Postprandial Metabolic Responses Differ by Age Group and Physical Activity Level.

OBJECTIVES: To compare the postprandial metabolic responses to a high-fat meal in healthy adults who differ by age and physical activity level. DESIGN: Cross-sectional, quasi-experimental design. SETTING: Physical Activity and Nutrition Clinical Research Consortium (PAN-CRC) at Kansas State University (Manhattan, KS, USA). PARTICIPANTS: Twenty-two healthy adults: 8 younger active (YA) adults (4M/4W; 25 ± 5 yr), 8 older active (OA) adults (4M/4W; 67 ± 5 yr), and 6 older inactive (OI) adults (3M/3W; 68 ± 7 yr). INTERVENTION: Following an overnight (10-hour) fast and having abstained from exercise for 2 days, participants consumed a high-fat meal (63% fat, 34% CHO; 12 kcal/kg body mass; 927 ± 154 kcal). To assess the metabolic response, blood draws were performed at baseline and each hour following the meal for 6 hours. MEASUREMENTS: Fasting and postprandial triglycerides (TG), glucose, Total-C, and HDL-C were measured. Metabolic load index (MLI) and LDL-C were calculated. RESULTS: There were significant group x time interactions for TG (p < 0.0001) and MLI (p = 0.004). The TG total area-under-the-curve (tAUC) response was significantly lower in YA (407.9 ± 115.1 mg/dL 6 hr) compared to OA (625.6 ± 169.0 mg/dL 6 hr; p = 0.02) and OI (961.2 ± 363.6 mg/dL 6 hr; p = 0.0002), while the OA group TG tAUC was lower than the OI group (p = 0.02). The TG peak was significantly lower in YA (90.5 ± 27.0 mg/dL) than OA (144.0 ± 42.2 mg/dL; p = 0.03) and OI (228.2 ± 96.1 mg/dL; p = 0.0003), and was lower in the OA group compared to the OI group (p = 0.03). Glucose was significantly lower 1 hour after the meal in YA (89.4 ± 10.1 mg/dL; p = 0.01) and OA (87.3 ± 22.3 mg/dL; p = 0.005) versus OI (110.7 ± 26.9 mg/dL). MLI tAUC was significantly lower in YA (936.8 ± 137.7 mg/dL 6 hr; p = 0.0007) and OA (1133.0 ± 207.4 mg/dL; p = 0.01) versus OI (1553.8 ± 394.3 mg/dL), with no difference (p = 0.14) between YA and OA groups. Total-C and LDL-C were generally lower in younger compared to older participants at baseline and throughout the postprandial period, while no group or time effects were evident in HDL-C. CONCLUSION: Both physical activity status and aging appear to affect the postprandial metabolic, namely TG, response to a high-fat meal. These findings point to an inherently diminished metabolic capacity with aging, but suggest that physical activity may help minimize this decrement.

Effects of oral administration of sodium citrate or acetate to pigs on blood parameters, postmortem glycolysis, muscle pH decline, and quality attributes of pork.

