AN HEALTHY DIET AND AN HEALTHY FOOD ADDED WITH L-ARGININE: BIOAVAILABILITY AND BENEFICIAL EFFECTS
Background The use of L-Arginine as food supplement to a normal diet, in relatively large doses, has been proved to have a salutary effect on cardiovascular diseases and glucose metabolism. L-Arginine was found to be bio-available and effective in the prevention of impairment of glucose metabolism and endothelial dysfunction. Objective: To obtain a food product having a high content (at least 10%) of L-arginine completely bio-available (> 99%), being also palatable, homogeneous, having low amounts of sugar and optionally suitable for insulin-resistant and/or carbohydrate-intolerant subjects. Methods The food product was produced at a low temperature range which prevents the degradation of the amino acid by Maillard reactions or other heat dependent degradations and by means of sonication. To evaluate the bio-availability and the vascular and metabolic effects of L-Arginine (6.6 g) contained in the food preparation (6 biscuits) compared either to the same food preparation (6 biscuits) without the addition of L-Arginine either to 6.6 g of powdered L-Arginine, seven healthy subjects (2M/5F) participated in the study. It was asked to all subjects to follow a 2000 kcal/die standard diet, according to LARN recommendations and to complete a 3 day food diary (two working days and one holiday day) before every test to obtain accurate information on short-term food intake. Food diaries were evaluated with software to decode foods, modified introducing the L-Arginine contents in more than 800 different foods. The average daily intake of L-Arginine was estimated about 2.5 g/day. Subjects underwent 3 different tests, in random order, with at least a 14-day interval.  The first test consisted in an oral administration of 6 biscuits containing 1.1 g each of L-arginine for a total of 6.6 g. The portion of 6 biscuits contained total amount of 21.9 g of carbohydrates (17.9 g of starch and 4.0 g of sugars), 3.6 g of proteins, 7.5 g of fats and 4.3 g of fibers. A fixed amount of 250 ml of natural water was taken with the food preparation.  The second test consisted in an oral administration of the 6 biscuits prepared with the same sonication process but without the addition of L-Arginine. A fixed amount of 250 ml of natural water was taken with the food preparation.  The third test consisted in the oral administration of 6.6 g of powdered L-Arginine diluted in 250 ml of natural water. Blood glucose, insulin, NOx, cGMP and L-Arginine were measured. Forearm blood flow (FBF) and reactive hyperaemia were measured by strain-gauge venous occlusion plethysmography. Peripheral resistance was calculates as a ratio between mean blood pressure and the FBF. Results L-Arginine levels were similar during the test when Biscuit +L-ARG 6.6 g and Powdered L-ARG were administered. In both cases, levels were significantly higher as compared with Biscuit alone, suggesting a complete bio-availability of L-Arginine from the biscuit. A significant increase of nitric oxide (NOx) and cGMP levels were significantly increased with Biscuit +L-ARG 6.6 g and Powdered L-ARG as compared to Biscuit. AUC NOx and cGMP were significantly increased (p<0.04vs Biscuit). Percentage incremental increase of post-ischemic blood flow significantly increased with Biscuit +L-ARG 6.6 g and Powdered L-ARG, suggesting a functional effect of L-ARG added to the food preparation. Further, at 240 minute mean arterial blood pressure and peripheral vascular resistances slightly declined with Biscuit +L-ARG 6.6 g without reaching a statistical significance. At metabolic levels, the addition of L-ARG to a biscuit decreased insulin levels in the presence of similar glycemic levels, in particular a significant decrease of AUCinsulin during the test with Biscuit +L-ARG 6.6 g in comparison to Biscuit alone was found (p<0.05). To achieve a dose-response curve on insulin sensitivity, two further tests were performed in which 3.3 g of L-Arginine (3 biscuits) or 6.6 g of L-Arginine (6 biscuits) on 4 healthy subjects (2M/2F). After an overnight fast, samples for blood glucose and insulin measurements were taken at 0, 30, 60, 90, 120 min. Basal blood pressure was taken in supine position after 10 min of rest, and the mean of two measurements was used as the value, after that blood pressure was also taken every 60 min until the end of the test. From the results of glucose and insulin, two indices were derived: a Modified Matsuda, (index of whole-body insulin sensitivity) and the Disposition Index (index of the product of insulin sensitivity and first phase insulin secretion). We were able to define that both indices were significantly increased with 6 Biscuits having 6.6 g of L-Arginine while intermediate values were found when 3 Biscuits (3.3 g) were eaten as compared to Biscuits without L-Arginine addition. Conclusion: The data of the present thesis suggest that a healthy biscuit added with L-Arginine ameliorate endothelial function and insulin sensitivity in healthy subjects and after a dose response curve, beneficial effects is achieved when three or six biscuits are administered. Further studies are needed to evaluate the beneficial effects of a chronic administration of 6 biscuits in a population of subjects with impaired glucose tolerance and Metabolic Syndrome.
Nutrition, L-Arginine, endothelial function, nitric oxide, insulin sensitivity, Settore MED/13 - Endocrinologia
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