Journal Title (Medline/Pubmed accepted abbreviation): J. Appl. Physiol.
Page numbers: 1710-1715
doi (if applicable): 10.1152/japplphysiol.00205.2010
Summary of Background and Research Design
Background: Exercise induces oxidative stress that can be combated to various extents by consuming antioxidants. Purple sweet potato leaves (PSPLs) have high amounts of polyphenol and flavonoid antioxidants.
Hypothesis/Research Question: Does intake of PSPLs for 1 wk affect oxidant-antioxidant balance in healthy, non-trained men who exercised at 70% their VO2max for 1 hr?
Subjects: 15 untrained males, age 23.6 ± 1.0, BMI 22.1 ± 0.5
Experimental design: crossover design
Treatments and protocol:
PSPLs were stir fried in soy oil and administered in 200 g daily portions. For the PSPL diet, PSPLs were divided between breakfast and lunch and provided by the researchers. Breakfast and lunch was provided for the control group, too.
Three weeks before intervention, the subjects’ VO2max was determined. Subjects ran on a treadmill at 9 km/h (5.6 mph) for 2 min. While measuring oxygen uptake, treadmill speed was increased by 3% every 3 min until volitional exhaustion. Within one week, the same running protocol was followed. VO2max was determined for both sessions and averaged for the calculation of the workload for study exercise sessions.
For intervention, subjects followed the PSPL diet or the control diet for 1 wk with a 1 wk run-in period before PSPL consumption and a 2 wk washout period in between treatments. For the whole 5 wks of the study participants were asked to eat a low polyphenol diet.
After each 1 wk intervention, an exercise protocol was followed. Subjects arrived in the morning after a 10 hr overnight fast. Subjects received a standard breakfast (513 kcal, 92.1 g carbohydrates) 60 min before exercise. Subjects ran on the treadmill for 1 hr at 70% VO2max. Blood samples were acquired from a vein before exercise, immediately after exercise, and 1 hr and 3 hr post-exercise.
Blood was analyzed for total polyphenols in plasma, antioxidant status, protein carbonyl content (a marker of protein oxidation), plasma concentration of interleukin-6 cytokine (IL-6, a marker of inflammation), and heat shock protein 72 (HSP72) expression (a defense marker that has been correlated with stress mechanisms such as oxidation and inflammation) within peripheral blood mononuclear cells.
Summary of research findings:
PSPL consumption significantly increased plasma polyphenols pre-exercise [0.28 mg gallic acid equivalents (GAE)/mL after 1 wk of PSPL intervention vs. 0.19 mg GAE/mL after control diet]. After exercise, plasma levels were similar. PSPL consumption decreased TBARS, a marker of oxidative stress, about 63% both at pre-exercise and 3 hrs post-exercise compared with the control diet. Protein carbonyl was significantly decreased (PSPL vs. control) immediately and 1 hr after exercise. IL-6 was reduced at all time points for PSPL versus conrol, though only reached statistical significance 1 hr post-workout. Finally, FFRP was significantly elevated versus control at the pre-, 1-h post-, and 3 h post-exercise time points.
Interpretation of findings/Key practice applications:
Consumption of purple sweet potato leaves improves the antioxidant capacity of the plasma and reduces the negative effects of exercise in untrained subjects.
The subjects were asked to follow a low polyphenol diet for 1 wk before and then during the study. It is unknown what their antioxidant status would be if they followed their normal diet. There is a chance that the reduced bars for the control group was a result of the dearth of polyphenols in their diet and the PSPLs were simply bringing their plasma antioxidant levels back to normal.
It would be interesting to compare PSPLs to other vegetables, especially those that are more common in North America.