Miriam E. Clegg

Exercise and postprandial lipaemia: effects on peripheral vascular function, oxidative stress and gastrointestinal transit

Postprandial lipaemia may lead to an increase in oxidative stress, inducing endothelial dysfunction. Exercise can slow gastric emptying rates, moderating postprandial lipaemia. The purpose of this study was to determine if moderate exercise, prior to fat ingestion, influences gastrointestinal transit, lipaemia, oxidative stress and arterial wall function. Eight apparently healthy males (age 23.6 ± 2.8 yrs; height 181.4 ± 8.1 cm; weight 83.4 ± 16.2 kg; all data mean ± SD) participated in the randomised, crossover design, where (i) subjects ingested a high-fat meal alone (control), and (ii) ingested a high-fat meal, preceded by 1 h of moderate exercise. Pulse Wave Velocity (PWV) was examined at baseline, post-exercise, and in the postprandial period. Gastric emptying was measured using the 13C-octanoic acid breath test. Measures of venous blood were obtained prior to and following exercise and at 2, 4 and 6 hours post-ingestion. PWV increased (6.5 ± 1.9 m/sec) at 2 (8.9 ± 1.7 m/sec) and 4 hrs (9.0 ± 1.6 m/sec) post-ingestion in the control group (time × group interaction, P < 0.05). PWV was increased at 2 hrs post-ingestion in the control compared to the exercise trial; 8.9 ± 1.7 vs. 6.2 ± 1.5 m/sec (time × group interaction, P < 0.05). Lipid hydroperoxides increased over time (pooled exercise and control data, P < 0.05). Serum triacylglycerols were elevated postprandially (pooled exercise and control data, P < 0.05). There were no changes in gastric emptying, cholesterol, or C-reactive protein levels. These data suggest that acute exercise prior to the consumption of a high-fat meal has the potential to reduce vascular impairments.

Energy and macronutrient composition of breakfast affect gastric emptying of lunch and subsequent food intake, satiety and satiation.

Satiety and food intake are closely related to gastrointestinal transit and specifically gastric emptying. High-fat (HF) meals empty more slowly from the stomach yet are less satiating than isoenergetic low-fat (LF) meals. The current study examines how gastric emptying and satiety at lunch are affected by energy and macronutrient content of breakfast. Nine male volunteers consumed either (1) a HF breakfast, (2) a LF breakfast isoenergetic to HF (LFE) or (3) a LF breakfast of equal mass to HF (LFM). Gastric emptying half time measured using the sodium [(13)C] acetate breath test was delayed after HF compared to LF meals (HF: 102 + or - 11, LFE: 96 + or - 13, LFM: 95 + or - 13 min, mean + or - SD). Fullness increased and desire to eat decreased following the LFE breakfast measured using visual analogue scales. Eating a HF breakfast increased the energy, fat and protein from an ad libitum buffet meal given 4h after lunch. In conclusion, eating a HF breakfast delayed gastric emptying of lunch and increased food intake 7 h later compared to a LFM breakfast. These data suggest both mass and energy content of food regulate subsequent appetite and feeding and demonstrate the hyperphagic effect of a single HF meal.

Medium-chain triglycerides are advantageous in promoting weight loss although not beneficial to exercise performance

Medium-chain triglycerides (MCT) are triglycerides with a fatty acid chain length varying between 6 and 10 carbon atoms. MCT differ from long-chain triglycerides as they are relatively soluble in water and, hence, rapidly hydrolysed and absorbed. MCT are transported in the blood through the portal system, consequently they bypass adipose tissue that makes them less susceptible to hormone-sensitive lipase and deposition into adipose tissue stores. Due to these properties, MCT have been researched for both benefits to exercise performance and health. The present review aims to assess whether MCT are beneficial in either of these situations. MCT have been proposed as a means to maximizing an athletes ability to maintain their glycogen stores so they can be more competitive. However, only two studies to date have shown an improvement in exercise performance. From a health perspective, MCT increase fat oxidation and energy expenditure as well as reduce food intake and beneficially alter body composition. Results indicate that MCT feeding is ineffective in improving exercise performance and future work should focus on the health benefits and applications of MCT.

