Type-2 diabetes mellitus is one of the most costly and burdensome chronic diseases of our time and a condition that is increasing in epidemic proportions worldwide . Its complications are a significant cause of morbidity and mortality and a tremendous economic burden to society. Some of the risk factors for its development, such as obesity, physical inactivity and high energy diet, can potentially be modified. Compelling evidence now exists, from well-designed randomized studies [2-4], that the disease can be prevented or delayed in subjects at high risk of its development, i.e. subjects with impaired glucose tolerance or impaired fasting glucose. The interventions studied include lifestyle modifications (with diet and exercise) and drug treatment. Weight loss with lifestyle modification seems to be the most effective way of preventing diabetes mellitus so far, given the fact that it addresses other cardiovascular disease risk factors as well (hypertension and dyslipidemia). In the established diabetic also, physical activity and diet continue to be a fundamental form of therapy.
Medical nutrition therapy (MNT) guidelines for persons with diabetes have changed a lot over the previous few decades. Before the discovery of insulin, in 1921, starvation therapies were applied, with nearly total restriction of food. After the introduction of insulin in the treatment regimen, the fear that 'sugar is bad in diabetes' led to the adoption of low carbohydrate diets which were consequently high in fat. Later on, it was realized that high fat diets were the ones causing problems, leading to increased cardiovascular risk. Thus, a whole array of studies was initiated in search of the optimal composition of the diet in diabetic persons. Since many issues are still topics of scientific debate, they endorse the principle of individualization in MNT for diabetes and set guidelines accordingly.
Today there is no one 'diabetic' diet. The recommended diet can only be defined as a prescription based on the assessment of treatment goals and outcomes, taking into consideration the individual needs and preferences of the people. Nutrition recommendations represent a thoughtful synthesis of a multitude of current data. The nutrition recommendations of the major scientific organizations, the American Diabetes Association (ADA) , the Diabetes and Nutrition Study Group (DNSG) of the European Association for the Study of Diabetes (EASD) , the Canadian Diabetes Association , the Joslin Diabetes Center and Joslin Clinic , the American Association of Clinical Endocri-nologists (AACE)  and Diabetes UK , will be reviewed here and their similarities and disagreements analyzed.
It should be emphasized that the recommendations are based on the best available evidence of these scientific organizations, categorized according to their strength. The ADA grades their recommendations into four categories: those with strong supporting evidence, those with some supporting evidence, those with limited supporting evidence and those based on expert consensus. The DNSG of the EASD grade their recommendations according to their strength of evidence based on 5 evidence classes (Ia, Ib, IIa, IIb, III) and a separate class (IV) reserved for statements from expert committees based on the Scottish Intercollegiate Guidelines Network .
The classes of the recommendations are:
Ia Meta-analysis of randomized controlled trials
Ib At least one randomized controlled trial
IIa At least one well-designed controlled study without randomization
IIb At least one other type of well-designed quasi-experimental study
III Well-designed nonexperimental descriptive studies, such as comparative studies, correlation studies and case studies
IV Expert committee reports or opinions and/or clinical experiences of respected authorities
The grades of the recommendations are as follows:
(A) Requires at least one randomized controlled trial as part of a body of literature of overall good quality and consistency addressing the specific recommendation (evidence levels Ia, Ib).
(B) Requires the availability of well-conducted clinical studies but no randomized clinical trials on the topic of recommendation (evidence levels IIa, IIb, III).
(C) Requires evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities. Indicates an absence of directly applicable clinical studies of good quality (evidence level IV).
The Joslin Diabetes Center follows the same pattern of evidence as the ADA, whereas the Canadian Diabetes Association and the AACE do not provide a grading system for their recommendations. The Diabetes UK recommendations are based on the ADA and DNSG technical reviews.
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