CHO Absorption Research Articles

#4452 ICODEXTRIN EFFICIENCY IN FLUID AND SODIUM REMOVAL REMAINS STABLE DURING LONG PERITONEAL DWELLS

Abstract Background and Aims Inadequate fluid and sodium removal has been shown to increase risk of overhydration and hypertension. In peritoneal dialysis, icodextrin-based solution provides sustained ultrafiltration, and therefore can be used for the long exchanges, especially in patients with fast solute transport rates in whom the effective ultrafiltration period is shortened. We investigated to which extent the efficiency of icodextrin in fluid and sodium removal is changing during 16-hour peritoneal dwells. Method Data on intraperitoneal volume, and concentrations of icodextrin and sodium in dialysate during 16 hours of peritoneal dwells with icodextrin-based solution were analysed in 11 clinically stable patients. Labeled serum albumin (RISA) was used as a volume marker and dialysate samples of 12 mL were collected at 8, 12, and 16 hours of peritoneal dwell. Residual volume was evaluated from marker dilution after 16 hours by rinsing peritoneal cavity with 2 L of fresh 1.36% glucose dialysis fluid. Ultrafiltration (UF) was calculated for each patient and each sampling time as the difference between drained and initially infused volume corrected for the sample volume. The total absorption of icodextrin-derived carbohydrates (AbsCHO) was calculated for each patient as the difference between initially infused and drained carbohydrates mass. The icodextrin ultrafiltration efficiency (UFE) was calculated for each sampling time as the ultrafiltration divided by the amount of icodextrin mass absorbed (AbsCHO). The efficiency of icodextrin in sodium removal (NaRE) was calculated for each sampling time as the sodium mass removed (difference between drained and initially infused sodium mass) divided by the corresponding icodextrin mass absorbed (AbsCHO). Correction for the residual volume and samples collections were applied for AbsCHO, UFE and NaRE calculations. Results After 16-hour dwell with icodextrin-based solution the ultrafiltration was positive in all except one patient, being on average (mean±SD) 669±369 mL. During the dwell, icodextrin was slowly absorbed from the peritoneal cavity, see Figure 1, left panel. At 16 hours, the mean cumulative CHO absorption (AbsCHO) reached 68.0±20.7 g (44±13% of initial CHO mass) while 56% of initial icodextrin mass infused still remained in dialysate, Figure 1, left panel. Icodextrin UF efficiency (UFE) calculated at 8, 12, and 16 hours remained stable (p = 0.6, ANOVA repeated measures) and was on average 9.9±5.8 mL/g, Figure 1, right panel. Moreover, icodextrin sodium removal efficiency (NaRE) also remained stable after 8 hours (p = 0.6, ANOVA repeated measures) and was on average 1.2±0.7 mmoL/g, Figure 1, right panel. Conclusion During 16 hours of peritoneal dialysis dwells with icodextrin-based solution, icodextrin was slowly absorbed with 56% of the osmotic agent remaining in the dialysate after 16 hours. The efficiency of icodextrin in terms of fluid (UFE) and sodium (NaRE) removal remained stable and did not subside from 8 to 16 hours of the dwell.

Fluid and Carbohydrate Absorption by Small Intestine After Duodenojejunum Perfusion with Hypertonic Sports Drinks in Healthy Young Men

This study aimed to test whether hypertonic sports drinks (SD) containing multiple types of carbohydrate (CHO) promote fluid absorption in healthy young men. Eight healthy males (20‐30 y old) were randomly infused with three SD containing multiple types of CHO (6‐13% total CHO, 336 ‐ 678 mOsm/kg) at a rate of 15 ml/min using a triple‐lumen nasojejunal tube. Fluid samples collected from the proximal and distal ports located at approximately 10 and 50 cm from the pyloric sphincter were analyzed for osmolality and concentrations of a non‐absorbable marker PEG, CHO, sodium and potassium. Infusion of SD with 6% CHO (336 mOsm/kg) resulted in net fluid absorption whereas SD with 11‐13% CHO (653‐678 mOsm/kg) induced fluid secretion in the test segment and reductions in luminal fluid osmolality towards isotonicity. Rates of CHO absorption were similar among, and net secretion of Na+ and K+ were observed in, all SD tested. SD having 11‐13% CHO induced a higher rate of electrolyte secretion than those with 6% CHO. Plasma glucose was doubled at 30 min after infusion of all test solutions. Thus, the presence of multiple types of CHO in the hypertonic test beverages could not offset the influence of hypertonicity on fluid absorption. Moreover, rates of CHO absorption seem independent of CHO concentrations in the SD (Gatorade Sports Science Institution, USA)

