Tag Archives: prevent type 2 diabetes

Mediterranean Diet Reduces Risk of Type 2 Diabetes

The traditional Mediterranean diet has long been associated with lower risk of developing cardiovascular disease, cancer, and dementia.  The diet is rich in olive oil, fruits, nuts, cereals, vegetables, and fish but relatively low in dairy products and meat.  Several recent studies suggest the Mediterranean diet may also help prevent type 2 diabetes.

Researchers at the University of Navarra in Spain followed 13,380 non-diabetic university graduates, many of them health professionals, over the course of 4.4 years.  Average age was 38.  I assume most of the study participants lived in Spain, if not elsewhere in Europe (the article doesn’t say).  Dietary habits were assessed at the start of the study with a food frequency questionnaire.  Food intake for each participant was scored by adherence to the traditional Mediterranean diet.  Participants were labelled as either low, moderate, or high in adherence.  Over an average follow-up of 4.4 years, 33 of the study participants developed type 2 diabetes.  Compared to the participants who scored low on adherence to the Mediterranean diet, those in the high adherence category had an 83% lower risk of developing diabetes.  The moderate adherence group also had diminished risk, 59% less.

How could the Mediterranean diet protect against diabetes?  The authors note several potential mechanisms: high intake of fiber, low amounts of trans fats, moderate alcohol intake, high vegetable fat  intake, and high intake of monounsaturated fats relative to saturated fats.  Olive oil, loaded with monounsaturated fats, is the predominant fat in the Mediterranean diet.  In summary from the authors:

Diets rich in monounsaturated fatty acids improve lipid profiles and glycaemic control in people with diabetes, suggesting that a high intake improves insulin sensitivity.  Together these associations suggest the hypothesis that following an overall pattern of Mediterranean diet can protect against diabetes.  In addition to having a long tradition of use without evidence of harm, a Mediterranean diet is highly palatable, and people are likely to comply with it.

Please give serious consideration to the Mediterranean diet, especially if you are at risk for developing type 2 diabetes.  Major risk factors include sedentary lifestyle, overweight, and family history of diabetes.

Steve Parker, M.D.

Reference: Martinez-Gonzalez, M.A., et al.  Adherence to Mediterranean diet and risk of developing diabetes: prospective cohort study.  British Medical Journal, BMJ,doi:10.1136/bmj.39561.501007.BE (published online May 29, 2008).

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Mediterranean Diet Cuts Risk of Diabetes After Heart Attack

In a blog post last year I discussed how the Mediterranean diet reduces the incidence of type 2 diabetes in healthy people.  I found another scientific journal article that examined the effect of various lifestyle factors that might influence the onset of type 2 diabetes in a different population: people who have had a recent heart attack.

Dariush Mozaffarian and colleauges studied 8291 Italians who had suffered a heart attack within the previous three months, but who did not have diabetes at the time of the heart attack.  Each study participant was followed for an average of 3.2 years to see if diabetes developed.  The researchers devised a Mediterranean diet score (range 0-15) incorporating consumption of cooked and raw vegetables, fruit, fish  and olive oil.  They also looked at consumption of butter, oils other than olive oil, cheese, wine, and coffee.  Participants’ dietary habits were assessed and scored three times over 1.5 years.  A number of other demographic, clinical, and lifestyle risk-factors were assessed.

The study did not survey other components of the Mediterranean diet, such as legumes, nuts, and grains.  This is a weakness of the study.  I suspect it relates to the fact they were using information from the GISSI-Prevenzione study, which was designed to evaluate fish oil and vitamin E in people who had had a heart attack, and researchers did not want to burden outpatient cardiology offices with full-scale questionnaires.

Over the three years of the study, 12% of participants developed new-onset diabetes, or 3.7% per year.  If not for the recent heart attack, the expected incidence rate for development of diabetes would be roughly 1.2% per year.  An even larger percentage, over 25%, of participants developed impaired fasting glucose, a kind of prediabetes that often develops into full-blown diabetes over time.