The objective of this study was to determine the effects of oral administration of sodium citrate (CIT) or acetate (ACE) to pigs on blood parameters, postmortem glycolysis, pH decline, and quality attributes of pork. Previous studies have shown that CIT has the potential to inhibit phosphofructokinase (PFK), a key enzyme in postmortem muscle glycolysis. In Exp. 1, CIT, ACE, or water was orally administered (0.75 g/kg of BW) to 24 pigs. After a 30-min rest, pigs were exercised, and blood samples were taken at 45 and 75 min after oral treatment. Citrate and ACE tended (P = 0.08) to increase blood pH and increased (P = 0.02) bicarbonate levels immediately after exercise. After a 30-min rest, blood pH of pigs administered ACE tended (P = 0.09) to remain higher, whereas blood pH of CIT-treated pigs was similar to that of control pigs. Bicarbonate levels in ACE- and CIT-treated pigs were still greater (P < 0.05) than those of control pigs at 75 min after oral treatment. In Exp. 2, 30 pigs were administered CIT, ACE, or water 45 min before stunning (electric plus captive bolt). Antemortem treatments had no effect (P > 0.10) on muscle pH or postmortem concentrations of the glycolytic metabolites of glucose-6 phosphate, fructose-6 phosphate, fructose-1,6 bisphosphate, glyceraldehyde-3 phosphate, dihydroxyacetone phosphate, or lactate. Minor, but inconsistent, differences in quality attributes were found in LM chops, and no differences in quality attributes were found between control and CIT- or ACE-treated pigs for inside and outside semimembranosus muscles (P > 0.10). There was no significant inhibition of the PFK enzyme by orally administered CIT or ACE; however, the PFK glycolytic metabolite data analysis indicated that PFK was a main regulatory enzyme in postmortem muscle.

Effects of pre-rigor injection of sodium citrate or acetate, or post-rigor injection of phosphate plus salt on post-mortem glycolysis, pH, and pork quality attributes.

Forty pork carcass sides were assigned to one of four treatments: pre-rigor citrate (CIT) or acetate injection (ACE); post-rigor phosphate and salt injection (PHOS); and non-injected control (CON). Loins in 20 sides were injected at 50min post-mortem with 4% solutions of CIT or ACE to approximately 110% of projected loin weights, and 10 loins were injected at 24h post-mortem to 106.6% with a solution of 4.4% PHOS and 2.2% salt. Although CIT increased pH (P<0.05), neither CIT nor ACE altered (P>0.05) glycolytic metabolite concentrations. The pH increase in muscles from the CIT treatment was most likely due to its buffering ability rather than to its glycolytic inhibition. Pre-rigor CIT injection improved tenderness without the detrimental effects on color or flavor found with PHOS, but neither CIT nor ACE altered glycolytic metabolites or improved firmness, wetness, or fresh visual color over CON. Poor flavor attributes of the ACE treatment will hinder its use as an ingredient for pork enhancement solutions.

Training status influences T-cell responses in women following acute resistance exercise.

The purpose of this investigation was to examine white blood cell counts (WBC), immunoglobulin (IgA, IgG, IgM) levels, and T-cell proliferation following acute resistance training in 9 untrained (UT) and 6 trained (TR) women. Resistance training on 7 Universal machines at the subject's 10 repetition maximum (IORM) was performed at 89 +/- 5% for UT and 88 +/- 3% for TR. Blood was analyzed for WBCs and Ig levels pre-exercise, immediately postexercise, and 1.5, 3, and 24 hours postexercise. T-cell proliferation was determined pre-exercise and 3 hours postexercise through response to phytohemagglutanin (PHA). WBCs were significantly elevated in the UT subjects 1.5 and 3 hours postexercise compared with pre- and immediately postexercise; no differences (p < 0.05) were observed in TR subjects. No significant differences were found for Ig levels either between or within groups, although there was a trend for decreased IgG following exercise. T-cell proliferation was significantly decreased in the UT at 3 hours postexercise (0.27 +/- 0.06 units) compared with pre-exercise (0.41 +/- 0.06 units), whereas the proliferative response in TR was not significantly different from pre-exercise (0.48 +/- 0.04 units) to 3 hours postexercise (0.34 +/- 0.06 units). These data indicate that UT subjects experience an increase in WBC counts and a decrease in T-cell proliferative ability after acute resistance training, whereas TR subjects experience no significant change in these parameters.

Protein requirement of elderly women: nitrogen balance responses to three levels of protein intake.