Automated Peritoneal Dialysis Prescriptions for Enhancing Sodium and Fluid Removal: A Predictive Analysis of Optimized, Patient-Specific Dwell Times for the Day Period

Remaining edema-free is a challenge for many automated peritoneal dialysis (APD) patients, especially those with fast ("high") transport characteristics. Although increased use of peritoneal dialysis (PD) solutions with high glucose concentrations may improve volume control, frequent use of such solutions is undesirable. We used the 3-pore kinetic model to evaluate 4 alternative therapy prescriptions for the APD day exchange in anuric patients with high, high-average, and low-average transport characteristics. Four prescriptions were modeled: Therapy 1: Optimal, individualized dwell times with a dry period. Therapy 2: Use of a midday exchange. Therapy 3: Use of an icodextrin-containing dialysate during a 14-hour dwell. Therapy 4: Use of optimal, individualized dwell times, followed by an icodextrin dwell to complete the daytime period. The alternative therapies were compared with a reference standard therapy using glucose solution during a 14-hour dwell. The nighttime prescription was identical in all cases (10 L over 10 hours), and all glucose solutions contained 2.27% glucose. Net ultrafiltration (UF), sodium removal (NaR), total carbohydrate (CHO) absorption, and weekly urea Kt/V for a 24-hour period were computed and compared. The UF and NaR were substantially higher with therapy 1 than with standard therapy (1034 mL vs 621 mL and 96 mmol vs 51 mmol respectively), without significant changes in CHO absorption or urea Kt/V. However, therapy 1 resulted in reduced β2-microglobulin clearance (0.74 mL/min vs 0.89 mL/min with standard therapy). Compared with therapy 1, therapy 2 improved UF and NaR (1062 mL vs 1034 mL and 99 mmol vs 96 mmol); however, that improvement is likely not clinically significant. Therapy 2 also resulted in a higher Kt/V (2.07 vs 1.72), but at the expense of higher glucose absorption (difference: 42 g). The UF and NaR were highest with a long icodextrin-containing daytime dwell either preceded by a short optimized dwell (1426 mL and 155 mmol) or without such a dwell (1327 mL and 148 mmol). The 3-pore model predictions revealed that patient-specific optimal dwell times and regimens with a longer day dwell might provide improved UF and NaR options in APD patients with a variety of peritoneal membrane transport characteristics. In patients without access to icodextrin, therapy 1 might enhance UF and NaR and provide a short-term option to increase fluid removal. Although that approach may offer clinicians a therapeutic option for the overhydrated patient who requires increased UF in the short term, APD prescriptions including icodextrin provide a means to augment sodium and fluid removal. Data from clinical trials are needed to confirm the predictions from this study.

Fructose–Maltodextrin Ratio Governs Exogenous and Other CHO Oxidation and Performance

Fructose coingested with glucose in carbohydrate (CHO) drinks increases exogenous-CHO oxidation, gut comfort, and physical performance. This study aimed to determine the effect of different fructose-maltodextrin-glucose ratios on CHO oxidation and fluid absorption while controlling for osmolality and caloricity. In a crossover design, 12 male cyclists rode 2 h at 57% peak power then performed 10 sprints while ingesting artificially sweetened water or three equiosmotic 11.25% CHO-salt drinks at 200 mL·15 min, comprising weighed fructose and maltodextrin-glucose in ratios of 0.5:1 (0.5 ratio), 0.8:1 (0.8 ratio), and 1.25:1 (1.25 ratio). Fluid absorption was traced with D2O, whereas C-fructose and C-maltodextrin-glucose permitted fructose and glucose oxidation rate evaluation. The mean exogenous-fructose and exogenous-glucose oxidation rates were 0.27, 0.39, and 0.46 g·min and 0.65, 0.71, and 0.58 g·min in 0.5, 0.8, and 1.25 ratio drinks, representing mean oxidation efficiencies of 54%, 59%, and 55% and 65%, 85%, and 86% for fructose and glucose, respectively. With the 0.8 ratio drink, total exogenous-CHO oxidation rate was 18% (90% confidence interval, ±5%) and 5.2% (±4.6%) higher relative to 0.5 and 1.25 ratios, respectively, whereas respective differences in total exogenous-CHO oxidation efficiency were 17% (±5%) and 5.3% (±4.8%), associated with 8.6% and 7.8% (±4.2%) higher fructose oxidation efficiency. The effects of CHO ratio on water absorption were inconclusive. Mean sprint power with the 0.8 ratio drink was moderately higher than that with the 0.5 ratio (2.9%; 99% confidence interval, ±2.8%) and 1.25 ratio (3.1%; ±2.7%) drinks, with total- and endogenous-CHO oxidation rate, abdominal cramps, and drink sweetness qualifying as explanatory mechanisms. Enhanced high-intensity endurance performance with a 0.8 ratio fructose-maltodextrin-glucose drink is characterized by higher exogenous-CHO oxidation efficiency and reduced endogenous-CHO oxidation. The gut-hepatic or other physiological site responsible requires further research.