Was there anything about the people who developed diabetes that distinguished them from those who did not?  Yes – they tended to have older age, higher body mass index, high blood pressure, and they smoked.  Current smoking was associated with a 60% higher risk.  Every unit of higher body mass index, e.g, going from BMI 26 to 27, increased the risk by 9%.  High blood pressure increased the risk by 22%.

What about Mediterranean diet score?  The higher Mediterranean diet scores – score of 11-15 compared to 0-5 – were associated with 35% lower risk of diabetes.  A reduction in onset of impaired fasting glucose was similar.

The authors cite another study of 2499 patients with stable angina pectoris or remote heart attack (over 6 months perviously).  Twenty-two percent of them (one in five) developed diabetes or impaired fasting glucose over six years of follow-up, a rate of 4.1% per year.

The researchers write:

The lower risk associated with a Mediterranean-type diet suggests that diet could help reduce incidence of prediabetes and diabetes after a myodcardial infarction.  Many, though not all, trials have indicated that a Mediterranean-type diet lowers risk factors linked to insulin resistance and diabetes, including serum triglycerides, HDL cholesterol, systemic inflammation, endothelial function, and insulin sensitivity.  These physiological effects in short-term randomized trials provide biological plausibility for the inverse association between consumption of a Mediterranean-type diet and incidence of [impaired fasting glucose] and diabetes in this study.

What are the take-home points of this study for people – Italians, at least – who have had a recent heart attack?

  1. A recent heart attack is a risk factor for development of diabetes and prediabetes.
  2. The risk of developing diabetes and prediabetes may be significantly reduced by smoking cessation, prevention of weight gain, and consumption of typical Mediterranean foods.

Patients with both heart attacks and diabetes  have significantly worse outcomes  than people with only one of these conditions.  Since we can prevent many cases heart attack and diabetes through diet modification, why not?

Steve Parker, M.D.

Reference:  Mozaffarian, Dariush, et al.  Incidence of new-onset diabetes and impaired fasting glucose in patients with recent myocardial infarction and the effect of clinical and lifestyle risk factors.  Lancet, 370 (2007) 667-675.


Filed under coronary heart disease, Mediterranean Diet

Misleading “Mediterranean Diet” Headline at the Washington Post

Perhaps you read the December 17, 2008, Washington Post (online) article, “Mediterranean-Style Diet Best for Blood Sugar Control.”

The same headline was used by MedlinePlus: Trusted Health Information for You, a service of the U.S. government.  The two articles may be exactly the same.

A physician spokeswoman for the American Heart Association is quoted in the story saying that “…the best diet is a Mediterranean-type diet…”

I mention this only because the Canadian study to which she refers is not a test of the Mediterranean diet in people with diabetes.

[Did you know that some people with diabetes are offended if you call them “diabetics”?  To call them diabetics defines them by their disease.  They’re not diseases, they’re individual humans.]

There are certainly some studies indicating that the traditional Mediterranean diet may be a good one for people with diabetes, and that the Mediterranean diet can prevent type 2 diabetes, but this Canadian study is not one of them.

Steve Parker, M.D.

Reference:  Jenkins, David,  et al.  Effect of a Low-Glycemic Index or High-Cereal Fiber Diet on Type 2 Diabetes: A Randomized Trial.  Journal of the American Medical Association, 300 (2008): 2,742-2,753.

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Filed under Causes of Diabetes, Mediterranean Diet

Glycemic Index and Chronic Disease Risk (Mostly in Women)

"Would you like some high-glycemic index bread?"

"Would you like some high-glycemic index bread?"

I recently blogged about glycemic index (GI), glycemic load (GL), and glycemic diets in preparation for today’s post.

The concept of glycemic index was introduced by Jenkins et al in 1981 at the University of Toronto.

Studies investigating the association between disease risk and GI/GL have been inconsistent.  By “inconsistent,” I mean some studies have made an association in one direction or the other, and other studies have not.  Diseases possibly associated with high-glycemic diets have included diabetes, cardiovascular disease, cancer, gallbladder disease, and eye disease.

“Diet” in this post refers to a habitual way of eating, not a weight loss program.

