Experts criticise claims in new diabetes book

Author Dr Neal Barnard visits New Zealand this week (8th and 9th December) to promote his book The Reverse Diabetes Diet amidst criticism from New Zealand diabetes experts.

Dr Barnard claims that his approach, which is based on a low-fat vegan diet, can control blood sugar, repair insulin function and minimise medication within weeks; but local experts have critisised the books title, which is misleading in suggesting that  Type 1 diabetes can be reversed, and have expressed concern about the nutritional adequacy of the diet, which without careful planing may not meet the nutrition needs of some population groups such as pregnant women.

The comments from New Zealand experts in diabetes are as follows:

Jim Mann is Professor in Human Nutrition and Medicine at the University of Otago. He comments:

“The Reverse Diabetes Diet by Dr Neal Barnard promotes a low-fat vegan diet, and claims that by following this diet it is possible to reverse diabetes.

“The book opens with the statement that it “presents a totally new method for preventing, controlling and reversing diabetes”; however, there is nothing new in the suggestion that a low-fat vegan diet, which helps to promote weight loss, can be very helpful for managing diabetes. My main concern, however, is that some of the claims made by the author are over-rated; in particular, to imply that Type 1 diabetes can be reversed is mischievous.

“Following a low-fat vegan diet, as recommended in this book, can be a healthy way to manage diabetes for some people, although careful planning is important to ensure the nutritional adequacy of the diet, as major food groups such as meat and dairy products will be excluded.

“Also, it is worth pointing out that there are many dietary approaches that can help manage diabetes and it is not essential to follow a low-fat vegan diet – which many people may find hard to stick to. The key for managing Type 2 diabetes is maintaining a healthy weight and this can be achieved without having to resort to a vegan diet.”

Elaine Rush is Professor of Nutrition at Auckland University of Technology. She comments:

“A comprehensive, well-researched book about the why and how blood glucose and lipids can be improved and body weight reduced with a plant-based, low glycaemic index, low-fat diet. This diet is nutrient dense and relatively low in energy for each mouthful so long as “nuts, seeds, olives, avocados and some soya products .. naturally high in oil” are kept to a minimum. (page 52).

“Not all diabetes can be reversed and therefore the title of this book is misleading.  Type 1 diabetes mellitus (~5% of cases) is irreversible; the more common Type 2 diabetes mellitus may be reversible in the early stages. The differences in types of diabetes are explained further in the first chapter but it certainly is not a black and white situation that diabetes is able to be prevented.  There is definitely strong evidence that Type 2 diabetes may be delayed through lifestyle changes including diet and exercise. 

“That being said the book does include sound advice for an overweight adult, newly diagnosed with Type 2 diabetes or high blood sugar for a healthy balanced dietary pattern but the whole book has to be read carefully.  When on a plant based low-fat diet it is very likely that inadequate vitamin B12, vitamin D and iron will be provided by the foods and Dr Barnard recommends daily supplements including multivitamins. Clearly this book is aimed at the literate, those who come from a European style culture and those who can cook.  It is not a suitable diet for children or women who plan to get pregnant without expert support. The availability and cost of the ingredients may also be a barrier to some as unfortunately the whole (unprocessed) foods such as lentils and soy products are not readily available in every supermarket in New Zealand.

Dr Wendy Grylls is a Nutritionist and Registered Dietitian with a research background in diabetes. She comments:  

“Dr Neal Barnard, who originally trained as a psychiatrist, is a vegan and animal rights activist. His book, The Reverse Diabetes Diet, promotes a vegan diet which is high in carbohydrates (of low glycaemic index and/or high in fibre), very low in fat and free of both cholesterol and animal protein. While the regime has a number of nutritional merits, it is extreme. The vegan diet is healthier than the opposing Atkins diet (low-carbohydrate, low-fibre, high-fat, high-cholesterol and high animal protein) but both diets eliminate entire food groups. This seriously restricts dietary variety which reduces the likelihood of long term compliance. The vegan diet is low in some micronutrients and supplementation with vitamins, particularly Vitamin B12, is needed. Healthy balanced diets do not require nutritional supplementation.

“The term “reverse” diabetes is potentially misleading and most diabetes health professionals prefer to use the description “well controlled” when metabolic indicators such as HbA1c (a longer term laboratory measure of blood glucose control) and blood lipids fall within normal ranges. The research paper which supports this diet (1) concludes that it is the weight reducing effect of the vegan diet which is largely responsible for the reduction in HbA1c This is not surprising and weight loss has always been recommended as the most effective treatment for obese people with Type 2 diabetes in all major diabetes nutrition recommendations.