Ultrafiltration Characteristics of Glucose Polymers with Low Polydispersity

Icodextrin, a glucose polymer with a polydispersity [ratio of weight-average molecular weight (Mw) to number-average molecular weight] of approximately 2.6, has been shown, compared with glucose, to provide superior ultrafiltration (UF) efficiency [ratio of UF to carbohydrate (CHO) absorbed] when used as an osmotic agent during a long-dwell peritoneal dialysis exchange. In an experimental rabbit model, we evaluated the effect of Mw on the UF and UF efficiency of glucose polymers with low polydispersity. A crossover trial in female New Zealand White rabbits (2.20 - 2.65 kg) with surgically implanted peritoneal catheters evaluated two glucose polymers at nominal concentrations of 7.5 g/dL: a 6K polymer (Mw: 6.4 kDa; polydispersity: 2.3) and a 19K polymer (Mw: 18.8 kDa; polydispersity: 2.0). Rabbits were randomized to receive either the 6K (n = 11) or the 19K (n = 12) solution during the first exchange (40 mL/kg body weight). The alternative solution was evaluated in a second exchange 3 days later. During each 4-hour dwell, the UF and total glucose polymer CHO absorbed were determined. The UF was higher for the 6K (p < 0.0001) than for the 19K polymer (mean ± standard deviation: 73.6 ± 30.8 mL vs. 43.0 ± 20.2 mL), as was the amount of CHO absorbed (42.5% ± 9.8% vs. 35.7% ± 11.0%, p = 0.021). In spite of higher CHO absorption, an approximately 50% higher (p = 0.029) UF efficiency was achieved with the 6K polymer (28.3 ± 18.8 mL/g) than with the 19K polymer (19.0 ± 11.3 mL/g). The results were independent of the order of the experimental exchanges. Glucose polymers with low polydispersity are effective osmotic agents in a rabbit model. The low-Mw polymer was more effective at generating UF and had a higher UF efficiency, but those results came at the expense of the polymer being more readily absorbed from the peritoneal cavity.

Comparing Effects of Carbohydrate (CHO) Blockers and Trivalent Chromium on CHO-Induced Insulin Resistance and Elevated Blood Pressure in Rats

Objective: In Sprague-Dawley rats (SD), we compared two categories of natural dietary supplements that influence carbohydrate (CHO) metabolism via different basic mechanisms to ameliorate insulin resistance (IR) and elevated blood pressure (BP) associated with heavy sugar/starch consumption. Two dietary supplements (bean extract and l-arabinose) are often referred to as carb blockers (CBs), because they slow the gastrointestinal absorption of CHO. Trivalent chromium (CR) falls into a group of so-called insulin sensitizers, because its major effect is to enhance peripheral insulin sensitivity. Method: We divided 48 mature male SD into 4 groups of 12. The first group received powdered baseline diet alone (Con). The remaining 3 SD groups (groups 2–4) ingested regular rat chow containing 20% w/w sucrose and 20% w/w rice starch. The second group received only this CHO-enriched chow. To the high-CHO diets of the remaining two groups, either CB to slow CHO absorption (CHO + CB) (group 3) or an insulin sensitizer, trivalent CR (CHO + CR; group 4), was added. Results: Compared to Con group 1, adding high CHO content to the diet of group 2 significantly increased circulating glucose levels and systolic BP (SBP). Addition of CB or CR to the feed of groups 3 and 4 overcame the perturbations that occurred with high CHO challenge in group 2; that is, they lowered circulating glucose concentrations to Con levels, enhanced response to exogenous insulin, and overcame the gradual elevation of SBP. Compared to group 2, the two treatment groups (3 and 4) also showed decreased renin–angiotensin system activity, decreased serum angiotensin-converting enzyme activity, and enhanced nitric oxide activity. Conclusions: Our data indicate that high doses of CB and CR, despite their different mechanisms of action, can completely overcome CHO-induced IR and BP elevations. The data further suggest that CB and CR affect only the changes brought on by heavy CHO ingestion, because IR and SBP in groups 3 and 4 mirrored Con values (group 1), never producing values lower than baseline. Earlier use of CB and CR in the life cycle appears more effective in overcoming CHO-induced perturbations than later use.

