending on diabetes subgroups.