“Dr Barnard claims his research on dietary fat and insulin resistance is “new” but a whole symposium devoted to this subject was held in 1992 and there are many research publications on this topic dating back to the early nineteen nineties. In fact, very low-fat diets, which were high in leguminous carbohydrate (although not vegan), were found to improve metabolic control of Type 2 diabetes in research trials in the early nineteen eighties. However these diets did not meet with widespread patient acceptance.

“Vegan convenience food is not as readily available in New Zealand as in the United States so claims that this diet is easy for people who dislike cooking are not valid here. Vegan diets may be detrimental to other family members such as young children, as their bulk and lower energy density may inhibit adequate growth. Lower bioavailability of iron may increase the risk of iron deficiency anaemia in some susceptible groups e.g. pregnant women. 

“Dr Barnard does not back up some of his claims with adequate, balanced referencing. For example he states, “Although there is somewhat less calcium in broccoli than in milk, the absorption fraction is higher for broccoli and nearly all other greens than for milk.”(see page 67). In fact, the absorption fraction of calcium from milk and most green vegetables is similar. A cup of skim milk provides 377mg calcium (and less than a gram of saturated fat), whereas a cup of broccoli provides only 59 mg. One has to eat a lot of broccoli to meet the recommended intake of calcium! Barnard misleads readers when he unfavourably compares skim milk (which has a low glycaemic index and several valuable nutrients) with high glycaemic index, “empty energy” fizzy drink (see page 48). He also does not stress that natural soy milk is a poor source of calcium and requires fortification. The availability of calcium from some fortified soy beverages has also been questioned (2).

“In conclusion, it would be difficult for the lay reader to “sort the wheat from the chaff” in this book.”

Specialist Diabetes Dietitian Lynne Ferguson works for Counties Manukau District Health Board in Auckland. She comments:

“Dr Neal Barnard, in his book The Reverse Diabetes Diet, is advocating that all people with Type 1 or Type 2 diabetes change to a low-fat vegan diet.

“This book is it not one that I would recommend, as it does not follow evidence-based best-practice guidelines as set out in the 2003 Ministry of Health document Management of Type 2 Diabetes. Guidelines promoted by Dr Barnard are very different to standard care in New Zealand, and mixed messages could be confusing for people with diabetes. For example, no dairy products would increase the risk of osteoporosis, a major problem in New Zealand; and no meat, chicken or fish may result in a poor iron status, as these foods are the best dietary sources of haem-iron, which is easily absorbed by the body. Glycaemic Index is emphasized, but the figures used are not for New Zealand foods, therefore, information is incorrect.

“The book also states that there is no limit on how much you can eat and you don’t have to count calories or carbohydrate. This could lead to deterioration of HbA1c (which is a measure of blood glucose levels) if taken to extreme. Very restrictive diets are very hard to follow and are often only followed for a short period of time.”           


1. Barnard et al. A low-fat vegan diet improves glycaemic control and cardiovascular risk factors in a randomised clinical trial in individuals with Type 2 diabetes. Diabetes Care, 2006; 29:1777-1783.

2. Heaney RP, Rafferty K. The settling problem in calcium-fortified soybean drinks. Journal of the American Dietetic Association, 2006;106: 1753.

Further Information

To talk to these or any other New Zealand scientists about diabetes, please contact the Science Media Centre on tel: 04 499 5476 or email:

Dr. Barnard is available for interview during his visit to New Zealand on Monday 8 and Tuesday 9 December 2008, and will be speaking free of charge at 1-hour public events in Auckland and Wellington during his visit:

  • Auckland, New ZealandMonday, Dec. 8, 2008, 3:00 p.m. Public lecture, free entry, phone 04 385 7070 to book. Raw Power Café, 10 Vulcan Lane (off High Street), Auckland  
  • Auckland, New ZealandMonday, Dec. 8, 2008, 6:00 p.m. Public lecture, free entry, phone 09 377 0209 to book Central City Library, Whare Wananga, Level 2, 44 – 46 Lorne Street, Auckland  
  • Wellington, New ZealandTuesday, Dec. 9, 2008, 12:30 p.m. Public lecture, free entry, phone 04 385 7070 to book Victoria University of Wellington, Rutherford House, Pipitea Campus, Bunny Street, Lecture Theatre 2, Wellington  
  • BOOKED OUT Auckland, New Zealand – Tuesday, Dec. 9, 2008, 7:15 p.m Diabetes New Zealand, Auckland members event with Dr Barnard and Diabetes New Zealand Head Dietitian Teresa Cleary

The Reverse Diabetes Diet by Dr Neal Barnard is distributed in New Zealand by Macmillan, ISBN 9781405099943, RRP $37.99.

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