Researchers with the University of Sydney (Sydney, Australia) identified the best-designed published research reports investigating the relationship between certain chronic diseases and glycemic index and load.  The studied diseases were type 2 diabetes, coronary heart disease, stroke, breast cancer, colorectal cancer, pancreatic cancer, endometrial cancer, ovarian cancer, gallbladder disease, and eye disease.


Literature databases were searched for articles published between 1981 and March, 2007.  The researchers found 37 studies that enrolled 1,950,198 participants ranging in age from 24 to 76, with BMI’s averaging 23.5 to 29.  These were human prospective cohort studies with a final outcome being occurrence of a chronic disease (not its risk factors).  Twenty-five of the studies were conducted in the U.S., five in Canada, five Europe, and two in Australia.  Ninety percent of participants were women [for reasons not discussed].  Food frequency questionnaires were used in nearly all the studies.  Individual studies generated between 4 to 20 years of follow-up, and 40,129 new cases of target diseases were identified.

Associations between GI, GL, and risk of developing a chronic disease were measured as rate ratios comparing the highest with the lowest quantiles.  For example, GI and GL were measured in the study population.  The population was then divided into four groups (quartiles), reflecting lowest GI/GL to medium to highest GI/GL diets.  The lowest GI/GL quartile was compared with the highest quartile to see if disease occurrence was different between the groups.  Some studies broke the populations into tertiles, quintiles, deciles, etc.


Comparing the highest with the lowest quantiles, studies with a high GI or GL independently

  • increased the risk of type 2 diabetes by 27 (GL) or 40% (GI)
  • increased the risk of coronary heart disease by 25% (GI)
  • increased the risk of gallbladder disease by 26% (GI) or 41% (GL) [gallstones and biliary colic, I assume, but the authors don’t specify]
  • increased the risk of breast cancer by 8% (GI)
  • increased risk of all studied diseases (11) combined by 14% (GI) or 9% (GL)

Overall, high GI was more strongly associated with chronic disease than was high GL
So low-GI diets may offer greater protection against disease than low-GL diets.

Comments from the Researchers

They speculate that low-GI diets may be more protective than low-GL because the latter can include low-carb foods such as cheese and meat, and low-GI, high-carb foods.  Both eating styles will reduce glucose levels after meals while having very different effects in other areas such as pancreas beta cell function, free fatty acid levels, triglyceride levels, and effects on satiety.

High GI and high GL diets, independently of known confounders, modestly increase the risk of chronic lifestyle-related diseases, with more pronounced effects for type 2 diabetes, coronary heart disease, and gallbladder disease.

Direct quotes:

. . . 90% of participants were female; therefore, the findings may not be generalizable to men.

There are plausible mechanism linking the development of certain chronic diseases with high-GI diets.  Specifically, 2 major pathways have been proposed to explain the association with type 2 diabetes risk.  First the same amount of carbohydrate from high-GI food produces higher blood glucose concentrations and a greater demand for insulin.  The chronically increased insulin demand may eventually result in pancreatic beta cell failure, and, as a consequence, impaired glucose tolerance.  Second, there is evidence that high-GI diets may directly increase insulin resistance through their effect on glycemia, free fatty acids, and counter-regulatory hormone secretion.  High glucose and insulin concentrations are associated with increased risk profiles for cardiovascular disease, including decreased concentrations of HDL cholesterol, increased glycosylated protein, oxidative status, hemostatic variables, and poor endothelial function

Low-GI and/or low-GL diets are independently associated with a reduced risk of certain chronic diseases.  In diabetes and heart disease, the protection is comparable with that seen for whole grain and high fiber intakes.  The findings support the hypothesis that higher postprandial glycemia is a universal mechanism for disease progression.

My Comments

Studies like this tend to accentuate the differences in eating styles since they compare the highest with the lowest post-prandial (after meal) glucose levels.  Most people are closer to the middle of the pack, so a person there has potentially less to gain by moving to a low-GI diet.  But still some to gain, on average, particularly in regards to avoiding type 2 diabetes and coronary heart disease.

[To be fair, many population-based studies use this same quantile technique.  It increases the odds of finding a statistically significant difference.]

