4. Discussion
rheumatoid arthritis, metabolic disease
RHEUMATOID ARTHRITIS, REGRESSION, OXIDATIVE STRESS, METABOLIC DISEASE
The findings of this study support the hypothesis that the timing of grape consumption modulates the body’s response to an oxidative stress challenge. Higher F2-isoprostane urine excretion following consumption of a high-fat meal was seen in the morning compared to the evening, and this response was blunted by co-ingestion of the equivalent of 1.5 servings of whole grapes. Our hypothesis is based on the circadian rhythm of immune defense [Support for pursuing the investigation of timed bioactive food consumption is provided by chronotherapy studies showing improved effectiveness of glucocorticoids in patients with rheumatoid arthritis when administered to target peak times of cytokine release and symptom severity [The current study builds on the concept of chrononutrition in a new way. Chrononutrition research has focused on identifying optimal eating time periods for improving weight management and symptoms of metabolic disease [In this study, we measured urine grape metabolites to assess the absorption of the grape’s antioxidant and anti-inflammatory components and identify possible correlations with the oxidative stress response. Contrary to our expectations, higher metabolite excretion was not related to lower F2-isoprostane levels in regression models. The current finding of a positive relationship between urine F2-isoprostane and quercetin concentrations has been reported previously [The finding of higher F2-isoprostane levels and oxidative stress biomarkers in female vs. male individuals has been reported previously [Strengths of this study include the randomized, blinded, placebo-controlled design and consumption of the high-fat meal and treatment under observation. Further, participants followed a low-antioxidant diet for two days and fasted for 12 h before the study visit in order to minimize the effects of the background diet on outcomes. Adherence to the low-antioxidant diet was confirmed with diet records. Also, urine F2-isoprostane concentrations were quantified using LC/MS-MS, a more reliable method compared to enzyme-linked immunoassays [