OLIVE OIL, MEDITERRANEAN DIET AND DIABETES MELLITUS

Authors: Prof Gerd Assmann and Prof. Ursel Wahrburg Arteriosclerosis Research Institute, Munster University, Germany. Italian edition by Doct. Fabrizio Jossa, Department of Clinic and experimental medicine, Federico II University-Naples.

Introduction

The prevalence of diabetes mellitus (type-2) is rapidly increasing in the most industrialized countries. Beyond the genetic cause , environmental factors, first obesity and lack of physical exercise can hard influence the etiopathogenesis of diabetes mellitus. The diabetes mellitus is a chronic metabolic disease due to a reduced insulin secretion (diabetes type 1) or to an insulin resistance (type2) characterized by anomalies involving not only the glycolic but also the protein and lipid metabolism(often a dyslipedemia coexists with diabetes-type 2). The diabetic risks arteriosclerosis, cardiovascular diseases and other clinic complexities (microangiopathies, renal diseases, neuropathies and hypertension). The main aim of the therapy is to improve the global metabolic balance of the diabetic patient; this can be obtained through ”ad hoc” therapies as the glycolic control, of the lipoproteins and lipid concentrations, a balanced weight, prevention. The diet plays a key-role in the therapy. As for the diabetes (type 2) there are two main points:
1. The production of obesity or over weight,
2. A good diet able to have positive effects on glucose and lipoproteins.
The following guidelines are derived from the most recent scientific studies on dietary therapy of diabetes, with a particular regard to the Mediterranean diet, that revealed an effective action against this disease.

Obesity therapy

About 60-90% of the diabetic patients are obese (5). As obesity can cause not only type-2 diabetes but even disypidemia , hypertension and atherosclerosis, the main aim of this diet is to reduce weight. The best way to lose weight is to associate a balanced diet( with 250-500 kcal reduction) with some physical activity. The Mediterranean diet could represent a good strategy for diabetic patients. Even a limited lost in weight can favourably influence the glycolic levels and low density protein concentration, particularly atherogenetic. Furthermore this weight- reduction favours a normalization of blood pressure and consequently, if the patient suffers from hypertension he can also reduce the use of medicines.

The diet for diabetes

A diet rich in carbohydrates (55/60% of the total needs) but with only a low content in saturated fatty acids( -10% of the energy need) is really effective in type-2 diabetes therapy. Anyway, recent studies evidenced that a high total fat- enriched diet can have positive effects on this disease, thanks to an increase of monounsaturated fatty acids (MUFA) and a contemporaneous reduction of saturated fatty acids (SFA). These characteristics are typical of the Mediterranean diet, where the olive oil is the key-source of food fats. It was even evidenced how a high carbohydrates enriched diet versus a MUFA enriched diet (both diets have low SFA content) can provoke an increase of the plasmatic concentration of triglycerides and a reduction of HDL cholesterol (7,8,16). A MUFA enriched diet causes a meaningful reduction of triglycerides and of the concentration of low density proteins rich in cholesterol (VLDL-cholesterol): at the same time this diet can increase the plasmatic levels of HDL cholesterol without affecting the blood concentration of LDL cholesterol, but resulting very effective in balancing the glycolic lay-out in the diabetic patient (3,4,7,9,18,23,24). Some studies have finally underlined that a diet rich in carbohydrates and fibres is not always negative for the diabetes (22).A recent meta- analysis by Garg, sums up the results of control-studies, comparing the metabolic effects of a diet rich in carbohydrates versus a diet rich in MUFA. The MUFA-enriched diet determines a better glycolic balance than the carbohydrate-enriched diet. This immediately reduces the plasmatic concentrations of triglycerides and the HDL cholesterol and 22% with a slight increase of HDL cholesterol, without varying LDL cholesterol too much. The improvement of the glycolic metabolism obtained with this diet is not due to variations of insulin-sensitivity, but to a reduction of carbohydrates. This diet reduces also the atherogenetic risk. Further studies are needed as for the influence of MUFA diets on blood pressure. So the authors adviced this kind of diet in the diabetes ‘therapy. Even the Committee on Nutrition of the American Heart Association Science Advisory and Coordinating Committee agree with these advice. Moreover the American document stresses the importance to give a personalized diet that takes into consideration the patients’ weight, needs and tastes.

Dietary advice for Diabetes Mellitus therapy

The dietary guidelines for diabetic patients have been recently analysed and updated on the basis of most recent knowledge and scientific evidence present in literature, they can be summed up as follows: as there are no univocal or conclusive data in this field, the general advice is no change in the daily consumption of proteins in the diabetic diet; being limited between 10-20% of the daily caloric need; the rest of the caloric need (80-90%) will be shared between carbohydrates and food fats. Less than 10% of these calories is produced by SFA and the unsaturated fats (PUFA), while the other 60-70% is delivered by MUFA and carbohydrates. It is to be underlined that the quantity of calories coming from fats and carbohydrates can vary and it should be calculated according to the personal caloric needs of the Individual. The SFA and cholesterol reduction can reduce also the cardiovascular risk. In fact, less than 10% of the total energy is provided by SFA and the daily cholesterol level should never overcome 300 mg. Moreover, if the plasmatic level of LDL cholesterol is particularly high, a further SFA reduction is recommended: not more than 7% of the daily caloric need.

The role of the Mediterranean diet and of the olive oil in the dietary therapy of diabetes

The traditional Mediterranean diet is characterized by:
- high quantities of vegetarian food (vegetables in general, bread and some other types of cereals, potatoes, pulses, fruit, nuts, etc)
- genuine season-food not industrial- manufactured representing local typical products
- olive oil, the main source of food fats
- moderate use of cheese and derived milk products
- meals with fish and white meat (poultry);
- rare consumption of red meat;
- small quantities of wine (at meals)
The Mediterranean diet is based on a low content of SFA and cholesterol and it is particularly rich in complex carbohydrates and vegetal fibres. The daily consumption of olive oil as dressing, makes a diet particularly rich in MUFA (15-20% energy) with total fat contents covering 25-30% the global caloric need. In this sense the Mediterranean diet can be considered a non-medical solution, for its low SFA contents and for its sugar support provided by complex carbohydrates. One of the peculiarities of this diet is that it can be changed according to the individual needs, by modifying the daily oil quantity. If there is a problem of overweight the olive can be limited.

Summary

Weight control is the basis of type 2 – diabetes mellitus: this can be obtained regulating the energetic balance (moderate reduction of the total daily need with the contextual increase of physical activity). Recent guidelines recommend to take into consideration the patients’ needs, preferences, tastes. The SFA content is to be low both in high carbohydrates enriched diet and in the MUFA diets. These are the typical characteristics of the Mediterranean diet with low saturated fat quantities but rich in cereals, fruit, vegetable, pulses; a correct use of olive oil allows to change in a good way the MUFA and carbohydrates contents. The Mediterranean diet offers a great variety of food, that it is usually liked by patients.

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