Three-Pore Model Predictions of 24-Hour Automated Peritoneal Dialysis Therapy Using Bimodal Solutions

Recently, bimodal peritoneal dialysis (PD) solutions containing low concentrations of Na have been shown to increase 24-hour ultrafiltration (UF) or UF efficiency (UF volume per gram of carbohydrate or CHO absorbed) and Na removal in high ("fast") transport patients during automated PD therapy. We used computer simulations to compare UF efficiency and Na removal at equivalent 24-hour UF volumes using either a generic bimodal solution (2.27% glucose + 7.5% icodextrin) during the long dwell or an increase in the glucose concentration during the short dwells, with all solutions containing Na at the conventional concentration (132 mEq/L). The 3-pore model has been shown to accurately predict peritoneal transport for PD solutions containing glucose or icodextrin, or both. Here, we used that model to calculate 24-hour UF volume, CHO absorption, and Na removal for high (H), high-average (HA), and low-average (LA) transport patients on automated PD. Nighttime therapy consisted of 1.36% or 2.27% glucose solution (or both), and daytime therapy consisted of either Extraneal (Baxter Healthcare Corporation, Deerfield, IL, USA) or a bimodal solution. As expected, addition of glucose to either the long dwell or the short dwells resulted in increased UF volume and glucose absorption. The increase in UF was a function of patient transport type (bimodal range: 288 - 490 mL; short-dwell range: 323 - 350 mL), and the increase in CHO absorption was smaller with glucose added to short dwells than with bimodal solution (range: 18 - 30 g vs. 34 - 39 g). The 24-hour UF efficiency was higher when high glucose concentrations were used during short-dwell exchanges than when a bimodal PD solution was used for the long dwell (0.6 to 1.2 mL/g vs. -0.1 to 0.5 mL/g). By contrast, Na removal was lower with the short-dwell exchanges (28.3 - 30.7 mmol vs. 36.2 - 53.3 mmol), likely because of more pronounced Na sieving. Our modeling studies predict that generic bimodal PD solutions will provide higher Na removal but not higher 24-hour UF efficiency compared with current automated PD prescriptions using Extraneal for the long dwell and glucose-containing solutions for the short dwells. The modeling predictions from this study require clinical validation.

Water and Solute Absorption From Carbohydrate-Electrolyte Solutions in the Human Proximal Small Intestine: A Review and Statistical Analysis

The purpose of this study is to summarize water, carbohydrate (CHO), and electrolyte absorption from carbohydrate-electrolyte (CHO-E) solutions based on all of the triple-lumen-perfusion studies in humans since the early 1960s. The current statistical analysis included 30 reports from which were obtained information on water absorption, CHO absorption, total solute absorption, CHO concentration, CHO type, osmolality, sodium concentration, and sodium absorption in the different gut segments during exercise and at rest. Mean differences were assessed using independent-samples t tests. Exploratory multiple-regression analyses were conducted to create prediction models for intestinal water absorption. The factors influencing water and solute absorption are carefully evaluated and extensively discussed. The authors suggest that in the human proximal small intestine, water absorption is related to both total solute and CHO absorption; osmolality exerts various impacts on water absorption in the different segments; the multiple types of CHO in the ingested CHO-E solutions play a critical role in stimulating CHO, sodium, total solute, and water absorption; CHO concentration is negatively related to water absorption; and exercise may result in greater water absorption than rest. A potential regression model for predicting water absorption is also proposed for future research and practical application. In conclusion, water absorption in the human small intestine is influenced by osmolality, solute absorption, and the anatomical structures of gut segments. Multiple types of CHO in a CHO-E solution facilitate water absorption by stimulating CHO and solute absorption and lowering osmolality in the intestinal lumen.

Inhibition by Natural Dietary Substances of Gastrointestinal Absorption of Starch and Sucrose in Rats 2. Subchronic Studies

Acute oral consumption of various natural inhibitors of amylase (bean and hibiscus extracts) and sucrase (L-arabinose) reduce absorption of starch and sucrose respectively in rats and pigs measured by lessened appearance of circulating glucose levels. The present subchronic study was designed to determine whether these selected inhibitors of gastrointestinal starch and sucrose absorption (so-called "carb blockers") remain effective with continued use and to assess their metabolic influences after prolonged intake. Sprague-Dawley rats were gavaged twice daily over nine weeks with either water or an equal volume of water containing a formula that included bean and hibiscus extracts and L-arabinose. To estimate CHO absorption, control and treated Sprague-Dawley rats were gavaged with either water alone or an equal volume of water containing glucose, rice starch, sucrose, or combined rice starch and sucrose. Circulating glucose was measured at timed intervals over four hours. The ability to decrease starch and sucrose absorption use. No toxic effects (hepatic, renal, hematologic) were evident. Blood chemistries revealed significantly lower circulating glucose levels and a trend toward decreased HbA1C in the nondiabetic rats receiving the natural formulation compared to control. Subchronic administration of enzyme inhibitors was also associated with many metabolic changes including lowered systolic blood pressure and altered fluid-electrolyte balance. We postulate that proper intake of natural amylase and sucrase inhibitors may be useful in the prevention and treatment of many chronic disorders associated with perturbations in glucose-insulin homeostasis secondary to the rapid absorption of refined CHO.

