1.
Comparing Acute, High Dietary Protein and Carbohydrate Intake on Transcriptional Biomarkers, Fuel Utilisation and Exercise Performance in Trained Male Runners.
Furber, M, Pyle, S, Roberts, M, Roberts, J
Nutrients. 2021;13(12)
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Dietary modification to improve exercise endurance has become a popular strategy. The reduction of carbohydrates to enhance adaptations due to training has been shown on a cellular level. In low carbohydrate diets, fat is the usual substitute, however long-term adherence to this is often difficult. Using protein instead of fat may be an alternative, but there is little research on this. This study aimed to investigate the impact of a short-term high-protein, reduced carbohydrate diet compared to a high-carbohydrate diet in combination with endurance running on exercise performance and cellular adaptations. The results showed that any cellular adaptations were due to fuel availability, rather than the fuel type and that a high protein diet compromised high intensity exercise performance. It was concluded that a high-protein, low-carbohydrate diet in combination with endurance training is of no benefit to endurance running performance. This study could be used by healthcare professionals to recommend that athletes and especially runners who wish to improve endurance do not switch to a high-protein, low carbohydrate diet and that other dietary modifications are investigated.
Abstract
Manipulating dietary macronutrient intake may modulate adaptive responses to exercise, and improve endurance performance. However, there is controversy as to the impact of short-term dietary modification on athletic performance. In a parallel-groups, repeated measures study, 16 trained endurance runners (maximal oxygen uptake (V˙O2max): 64.2 ± 5.6 mL·kg-1·min-1) were randomly assigned to, and provided with, either a high-protein, reduced-carbohydrate (PRO) or a high-carbohydrate (CHO) isocaloric-matched diet. Participants maintained their training load over 21-consecutive days with dietary intake consisting of 7-days habitual intake (T1), 7-days intervention diet (T2) and 7-days return to habitual intake (T3). Following each 7-day dietary period (T1-T3), a micro-muscle biopsy was taken for assessment of gene expression, before participants underwent laboratory assessment of a 10 km treadmill run at 75% V˙O2max, followed by a 95% V˙O2max time to exhaustion (TTE) trial. The PRO diet resulted in a modest change (1.37-fold increase, p = 0.016) in AMPK expression, coupled with a significant increase in fat oxidation (0.29 ± 0.05 to 0.59 ± 0.05 g·min-1, p < 0.0001). However, a significant reduction of 23.3% (p = 0.0003) in TTE post intervention was observed; this reverted back to pre levels following a return to the habitual diet. In the CHO group, whilst no change in sub-maximal fuel utilisation occurred at T2, a significant 6.5% increase in TTE performance (p = 0.05), and a modest, but significant, increase in AMPK (p = 0.042) and PPAR (p = 0.029) mRNA expression compared to T1 were observed; with AMPK (p = 0.011) and PPAR (p = 0.044) remaining significantly elevated at T3. In conclusion, a 7-day isocaloric high protein diet significantly compromised high intensity exercise performance in trained runners with no real benefit on gene markers of training adaptation. A significant increase in fat oxidation during submaximal exercise was observed post PRO intervention, but this returned to pre levels once the habitual diet was re-introduced, suggesting that the response was driven via fuel availability rather than cellular adaptation. A short-term high protein, low carbohydrate diet in combination with endurance training is not preferential for endurance running performance.
2.
Elevated methane levels in small intestinal bacterial overgrowth suggests delayed small bowel and colonic transit.
Suri, J, Kataria, R, Malik, Z, Parkman, HP, Schey, R
Medicine. 2018;97(21):e10554
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Whilst the most conclusive way to diagnose SIBO is to use an invasive procedure (endoscopy) to take samples from the middle section of the small intestine (jejunum), lactulose breath testing of methane and hydrogen gasses has become the most commonly used test to rule SIBO in or out. This cohort study used historic data (retrospective) of 78 individuals to compare intestinal transit time in patients with a positive lactulose breath test to those with a negative result, as well as compare patients with hydrogen-positive results with those with methane-positive results. All patients experienced gastrointestinal (GI) symptoms of nausea, bloating, constipation, diarrhea and gas to varying degrees. No significant difference in GI symptom severity was found between those with a positive lactulose breath test and those with a negative result. However, those with a hydrogen-gas positive result had a significantly higher level of reported nausea compared to the methane-gas positive patients. A positive SIBO result on the breath test also did not affect GI transit time in comparison to a negative result. However, those with a methane-gas peak on their positive lactulose breath test had a statistically significant slower GI transit time when compared to those with a hydrogen-positive result.
