Eleven articles were reviewed in a systematic review (filtered from 1240 articles) by Toumpanakis et al (2018).

433 patients included with mean age 54.8 years. Plant-based diets are associated with significant improvement in emotional well-being, physical well-being, depression, quality of life, general health, HbA1c levels, weight, total cholesterol, and low-density lipoprotein cholesterol (Toumpanakis, Turnbull, & Alba-Barba, 2018).

Compared with several diabetic associations’ official guidelines and other comparator diets, plant-based diets can significantly improve psychological health, quality of life, HbA1c levels and weight and therefore the management of diabetes.

Satija et al (2016) reviewed three large prospective cohort studies (nurse’s health study, nurse’s health study 2 and health professionals follow-up study.

Of a total sample of 200,727 participants and concluded that a plant-based diet is associated with significantly lower risk of T2D. Plant-based diets offer high protection against the development of diabetes as it contains antioxidants, fibre, micronutrients and unsaturated fatty acids (Satija, et al., 2016)

The American Association of Clinical Endocrinologists and the American College of Endocrinology have released guidelines in which they suggest that plant-based diet is the optimal nutrition plan for people with diabetes as it promotes the well-being and the better management of diabetes (Garber, Abrahamson, Barzilay, & al, 2018)

The BROAD study is a randomised controlled trial using a whole food plant-based diet in the community for obesity, ischaemic heart disease or diabetes (Wright, Wilson, Smith, Duncan, & McHugh, 2016) Those with a low-fat plant-based diet experienced an average weight drop 11.5kg at 12m, average Hba1c reduction 5.3 mmol/mol TC reduction after a 12-week intervention.

The diet enabled reduction in energy density: lower fat, higher water and fibre. An important part of this intervention was not being hungry is important in enabling adherence. It was compared to liquid diets and noted that liquid diets are not intended for long-term use and recognised the importance of ‘eating to satisfaction’

A meta-analysis (Yokoyama, 2014) focusing on vegetarian diets (defined as those excluding meat, poultry and fish, but including eggs and dairy) in diabetes revealed a significantly improved glycated haemoglobin (HbA1c) in people who followed a vegetarian diet pattern.

The Adventist Health Study 2 studied disease prevalence of different eating patterns on over 61,000 individuals. The incidence of type 2 diabetes was 2.9% in vegans, and 7.6% in non-vegetarians which was adjusted for BMI.

The incidence gradually reduced depending on the amount of meat present in the diet (Tonstad, Butler, & Yan, 2009), and identified that even small increases in meat increased diabetes risk. The Adventist Mortality Study and Adventist Health Study showed a 17-year adherence to a diet with at least weekly meat intake was associated with a 74% increase in odds of developing diabetes compared to long-term adherence of a vegetarian diet (zero meat intake).

The association was attenuated but persisted when controlling for weight and weight change (Vang, Singh, Lee, & al, 2008).

Similar findings have been found in a study of over 4,000 Taiwanese Buddhists; the rate of diabetes was approximately half in vegetarian men compared to omnivores.

Satija et al (2016) analysed data from 4.1 million person-years of the Nurses health studies (1 and 2) and the Health Professionals Follow-up study and those most adherent to a healthful plant-based dietary index had 34% lower risk of developing diabetes to those least adherent, which associations independent of BMI and other risk factors (Satija, et al., 2016).

Barnard et al compared an RCT of a plant-based diet compared to the 2003 ADA guidelines (Barnard, Cohen, Jenkins, & al, 2009) with 99 individuals in the study.

The vegan diet was approximately 10% energy from fat, 15% from protein and 75% from carbohydrates. A focus on vegetables, fruit, grains and legumes. They were also advised to move towards low GI foods, e.g. beans and green vegetables.

43% (21 individuals) of the intervention group reduced their medications. 26% (13/50) of ADA group participants reduced their medications. Hba1c fell by 1.23 in vegan group (excluding medications) and 0.38 in ADA group (p=0.01). Average weight loss in plant-based group was 6.5kg compared to weight loss 3.1kgin ADA group (p<0.001).

LDL reductions of >21% in vegan group and >10% in ADA group. (p=0.02). Urinary albumin reductions were more significant (15.9mg/24 hr vs 10.9mg/24 hr).

Conversely high meat diets are associated with increased risk of developing diabetes (Satija, et al., 2016; Kim, Keogh, & Clifton, 2015; van Nielen, Feskens, & Mensink, 2014; Djousse, Khawaja, & Gaziano, 2016). Van Nielen (2014) identified high animal protein consumption was identified as a 22% higher risk of developing compared to lowest quintile of animal protein consumption.

Similarly, the nurse health studies and health professional studies identified a 13% increase in type 2 diabetes between quintiles of animal protein consumption (Malik, Li, Tobias, & al, 2016). This effect appears more pronounced in older populations with a geriatric study in Greece identifying a 34% increased incidence of type 2 diabetes with a 5% increase in protein intake from meat products despite adjustments for obesity, age, hypertension, obesity, hyperlipidaemia and other dietary behaviours (Pounis, Tyrovolas, Antonopoulou, & al, 2010).

Further cardiovascular impact – vegetarian diets
Ischaemic heart disease and mortality is reduced in plant-based diets by between 29% in a large meta-analysis study with also an 18% reduced cancer incidence than non-vegetarians (Huang, Yang, Zheng, & al, 2012). Results reported on the Esselstyn Program look at 198 patients of which 89% were adherent to a diet of ‘whole-food, plant-based, no meat (including poultry and fish), no dairy, no eggs, or added oils. The CV event rate was 0.6% compared to 62% in the non-adherence group (Esselstyn, Gendy, Doyle, & al, 2014).

Plant-based diets combined with low carb diets

Evidence appears to suggest that low-carb diets that are replaced with high amounts of animal products may be associated with higher risk of type 2 diabetes, whereas the opposite may be the case with plant-based approaches to moving towards lower carbohydrates.

The Health Professionals follow-up study identified a 37% higher risk of developing type 2 diabetes in low-carb compared to highest-carb intake quintiles, however if the low-carb diet was plant-based it was more protective (de Koning, Fung, & Liao, 2011) with similar results in the Nurses Follow up study looking at low-carb approaches increasing risk of gestational diabetes when low-carb favoured animal-based products (Bao, Li, Chavarro, & al, 2016)