Adverse gastrointestinal events were more common with high-protein diets .
Multivariable meta-regression analysis showed no significant dose response with higher protein intake .
Conclusions : Higher-protein diets  probably improve adiposity , blood pressure and triglyceride levels , but these effects are small and need to be weighed against the potential for harms
Background / Objectives : Numerous r and omised controlled trials ( RCTs ) published in first tier medical journals have evaluated the health effects of diets high in protein .
We conducted a rigorous systematic review of RCTs comparing higher- and lower-protein diets .
Effects of different dietary protein intakes on body composition and vascular reactivity
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 : R and omized prospect i ve 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 clinical ly healthy male volunteers , regularly performing a mixed training three times weekly for 90 min . Intervention : The participants were r and omly prescribed a diet with high ( 1.9 g/kg BW ) or normal ( 1.3 g/kg BW ) protein content . 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 . On the other h and , postischaemic flow-mediated dilation of 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
Adverse gastrointestinal events were more common with high-protein diets .
Multivariable meta-regression analysis showed no significant dose response with higher protein intake .
Conclusions : Higher-protein diets  probably improve adiposity , blood pressure and triglyceride levels , but these effects are small and need to be weighed against the potential for harms
Background / Objectives : Numerous r and omised controlled trials ( RCTs ) published in first tier medical journals have evaluated the health effects of diets high in protein .
We conducted a rigorous systematic review of RCTs comparing higher- and lower-protein diets .