Abstract
Limited research exists regarding the relationship between small intestinal bacterial overgrowth (SIBO), small bowel transit (SBT), and colonic transit (CT). Furthermore, symptom analysis is limited between the subtypes of SIBO hydrogen producing (H-SIBO) and methane producing (M-SIBO). The primary aims of this study are to: compare the SBT and CT in patients with a positive lactulose breath test (LBT) to those with a normal study; compare the SBT and CT among patients with H-SIBO or M-SIBO; compare the severity of symptoms in patients with a positive LBT to those with a normal study; compare the severity of symptoms among patients with H-SIBO or M-SIBO.A retrospective review was performed for 89 patients who underwent a LBT and whole gut transit scintigraphy (WGTS) between 2014 and 2016. Seventy-eight patients were included. WGTS evaluated gastric emptying, SBT (normal ≥40% radiotracer bolus accumulated at the ileocecal valve at 6 hours), and CT (normal geometric center of colonic activity = 1.6-7.0 at 24 hours, 4.0-7.0 at 48 hours, 6.2-7.0 at 72 hours; elevated geometric center indicates increased transit). We also had patients complete a pretest symptom survey to evaluate nausea, bloating, constipation, diarrhea, belching, and flatulence.A total of 78 patients (69 females, 9 males, mean age of 48 years, mean BMI of 25.9) were evaluated. Forty-seven patients had a positive LBT (H-SIBO 66%, M-SIBO 34%). Comparison of SBT among patients with a positive LBT to normal LBT revealed no significant difference (62.1% vs 58.6%, P = .63). The mean accumulated radiotracer was higher for H-SIBO compared to M-SIBO (71.5% vs 44.1%; P < .05). For CT, all SIBO patients had no significant difference in geometric centers of colonic activity at 24, 48, and 72 hours when compared to the normal group. When subtyping, H-SIBO had significantly higher geometric centers compared to the M-SIBO group at 24 hours (4.4 vs 3.1, P < .001), 48 hours (5.2 vs 3.8, P = .002), and at 72 hours (5.6 vs 4.3, P = .006). The symptom severity scores did not differ between the positive and normal LBT groups. A higher level of nausea was present in the H-SIBO group when compared to the M-SIBO group.Overall, the presence of SIBO does not affect SBT or CT at 24, 48, and 72 hours. However, when analyzing the subtypes, M-SIBO has significantly more delayed SBT and CT when compared to H-SIBO. These results suggest the presence of delayed motility in patients with high methane levels on LBT.
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Effects of Low Versus Moderate Glycemic Index Diets on Aerobic Capacity in Endurance Runners: Three-Week Randomized Controlled Crossover Trial.
Durkalec-Michalski, K, Zawieja, EE, Zawieja, BE, Jurkowska, D, Buchowski, MS, Jeszka, J
Nutrients. 2018;10(3)
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During athletic performance, adequate amounts of carbohydrates are required to prolong the onset of fatigue. Research on whether the glycaemic index (GI) of ingested carbohydrates effects performance has been explored but has produced equivocal results. The aim of this randomised crossover study was to assess the effect of low- and moderate- GI diets on the aerobic capacity and endurance performance in 21 runners. Participants consumed a low- and moderate- GI, high carbohydrate and nutrient balanced diets for three weeks each with a two-week washout period. Aerobic capacity and body composition were measured at the beginning and end of each diet period through various athletic performance tests. This study found that after a low-GI, high-carbohydrate diet, improvements were seen in time to exhaustion and running performance. Gas exchange was improved by both diets. The low-GI carbohydrate diet helped athletes to maintain a more stable blood glucose concentration during exertion tests. Based on these results the authors suggest considering GI when planning a diet for performance athletes, and also urge further research be completed to better understand the effects of long-term GI diets with regards to exercise performance.
