Effects of plant-and animal-based-protein meals for a day on serum nitric oxide and peroxynitrite levels in healthy young men

Plant-based diets that replace animal-based proteins with plant-based proteins have received increased attention for cardiovascular protection. Nitric oxide (NO) plays an essential role in the maintenance of endothelial function. However, under higher oxidative stress, NO generation produces peroxynitrite, a powerful oxidant and vasoconstrictor. Diet-replaced protein sources has been reported to decrease oxidative stress. However, the effects of plant-based protein on NO and peroxynitrite have not yet been clarified. Therefore, this study aimed to compare the effects of plant-and animal-based-protein meals for a day on NO, peroxynitrite, and NO/peroxynitrite balance. A crossover trial of two meal conditions involving nine healthy men was performed. Participants ate standard meals during day 1. On day 2, baseline measurements were performed and the participants were provided with plant-based-protein meals or animal-based-protein meals. The standard and test meals consisted of breakfast, lunch, and dinner and were designed to be isocaloric. Plant-based-protein meals contained no animal protein. Blood samples were collected in the morning after overnight fasting before and after the test meals consumption. In the plant-based-protein meal condition, serum NOx levels (the sum of serum nitrite and nitrate) significantly increased, while serum peroxynitrite levels did not change significantly. Animal-based-protein meals significantly increased serum peroxynitrite levels but showed a trend of reduction in the serum NOx levels. Furthermore, serum NO/peroxynitrite balance significantly increased after plant-based-protein meals consumption, but significantly decreased after animal-based-protein meals consumption. These results suggest that, compared with animal-based-protein meals, plant-based-protein meals increase NO levels and NO/peroxynitrite balance, which reflects increased endothelial function.