Paolo C. Colombani

Carbohydrate to protein ratio in food and cognitive performance in the morning.

The effect of different carbohydrate to protein ratios in food on cognitive functions and the relation between postprandial metabolic and cognitive changes were studied in 15 healthy male students. Subjects were tested in three sessions, separated by 1 week, for short-term changes in mood states, objective cognitive functions, blood parameters, and indirect calorimetry using a repeated-measures, counterbalanced cross-over design. Measurements were made after an overnight fast before and hourly during 3.5 h after test meal ingestion. The isoenergetic (1670 kJ) test meals consisted of three carbohydrate to protein ratios, i.e. a carbohydrate-rich (CHO[4:1]), balanced (BAL[1:1]), and protein-rich (PRO[1:4]) meal, respectively. Overall accuracy in short-term memory was best after the PRO[1:4] meal concomitant to the least variation in glucose metabolism and glucagon to insulin ratio (GIR). Related to changes in glucose metabolism and/or in the ratios of large neutral amino acids (LNAA), respectively, attention and decision times were transiently improved within the first hour after the CHO[4:1] meal, whereas after the first hour the BAL[1:1] and PRO[1:4] meal resulted in improved performance. Overall reaction times of a central task were fastest after the BAL[1:1] meal concomitant to the highest overall tyrosine (Tyr) to LNAA ratio. Our findings suggest that the carbohydrate to protein ratio in food specifically influences higher cognitive functions in the morning. Except for a transient positive effect of rising blood glucose after a carbohydrate-rich meal, a protein-rich or balanced meal seems to result in better overall cognitive performance presumably because of less variation in glucose metabolism and/or higher modulation in LNAA ratios indicated by the overall GIR.

Cognitive performance and its relationship with postprandial metabolic changes after ingestion of different macronutrients in the morning.

The effect of carbohydrate, protein and fat ingestion on simple as well as complex cognitive functions and the relationship between the respective postprandial metabolic changes and changes in cognitive performance were studied in fifteen healthy male students. Subjects were tested in three sessions, separated by 1 week, for short-term changes in blood variables, indirect calorimetry, subjective performance and different objective performance tasks using a repeated-measures counterbalanced cross-over design. Measurements were made after an overnight fast before and hourly during 3 h after test meal ingestion. Test meals consisted of either pure carbohydrates, protein or fat and were served as isoenergetic (1670 kJ) spoonable creams with similar sensory properties. Most aspects of subjective performance did not differ between test meals. For all objective tasks, however, postprandial cognitive performance was best after fat ingestion concomitant with an almost constant glucose metabolism and constant metabolic activation state measured by glucagon:insulin (G:I). In contrast, carbohydrate as well as protein ingestion resulted in lower overall cognitive performance, both together with partly marked changes in glucose metabolism and metabolic activation. They also differently affected specific cognitive functions in relation to their specific effect on metabolism. Carbohydrate ingestion resulted in relatively better short-term memory and accuracy of tasks concomitant with low metabolic activation, whereas protein ingestion resulted in better attention and efficiency of tasks concomitant with higher metabolic activation. Our findings support the concept that good and stable cognitive performance is related to a balanced glucose metabolism and metabolic activation state.

Effects of L-carnitine supplementation on physical performance and energy metabolism of endurance-trained athletes: a double-blind crossover field study.

A double-blind crossover field study was performed to investigate the effects of acute L-carnitine supplementation on metabolism and performance of endurance-trained athletes during and after a marathon run. Seven male subjects were given supplements of 2 g L-carnitine 2 h before the start of a marathon run and again after 20 km of the run. The plasma concentration of metabolites and hormones was analysed 1 h before, immediately after and 1 h after the run, as well as the next morning after the run. In addition, the respiratory exchange ratio (R) was determined before and at the end of the run, and a submaximal performance test was completed on a treadmill the morning after the run. The administration of L-carnitine was associated with a significant increase in the plasma concentration of all analysed carnitine fractions (i.e. free carnitine, short-chain acylcarnitine, long-chain acylcarnitine, total acid soluble carnitine, total carnitine) but caused no significant change in marathon running time, in R, in the plasma concentrations of carbohydrate metabolites (glucose, lactate, pyruvate), of fat metabolites (free fatty acids, glycerol, β-hydroxybutyrate), of hormones (insulin, glucagon, cortisol), and of enzyme activities (creatine kinase, lactate dehydrogenase). Moreover, there was no difference in the result of the submaximal performance test the morning after the run. In conclusion, acute administration of L-carnitine did not affect the metabolism or improve the physical performance of the endurance-trained athletes during the run and did not alter their recovery.

Hyponatremia among runners in the Zurich Marathon.