Abstract
The glycemic index (GI) of ingested carbohydrates may influence substrate oxidation during exercise and athletic performance. Therefore, the aim of this study was to assess the effect of low- and moderate-GI three-week diets on aerobic capacity and endurance performance in runners. We conducted a randomized crossover feeding study of matched diets differing only in GI (low vs. moderate) in 21 endurance-trained runners. Each participant consumed both, low- (LGI) and moderate-GI (MGI) high-carbohydrate (~60%) and nutrient-balanced diets for three weeks each. At the beginning and end of each diet, participants had their aerobic capacity and body composition measured and performed a 12-min running test. After LGI, time to exhaustion during incremental cycling test (ICT) and distance covered in the 12-min run were significantly increased. The MGI diet led to an increase in maximal oxygen uptake ( V ˙ O₂max), but no performance benefits were found after the MGI diet. The LGI and MGI diets improved time and workload at gas exchange threshold (GET) during ICT. The results indicate that a three-week high-carbohydrate LGI diet resulted in a small but significant improvement in athletic performance in endurance runners. Observed increase in V ˙ O₂max on MGI diet did not affect performance.
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Effects of Providing High-Fat versus High-Carbohydrate Meals on Daily and Postprandial Physical Activity and Glucose Patterns: a Randomised Controlled Trial.
Parr, EB, Devlin, BL, Callahan, MJ, Radford, BE, Blankenship, JM, Dunstan, DW, Hawley, JA
Nutrients. 2018;10(5)
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The timing of habitual meal consumption and composition is known to be an important factor in health status, particularly for blood glucose regulation. The aim of this randomised crossover study was to assess the effects of altering meal timing and diet composition on postprandial glucose and physical activity levels. Eight overweight or obese men with a sedentary lifestyle completed two 12-day measurement periods including a 7-day habitual period followed by a 5-day experimental period, with an 8-day washout period. The two conditions tested were a high-fat, low carbohydrate diet (HFD) and a high-carbohydrate, low-fat diet (HCD) and participants were instructed to consume meals at standardised times throughout both conditions. Body composition, oxygen consumption and blood glucose were measured at baseline and between each experimental condition. This trial found the provision of meals did not alter overall activity patterns or postprandial activity patterns. The authors observed increased sedentary activity across the day, and identify evening time as an important target for sedentary time to be minimised. Based on these results, the authors suggest that future dietary interventions consider habitual meal consumption and composition to best replicate real-world behaviours.
Abstract
We determined the effects of altering meal timing and diet composition on temporal glucose homeostasis and physical activity measures. Eight sedentary, overweight/obese men (mean ± SD, age: 36 ± 4 years; BMI: 29.8 ± 1.8 kg/m²) completed two × 12-day (12-d) measurement periods, including a 7-d habitual period, and then 5 d of each diet (high-fat diet [HFD]: 67:15:18% fat:carbohydrate:protein versus high-carbohydrate diet [HCD]: 67:15:18% carbohydrate:fat:protein) of three meals/d at ±30 min of 0800 h, 1230 h, and 1800 h, in a randomised order with an 8-d washout. Energy intake (EI), the timing of meal consumption, blood glucose regulation (continuous glucose monitor system (CGMS)), and activity patterns (accelerometer and inclinometer) were assessed across each 12-d period. Meal provision did not alter the patterns of reduced physical activity, and increased sedentary behaviour following dinner, compared with following breakfast and lunch. The HCD increased peak (+1.6 mmol/L, p < 0.001), mean (+0.5 mmol/L, p = 0.001), and total area under the curve (+670 mmol/L/min, p = 0.001), as well as 3-h postprandial meal glucose concentrations (all p < 0.001) compared with the HFD. In overweight/obese males, the provision of meals did not alter physical activity patterns, but did affect glycaemic control. Greater emphasis on meal timing and composition is required in diet and/or behaviour intervention studies to ensure relevance to real-world behaviours.