Gastric Emptying and Intestinal Absorption of a Low-Carbohydrate Sport Drink during Exercise

The purpose of this study was to determine if lowering carbohydrate (CHO) concentration in a sport drink influences gastric emptying, intestinal absorption, or performance during cycle ergometry (85 min, 60% VO(2peak)). Five subjects (25 +/- 1 y, 61.5 +/- 2.1 mL . kg(-1) . min(-1) VO(2peak)) ingested a 3% CHO, 6% CHO, or a water placebo (WP) beverage during exercise. Gastric emptying was determined by repeated double sampling and intestinal absorption by segmental perfusion. Total solute absorption and plasma glucose was greater for 6% CHO; however, neither gastric emptying, intestinal water absorption, or 3-mi time trial performance (7:58 +/- 0:33 min, 8:13 +/- 0:25 min, and 8:25 +/- 0:29 min, respectively, for 6% CHO, 3% CHO, and WP) differed among solutions. These results indicate lowering the CHO concentration of a sport drink from 6% CHO does not enhance gastric emptying, intestinal water absorption, or time trial performance, but reduces CHO and total solute absorption.

High Exogenous Carbohydrate Oxidation Rates Following Glucose And Fructose Ingestion During Exercise In The Heat

Exercise in the heat results in greater reliance on carbohydrate (CHO) metabolism. However, the oxidation rate of ingested CHO is reduced in the heat compared with a cool environment possibly due to reduced CHO absorption in the heat. Interestingly, combined ingestion of glucose and fructose (GLU+FRUC) during exercise in a cool environment results in 20–55% higher exogenous CHO oxidation rates compared with ingestion of an isoenergetic amount of glucose (GLU) only. Exercise in the heat is also accompanied by significant losses of fluid and when not replaced, this may impair endurance performance. A CHO beverage that leads to high CHO and fluid delivery rates may have important implications for exercise performed in hot environments. PURPOSE The first purpose of this study was to investigate whether a GLU+FRUC beverage would result in a higher exogenous CHO oxidation rate and a higher fluid availability during exercise in the heat compared with a beverage containing an isoenergetic amount of GLU only. A second aim of the study was to examine whether ingestion of GLU at a rate of 1.5 g/min during exercise in the heat would lead to a reduced rate of muscle glycogen oxidation when compared with ingestion of water (WAT). METHODS Eight trained male cyclists (VO2max: 64±1 ml/kg/min) cycled on three different occasions for 120 min at 50% maximum power output (64±1 VO2max) at an ambient temperature of 31.9±0.1°C. Subjects received, in random order, a solution providing either 1.5 g/min of GLU, 1.0 g/min of GLU + 0.5 g/min of FRUC, or WAT. 2H2O was added to all drinks administered at t=60 min. A continuous infusion of [6,6–2H2]-glucose was performed in GLU and WAT. RESULTS Exogenous CHO oxidation rates during the last hour of exercise were ∼36% higher (P < 0.05) in GLU+FRUC compared with GLU and peak oxidation rates were 1.14±0.05 g/min and 0.77±0.08 g/min, respectively. Endogenous CHO oxidation was significantly lower (P < 0.05) in GLU+FRUC compared with WAT. No other differences were found in endogenous CHO oxidation rates between trials. Muscle glycogen oxidation was not different following ingestion of GLU or WAT. Plasma deuterium enrichments were significantly higher (P < 0.05) in WAT and GLU+FRUC compared with GLU. Furthermore, at 60 and 75 min of exercise, plasma deuterium enrichments were higher (P < 0.05) in WAT compared with GLU+FRUC. CONCLUSION Ingestion of GLU+FRUC during exercise in the heat resulted in higher exogenous CHO oxidation rates and fluid availability when compared with ingestion of GLU and reduced endogenous CHO oxidation when compared with ingestion of WAT. Supported by a grant of GlaxoSmithKline, Consumer Healthcare (UK)

High Exogenous Carbohydrate Oxidation Rates Following Glucose And Fructose Ingestion During Exercise In The Heat

