High fat-low carbohydrate (HFLC) diets are a common approach to enhancing overall health and performance in endurance runners. Total macronutrient contents in plasma may change in response to diet and exercise. PURPOSE: To examine the responses of total plasma macronutrient contents in trained males following dietary manipulation in combination with aerobic exercise. METHODS: Eight distance runners that typically consumed high-carbohydrate (HC) diets switched to a HFLC diet for 3 weeks. The caloric intake during the HFLC intervention derived from 70% fats with ≤ 50g of carbohydrates. Participants maintained their normal fitness routines. Indoor treadmill exercise for 50 minutes at varying race paces followed by an outdoor 5-km time trial were completed during the HC and HFLC trials. Overnight fasting blood samples were collected before (baseline) and after exercise (24-hours) to analyze changes in total plasma lipids, proteins, and carbohydrates using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR FT-IR). The O-H stretch vibrational band of water was used to normalize the IR spectra of the plasma. Protein content was quantified by measuring the amide I peak intensity at 1600–1700 cm-1 which corresponded to the C=O stretch vibration mode. For the lipids and carbohydrates, the plasma samples were lyophilized and measured at 2800–3000 cm-1 intensities (C-H stretching vibration in acyl chains) and 800–1200 cm-1 (C-O-C vibration mode), respectively. RESULTS: The ATR FT-IR analysis found that, independent of diet or exercise, there were no significant changes in total plasma proteins (HC baseline=135.20±4.20, HC post-exercise = 134.44±4.31, HFLC baseline=135.24±3.91, and HFLC post-exercise=135.93±2.52 AU). However, a significant accumulation of lipids (30.06±7.75 AU, 95% CI=6.93) and carbohydrates (42.92±11.62 AU, 95% CI=10.39) were observed at the HC baseline as compared to the HFLC baseline (28.29±7.56 and 38.47±13.08, respectively). In addition, total lipids in the HC diet significantly decreased at 24-hours post-exercise (from 30.06±7.75 to 28.51±7.91 AU, p=0.016). CONCLUSION: Amid the high carbohydrate diet, 24 hours post-exercise total lipid contents decreased, suggesting that lipids consumed as a primary energy substrate during exercise did not recover to baseline levels within 24 hours. Additionally, both lipids and carbohydrate contents were elevated following high-carbohydrate diet, possibly due to elevated plasma lipids resulting from decreased insulin sensitivity. In contrast, no significant changes occurred with the high fat diet.



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