BACKGROUND: For elderly women, insufficient data exist to assess the accuracy of the assumed mean protein requirement of 0.6 g of protein x kg(-1) x day(-1), and the adequacy of the current Recommended Dietary Allowance (RDA) of 0.8 g of protein x kg(-1) x day(-1). The aims of this study were to assess the mean protein requirement and suggested safe and adequate protein intake (protein allowance) of elderly women using a shorter-term nitrogen balance protocol. METHODS: During three separate 18-day trials, 11 elderly women (age range, 70-81 years) were randomly fed eucaloric diets designed to provide either 0.50, 0.75, or 1.00 g of protein x kg(-1) x day(-1). Nitrogen balance was determined at Weeks 2 and 3 (Days 7-10 and 14-17, respectively) of each trial using data from total nitrogen analyses of duplicate food composites, 24-hour urine collections, and stool collections. The mean protein requirement was calculated using linear regression of individual women's data from all three trials and inverse prediction. RESULTS: At protein intakes of 0.53 +/- 0.02, 0.76 +/- 0.02, or 1.06 +/- 0.05 g of protein x kg(-1) x day(-1), net nitrogen balances during Week 2 were -14.5 +/- 3.1, 3.8 +/- 2.5 and 23.4 +/- 3.3 mg of nitrogen x kg(-1) x day(-1), respectively, for these body weight- and body composition-stable women. At Week 3, the net nitrogen balances were -0.1 +/- 2.7, 8.5 +/- 3.6 and 42.0 +/- 3.0 mg of nitrogen x kg(-1) x day(-1). From Week 2 to Week 3, shifts to more positive nitrogen balances occurred due to decreases in urinary nitrogen excretion. The mean protein requirement at Week 2 was calculated to be 0.70 +/- 0.09 g of protein. kg(-1) x day(-1) (coefficient of variation [CV] = 13%) and at Week 3 was calculated to be 0.56 +/- 0.09 g of protein x kg(-1) x day(-1) (CV = 17%). From these data, an adequate protein allowance was estimated to be greater than the RDA at Week 2 (0.90 g of protein x kg(-1) x day [d](-1)), and not different than the RDA at Week 3 (0.76 g of protein x kg(-1) x d(-1)). CONCLUSIONS: The decrease over time in urinary nitrogen excretion from Week 2 to Week 3 suggests that these elderly women did not achieve a metabolic steady state during this shorter-term nitrogen balance study. Collectively, these data suggest that the total protein needs of elderly women are at or above the current RDA for protein. However, the results of this study indicate that shorter-term nitrogen balance protocols are insufficient to firmly establish the RDA for protein of elderly women, and further research is required using alternative criteria measures.

Glycogen replenishment and repeated maximal effort exercise: effect of liquid carbohydrate.

We investigated the effects of carbohydrate ingestion on glycogen replenishment and subsequent short duration, high intensity exercise performance. During Session 1, aerobic power was determined and each subject (N = 6) was familiarized with the 100-kJ cycling test (100KJ-Test). During the treatment sessions, the subjects performed a 100KJ-Test (Ride-1), then consumed 0.7 g.kg body mass-1 of maltodextrin (CHO) or placebo (PLC), rested 60 min, and then performed a second 100KJ-Test (Ride-2). Muscle tissue was collected before (Pre-1) and after Ride-1 (Post-1), and before (Pre-2) and after Ride-2 (Post-2), and analyzed for glycogen concentration. Both treatments yielded a significant increase in glycogen levels following the 60-min recovery, but there was no difference between treatments. Time to complete the 100KJ-Test increased significantly for PLC, but not for CHO. These data indicate that the decrease in performance during Ride-2 in PLC was not the result of a difference in glycogen concentration.

Acute L-glutamine ingestion does not improve maximal effort exercise.

