Mediterranean diet protects against type 2 diabetes
New research shows that a
Mediterranean-style diet and diets low in available carbohydrates can offer
protection against type 2 diabetes. The study is published in Diabetologia, the journal of the
European Association for the Study of Diabetes (EASD), and is by Dr Carlo La
Vecchia, Mario Negri Institute of Pharmacological Research, Milan, Italy, and
colleagues.
The authors studied patients from
Greece who are part of the ongoing European Prospective Investigation into
Cancer and nutrition (EPIC), led by Dr. Antonia Trichopoulou, from the
University of Athens. From a total of 22,295 participants, actively followed up
for just over 11 years, 2,330 cases of type 2 diabetes were recorded. To assess
dietary habits, all participants completed a questionnaire, and the researchers
constructed a 10-point Mediterranean diet score (MDS) and a similar scale to
measure the available carbohydrate (or glycaemic load [GL]) of the diet.
People with an MDS of over 6 were
12% less likely to develop diabetes than those with the lowest MDS of 3 or
under. Patients with the highest available carbohydrate in their diet were 21%
more likely to develop diabetes than those with the lowest. A high MDS combined
with low available carbohydrate reduced the chances of developing diabetes by
20% as compared with a diet low in MDS and high in GL.
The authors say: "The role of
the Mediterranean diet in weight control is still controversial, and in most
studies from Mediterranean countries the adherence to the Mediterranean diet
was unrelated to overweight. This suggests that the protection of the
Mediterranean diet against diabetes is not through weight control, but through
several dietary characteristics of the Mediterranean diet. However, this issue
is difficult to address in cohort studies because of the lack of information on
weight changes during follow-up that are rarely recorded."
They point out that a particular
feature of the Mediterranean diet is the use of extra virgin olive oil which
leads to a high ratio of monounsaturated to saturated fatty acids. But again
research here has been conflicting. One review of dietary fat and diabetes
suggests that replacing saturated and trans fats with unsaturated fats has
beneficial effects on insulin sensitivity and is likely to reduce the risk of
type 2 diabetes. However, in a randomised trial of high-cardiovascular-risk
individuals who were assigned to the Mediterranean diet supplemented with
either free extra virgin olive oil or nuts and were compared with individuals
on a low-fat diet (comparison group), there was no difference in diabetes
occurrence between the two variants of the Mediterranean diet when compared
with the comparison group.
Regarding GL, the authors say:
"High GL diet leads to rapid rises in blood glucose and insulin levels.
The chronically increased insulin demand may eventually result in pancreatic β
cell failure and, as a consequence, impaired glucose tolerance and increased
insulin resistance, which is a predictor of diabetes. A high dietary GL has
also been unfavourably related to glycaemic control in individuals with
diabetes."
They
conclude: "A low GL diet that also adequately adheres to the principles of
the traditional Mediterranean diet may reduce the incidence of type 2 diabetes.
Mediterranean diet may
lower risk of diabetes
Adoption of a Mediterranean diet is linked to
a lower risk of diabetes, especially among people at high risk for
cardiovascular disease, according to research presented at the American College
of Cardiology's 63rd Annual Scientific Session.
Data from the first pooled analysis of
studies evaluating the possible role of the Mediterranean diet on diabetes
development show that adherence to this diet was associated with a 21 percent
reduced risk of diabetes as compared to the control dietary groups. This
reduced risk was even more pronounced among people at high risk for
cardiovascular disease – among whom diabetes prevention is especially critical.
The analysis showed that patients in this subgroup were almost 27 percent less
likely to develop diabetes compared to controls.
"Adherence to the Mediterranean diet
may prevent the development of diabetes irrespective of age, sex, race or
culture," said Demosthenes Panagiotakos, Ph.D., professor at Harokopio
University, Athens, Greece, and lead investigator of this meta-analysis.
"This diet has a beneficial effect, even in high risk groups, and speaks
to the fact that it is never too late to start eating a healthy diet."
The researchers systematically reviewed
19 original research studies that followed more than 162,000 participants for
an average of 5.5 years. These studies spanned European and non-European
populations, which Panagiotakos said is important as most of the published
studies have been European-based and there has been some question of possible
confounding factors in these regions, including genetics, the environment,
lifestyle and lower stress levels.
But researchers found that regardless of
the study population – European or non-European or high or low risk of
cardiovascular disease – the association between the Mediterranean diet and
lower risk of diabetes remained. While there is no set Mediterranean diet, it
commonly emphasizes fresh fruits and vegetables, whole grains, beans, nuts,
fish, olive oil and even a glass of red wine.
"A meta-analysis captures the
limitations of individual studies, and this type of study is important to help
inform guidelines and evidence-based care," Panagiotakos said.
"Diabetes is an ongoing epidemic and its relation to obesity, especially in
the Westernized populations, is well known. We have to do something to prevent
diabetes and changing our diet may be an effective treatment."
The number of diabetes cases has doubled
worldwide in the past 30 years and has been linked to the growing obesity
epidemic. People with diabetes have trouble controlling their blood sugar
because they either do not produce the hormone insulin or do not use it
properly. If uncontrolled, diabetes can lead to complications including
blindness, kidney failure, cardiovascular disease and amputations.
Panagiotakos said he believes the
Mediterranean diet, in particular, lowers the risk of diabetes by helping to
guard against obesity. Earlier research has shown that following the
traditional Mediterranean diet is also linked to weight loss, reduced risk of
heart disease and related death, as well as lower blood pressure and blood
cholesterol levels.
Researchers initially identified more
than 400 related studies for their analysis but excluded the vast majority
based on criteria they set and study designs (for example, studies not actually
addressing the issue of diet and diabetes even though they were identified
through key words used, lack of a control group or randomization, inclusion of
people with diabetes or prediabetes or limiting the study only to a component
of the traditional Mediterranean diet). Diet was most often assessed by food
frequency questionnaires and 24-hour or three-day recall. The control dietary
groups varied but included the diets common to the study location.
Mediterranean Diet Better
Than Low-fat for Diabetes
In one of the longest-term randomized
trials of its kind, researchers compared the effects of a Mediterranean-style
diet versus a typical low-fat diet for diabetes management. The trial was
designed to assess the effectiveness, durability, and safety of the two diets
on the need for diabetes medications in overweight patients with
newly-diagnosed type 2 diabetes.
Researchers randomly assigned 215
patients to follow either a low carbohydrate, Mediterranean-style diet or a
low-fat diet for four years. Nutritionists and dietitians counseled both groups
in monthly sessions for the first year and bimonthly sessions for the next
three years. After four years, 44 percent of patients in the Mediterranean-style
diet group required antihyperglycemic drug therapy compared to 70 percent in
the low-fat diet group. Patients in the Mediterranean diet group also
experienced greater weight loss and an improvement in some coronary risk
factors.
Patients
on a Mediterranean diet mainly consume fruits, vegetables, nuts, seeds, fish,
and whole grains. The diet focuses on natural foods and healthy fats while
eliminating processed foods.
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