Fiber, Magnesium, and Diabetes

Summarized by Robert W. Griffith, MD
July 18, 2007

Summary

A large German study and a meta-analysis of 17 published studies show that cereal fiber and, in some instances, magnesium intake are associated with a protective effect against the onset of type-2 diabetes.

Introduction

We reiterate in these articles about risk factors for disease. But how about looking for the opposite of risk factors - preventive factors? For instance, things that help protect you from developing type 2 diabetes. The pressure here is considerable, given the expected increase in prevalence from 171 million worldwide in 2000 to 370 million by the year 2030. Soluble fiber has been thought to help by its effect on stomach emptying, absorption of macronutrients, and reduced post-meal glucose levels. Insoluble fiber can produce short-chain fatty acids in the intestine which influence insulin sensitivity. Magnesium deficiency has been linked to diabetes, so its intake level may be relevant in protection against the disease.

A prospective study and a meta-analysis of published studies on the importance of fiber and magnesium intake in helping prevent type 2 diabetes has been published in the Archives of Internal Medicine. This is a summary of the main findings.

What was done

Investigators at the German Institute of Human Nutrition, Potsdam, conducted a study of 9,700 men and 15,360 women aged 35 to 65 between the years 1994 and 2005. These participants were selected after any with diabetes had been excluded.

At baseline, a food frequency questionnaire was used to assess the frequency of intake and the portion size of 148 different foods over the previous 12 months, using categories ranging from "never" to "5 times a day or more". The amounts of fiber and magnesium consumed were adjusted for energy intake (i.e. calories consumed). The subjects were categorized into five classes, or quintiles, according to the amount of adjusted fiber or magnesium intake.

New cases of diabetes were identified by self-reporting, which was verified by a detailed questionnaire sent to the diagnosing physician. Information on educational level, smoking, work and leisure activities was also gathered.

In a separate piece of research, a meta-analysis was conducted on publications of prospective studies on fiber and magnesium intake in relation to the occurrence of type-2 diabetes. Nine suitable fiber and 8 suitable magnesium studies were found that could be pooled for analysis.

What was found

In the Potsdam study: The average age was 49, and about 40% of the participants were male. Those with higher fiber intake were more likely to be women, more physically active, and non-smokers; they also had higher magnesium intake, lower alcohol intake, and a more favorable lipid profile.

During the 7-year follow-up 844 new cases of type-2 diabetes were diagnosed. After adjusting for possible disturbing factors (age, sex, education, physical activity, and height/weight), there was no association between total fiber intake or magnesium intake and the likelihood of developing diabetes. There was also no association with soluble fiber and insoluble fiber examined separately.

However, further analyses showed that cereal fiber (which contained both soluble and insoluble fiber, and was most commonly eaten as muesli and whole-grain bread) had a significant protective effect against the occurrence of diabetes. There were smaller, non-significant, associations between fruit and vegetable fiber and a protective effect against diabetes; non-significant means that they could have occurred by chance alone.

The meta-analysis: The analyses of the 17 studies showed very similar results to the Potsdam study: high cereal fiber and high magnesium intake was associated with a protective effect against the occurrence of type-2 diabetes, while fruit and vegetable fiber intake did not.

Conclusions

The findings in the Potsdam study are borne out by the results of the meta-analysis of published studies. Cereal fiber and, in some studies, magnesium intake are associated with a protective effect against the onset of type-2 diabetes. Both in Germany - the country of the study - and in the countries where the meta-analysis studies were conducted (USA, Finland, Australia), "cereal fiber" translates into "whole-grain fiber".

It's clear that plenty of whole-grain fiber is highly desirable for a healthy diet. In Germany and elsewhere in Europe, rye bread is the most likely source. In the USA, brown rice, oatmeal, popcorn, and certain cereals are the best sources. The need for magnesium supplements has not been settled by these studies. However, a healthy diet is likely to contain enough magnesium to render the question moot.

Source

• Fiber and magnesium intake and incidence of type 2 diabetes. MB. Schulze , M. Schulz, C. Heidemann,  et al., Arch Intern Med, 2007, vol. 167, pp. 956--965

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