Vegan Diet Could Help Keep Diabetes Under Control

Liam Davenport

October 31, 2018

People with type 2 diabetes (T2D) who follow plant-based or vegan diets could not only experience greater weight loss and improvements in glucose and symptom control but also have improved wellbeing and quality of life, the results of a UK systematic review suggest.

Anastasios Toumpanakis, a doctoral candidate in health psychology at the School of Health Sciences, University of London, and colleagues examined 11 studies that looked at the impact of a plant-based or vegan diet in T2D patients.

They found that physical and emotional quality of life improved with a plant-based/vegan diet, and depressive symptoms lifted. In addition, symptoms of neuropathy improved more than that seen with control diets.

The findings also suggested that measures of glucose control improved with a plant-based/vegan diet over a control diet, while patients following them also lost more weight and had greater reductions in cholesterol levels and triglycerides.

The research was published online by BMJ Open Diabetes Research & Care on October 30th.

Significant Improvements

While acknowledging the small sample sizes of the included studies and the self-report nature of the data, the team nevertheless concludes "that plant-based diets accompanied by educational interventions can significantly improve…the management of diabetes".

The results follow those of a recent study suggesting that following a low-fat, plant-based vegan diet could reduce the risk of developing T2D through the reduction of visceral fat and by significantly improving both pancreatic beta-cell function and insulin resistance.

Another analysis indicated that only partially switching to a vegetarian diet, the so-called flexitarian diet, could offer health benefits, as well as costing less than other healthy diets.

Toumpanakis told Medscape News UK that, currently, the focus in treating diabetes "is more on treating and managing the symptoms than the cause itself".

He continued: "Diabetes is a complex chronic condition that cannot simply be managed by a prescription-focused treatment.

"We need to alter and enrich our approach as health professionals and offer more support, guidance and psycho-education in people with diabetes so they would be more able to take control of their condition in the long-term."

He believes that, as patients diagnosed with diabetes face "major changes" in their lives, interventions that focus on the psychological aspects of living with diabetes are required, alongside a greater focus on education and information on lifestyle interventions.

Toumpanakis said: "The potential impact of those lifestyle interventions could subsequently lead to an improvement of individual's psychological wellbeing and quality of life.

"Also, we need to consider and plan such lifestyle interventions, not as a one-off treatment plan but as a continuous and supportive plan, aiming to promote people's confidence and knowledge of diabetes."

Diabetes Costs and Risks

In the UK, more than 4.5 million people live with diabetes, and the disease is estimated to have cost the economy £24 billion in direct and indirect costs in 2010, a figure that is set to rise to £40 billion in 2035.

Not only is diabetes associated with an increased risk of cardiovascular disease, nephropathy and diabetic retinopathy, and an increased mortality risk, but also is often comorbid with depression.

Toumpanakis explained that depression in T2D is associated with several metabolic and behavioural risk factors, including reduced compliance with dietary and weight loss recommendations, increased caloric intake and reduced physical activity, all of which contribute to obesity.

In addition, depression is associated with increased inflammation, another risk factor in T2D, while antidepressant medications can cause weight gain and obesity.

He added: "Overall, the psychological stress associated with the management of diabetes could lead to elevated symptoms of depression."

It is therefore perhaps not surprising that depression comorbid with T2D "has been associated with poorer glycaemic control and poorer management of the condition".

Systematic Review

As previous studies have suggested a link between plant-based diets and improvements in psychological wellbeing, quality of life and HbA1c control in diabetes patients, the researchers conducted a systematic search of the available literature.

They examined the Allied and Complementary Medicine, Cochrane Central Register of Controlled Trials, Cumulative Index to Nursing and Allied Health Literature, E-Journals, Excerpta Medica Database, MEDLINE, Health Management Information Consortium, PsycARTICLES, PsycINFO, PubMed, SocINDEX and Web of Science databases for relevant studies, regardless of publication date.

After an initial 1240 articles were identified, 41 individual studies were selected, of which 11 met the inclusion criteria. They were published between 1999 and 2017, and included a total of 433 individuals.

The participants were aged between 27 and 80 years, at an average of 54.8 years. All but three studies focused solely on T2D patients, while the remainder included individuals with a high body mass index or T2D-related conditions.

The studies ranged in duration from 3 to 74 weeks, at an average of 23.2 weeks. The withdrawal rate was between 3.5% and 29.1%.