BACKGROUND: L-glutamine (GLN) may have an ergogenic effect during exercise considering its base generating potential. We attempted to determine whether GLN ingestion influences acid-base balance and improves high intensity exercise performance. METHOD: Ten trained males performed five exercise bouts on a cycle ergometer at 100% of VO2 peak. The first four bouts were 60 sec in duration, while the fifth bout was continued to fatigue. Each bout was separated by 60 sec of recovery. The exercise bouts were initiated 90 min after ingesting 0.03 g.kg body mass-1 of either GLN or placebo (PLC). Venous blood samples were collected pre-ingestion (PRE-IN), pre-exercise (PRE-EX), and following bouts four (B4) and five (B5) and analyzed for pH, bicarbonate concentration (HCO3), and lactate concentration (La-). Time to fatigue for B5 was used as a performance measure. RESULTS: pH, [HCO3], and [La-] were not significantly different (p > 0.05) between conditions for PRE-IN, PRE-EX, B4, and B5. Time to fatigue was not significantly different between conditions and averaged 263.4 +/- 24.5 sec and 263.2 +/- 19.4 sec for the GLN and PLC trials, respectively. CONCLUSIONS: These data indicate that acute ingestion of L-glutamine does not enhance either buffering potential or high intensity exercise performance in trained males.

Sodium citrate ingestion enhances 30 km cycling performance.

The purpose of this study was to examine the effects of sodium citrate (CIT) ingestion on 30 km cycling performance. Eight trained male cyclists (VO2max = 54.7 +/- 1.7 ml.kg-1.min-1) performed two 30 km cycling time trials. The trials were double blind and randomly assigned from CIT or placebo (PLC), with both dosages at 0.5 g.kg body wt-1. Blood samples were collected from an indwelling catheter at 10 km intervals and analyzed for PO2, PCO2, pH, and lactate concentration ([La]). Power output, heart rate (HR) and RPE were measured at 5 min intervals during the trials, while cycling performance was determined from time to complete the 30 km. A repeated measures ANOVA and dependent t-tests were used to locate differences between the trials. A significant difference (p < or = 0.01) was observed for pH and [La] during the trials with CIT being elevated above PLC throughout the ride. No significant differences (p > 0.01) were observed for any of the other dependent variables. However, power output and HR were slightly elevated during the CIT trial. Performance time was significantly faster (p < or = 0.05) for the CIT trial (3459.6 +/- 97.4 s) compared to the PLC trial (3562.3 +/- 108.5 s). The data indicate that favorable metabolic conditions were obtained following CIT ingestion and these likely contributed to the improvement in cycling performance.

The effects of buffer ingestion on metabolic factors related to distance running performance.

We examined the effects of sodium bicarbonate (BIC) and sodium citrate (CIT) ingestion on distance running performance. Seven male runners [mean VO2max = 61.7 (SEM 1.7) ml.kg-1.min-1] performed three 30-min treadmill runs at the lactate threshold (LT) each followed by a run to exhaustion at 110% of LT. The runs were double-blind and randomly assigned from BIC (0.3 g.kg body mass-1), CIT (0.5 g.kg body mass-1) and placebo (PLC, wheat flour, 0.5 g.kg body mass-1). Venous blood samples were collected at 5, 15 and 25 min during the run and immediately post-exhaustion (POST-EX) and analysed for pH, and the concentrations of lactate ([la-]b) and bicarbonate ([HCO3-]). Performance was measured as running time to exhaustion at 110% of LT (TIME-EX). The pH was significantly higher (P < or = 0.05) for the BIC and CIT trials during exercise, but not POST-EX compared to PLC. The [la-]b was significantly higher (P < or = 0.05) for the CIT trial compared to PLC during exercise, and for both CIT and BIC compared to PLC at POST-EX. Blood [HCO3-] was significantly higher (P < or = 0.05) during exercise for BIC compared to PLC. TIME-EX was not significantly different among treatments: BIC 287 (SEM 47.4)s; CIT 172.8 (SEM 29.7)s; and PLC 222.3 (SEM 39.7)s. Despite the fact that buffer ingestion produced favourable metabolic conditions during 30 min of high intensity steady-state exercise, a significant improvement in the subsequent maximal exercise run to exhaustion did not occur.