Exercise in the heat results in greater reliance on carbohydrate (CHO) metabolism. However, the oxidation rate of ingested CHO is reduced in the heat compared with a cool environment possibly due to reduced CHO absorption in the heat. Interestingly, combined ingestion of glucose and fructose (GLU+FRUC) during exercise in a cool environment results in 20–55% higher exogenous CHO oxidation rates compared with ingestion of an isoenergetic amount of glucose (GLU) only. Exercise in the heat is also accompanied by significant losses of fluid and when not replaced, this may impair endurance performance. A CHO beverage that leads to high CHO and fluid delivery rates may have important implications for exercise performed in hot environments. PURPOSE The first purpose of this study was to investigate whether a GLU+FRUC beverage would result in a higher exogenous CHO oxidation rate and a higher fluid availability during exercise in the heat compared with a beverage containing an isoenergetic amount of GLU only. A second aim of the study was to examine whether ingestion of GLU at a rate of 1.5 g/min during exercise in the heat would lead to a reduced rate of muscle glycogen oxidation when compared with ingestion of water (WAT). METHODS Eight trained male cyclists (VO2max: 64±1 ml/kg/min) cycled on three different occasions for 120 min at 50% maximum power output (64±1 VO2max) at an ambient temperature of 31.9±0.1°C. Subjects received, in random order, a solution providing either 1.5 g/min of GLU, 1.0 g/min of GLU + 0.5 g/min of FRUC, or WAT. 2H2O was added to all drinks administered at t=60 min. A continuous infusion of [6,6–2H2]-glucose was performed in GLU and WAT. RESULTS Exogenous CHO oxidation rates during the last hour of exercise were ∼36% higher (P < 0.05) in GLU+FRUC compared with GLU and peak oxidation rates were 1.14±0.05 g/min and 0.77±0.08 g/min, respectively. Endogenous CHO oxidation was significantly lower (P < 0.05) in GLU+FRUC compared with WAT. No other differences were found in endogenous CHO oxidation rates between trials. Muscle glycogen oxidation was not different following ingestion of GLU or WAT. Plasma deuterium enrichments were significantly higher (P < 0.05) in WAT and GLU+FRUC compared with GLU. Furthermore, at 60 and 75 min of exercise, plasma deuterium enrichments were higher (P < 0.05) in WAT compared with GLU+FRUC. CONCLUSION Ingestion of GLU+FRUC during exercise in the heat resulted in higher exogenous CHO oxidation rates and fluid availability when compared with ingestion of GLU and reduced endogenous CHO oxidation when compared with ingestion of WAT. Supported by a grant of GlaxoSmithKline, Consumer Healthcare (UK)

High Oxidation Rates from a Mixture of Glucose, Sucrose and Fructose Ingested During Prolonged Exercise

0151 It has been demonstrated that oxidation of carbohydrate (CHO) ingested during cycling exercise does not exceed ∼1 g/min. Suggestions have been made that intestinal CHO absorption could be a potential factor limiting the rate of exogenous CHO oxidation. Sucrose and fructose are absorbed by intestinal transport mechanisms that are, at least in part, different from intestinal glucose transport which may become saturated at an ingestion rate of 1.2 g/min. Recent studies from our laboratory have shown that a mixture of glucose and sucrose or glucose and fructose when ingested at a high rate (1.8 g/min) leads to peak oxidation rates of ∼1.25 g/min and results in ∼20 to 50% higher exogenous CHO oxidation rates compared with the ingestion of an isoenergetic amount of glucose. Combined ingestion of glucose, sucrose and fructose at high rates might provide CHO for these different transport mechanisms and this might further increase the rate of exogenous CHO oxidation. PURPOSE: The purpose of the present study was to examine whether a mixture of glucose, sucrose and fructose when ingested at a high rate would lead to exogenous CHO oxidation rates higher than 1.25 g/min. METHODS: Eight trained male cyclists (VO2max: 64±1 ml/kg/min) cycled on three different occasions in random order and separated by at least one week. Each trial consisted of 150-min of cycling at 50% of maximal power output (62±1% VO2max) while subjects received a solution providing either 2.4 g/min of glucose (GLU) or 1.2 g/min of glucose + 0.6 g/min of fructose + 0.6 g/min of sucrose (MIX) or plain water (WAT). RESULTS: Peak exogenous CHO oxidation rates were ∼44% higher (P <0.01) in the MIX (1.70±0.07 g/min) compared with the GLU trial (1.18±0.04 g/min). Endogenous CHO oxidation was lower (P <0.05) in MIX compared with GLU (0.76±0.12 and 1.05 ±0.06 g/min, respectively). CONCLUSION: In conclusion, when glucose, fructose and sucrose are ingested simultaneously at high rates (2.4 g/min) during cycling exercise, exogenous CHO oxidation rates can reach peak values of ∼1.7 g/min and endogenous CHO oxidation is reduced compared with the ingestion of an isoenergetic amount of glucose. Supported by a grant of GlaxoSmithKline, Consumer Healthcare (UK)

