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food for thought

Over the past three decades, the prevalence of Type 2 diabetes has risen dramatically worldwide.

According to the International Federation of Diabetes, by 2045 one in eight adults will be living with diabetes, an increase of 46 per cent.

A recent study of dietary and health data from 184 countries found that poor carbohydrate quality – eating too many refined grains and too few whole grains – was the leading dietary driver of Type 2 diabetes cases.

Now, a global study conducted in 20 countries adds to existing evidence that carbohydrate quality matters when it comes to staving off the disease.

The findings strongly suggest that eating foods with a low glycemic index – ones that don’t spike blood glucose and insulin after eating – is protective.

Here’s a breakdown of the latest research, plus what to eat to prevent blood sugar spikes.

Glycemic index and glycemic load defined

The glycemic index (GI), developed by University of Toronto researchers Dr. David Jenkins and Dr. Thomas Wolever in 1981, assigns carbohydrate-containing foods a score of 0 to 100 based on how rapidly they raise blood glucose compared to pure glucose.

A surge in blood glucose triggers an outpouring of the hormone insulin; over time these events can lead to glucose intolerance and Type 2 diabetes.

Foods with a high GI (70 or more) cause a sharp increase in blood glucose that declines rapidly. Examples include white bread, whole wheat bread, soda crackers, rice cakes, jasmine rice, instant rice, baked russet potato, instant oats, refined breakfast cereals, croissants, doughnuts, cakes and raisins.

Foods with a low GI (55 or less) lead to a slower and lower rise in blood glucose that declines gradually. Low GI foods include dense multigrain breads, sourdough bread, 100-per-cent bran cereals, steel-cut and rolled oats, barley, quinoa, brown rice, al dente pasta, beans and lentils, sweet potato, winter squash, most fruit and yogurt.

The glycemic load (GL) gives a more accurate picture of how foods affect your blood glucose. It considers not only the food’s glycemic index but also how much carbohydrate it contains per serving.

For example, if you eat a high glycemic food that contains only a small amount of carbohydrate, it won’t have much impact on blood glucose and its GL will be low.

The new research findings

The study, published April 5 in the journal Lancet Diabetes & Endocrinology, included 127,954 adults ages 35-70, enrolled in the PURE study (Prospective Urban and Rural Epidemiology).

Participants were from 20 low-income, middle-income and high-income countries and, at the study’s outset, did not have Type 2 diabetes.

Diet information was collected and used to calculate dietary glycemic index and glycemic load.

After 12 years, 7,326 participants had developed Type 2 diabetes.

Compared to those whose diets had the lowest GI and GL, those with the highest scores had a significantly greater risk of Type 2 diabetes. The increased risk was more pronounced in people with a high body mass index.

The researchers accounted for other factors that could influence diabetes risk such as family history, smoking, physical activity and intake of calories, fibre and whole grains.

The study’s strengths are its long duration of follow-up, large sample size and the inclusion of participants from low- to high-income countries.

Limitations include the fact that diet was measured only at the beginning of the study; dietary habits could have changed over time. Dietary information was also self-reported which is prone to error.

The study was observational; it doesn’t prove that a low glycemic diet prevents Type 2 diabetes.

How a high glycemic diet can harm metabolic health

This isn’t the first study to link high GI diets to an increased risk of Type 2 diabetes.

A review of large studies published earlier this year turned up similar findings.

High GI diets have been tied to reduced insulin sensitivity, impaired insulin secretion and poor blood glucose control.

Large spikes in blood glucose after eating have been shown to increase inflammation and oxidative stress, factors thought to promote the development of Type 2 diabetes.

Diet strategies to balance blood sugar

To lower the glycemic load of meals, choose unprocessed or minimally processed carbohydrates (e.g., whole grains, sweet potato, winter squash, beans and lentils, whole fruit) over refined carbohydrates.

These foods deliver fibre, which delays the rate that carbohydrates are digested and absorbed into the bloodstream.

Balance meals with protein and healthy fats, macronutrients that also slow down carbohydrate digestion.

Adding vinegar to meals (e.g., vinaigrette dressing) can also blunt the rise in postmeal glucose by slowing digestion and increasing glucose uptake by cells.

Consider food order too. Studies have found that eating vegetables, protein or fat first and eating refined carbohydrates last (e.g., white rice, pasta or bread) helps minimize blood sugar spikes.

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD

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