Grains, pulses and type 2 diabetes

Grains and pulses may help to lower the risk of developing type 2 diabetes by preventing hyperinsulinaemia:

• Wholegrain foods and pulses generally have a low glycaemic index.
• Dietary fibre, particularly soluble fibre, in grains and pulses have been shown to lower glucose levels and hence insulin demand.
• Phytochemicals in grains and pulses, such as saponins and phytates have been shown to lower glucose response after a meal.

Cereal fibre and type 2 diabetes - the evidence

Epidemiological studies
Several large cohort studies have investigated whether dietary factors, which reduce insulin levels, may reduce the risk of developing type 2 diabetes.

In the USA, of the 65 173 women participating in the Nurses' Health Study, 915 nurses were diagnosed with diabetes during the six years of the study1. In these women, risk of diabetes was linked to dietary glycaemic index, glycaemic load, cereal fibre and magnesium.

Cereal fibre intake reduced the risk of diabetes by 28%. Together, a high intake of cereal fibre and a low glycaemic load reduced the risk of type 2 diabetes two-and-a-half-fold compared to high glycaemic index and low cereal fibre intake.

The Health Professionals Follow-Up Study of 42 759 men found that the risk of developing diabetes in the 523 cases diagnosed after six years was related to a combination of high glycaemic load and low cereal fibre intake2. In this study, high glycaemic load combined with a low cereal fibre intake increased the risk of type 2 diabetes two-fold when compared to low glycaemic load and high cereal fibre intake.

Another large cohort study in 35 988 women, the Iowa Women's Health Study, found that over the six years of the study, higher consumption of total grains, wholegrains, total fibre, cereal fibre and magnesium were associated with a lower incidence of type 2 diabetes3.

These studies consistently show that cereal fibre reduces the risk of type 2 diabetes. Those with the highest intake of cereal fibre (7-10 g/day) reduced their risk of developing type 2 diabetes by around 30% compared to those with the lowest intake of cereal fibre (2-4 g/day). Dietary fibre from fruit, vegetables and pulses does not appear to reduce the risk of type 2 diabetes to the same extent.

A high intake of magnesium was also shown to reduce the risk of developing type 2 diabetes. Wholegrains are a good source of magnesium.

Grain-based foods and type 2 diabetes - the evidence

Epidemiological studies
In the Iowa study the risk of diabetes was reduced by 21% in women eating more than 17.5 servings of whole-grain foods a week compared with those eating less than three servings a week, and by 32% in those eating more than 33 servings of grains a week compared to less than 13 servings per week3. Consumption of pulses did not significantly reduce the risk of developing type 2 diabetes, possibly due to low intakes in this population (the highest intake was more than 4.5 servings/week and the lowest, less than 1.5 servings/week).

Although studies have not consistently reported a protective effect from the type and amount of carbohydrate (expressed as glycaemic load), the findings suggest that eating 2-4 servings per day of whole-grain foods can decrease the risk of developing type 2 diabetes in men and women.

References
1. Salmeron J, Manson JE, Stampfer MJ et al. Dietary fiber, glycemic load, and risk of non-insulin-dependent Diabetes Mellitus in women. JAMA 1997;277 (6): 472-477
2. Salmeron J, Ascherio A, Rimm EB et al. Dietary fiber, glycemic load, and risk of NIDDM in men. Diabetes Care 1997;20 (4):545-550
3. Meyer KA, Kushi LH, Jacobs DR et al. Carbohydrates, dietary fiber and incident type 2 diabetes in older women. Am J Clin Nutr 2000;71:921-930

For Further research