Adaptation of exercise ventilation during an actively-induced hyperthermia following passive heat acclimation

Hyperthermia-induced hyperventilation has been proposed to be a human thermolytic thermoregulatory response and to contribute to the disproportionate increase in exercise ventilation (VE) relative to metabolic needs during high-intensity exercise. In this study it was hypothesized that VE would adapt similar to human eccrine sweating (E(SW)) following a passive heat acclimation (HA). All participants performed an incremental exercise test on a cycle ergometer from rest to exhaustion before and after a 10-day passive exposure for 2 h/day to either 50 degrees C and 20% relative humidity (RH) (n = 8, Acclimation group) or 24 degrees C and 32% RH (n = 4, Control group). Attainment of HA was confirmed by a significant decrease (P = 0.025) of the esophageal temperature (T(es)) threshold for the onset of E(SW) and a significantly elevated E(SW) (P < or = 0.040) during the post-HA exercise tests. HA also gave a significant decrease in resting T(es) (P = 0.006) and a significant increase in plasma volume (P = 0.005). Ventilatory adaptations during exercise tests following HA included significantly decreased T(es) thresholds (P < or = 0.005) for the onset of increases in the ventilatory equivalents for O(2) (VE/VO(2)) and CO(2) (VE/VCO(2)) and a significantly increased VE (P < or = 0.017) at all levels of T(es). Elevated VE was a function of a significantly greater tidal volume (P = 0.003) at lower T(es) and of breathing frequency (P < or = 0.005) at higher T(es). Following HA, the ventilatory threshold was uninfluenced and the relationships between VO(2) and either VE/VO(2) or VE/VCO(2) did not explain the resulting hyperventilation. In conclusion, the results support that exercise VE following passive HA responds similarly to E(SW), and the mechanism accounting for this adaptation is independent of changes of the ventilatory threshold or relationships between VO(2) with each of VE/VO(2) and VE/VCO(2).

The addition of raspberries and blueberries to a starch-based food does not alter the glycaemic response

It is now known that health benefits associated with diets rich in fruit and vegetables may be partly derived from intake of polyphenols. Berry polyphenols may influence carbohydrate metabolism and absorption and hence postprandial glycaemia. To date, studies related to polyphenol effects on the glycaemic response have been completed only in liquids using either monosaccharides or disaccharides. It remains to be determined whether berries known to be rich in polyphenols can reduce the glycaemic response (GR) to a solid polysaccharide meal. The aim of the present study was to investigate whether berries alter postprandial hyperglycaemia and consequently the GR to a starchy food. Blood glucose was tested on seven occasions, on three occasions using a reference food and on four occasions using pancakes supplemented with either raspberries or blueberries or control pancakes containing similar amounts of fructose and glucose. Results showed that there were no differences in GR (blueberry 51·3 (SEM 5·7); raspberry 54·7 (SEM 5·6); blueberry control 43·9 (SEM 4·2); raspberry control 41·8 (SEM 6·4)), GR area under the curve or satiety index between any of the tests. The present study indicates that the ability of berries to reduce blood glucose from starch-based foods is unsubstantiated.

Postmastication digestion factors influence glycemic variability in humans.

The glycemic response (GR) to food is influenced by both intrinsic and extrinsic factors. A consistent observation in GR studies is the wide within- and between-individual variations. The authors hypothesize that between-individual variations in the GR, insulin response (IR) and gastric emptying occur even when food particle size is standardized. Volunteers were tested on 2 nonconsecutive days after an overnight fast in randomized order. On 1 day, the volunteers consumed large (>2000 μm) rice particles, and on the second day, small rice particles (500-1000 μm). Subsequently, gastric emptying using the sodium [(13)C] acetate breath test (for 240 minutes) and GR and IR (for 120 minutes) from finger-prick blood samples were measured. The incremental area under the curve (IAUC) for the GR for small particles varied 45% more compared with whole rice. The small particles elicited a significantly greater GR IAUC than the large particles. The standard deviations associated with the IR IAUC for the small particles was 140% greater than that of the large particles. The total IAUC for IR was also significantly greater for the small particles than the large particles. The between-individual variations associated with gastric emptying times were similar for both samples. The gastric emptying latency phase, lag, and half time were significantly shorter for the small particles. Ingesting small particles causes faster gastric emptying and produces greater glycemic and IRs. Between-individual variations in GR and IR can be observed even when all the food associated factors including ingested particle size (mastication) are controlled for in humans.

Gastrointestinal transit, post-prandial lipaemia and satiety following 3 days high-fat diet in men

Background/Objectives:High-fat (HF) diets of 2 weeks have been shown to accelerate gastric emptying (GE). To date, no studies have shown any alteration in GE following shorter HF diets. The aim of this study was to assess if an HF, high-energy diet of 3 days can adapt gastrointestinal (GI) transit, blood lipids and satiety.Subjects/Methods:Eleven male volunteers participated in a study consisting of three, 3-day interventions each separated by a test day. During the first intervention, volunteers recorded their diet. In the second and third interventions, volunteers repeated their food diary plus either a low-fat yogurt or HF yogurt supplement in randomized order. Test days involved measurement of GE using the 13C octanoic-acid breath-test, mouth-to-caecum transit time (MCTT) using the inulin H2 breath test and satiety using visual analogue scales. Blood samples for measurement of lipaemia were taken using a venous cannula.Results:MCTT was different between the three test days (P=0.038), with the shortest MCTT following the HF intervention. GE was shortest following the HF intervention. There were no differences in satiety between the interventions. The HF intervention reduced triglycerides, total cholesterol and low-density lipoprotein cholesterol, and increased high-density lipoprotein cholesterol.Conclusion:This study shows that changes in GI transit owing to an HF diet can occur in a time period as short as 3 days.

