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2 2 - 0 1 - 2 0 0 6 Effects of different dietary protein intakes on body composition and vascular reactivity
LA Ferrara, P Innelli, V Palmieri, S Limauro, G De Luca, F Ferrara, E Liccardo and A Celentano Objective: To assess the effects of a diet rich in protein of animal origin in comparison to one with a protein intake of about 15% of the total daily calories on body composition and arterial function. Design: Randomized prospective study with parallel groups. Body weight (BW), blood pressure (BP), main parameters of carbohydrate and lipid metabolism, body mass composition by bioelectrical impedance analysis, forearm blood flow at rest and in the postischaemic phase by strain gauge plethysmography and flow-mediated dilation of the brachial artery by echography were measured at baseline and after 6 months of the dietary intervention. Subjects: In total, 15 clinically healthy male volunteers, regularly performing a mixed training three times weekly for 90 min. All of them were performing a regular 90-min mixed-aerobic and anaerobic-training three times weekly. The training schedule included a 30-min warm-up, a 35-min phase of technical specific work and a 25-min cooling down phase. Intervention: The participants were randomly prescribed a diet with high (1.9 g/kg BW) or normal (1.3 g/kg BW) protein content. Caloric intake of the diets was tailored for each subject according to his metabolic requests, calculated using predictive equation for metabolic requirements plus the caloric expenditure related to the physical exercise. The % energy intake from lipids was similar, whereas the diets differed regarding carbohydrates and protein composition. In particular, the HP diet derived a 50% of the total calories from carbohydrates, 28% from lipids (8% saturated, 16% monounsaturated and 4% polyunsaturated fats) and a 22% from proteins. The NP diet, on the other hand, derived 60% from carbohydrates, 25% from lipids (6% from saturated, 16% from monounsaturated, 3% from polyunsaturated) and 15% from proteins. No difference in calcium, iron, sodium, potassium and magnesium intake was detected. Cholesterol intake was significantly higher in the HP diet, whereas fibre intake was similar in the two diets. Statistical analysis: Differences between means were evaluated by the t-tests for paired or unpaired data and by one way analysis of variance. The strength of correlation between variables was investigated by bivariate Pearson correlation. Results: Serum cholesterol significantly decreased with both diets in comparison to baseline values, whereas BW was slightly but significantly reduced only by the high-protein (HP) diet. No change was detected in BP and the other metabolic parameters. Body mass composition was not significantly modified by either diet. At variance with the general belief that HP intake helps subjects performing physical activity – improving their body mass by the increase in lean body mass and the concomitant reduction in fat-free mass – no significant change was detected at the end of the two diets in comparison to baseline values. [Tabel] On the other hand, postischaemic flow-mediated dilationof the brachial artery was enhanced by the sole normal protein (NP) diet, whereas no change in the forearm blood flow, both at rest and in the postischaemic phase, was detected. Conclusions: These preliminary results indicate that HP diet was found to be not useful in increasing the muscle mass in comparison to a NP intake. In contrast to this, the latter diet seems to enhance the endothelial function of the arterial vessels with a more pronounced dilatation of the lumen in response to the increase in blood flow. A possible limitation of the study is related to the choice of the protein content of the HP diet. The rationale for using a protein content of 1.9 g/kg BW is derived from the observation that people who practice regular physical activity often derive 20% of their daily energy from proteins; despite that nutritionists recommend even to athletes a daily protein intake not exceeding 1.7 g/kg. On the other hand, this diet does not achieve the very HP intake of 25% of the daily calories, which is seen in subjects using low-carbohydrate HP diets for weight loss. It should be interesting to evaluate in such subjects if this type of diet might influence the endothelial function even more negatively than the 1.9 g/kg BW diet did in the present investigation.
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[Definitie:] "An ergogenic aid is any substance or phenomenon that enhances performance."
(Wilmore and Costill) 
