A number of studies suggest that postprandial hyperglycemia produces oxidative stress, leading to complications associated with diabetes. However, hyperglycemia-induced oxidative stress may affect groups of people other than diabetics, such as smokers and athletes with specific diet plans. Based on previous reports that seated breathing meditation reduces hyperglycemia, the present study was designed to determine the effects of diaphragmatic breathing on postprandial plasma glycemia, insulin, oxidative stress, and antioxidant levels in athletes with normal glucose metabolism.Data collected before and after consumption of a 900-calorie breakfast composed of 80% carbohydrates, 10% proteins, and 10% lipids were analyzed. Ten (10) minutes after the meal, 8 subjects spent 40 minutes performing diaphragmatic breathing in a quiet place. The other 8 subjects, representing the control group, spent the same time sitting in an equivalent quiet place reading a magazine.Data from 16 amateur male cyclists age 30.12±4.9 years (±SD) were analyzed. Their mean height and weight were 177.81±5.3 cm and 71.40±5.2 kg, respectively. All subjects underwent a physical examination and were determined to be in good health.Blood samples were collected immediately before the meal as well as 1 hour and 2 hours after the meal, and plasma levels of glucose, insulin, reactive oxygen metabolites, and biologic antioxidant potential were determined. Heart rate was also recorded.Results show that in normal subjects, acute hyperglycemia induces free-radical production while reducing the antioxidant levels (p<0.05). Diaphragmatic breathing reduces heart rates (p<0.01), increases insulin (p<0.05), reduces glycemia (p<0.01), and reduces free-radical production as indicated by the higher antioxidants levels (p<0.05).Diaphragmatic breathing, likely through the activation of the parasympathetic nervous system, increases insulin, reduces glycemia, and reduces reactive oxygen species production.