PERSPECTIVES WITH DR ALAN BARCLAY

A POTTED HISTORY OF CARBOHYDRATE AND DIABETES



People have been trying to work out the optimal diet for people with diabetes for hundreds of years. Until recently, most offerings have been restrictive and unpalatable. Fad diets are nothing new. In the early 1900s, they included: the “oat-cure,” the “milk diet,” the “rice-cure,” and “potato therapy,” diets often supplemented with a liberal dose of opium to suppress appetite ...

In 1912, Dr Fred Allen developed his “1000 Calorie Diet” (4200kJ), a very low carbohydrate diet with a kick-start seven-day fast before other foods were gradually reintroduced. Participants were told to boil their low-carbohydrate vegetables three times in water to remove starch. People became very emaciated and weak. From Allen’s later research on pancreatectomised dogs he concluded glucose was more rapidly absorbed than starch, a principle he expanded to include all “simple sugars” (fructose, galactose, lactose, maltose, sucrose, etc.). It was this “research” that led to low sugar diets being recommended to people with diabetes for most of the 20th century.

Despite H.R. Geyelin demonstrating (1923) that a higher carbohydrate diet did not upset blood glucose levels if adequate insulin was supplied, most doctors recommended low carbohydrate intakes (15% to 40% of total calories) until the late 1940s. Dr Elliot Joslin for example, plumped for 20% of calories from carbohydrate and 70% from fat.

Breakthrough 1: In 1950, the American Diabetic Association and American Dietetic Association developed the first Exchange Lists, which focused on six food groups with similar macronutrient (carbohydrate, fat and protein) levels. This system operated on the assumption that any food within a group was interchangeable because they would have the same impact on blood glucose levels. A good idea, but not entirely successful because the carb exchanges rarely had the same impact.

With an increasing number of deaths of people with diabetes from heart and blood vessel diseases, major diabetes associations reviewed their dietary recommendations in the 1970s dropping fat to less than 35% of calories and increasing carbohydrate to 55% to 60% of calories. It may have made life easier for people with diabetes, but it didn’t solve the problem of blood glucose levels.

Breakthrough 2: Building on the work of American dietitian Dr Phyllis Crapo and Australian endocrinologist Dr Mark Wahlqvist, Dr David Jenkins, Dr Tom Wolever and colleagues developed the concept of slow-release carbohydrates and the glycemic index. The concept generated much interest, even more heat and some most useful light as major diabetes associations cautiously revised their restrictions on “simple sugars” due to the growing body of evidence that they don’t adversely affect blood glucose levels in people with diabetes.

Breakthrough 3: In 1997, the World Health Organisation/Food and Agriculture Organisation recommend that the terms “simple sugar” and “complex carbohydrate” are no longer used to describe carbohydrate foods. They recommend the use of the GI as the best guide to the effect of carbohydrate foods on blood glucose levels.

The first studies showing that lower GI diets may also improve triglyceride and cholesterol levels were published in 1997.

Breakthrough 4: Harvard researchers develop the concept of Glycemic Load (GL = GI x available carbohydrate per serve), and diets with a high glycemic load are linked to the development of type 2 diabetes and heart and blood vessel disease in women and men.

In 2004, a systematic review and meta-analysis supported the recommendation of a higher carbohydrate, lower glycemic index, high fibre diet that is low in saturated fat and moderate in protein for people with diabetes. Dietary recommendations from the major international diabetes associations closely reflected the results.

“A low-GI diet can improve glycaemic control in diabetes without compromising hypoglycaemic events” concludes the first Cochrane Review of the evidence from randomised controlled trials on the GI in the management of diabetes.

Breakthrough 5: In 2013, the American Diabetes Associations systematically reviews the scientific evidence and concludes: “there is not an ideal percentage of calories from carbohydrate, protein, and fat for all people with diabetes (B); therefore, macronutrient distribution should be based on individualized assessment of current eating patterns, preferences, and metabolic goals. (E)”. In support of this, an independent group conducted a systematic review of randomised controlled trials of more than 6 months duration and determined that Mediterranean, low GI, higher protein and low carbohydrate diets are all effective in lowering glycated haemoglobin (HbA1c), with Mediterranean diets the most effective at 0.47% points and low carbohydrate diets the least effective at 0.12% points.

In 2014, a systematic review and meta-analysis that looked at people with diabetes who consumed a vegetarian diet for an average of 24 weeks (just under 6 months) found they reduced their HbA1c by 0.39% – that’s close to the Mediterranean diet and vegetarian diets are naturally very high in carbohydrates (an average of 75% of energy). But they also tend to include lots of legumes, which have very low GI values.

We now know that glycemic load is the most powerful predictor of blood glucose and insulin levels. You can lower GL by substituting low GI foods for high GI foods, or by consuming less carbohydrate, or by a bit of both.

The bottom line: There is no single best diet for all people with diabetes to manage their BGLs. It’s over to what works for you and what you can stick with long term. See your Accredited/Registered Dietitian to help you put together some healthy eating guidelines. And stick to them. And remember, a diet that’s good for people with diabetes, is good for everybody, so the whole family can enjoy it.

 

Alan Barclay, PhD is a consultant dietitian. He worked for Diabetes Australia (NSW) from 1998–2014 and is a member of the editorial board of Diabetes Management Journal (Diabetes Australia). He is author/co-author of more than 30 scientific publications, and author/co-author of  The good Carbs Cookbook (Murdoch Books), Reversing Diabetes (Murdoch Books), The Low GI Diet: Managing Type 2 Diabetes (Hachette Australia) and The Ultimate Guide to Sugars and Sweeteners (The Experiment, New York).