Only two of the 37 studies examined coronary heart disease, the cause of heart attacks.  One study was the massive Nurses’ Health Study database with 75,521 women.  The other was the Zutphen (Netherlands) Elderly Study which examined men 64 and older.  Here’s the primary conclusion of the Zutphen authors verbatim:

Our findings do not support the hypothesis that a high-glycemic index diet unfavorably affects metabolic risk factors or increases risk for CHD [coronary heart disease] in elderly men without a history of diabetes or CHD.

So there’s nothing in the meta-analysis at hand to suggest that high-GI/GL diets promote heart disease in males in the general population.

However, the recent Canadian study in Archives of Internal Medicine found strong evidence linking CHD with high-glycemic index diets.  Although not mentioned in the text of that article, Table 3 on page 664 shows that the association is much stonger in women than in men.  Relative risk for women on a high-glycemic index/load diet was 1.5 (95% confidence interval = 1.29-1.71), and for men the relative risk was 1.06 (95% confidence interval = 0.91-1.20).  See reference below.

Nine of the 37 studies examined the occurrence of type 2 diabetes.  Only one of these studied men only – 42,759 men: the abstract is not available online and the Sydney group does not mention if high-GI or high-GL was positively associated with onset of diabetes in this cohort.  Two of the diabetes studies included both men and women, but the abstracts don’t break down the findings by sex.  [I’m trying to deduce if the major overall findings of this meta-analysis apply to men or not.]

I don’t know anybody willing to change their diet just to avoid the risk of gallstones.  It’s only after they develop symptomatic gallstones that they ask me what they can do about them.  The usual answer is surgery.

The report is well-done and seems free of commercial bias, even though several of the researchers are authors or co-authors of popular books on low-GI eating.

Steve Parker, M.D.


Barclay, Alan W.; Petocz, Peter; McMillan-Price, Joanna; Flood, Victoria M.; Prvan, Tania; Mitchell, Paul; and Brand-Miller, Jennie C.  Glycemic index, glycemic load, and chronic disease risk – a meta-analysis of observational studies [of mostly women].  American Journal of Clinical Nutrition, 87 (2008): 627-637.

Brand-Miller, Jennie, et al.  “The New Glucose Revolution: The Authoritative Guide to the Glycemic Index – The Dietary Solution for Lifelong Health.”  Da Capo Press, 2006.

Mente, Andrew, et al.  A Systematic Review of the Evidence Supporting a Causal Link Between Dietary Factors and Coronary Heart DiseaseArchives of Internal Medicine, 169 (2009): 659-669.


Filed under Causes of Diabetes, Glycemic Index and Load

High Glycemic Load and Low Grain Fiber Increase Risk of Type 2 Diabetes in Men

Minimally refined grain

Minimally refined grain

A study published in 1997 helped establish the association between glycemic load, dietary fiber, and type 2 diabetes in men.


Over 42,000 mostly middle-aged men in the Health Professionals Follow-up Study, without diabetes at baseline, were followed over six years to see if  diet composition was related to onset of type 2 diabetes.  Food intake was determined by a questionnaire.  95% of participants were white.


523 cases of type 2 diabetes developed.  Men with the highest glycemic index eating pattern were 37% more likely to develop diabetes compared to the lowest glycemic index.

Cereal (grain) fiber was inversely related to risk of diabetes.  That is, the higher the intake of grain fiber, the lower the risk of developing diabetes.

The combination of high glycemic load and low cereal fiber yielded the highest rate of diabetes.

Total dietary fiber was not associated with reduced risk of diabetes.

Fiber from fruits and vegetables was not associated with diabetes one way or the other.

As other studies found, total carbohydrate intake was not related to risk of diabetes.

Take-Home Points

These findings may or may not apply to women and non-white ethnic groups.

Grains in a minimally refined form reduced the incidence of diabetes in this population.

Diets with a high glycemic load increase the risk of diabetes, at least in men.

Elsewhere, I’ve reviewed studies indicating that, in women, both high glycemic load and high glycemic index eating increase the risk of type 2 diabetes.  Click here for details.