HIGH OXIDATION RATES OF MULTIPLE TRANSPORTABLE CARBOHYDRATES DURING PROLONGED CYCLING EXERCISE

Studies that have investigated exogenous carbohydrate (CHO) oxidation during cycling exercise have reported peak oxidation rates of approximately 1 g/min. Suggestions have been made that intestinal CHO absorption is a limiting factor for exogenous CHO oxidation. Different CHOs use different intestinal transporters and hence ingestion of multiple transportable CHOs might increase the availability of CHO in the blood stream for oxidation. PURPOSE The purpose of the present study was to investigate whether combined ingestion of two CHOs that are absorbed by different intestinal transport mechanisms would lead to exogenous CHO oxidation rates higher than 1.0 g/min. METHODS Nine trained male cyclists (VO2max: 64±2 ml/kg/min) performed 4 exercise trials in random order and separated by at least one week. Each trial consisted of 150-min of cycling at 50% of maximal power output (60±1% VO2max) while subject received a solution providing either 1.8 g/min of glucose (GLU), 1.2 g/min of glucose + 0.6 g/min of sucrose (GLU+SUC), 1.2 g/min of glucose + 0.6 g/min of maltose (GLU+MAL) or water (WAT). RESULTS Peak exogenous CHO oxidation rates were significantly higher (P < 0.05) in the GLU+SUC trial (1.25±0.07 g/min) compared with the GLU and GLU+MAL trial (1.06±0.08 and 1.06±0.06 g/min, respectively). No difference was found in (peak) exogenous CHO oxidation rates between GLU and GLU+MAL. CONCLUSION When a mixture of glucose and sucrose is ingested at high rates (1.8 g/min) during cycling exercise, exogenous CHO oxidation rates reach peak values of ∼1.25 g/min. Furthermore, exogenous CHO oxidation rates are similar when a mixture of glucose and maltose is ingested compared with the ingestion of an isoenergetic amount of glucose. These findings support the hypothesis that exogenous CHO oxidation may be limited by the rate of intestinal CHO absorption. Supported by a grant of GlaxoSmithKline, Consumer Healthcare (UK)

Oxidation of carbohydrate feedings during prolonged exercise: current thoughts, guidelines and directions for future research.

Although it is known that carbohydrate (CHO) feedings during exercise improve endurance performance, the effects of different feeding strategies are less clear. Studies using (stable) isotope methodology have shown that not all carbohydrates are oxidised at similar rates and hence they may not be equally effective. Glucose, sucrose, maltose, maltodextrins and amylopectin are oxidised at high rates. Fructose, galactose and amylose have been shown to be oxidised at 25 to 50% lower rates. Combinations of multiple transportable CHO may increase the total CHO absorption and total exogenous CHO oxidation. Increasing the CHO intake up to 1.0 to 1.5 g/min will increase the oxidation up to about 1.0 to 1.1 g/min. However, a further increase of the intake will not further increase the oxidation rates. Training status does not affect exogenous CHO oxidation. The effects of fasting and muscle glycogen depletion are less clear. The most remarkable conclusion is probably that exogenous CHO oxidation rates do not exceed 1.0 to 1.1 g/min. There is convincing evidence that this limitation is not at the muscular level but most likely located in the intestine or the liver. Intestinal perfusion studies seem to suggest that the capacity to absorb glucose is only slightly in excess of the observed entrance of glucose into the blood and the rate of absorption may thus be a factor contributing to the limitation. However, the liver may play an additional important role, in that it provides glucose to the bloodstream at a rate of about 1 g/min by balancing the glucose from the gut and from glycogenolysis/gluconeogenesis. It is possible that when large amounts of glucose are ingested absorption is a limiting factor, and the liver will retain some glucose and thus act as a second limiting factor to exogenous CHO oxidation.

Effects of solution osmolality on absorption of select fluid replacement solutions in human duodenojejunum

