Diabetic Mediterranean Diet

Plant-based diets may offer special benefits to people with diabetes, according to a recent review article by U.S. researchers who reviewed the pertinent English language literature published since 1966.  They found 116 potentially relevant articles, 10 of which were directly related to diabetes management and glucose control.

The authors failed to define “vegetarian” early on.  Some vegetarians eat eggs, some eat cheese, some drink milk.  I assume vegans eat no animal products whatsoever.  On the last page of the review the authors write that a vegetarian “does not eat meat, fish, or poultry” although it’s not clear if that applies throughout the review.  There are many references to “low-fat vegetarian” diets, with little or no mention of moderate- or high-fat vegetarian diets.

The authors often refer to vegetarian diets as “plant-based.”  No doubt, they are.  But even the healthy Mediterranean diet is considered plant-based, while clearly not vegetarian.

It’s also unclear whether they focused on type 1 or type 2 diabetes.  My sense is, probably type 2.

Here are the major points: 

1. Are vegetarians less likely to develop diabetes?  Observational studies have found a lower prevalence of diabetes among vegetarians compared to non-vegetarians, especially among Seventh Day Adventists.  In other studies, meat consumption is linked to higher risk of diabetes among women. 
2. Do vegetarian diets help control diabetes?  Several small studies showed that low-fat near-vegetarian and vegan diets improved glucose control and insulin sensitivity and reduced diabetes medication use, compared with a traditional diabetes diet – which is typically low-fat and high-carb.  I’m not sure, but I assume that the intervention diets were not heavy in refined, processed carbohydrates, but instead consisted of natural whole plant foods.  “Weight loss accounts for much although not all, of the effect of plant-based diets on glycemic control,” they write.
3. Heart disease is quite common in older diabetics.  Do vegetarian diets offer any cardiac benefits?  They cite Dr. Ornish’s Lifestyle Heart Trial of a low-fat vegetarian diet and intensive lifestyle intervention: smoking cessation, stress management (meditation?), mild exercise, and group meetings.  Dr. Ornish’s program reduced LDL cholesterol by 37%, reversed heart artery blockages in 82% of participants, and found 60% lower risk of cardiac events compared to the control group. Dr. Ornish’s Multisite Lifestyle Cardiac Intervention Program also documented impressive cardiac results at 12 weeks, but had no control group.  Dr. Caldwell Esselstyne is also mentioned in this context.
4. Vegetarian diets are linked to lower blood pressure, which may help prolong life and prevent heart attacks and strokes.
5. Antioxidant-rich foods like fruits and vegetables—common in the Mediterranean diet and vegetarian diets—may lower cardiovascular disease risk. 
6. People with diabetes are at risk for impaired kidney funtion.  In women with impaired baseline kidney funtion, high animal protein intake is associated with continued kidney deterioration. 
7. A small study showed dramatic improvement in type 2 diabetics with painful neuropathy over 25 days on a low-fat vegan diet and a daily 30-minute walk.  Many participants were able to reduce diabetes drug dosages.
8. Do any diabetes advocacy associations endorse vegetarian diets for people with diabetes?  The American Dietetic Association deems that vegetarian and vegan diets, if well-planned, are nutritionally adequate. I don’t know the position of the American Diabetes Association.  Vegetarians need planning to get adequate vitamin D, B12, and calcium.
9. “Low-fat vegetarian and vegan diets do not require individuals to limit energy or carbohydrate intake….”  If true (and these guys should know), that might broaden the diet’s appeal.
10. I saw no mention of decreased overall mortality in vegetarians.

My Comments

Have you heard of the Physicians Committee for Responsible Medicine?  Their president is Neal Barnard, the lead author of the study at hand.  He has a new book on reversal of diabetes with a low-fat vegetarian diet.

The authors cite a journal article (reference #16) in support of plant-based diets, but the article doesn’t mention a vegetarian or vegan diet—it’s high-carb, high-fiber diet.  I didn’t review all 92 of their references to see if any others were misleading.

“Plant-based diets” must be a euphemism for vegetarian diets.  Too many people shut down when you talk to them about vegetarian diets.

I won’t rule out the possibility that vegetarian/vegan diets may be helpful in management of diabetes.  Such diets are, of course, 180 degrees different from the very low-carb diets I’ve reviewed favorably in these pages!  Both models, ideally, move away from the over-processed, concentrated carbohydrates so prevalent in Western culture.  Perhaps that’s the unifying healthy theme, if there is one. 

Or different sub-types of diabetes respond better to particular diets.

I heartily agree with the authors that larger clinical trials of vegetarian diets in diabetics are needed.  I’d love to see a long-term randomized controlled trial comparing a very low-carb diet diet with a low-fat vegetarian diet.  That’s the best way to settle which is better for diabetics: vegetarian or low-carb.

It’ll never be done.

Has a vegetarian diet helped control your diabetes?

Steve Parker, M.D.

Reference:  Barnard, Neal, et al.  Vegetarian and vegan diets in type 2 diabetes management.  Nutrition Reviews, 67(2009): 255-263.   doi: 10.1111/j.1753-4887.2009.00198.x