Whole Grains in Diabetics: A Double-Edged Sword

 Whole grain and bran consumption are linked to reduced overall death rates and cardiovascular disease deaths in white women with type 2 diabetes, according to recent research from Boston-based investigators.

This is an important association since diabetics are prone to develop cardiovascular disease and suffer premature death.  Anything that can easily counteract those trends is welcome.

Several prior studies have found lower rates of cardiovascular disease in the general public eating whole grains.  I’m referring to fewer heart attacks and strokes, and fewer deaths from cardiovascular disease.

On the other hand, the carbohydrate content of whole grain products has the potential to complicate day-to-day management of diabetes by spiking blood sugars too high.  Too-high blood sugars aren’t healthy.  So, there’s the double edge.

What’s the Evidence That Whole Grains and Bran Prevent Death in Diabetics ?

The Harvard researchers followed 7,822 type 2 diabetic women in the massive Nurses’ Health Study over 26 years, during which 852 women died from any cause, including 295 from cardiovascular disease (195 from coronary heart disease, 100 from stroke).  Food-frequency questionnaires were administered periodically to the participants, with attention to whole grain and its components: cereal fiber, bran, and germ.  The hard clinical end-point in this study was death—from any and all causes, and from cardiovascular disease.   

Results

• After adjustment for age and lifestyle and other dietary factors, only bran consumption was inversely associated with all-cause mortality: 25% lower risk of death for those eating an average of 10 g per day compared to 1 g per day.  In other words,the women who ate the most bran had the lowest risk of dying from any cause.
• After adjustment for age and lifestyle and other dietary factors, whole grain intake trended towards protection against all-cause death, but not quite to the point of statistical significance.  Average highest consumption was 33 g per day, compared to lowest intake at 5 g per day. 
• Bran consumption was consistently associated with lower risk of cardiovascular death: 35% lower risk comparing highest (10 g/day) with lowest consumption (1 g/day). 
• “Added bran” was as protective against cardiovascular death as naturally occuring bran. 
• Whole grain tended to protect against cardiovascular death, but did not reach statistical significance in the model adusting for lifestyle and other dietary variables (even when comparing 33 g/day to 5 g/day)
• Whole grain and cereal fiber were inversely associated with all-cause and cardiovascular mortality when the investigators adjusted only for age, disregarding the possible effects of smoking, alcohol, overweight, physical activity, family history of heart disease, hormone therapy, duration of diabetes, total energy intake, fat intake (polyunsatrurated, trans-, saturated), magnesium, and folate.

The Researchers’ Conclusions

Whole-grain and bran intakes were associated with reduced all-cause and cardiovascular disease-specific mortality in women with diabetes mellitus. These findings suggest a potential benefit of whole-grain intake in reducing mortality and cardiovascular risk in diabetic patients.

The authors point out that whole grain and its components may be protective since they:

• reduce blood lipids
• lower blood pressure
• reduce hyperinsulinemia and improve glucose control
• improve performance of the arterial wall lining (endothelium)
• reduce oxidative stress and iflammation

My Comments

Whole grain and bran consumption may indeed protect against death and cardiovascular disease in diabetic white women, but the effect is by no means dramatic.  I had speculated earlier whether whole grain intake might be particularly protective in diabetics, but this study suggests not.  Clearly, whole grains are no panacea. 

Diabetics hoping to avoid cardiovascular disease are well-advised to pay attention to—and modify—non-dietary risk factors for heart disease, such as obesity, smoking, and sedentary lifestyle.  Non-dietary issues probably outweigh the effects of diet, assuming blood sugars are reasonably controlled.

The traditional Mediterranean diet—prominently featuring whole grains—is associated with longer lifespan and less cardiovascular disease.   Canadian researchers in 2009 found moderately strong evidence that whole grains protect against coronary heart disease in the general population.  Yet a 2009 study did not find cereals contributing to the longer lifespan. 

I’m starting to think that the effect of diet on chronic disease is not as powerful as we have hoped.  

Steve Parker, M.D.

Reference: 
He, M., van Dam, R., Rimm, E., Hu, F., & Qi, L. (2010). Whole-Grain, Cereal Fiber, Bran, and Germ Intake and the Risks of All-Cause and Cardiovascular Disease-Specific Mortality Among Women With Type 2 Diabetes Mellitus Circulation, 121 (20), 2162-2168 DOI: 10.1161/CIRCULATIONAHA.109.907360