Nine studies were controlled, of which seven were randomised controlled trials. Two studies used a parallel design and one a cluster design.

A vegan diet was examined in eight studies, while one looked at a plant-based diet with the option of one portion of low-fat yoghurt per day. In six studies, patients were given information on optimal nutrition.

Plant Diet Benefits

Across the studies, plant-based or vegan diets were associated with significant improvements in overall quality of life (p<0.05), and in psychological and physical components of quality of life (p<0.001 and p<0.0001, respectively), which was not seen with control diets.

Moreover, levels of depression decreased significantly with a plant-based/vegan diet (p=0.03).

Both dietary and control groups saw decreases in perceived pain and neuropathy symptoms, however, the reduction was significantly greater with the plant-based/vegan diet (p=0.04).

While control patients reported significant reductions in foot conductance (p=0.03), the was not see with the plant-based/vegan diet, which the researchers say suggests "that the intervention might have stopped or slowed down the progress of nerve impairment".

Intervention patients also saw significant improvements over control participants in self-esteem (p<0.01).

Of nine studies reporting changes in HbA1c levels, the reduction was greater with the plant-based/vegan diet than in the control groups, at a mean reduction of 0.55% versus 0.19%.

Mean fasting blood glucose levels also decreased more with the dietary intervention, at 22.91 mg/dL versus 11.58 mg/dL in the control groups, and the intervention was associated with greater reductions in levels of total and low-density lipoprotein cholesterol and triglycerides.

Furthermore, patients on the plant-based/vegan diets lost more weight than those in the control groups, at a mean loss of 5.23 kg versus 2.83 kg.

In six studies, the intervention was associated with greater reductions in diabetic medications than in the control groups, and some patients were able to discontinue antihypertensive medications.

The team also reports that, while the plant-based/vegan diets were "slightly more demanding" initially, adherence was greater with the plant-based/vegan diet, "suggesting high rates of acceptability of the plant-based diet among the participants of the intervention groups".

Next, Toumpanakis would like to conduct research into "the effects of nutrition in chronic conditions and how nutrition could be used as a tool of managing those conditions".

"It is a research field that continues to expand and in my opinion has to offer many important insights," he said.

To those ends, he is planning a diabetes intervention that "takes into account the psychological, social, medical and nutritional factors of the condition," adding that he is "also planning to review controlled trial studies on the effects of plant-based diets in cardiovascular diseases".

Reaction

Several experts have issued statements reacting to the study findings.

Dr Katarina Kos, senior lecturer in diabetes and obesity, University of Exeter, said: "Diets in the intervention and control group were not matched for calories in any of the studies. The success of this diet in people with diabetes was probably down to the fact a vegan diet tends to be low in calories and some were specifically low in fat – a non-vegan low-calorie diet might work just as well to have the same effect."

Dr Nicola Guess, lecturer in nutritional sciences and diabetes, King's College London, said: "The content of the control diet is key here. Most studies in the control groups had the same amount of carbohydrate as the plant-based diet, just that the type of carbohydrate was different. This is important because foods high in fibres (fibres are a type of carbohydrate) help improve insulin sensitivity, lower blood glucose and overall help with management of type 2 diabetes. In contrast, a large proportion of energy in the diet from refined carbohydrates (like white bread or cereals) can worsen glucose control.  This might have been the case in the control groups in these studies. 

"Not all of the studies report exactly what the control group was eating, but in some the control group was merely asked to follow their usual diet. It's therefore not a surprise the plant-based diet got better weight loss and better improvements in health outcomes."

Prof Tom Sanders, professor emeritus of nutrition and dietetics, King's College London, said: "It is important to consider what foods are actually eaten, and vegan diets are based on the exclusion of food of animal origin. 

"Many western vegans eat well balanced diets based round wholegrain cereals, nuts, pulses and plenty of fruit and vegetables – the diet also needs supplementing with vitamin B12.  A balanced vegan diet usually results in weight loss, and this would be predicted to reduce risk of type 2 diabetes and improve glucose control providing the carbohydrate is obtained from wholegrain rather than refined carbohydrates. 

"A vegan diet based on high intakes of refined carbohydrate foods such as white bread, white rice, cakes, biscuits, jam and confectionery would not be a good remedy."

Publication fees for this study were covered by the City, University of London.

No conflicts of interest declared.

BMJ Open Diab Res Care 2018;6:e000534. doi:10.1136/bmjdrc-2018-000534

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