These experiments examined relationships between initial osmolality and carbohydrate (CHO) composition of an infused solution and osmolality and water and CHO absorption in a test segment. A triple-lumen tube with a 10-cm mixing segment and a 40-cm test segment was passed into the duodenojejunum. The infusion port was approximately 10 cm beyond the pyloric sphincter. Perfusion solutions were hypotonic (186 mosmol/kg; solution A), isotonic (283 mosmol/kg; solution B), and hypertonic (403 mosmol/kg; solution C). All solutions contained 18 meq Na+ and 3 meq K+. In the mixing segment, osmolality increased 83 mosmol/kg and decreased 90 mosmol/kg for solutions A and C, respectively. Corresponding changes in the test segment were an increase of 60 mosmol/kg and a decrease of 34 mosmol/kg. The osmolality of solution B did not change. In the test segment, mean osmolality and water and total solute fluxes were not significantly different among solutions, but solution C produced 27% greater fluid absorption than did solution A. When net fluid movement from mixing and test segments was determined, solution A produced 17% greater fluid absorption than did solution C. The mean increases in plasma and urine volumes over the 80-min test period were not significantly different. In the test segment, water flux correlated with CHO and Na+ fluxes but not with osmolality. In conclusion, 1) significant differences in solution osmolality were eliminated within the proximal duodenum and 2) perfusing 6% CHO solutions with osmolalities ranging from 186 to 403 mosmol/kg did not produce significant differences in fluid homeostasis (plasma volume) at the end of an 80-min test period.

680 MIXING CARBOHYDRATES(CHO) - ADDITIVE AND COMPETITIVE EFFECTS ON ABSORPTION

When intestinal absorptive function is limited, it may be possible to enhance CHO absorption by combining CHOs having different digestive-absorptive pathways. Employing single pass perfusion studies in partially atrophic amylase-free canine jejunal Thiry-Vella fistulae we found that absorption of glucose(G), sucrose(S), and long chain glucose polymers (LCGP) was saturable with infusion conc. of 882, 378, and 347 mg/dl respectively. Absorption of S and LCGP was additive even from solutions containing 900 mg/dl of each sugar (S=159±16, LCGP=70±6, mixture=235±22 μgms/cm/min.). Virtually no G was found in the fistula effluents (<0.1 mg/ml). Adding 900 mg S to 900 mg LCGO did not improve CHO absorption beyond values for 900 mg/dl of G infused alone (378±16 μgms/cm/min.). Addition of the Vmax conc. (400 mg/dl) of LCGP to the Vmax conc. of G (900 mg/dl) causes mutual inhibition of the absorption of both (G, 346±23 vs. 232±25; LCGP, 63±8 vs. 28; p<.001). Additive absorption occurs with addition of 400 mg/dl LCGP to 500 mg/dl of G (LCGP=56±8, G=152±8, mixture=208±10). Conclusions: 1)For G polymers and S, hydrolysis, not absorption of the resultant monosaccharides, is rate limiting for jejunal assimilation. 2)G and LCGP either interact in the glycocalyx or compete for absorptive pathways. 3)S does not compete with LCGP for absorption. Speculation: In formulating enteral feedings or rehydration solutions mixtures of S and LCGP may enhance absorption, but addition of LCGP to G may be deleterious.

Breath Hydrogen Analysis

Summary:Hydrogen gas (H2) is a product of the fermentation of dietary carbohydrate (CHO) by bacteria in the lumen of the gastrointestinal tract in man. Thus, H2 is actually an exogenously produced gas, which either is passed as flatus, or diffuses into the body and is exhaled. In the adult, a fairly constant fraction is expired, providing a reliable indicator of total colonic H2 production. Breath H2 analysis currently represents a useful clinical means of testing adults and older children for the malabsorption of CHO. Noninvasive and easy procedures for the collection of expired air have encouraged their increasingly widespread use in pediatrics. Evidence to date suggests that breath H2 analysis may provide the best available method for estimating semiquantitatively the degree of CHO malabsorption. The association of the results of breath H2 analysis with other clinical measures of CHO digestion and absorption is expected, but discrepancies can also be anticipated based on the nature of this particular trace gas method. The interpretation of the results of breath H2 analysis in neonates and young infants remains especially problematic because of confounding variables which are difficult to control and are measured infrequently.

Breath Hydrogen Analysis

Hydrogen gas (H2) is a product of the fermentation of dietary carbohydrate (CHO) by bacteria in the lumen of the gastrointestinal tract in man. Thus, H2 is actually an exogenously produced gas, which either is passed as flatus, or diffuses into the body and is exhaled. In the adult, a fairly constant fraction is expired, providing a reliable indicator of total colonic H2 production. Breath H2 analysis currently represents a useful clinical means of testing adults and older children for the malabsorption of CHO. Noninvasive and easy procedures for the collection of expired air have encouraged their increasingly widespread use in pediatrics. Evidence to date suggests that breath H2 analysis may provide the best available method for estimating semiquantitatively the degree of CHO malabsorption. The association of the results of breath H2 analysis with other clinical measures of CHO digestion and absorption is expected, but discrepancies can also be anticipated based on the nature of this particular trace gas method. The interpretation of the results of breath H2 analysis in neonates and young infants remains especially problematic because of confounding variables which are difficult to control and are measured infrequently.