The polyphenol-rich baobab fruit (Adansonia digitata L.) reduces starch digestion and glycemic response in humans

The baobab fruit (Adansonia digitata L.) is found throughout regions of Africa and is becoming increasingly recognized for its high nutrient and polyphenol content. Polyphenols have been beneficial for their effects on reducing the glycemic response (GR) and for improving various other metabolic parameters. Based on previous research, it was hypothesized that the baobab fruit extract would reduce starch digestion in vitro and would show potential for reducing the GR and for increasing satiety and diet-induced thermogenesis in humans. Six extracts of baobab from 6 different locations in Africa were measured for their antioxidant and polyphenol content using the ferric ion-reducing antioxidant power and the Folin-Ciocalteu methods, respectively. Baobab extract was baked into white bread at different doses to determine the optimal dose for reducing starch breakdown and sugar release from white bread after an in vitro digestion procedure. In vivo, baobab extract was consumed in solution at both a low-dose (18.5 g) and a high-dose (37 g) aqueous drink in 250 mL of water along with white bread, and resulting GR, satiety, and postprandial energy expenditure were measured. All extracts in this study were shown to be good sources of polyphenols. Baobab fruit extract added to white bread at 1.88 % significantly (P < .05) reduced rapidly digestible starch from white bread samples. In vivo, the baobab fruit extract at both low and high doses significantly (P < .05) reduced GR, although there was no significant effect on satiety or on energy expenditure.

Molecular weight of barley β-glucan influences energy expenditure, gastric emptying and glycaemic response in human subjects

Barley β-glucan (BG) has been shown to reduce glycaemic response (GR) in some studies. It is hypothesised that this reduction may be a function of its physical properties that delay gastric emptying (GE). The effect of these changes in GR and GE on diet-induced thermogenesis (DIT) is not known. The aim of the present study was to assess the effect of BG of different molecular weights and purities on GR, GE and DIT in healthy subjects. This was a randomised, single-blind, repeated-measures design where fifteen healthy subjects were tested on three occasions following an overnight fast. Following the baseline measurements, the volunteers were fed a soup containing high-molecular-weight BG (HBG), a soup containing low-molecular-weight BG (LBG) or a control soup with no BG (CHO). Following the consumption of the breakfast, GR was measured using finger-prick blood samples, GE was determined using the 13C-octanoic acid breath test and DIT was measured using indirect calorimetry. There was a difference in GR AUC between the soups after 60 min but not after 120 min. The CHO and LBG meals had a greater GR than the HBG meal. There were differences in all GE time points, with the HBG meal having the slowest GE time. There was a correlation between the GR and the initial GE times. There were differences in total DIT between the three test meals with the HBG meal having the lowest DIT. The present study indicates that HBG has the ability to delay GE due to increased viscosity, resulting in a decreased GR and DIT.

Soups increase satiety through delayed gastric emptying yet increased glycaemic response.

Background/Objectives:Previous studies have demonstrated the satiating properties of soups compared with solids; however, the mechanisms controlling soup-induced satiety are unknown. This study aimed to understand the physiological mechanisms causing soup to be more satiating.Subjects/Methods:A total of 12 volunteers were tested on three occasions after a solid meal, chunky soup or smooth soup test meal for gastric emptying (GE) using the sodium [1-13C] acetate breath test, satiety using visual analog scales (VAS) and glycaemic response (GR) using finger prick blood samples.Results:There was a significant difference in GE half-time (P=0.022) and GE ascension time (P=0.018), with the longest GE times for the smooth soup and the shortest for the solid meal. The GR area under the curve was significantly different between meals (P=0.040). The smooth soup had the greatest GR (87.0±49.5 mmol/l/min), followed by the chunky soup (65.4±48.0 mmol/l/min), with the solid meal having the lowest GR (61.6±36.8 mmol/l/min). Volunteers were fuller after the smooth soup compared with solid meal (P=0.034).Conclusions:The smooth soup induced greater fullness compared with the solid meal because of a combination of delayed GE leading to feelings of gastric distension and rapid accessibility of nutrients causing a greater glycaemic response.