Objective:Hyperhydration and exercise-associated hyponatremia (EAH) are critical issues during endurance events. We studied a cohort of marathon runners to examine EAHs prevalence in a marathon with a short time limit and to investigate underlying mechanisms that may be responsible for its development. Design:Observational cohort study. Setting:2006 Zurich Marathon (cool and rainy weather, time limit of 5 hours). Participants:167 marathon runners were recruited the month before the race. Main Outcome Measures:Body mass, plasma sodium, and osmolality were measured just before the start and immediately after the race. Fluid intake during the race was ascertained by a recall questionnaire. Results:Five subjects (3 %) developed asymptomatic EAH, and no symptomatic EAH was found. Body mass change during the race correlated similarly with postrace sodium levels (r = −0.72, P < 0.0001) and with sodium change during the race (r = −0.66, P < 0.0001). Postrace sodium levels correlated significantly with sodium change during the race (r = 0.74, P < 0.0001). Fluid intake correlated significantly (r = −0.43, P < 0.0001) with plasma sodium change between the start and finish of the race. Postrace sodium levels and postrace osmolality were significantly correlated (r = 0.68, P < 0.0001). Conclusion:In this study we observed a relatively low incidence of EAH in subjects running the marathon in around 2.5 to 5 hours and in a cool environment. Plasma sodium change during the race and postrace sodium levels correlated with body mass change. There was also a direct correlation between fluid intake and plasma sodium change during the race.

Glycemic index and load—dynamic dietary guidelines in the context of diseases

The concepts of glycemic index (GI) and glycemic load (GL) are among a new generation of so-called dynamic dietary guidelines. In contrast to classical static guidelines, these new guidelines do not primarily consider the absolute amount of energy or nutrient to be ingested within 24 h, but rather are focused on the postprandial response. It is claimed that low-GI and -GL diets favorably affect many noncommunicable diseases that are prevalent in developed countries, including type II diabetes, insulin resistance, obesity, cardiovascular disease (CVD), and cancer. During the past 20 years, considerable evidence has accumulated suggesting that low-GI or -GL diets indeed positively influence some but not all diseases. Because virtually no deleterious effects of low-GI and -GL diets have been documented thus far or are to be expected, the promotion of these diets should be considered in the management of noncommunicable diseases.

Effects of 3-week consumption of green tea extracts on whole-body metabolism during cycling exercise in endurance-trained men.

The consumption of green tea has been generally associated with beneficial effects on human whole-body metabolism and recent investigations with animals indicate favorable effects of green tea extracts (GTE) on energy metabolism during exercise and aerobic exercise performance. Therefore, the purpose of this study was to examine the effects of a three-week supplementation with GTE on human energy metabolism during submaximal cycling exercise. In a randomized, double-blind crossover setting, ten healthy endurance-trained men exercised for 2 hours at 50 % W(max) before and after three weeks of placebo or GTE supplementation (GTE containing about 160 mg x day(-1) total catechins, of which about 70 mg x day(-1) was epigallocatechin-3-gallate). The GTE supplementation did not influence indices of fat and energy metabolism (fatty acids, 3-beta-hydroxybutyrate, triacylglycerol, low-density-lipoprotein cholesterol, total cholesterol, lactate, glucose, oxygen uptake, respiratory exchange ratio, energy expenditure), inflammation processes (interleukin-6, C-reactive protein), and oxidative stress (thiobarbituric-acid reactive substances, oxidized low-density-lipoprotein cholesterol), but plasma creatine kinase concentration at rest and during exercise was significantly lower (p = 0.039) and high-density-lipoprotein cholesterol concentration at rest was significantly higher (p = 0.043) compared to placebo. In conclusion, these results suggest only slight effects on whole-body metabolism after supplementation with GTE.

The influence of walking performed immediately before meals with moderate fat content on postprandial lipemia

BackgroundPostprandial lipemia is an independent risk factor for coronary heart disease. Single bouts of moderate exercise may lower this risk, but the minimum duration of moderate intensity exercise that still lowers postprandial lipemia is not known. We, therefore, performed a dose-response study with a normal, daily life setting, to identify the minimum duration of moderate intensity walking that lowers postprandial lipemia in sedentary, healthy young men.MethodsSixteen men performed three activity trials (30, 60, or 90 min of treadmill walking at 50% of their individual VO2max) and a control trial with no physical activity in a repeated measures crossover design. The subjects walked immediately before ingestion of the first of two mixed meals, which were served 3 h apart. The meals had a moderate fat content (0.5 g per kg body mass and 33% of total energy per meal) and a macronutrient composition corresponding to current recommendations. Each meal provided one third of the subjects estimated daily energy requirement. Venous blood samples were taken in the fasted state, and then hourly for 6 h after the first meal to assess the postprandial phase. Postprandial lipemia (the incremental area under the curve (dAUC) of triacylglycerol) was compared with a mixed model analysis and Tukeys adjustment.ResultsPostprandial lipemia (dAUC of triacylglycerol) was, compared to the control trial, +2% (P = 1.00), -14% (P = 0.24), and -15% (P = 0.23) in the 30, 60, and 90 min walking trials, respectively.ConclusionModerate intensity walking of 60 and 90 min duration slightly, but insignificantly, reduced postprandial lipemia after two mixed meals with moderate fat content in sedentary, healthy young men, compared to inactivity. Therefore, it should be reconsidered if the acute exercise-induced reduction in postprandial lipemia usually observed in studies using high fat meals is of importance in a real, daily life setting.

