A review of interventional studies on plant-based diets for cardiometabolic outcomes in type 2 diabetes

Type 2 diabetes mellitus (T2DM) is a chronic metabolic condition characterised by hyperglycaemia due to dysfunctional insulin secretion and peripheral responses to insulin. Although advancements have served to improve quality of life in those with T2DM, a lack of preventive measures result in its prevalence being projected to more than double by 2050 (1) . Despite dietary risks being responsible for the annual loss of 142,000,000 age-standardised disability-adjusted life years (2) , the tenets of lifestyle medicine continue to be underutilised, partly owing to a predilection for pharmacotherapy in clinical medicine. Synergising lifestyle medicine and pharmacotherapy is a promising avenue for reducing the prevalence of T2DM, with plant-based diets (PBDs) being a cost-effective measure with potentially significant public health and environmental benefits (3) . Aim: This study aims to determine the trend of effects of PBDs on cardiometabolic outcomes in T2DM, by analysing the current body of interventional trials within the last 10 years. PubMed was searched using the string (“Diabetes Mellitus, Type 2“[Mesh]) AND “Diet, PlantBased“[Mesh] whilst filtering for randomised-controlled trials conducted in the last 10 years. Exclusion criteria: Studies wherein the primary intervention was not a PBD, studies assessing irrelevant outcomes, inability to access full-text, non-interventional studies, and studies wherein the control group followed a PBD. Inclusion criteria: Interventional trials implementing PBDs (vegan, vegetarian, or Mediterranean diets) as the sole intervention in patients either with T2DM or at risk of T2DM. Relevant outcomes were collected in Excel and classified into three categories, ‘Favours Plant-Based,’ ‘No Difference,’ and ‘Favours Control,’ based on whether statistically significant results (p < 0.05) were attained for each variable. The effect of PBDs on fifteen separate outcomes - including HbA1c, weight loss, systolic blood pressure, and lipid markers - was collected from the forty-four included studies, and categorised into the following categories: ‘Favours Plant-Based,’ ‘No Difference,’ and ‘Favours Control.' The most frequently assessed outcomes were HbA1c and weight loss, with HbA1c being the biomarker of choice to assess the progression of T2DM and weight loss being the factor having the largest effect on risk reduction in T2DM (4) . Across the 44 trials, the cumulative frequency of the selected outcomes was 120. 102 (85%) favored plant-based diets. 17 instances (14.17%) showed no significant difference between the plant-based and control groups, whilst only 1 instance (0.83%) favoured the control group. This review suggests that PBDs are an effective intervention for T2DM, particularly for glycaemic control and weight loss. Most studies assessed were on Mediterranean diets. Literature on strict PBDs displays comparably positive results (5) but research is necessary to compare the two. A systematic review and meta-analysis, which pools effect sizes for each outcome, would prove useful in quantifying the effect of PBDs compared to various controls.