Grains and Diabetes

Diabetes is Australia’s fastest growing chronic health problem and accounts for 10.5% of all deaths in Australia. In 2017-18, total number of Australians with diagnosed diabetes was 1.2 million people, but it is thought to affect far more with 1 in every 5 people with diabetes undiagnosed.

There is strong epidemiological evidence from around the world to suggest that eating a variety of whole grain foods is beneficial in the prevention and management of type 2 diabetes – this relationship is a consistent conclusion in systematic reviews.

Diabetes Prevention:
A Cochrane review published in 2008 concluded that high intakes of whole grain foods reduce the risk of developing type 2 diabetes by 21-33%, a finding consistently demonstrated in the 11 cohort studies and one randomised controlled trial included in the review. The prospective studies also consistently showed an association between high intakes of both whole grain foods and cereal fibre, and reduced risk of type 2 diabetes, ranging from 27-30% and 28-37% respectively.

A study which followed 43,000 men for 12 years found that those who ate the most whole grain foods, including brown rice, oats, and barley, were less likely to be diagnosed with type 2 diabetes than those who ate the least. Those who ate less than 1 serve of whole grain food per day were nearly 30% more likely to develop type 2 diabetes compared with men who consumed 3 servings of whole grains daily.

Since the Cochrane review, several other studies provide further supporting evidence. The MESA study of more than 5,000 US adults followed for seven years found a dietary pattern characterised by a high intake of whole grains and fruit was associated with a 15% lower diabetes risk.

For those who are at risk but have not yet developed diabetes, the progression of impaired glucose tolerance to type 2 diabetes can be delayed, and insulin resistance improved, by lifestyle changes that include exercise and a diet that includes whole grain foods.”

Professor Jim Mann Director of the Edgar National Centre for Diabetes and Obesity Research (ENCDOR) and the WHO Collaborating Centre for Human Nutrition.

Diabetes Management:
Whole grain and high-fibre cereal foods can also help in the management of people who already have diabetes. A review of 24 studies that incorporated whole grain foods into dietary interventions in subjects with type 2 diabetes found that, in all but two, there were improvements in glucose metabolism, including a reduction in insulin or oral hypoglycaemic agents, lowering fasting blood glucose, lowering glycosylated protein concentrations and reduced urinary glucose and C-peptide.

When testing insulin sensitivity in overweight people with type 2 diabetes on diets that incorporate refined or whole grains, whole grain diets have been found to facilitate a greater rate of glucose infusion. Insulin-resistant adults with normal blood glucose levels following an exercise and diet intervention program with increased intakes of whole grain foods have also been found to achieve weight loss and enhanced insulin sensitivity.

Long-term dietary intervention studies confirm that diets incorporating frequent consumption of whole grain foods can reduce the progression from impaired glucose tolerance to type 2 diabetes by up to 58%.

Improving Glycaemic Control and Insulin Sensitivity:
Epidemiological studies as well as dietary intervention and metabolic studies strongly support the suggestion that whole grain foods improve glycaemic control and insulin sensitivity. In the MESA study, there were significant inverse associations between whole grain intake (0.02 to 1.4 serves a day in the highest quintile) and fasting glucose (2.5%), fasting insulin (9%) and insulin resistance (9%).

In a weight loss intervention trial with overweight subjects at high risk of diabetes, those fed two serves of a whole grain-based liquid diet product had significantly better improvement in insulin resistance than controls fed an inulin-based product with equivalent levels of dietary fibre.

Suggested Mechanisms
While there are several plausible mechanisms by which whole grain and high cereal fibre foods might reduce diabetes risk and improve glycemic control, some uncertainties remain.

Insoluble Fibre:
The evidence that whole grain foods and insoluble dietary fibre derived from cereals protect against type 2 diabetes is strong and consistent among prospective studies. It is possible that this protection is afforded by the intact structure of the cereal grains slowing digestion and partially restricting absorption of the glycemic carbohydrate.

Long-term diabetes prevention benefits might also relate to the nutrient content of whole grains. The strongest evidence of this is linked to the higher magnesium content of whole grains, with prospective studies suggesting that low magnesium intake and status predates the diabetic condition.

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