We must wonder if  established cases of diabetes would respond positively to diets with low glycemic load and grains in a minimally refined form.  Or is it too late?

Steve Parker, M.D.

Reference:  Salmeron, Jorge, et al.  Dietary fiber, glycemic load, and risk of NIDDM in Men.  Diabetes Care, 20 (1997): 545-550

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Filed under Carbohydrate, Causes of Diabetes, Fiber, Glycemic Index and Load

Can Diabetes Be Prevented in Older Adults?

42-15653241A study published yesterday supports the idea that even in older adults, over 65, type 2 diabetes can be prevented in most cases by healthy lifestyle choices.

Researchers examined the participants in the Cardiovascular Health Study – 4,883 men and women over 65 at baseline – over the course of 10 years.  Median age at enrollment was 73.  Participants were followed clinically for 10 years.  New cases of diabetes over 10 years: 337.  Researchers suspected, based on previous studies in younger folks, that a reduced incidence of diabetes onset would be related to:

  • physical activity levels above the median (half of people exercise less than the median, half exercise more)
  • never smoking, or minimal and years ago
  • “healthy diet,” defined as high fiber, low glycemic index foods, lower trans fats, higher polyunsaturated-to-saturated fat ratio
  • low body mass index (not overweight)
  • waist circumference under 92 cm (36.2 inches) for men and 88 cm (34.6 inches) for women
  • low to moderate alcohol use

We’ll call these “lifestyle factors.”  Participants were analyzed to see how well they fit this profile and whether or not they developed diabetes.


The more each of these lifestyle factors characterized a person, the lower the risk of developing diabetes.

High physical activity and healthy diet by themselves reduced risk of diabetes by half.

Study authors estimate that healthy lifestyle choices could prevent eight or nine out of 10 cases of diabetes in older adults.

Take-Home Point

The researchers rightfully point out that their results are associations, not proof that these lifestyle factors prevent diabetes.  Given the totality of the evidence from this and other studies, I would adopt many of the low-risk lifestyle choices if I wanted to avoid diabetes.

Steve Parker, M.D.

Reference:  Mozaffarian, D., et al.  Lifestyle risk factors and new-onset diabetes mellitus in older adultsArchives of Internal Medicine, 169, (2009): 798-807.

Update April 30, 2009:

Research in younger populations has associated the following factors with prevention of type 2 diabetes:

  1. Avoid overweight, or lose weight if you are overweight (body mass index over 25)
  2. Regular physical activity
  3. Don’t start smoking, or quit if you do
  4. Pick the right parents

Some cases of diabetes are related to genetic factors beyond our control.  Having parents or close relatives with diabetes suggests that you may be genetically predisposed.  Genetics is not necessarily destiny, however.


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Diabetes Increases Dramatically

On June 24, 2008, the Centers for Disease Control released prevalence data for diabetes in the U.S.  Nearly 24 million people now have diabetes, up three percent over just two years.  This is eight percent of the population.  The vast majority of cases are of type 2 diabetes, not the type 1 usually diagnosed in childhood.

Another 57 million people have pre-diabetes, a condition that can turn into full-blown diabetes over time.  The two types of pre-diabetes are “impaired fasting glucose” and “impaired glucose tolerance.”

The CDC broke down diabetes prevalence for various age groups.  Twenty-three percent of people over 60 have diabetes.  Eleven percent of all adults have diabetes.

The 24 million figure includes six million who have diabetes but have not yet been diagnosed.

I expect to see even more diabetes cases in the future as our overweight population ages.

Risk factors for the development of type 2 diabetes include aging and genetic heritage.  You can’t do anything about those.  But two other major risk factors are under your control: habitual inactivity and excessive body fat.

If you don’t want to be one of these statistics, now you know what you need to do.

Steve Parker, M.D.

Additional information:

WebMD Diabetes Guide

American Diabetes Association

The Prevention or Delay of Type 2 Diabetes

Does Weight Loss Prevent Type 2 Diabetes?

Mediterranean Diet Reduces Risk of Type 2 Diabetes

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Filed under DM Prevalence