Vegetarian Diet Effect on Diabetes

July 22, 2019

expert reaction to study on the vegetarian diet and diabetes risk

Research, published in JAMA Internal Medicine, reports that plant based diets may be beneficial in the prevention of diabetes.

Prof Alexandra Johnstone, Senior Research Fellow at Rowett Institute of Nutrition and Health, University of Aberdeen, said:

"This is a high-impact study which has been conducted using standard epidemiological approaches to look at links between diet and health. The study looked at a large cohort (309,099 participants) to assess the link between plant-based diet and development of type 2 diabetes. It is noted that the studies all applied a self-report FFQ methodology (mentioned in the limitations) which is known to introduce bias; it is a questionnaire used to obtain frequency and, in some cases, portion size information about food and beverage consumption over a specified period of time, typically the past month or year.

"The authors control for age and BMI, but there are other lifestyle factors known to influence risk of developing diabetes (eg. family history; physical activity; ethnicity) which are not controlled for. The paper did not examine meat consumption, only plant-based diet studies were included, so it should not be confused with statements relating/comparing/contrasting to other diets (such as meat diets). There are 4 main studies that contribute to the main effect (out of the reported 9).

"The paper does support what has been reported before, that diets with high fibre content are associated with reduced risk of cardio-vascular and metabolic diseases. Future research needs to focus on what components of a plant-based diet are linked to preventative health effects. The research fits with current US and USA guidelines to consume more dietary fibre from plant sources to protect from some types of diseases. Interestingly, the paper also comments on the role of fibre on weight gain, for which there is poorer evidence. However, the people who consumed the diets in the selected studies may also apply other lifestyle approaches, such as more exercise, that contribute towards protective effects.

"Also, a dose response is not clearly identified in the paper in a way to translate to the question on how much to eat – how much fibre/plants should be consumed for a protective effect? They apply a 'healthful plant-based dietary index' and apply stats that I am not familiar with (cubic spline), so difficult to translate to real world."

Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King's College London (KCL), said:

"The conclusion that the risk of type 2 diabetes is lower in vegetarians is based on a meta-analysis of observational studies mainly from the USA with a couple from East Asia. Generally, vegetarians are lighter than meat-eaters and they eat more wholegrains – both factors that would decrease risk of developing diabetes. Some of the studies included religious groups (e.g. Seventh Day Adventists) who had different life-styles from the general population that may also affect risk of diabetes. The UK Oxford EPIC study found that those who rarely consumed meat had a lower risk of developing diabetes, but this effect disappeared when adjustments were made for body mass index (1).

"Paradoxically, the incidence of type 2 diabetes is high in South Asian vegetarians in the UK who follow their diet for religious reasons. It is uncertain why type 2 diabetes is so prevalent in South Asians and it may have its origins in early development. Indeed, a vegetarian or other plant-based diets that are high in free sugars and refined carbohydrates is likely to increase risk of type 2 diabetes especially when associated with low levels of physical activity. Consequently, the avoidance of meat does not necessarily reduce risk of type 2 diabetes."

Papier K, Appleby PN, Fensom GK, Knuppel A, Perez-Cornago A, Schmidt JA, Tong TYN, Key TJ. Vegetarian diets and risk of hospitalisation or death with diabetes in British adults: results from the EPIC-Oxford study. Nutr Diabetes. 2019 Feb 25;9(1):7. doi: 10.1038/s41387-019-0074-0.

Dr Ian Johnson, Nutrition researcher and Emeritus Fellow, Quadram Institute Bioscience, said:

"It is well established from population studies that vegetarians tend to have a lower body-mass index and a lower risk of heart disease and other chronic health problems than meat-eaters. However, the term "vegetarian" is applied to a whole range of different dietary habits ranging from those who only avoid red meat to vegans who avoid all foods of animal origin.

"This rigorous statistical analysis of nine previously published prospective studies shows that the more closely the participants approached an entirely plant-based dietary pattern, the lower their risk of developing type 2 diabetes. This was particularly true for diets containing large quantities of whole-grain cereals, nuts, fruits and vegetables, rather than foods based on highly refined flour and sugar. The benefits may come from reduced consumption of meat and other animal products, from protective effects of plant constituents such as dietary fibre, from a lower risk of overweight and obesity, or perhaps from a combination of all these effects. Whatever mechanisms may be at work, this study is consistent with current public health advice to consume substantial quantities of lightly processed plant foods rich in whole-grains and fibre, and to limit consumption of animal products. Importantly for the UK, where type 2 diabetes is a rapidly increasing burden on the NHS, this new analysis suggests that any shift toward this type of dietary pattern could be beneficial."

* ' Association Between Plant-Based Dietary Patterns and Risk of Type 2 Diabetes: A Systematic Review and Meta-analysis' by Qian et al. was published in JAMA Internal Medicine at 16:00 UK time on Monday 22^nd July.

DOI: 10.1001/jamainternmed.2019.2195

Declared interests

Prof Alex Johnstone: "Receives funding from the Medical Research Council, The University of Aberdeen, The Scottish Government, Biological Sciences Research Council, Economic and Social Research Council, Engineering and Physical Sciences Research Council, National Health Service Endowments award, Tennovus Charity, Chief Scientist Office and European Community. I also choose to eat a plant-based diet."

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."

Dr Ian Johnsone: "No conflict of interests to declare."