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expert reaction to study looking at plant based or vegan diets and type 2 diabetes

Research published in BMJ Open Diabetes Research & Care shows that plant-based diets were associated with  improvement in several areas including emotional well-being, physical well-being, depression, quality of life and general health. It also argues that plant-based diets can improve HbA1c levels and weight and therefore the management of diabetes.


Dr Katarina Kos, Senior Lecturer in Diabetes and Obesity, University of Exeter, said:

“What we learn from this systematic review of 9 trials is that (low fat) vegan or plant based diets, together with weekly education sessions, are effective in providing more weight loss which unsurprisingly leads to improvement in diabetes and in diabetes- and weight-related complications.  Benefits of weight loss for improvement in diabetes are well evidenced and accepted.

“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.

“It is impossible to make conclusions on psychological wellbeing independent of the weight loss effects and independent of the benefit of frequent weekly contact, which was in almost half the studies reserved only for the intervention group.  The evidence is limited to very small numbers (219 subjects in the intervention group), shortish study durations (average 23 weeks) and varied design with almost half of the studies not providing education or continuous contact to the control groups.  So we can’t draw any conclusions about how well people stuck to the diets, which varied between trials, or on the real life applicability of these diets e.g. in using it outside a study setting without frequent, at least once weekly contact.

“So, I will continue to recommend to those with type 2 diabetes a calorie reduced diet, which allows for some weight loss, and some regular contact, which helps the motivation and may include at least some regular weighing.”


Dr Nicola Guess, Lecturer in Nutritional Sciences and Diabetes, King’s College London, said:

“This study systematically reviewed controlled trials examining the effect of a plant-based diet on blood glucose control, medication use and measures of well-being in people with type 2 diabetes.  In a systematic review the authors pre-specify the criteria for which studies they are going to include.  This means that such reviews are less prone to bias.

“This systematic review suggests that plant-based diets can be useful in lowering blood glucose, improving well-being, and possibly reducing medication use compared to the control diet.  However, 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.

“Furthermore, none of these studies were blinded (so the participants knew which diet they were following) – so the placebo effect could also be at play here in terms of improving measures of wellbeing.

“Finally it’s important to note that none of these studies compared a plant-based diet to a low-carbohydrate diet for example.”


Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“The major limitation of this review is the small number of participants in the trials and the short duration of the intervention, especially as it can take 3-4 years on a vegan diet for vitamin B12 deficiency manifest itself.

“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 white bread, white rice, cakes, biscuits, jam and confectionery would not be a good remedy.”


‘Effectiveness of plant-based diets in promoting well-being in the management of type 2 diabetes: a systematic review’ by Anastasios Toumpanakis et al. was published in BMJ Open Diabetes Research & Care at 23:30 UK time on Tuesday 30 October 2018.


Declared interests

Dr Katarina Kos: “I have no conflict of interest.”

Prof Tom Sanders: “Honorary Nutritional Director of HEART UK.  Scientific Governor of the British Nutrition Foundation.  He is now emeritus but when he was doing research at King’s College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks.  In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011.  This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof Hough at the Queen Elizabeth College (QEC), which merged with King’s College London.  The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar.  Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006.  Tom also used to work for Ajinomoto on aspartame about 8 years ago.  Tom was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain.  Tom has previously acted as a member of the Global Dairy Platform Scientific Advisory Panel and Tom is a member of the Programme Advisory Committee of the Malaysian Palm Oil Board.  In the past Tom has acted as a consultant to Archer Daniel Midland Company and received honoraria for meetings sponsored by Unilever PLC.  Tom’s research on fats was funded by Public Health England/Food Standards Agency.”

None others received.

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