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.