No Effects of Three-week Consumption of a Green Tea Extract on Time Trial Performance in Endurance-trained Men

The purpose of this study was to examine the effects of three-week consumption of green tea extract (GTE) supplementation on time trial performance and metabolism during cycling in endurance athletes. Nine endurance-trained men participated in this double-blind and placebo-controlled cross-over study. At the end of the supplementation period with GTE (159 mg/day total catechins) or placebo, respectively, subjects cycled at 50 % of the individual maximal power output for 2 hours, followed by a 30-minute time trial. Respiratory gas exchange, fatty acids, 3-beta-hydroxybutyrate, lactate, glucose, interleukin-6, thiobarbituric acid reactive substances, creatine kinase, and C-reactive protein (CRP) were measured 1 hour before, during, and 1 hour after the exercise test. Blood lipids were measured at rest before cycling. There was no significant effect on performance, energy metabolism, or any other measured parameter, except for CRP, which was significantly reduced (p = 0.045) after GTE supplementation compared to placebo. GTE supplementation did not affect time trial performance and energy metabolism in endurance-trained men in the non-fasting state. Further studies with athletes, particularly in the fed state, but with higher GTE doses, are needed to address the question whether green tea may influence energy metabolism and performance in athletes.

Additive postprandial blood glucose-attenuating and satiety-enhancing effect of cinnamon and acetic acid.

Cinnamon and vinegar or acetic acid were reported to reduce the postprandial blood glucose response. We hypothesized that the combination of these substances might result in an additive effect. Therefore, we determined the 2-hour postprandial blood glucose and satiety response to a milk rice meal supplemented with either cinnamon or acetic acid on their own or in combination. Subjects (n = 27) consumed the meal on 4 occasions as either pure (control trial), with 4 g cinnamon, 28 mmol acetic acid, or the combination of cinnamon + acetic acid. Blood glucose and satiety were assessed before eating and 15, 30, 45, 60, 90, and 120 minutes postprandially. At 15 minutes, the combination of cinnamon + acetic acid resulted in a significantly reduced blood glucose concentration compared with the control meal (P = .021). The incremental area under the blood glucose response curve over 120 minutes did, however, not differ between the trials (P = .539). The satiety score of the cinnamon + acetic acid trial was significantly higher than that in the control trial at 15 (P = .024) and 30 minutes (P = .024), but the incremental area under the curve of the satiety response did not differ (P = .116) between the trials. In conclusion, the significant effect of the combination of cinnamon and acetic acid on blood glucose and satiety immediately after meal intake indicated an additive effect of the 2 substances. Whether larger doses of cinnamon and acetic acid may result in a more substantial additive effect on blood glucose or satiety remains to be investigated.

Effects of acute chromium supplementation on postprandial metabolism in healthy young men.

Background: Chromium (Cr) potentiates the action of insulin in the cell and improves glucose tolerance after long-term supplementation. Objective: We hypothesized that Cr may also have acute effects and might be beneficial in lowering the glycemic index of a meal. Methods: We studied the effects of short-term Cr supplementation using a randomized crossover design. Thirteen apparently healthy, non-smoking young men of normal body mass index performed three trials each separated by one week. Test meals, providing 75 g of available carbohydrates, consisted of white bread with added Cr (400 or 800 μg as Cr picolinate) or placebo. Results: After addition of 400 and 800 μg Cr incremental area under the curve (AUC) for capillary glucose was 23% (p = 0.053) and 20% (p = 0.054), respectively, lower than after the white bread meal. These differences reached significance if the subjects were divided into responders (n = 10) and non-responders (n = 3). For the responders AUC after 400 and 800 μg Cr was reduced by 36% and 30%, respectively (Placebo 175 ± 22, Cr400 111 ± 14 (p < 0.01), Cr800 122 ± 15 mmol · min/L (p < 0.01)). Glycemia was unchanged after addition of Cr in the non-responders. Responders and non-responders differed significantly in their nutrient intake and eating pattern, and total serum iron concentration tended to be lower in the responder group (p = 0.07). Conclusions: Acute chromium supplementation showed an effect on postprandial glucose metabolism in most but not all subjects. The response to Cr may be influenced by dietary patterns.