GI transit and absorption of solid food: multiple effects of guar

Fatty Acid Profiles of Serum Lipid Fractions Change Minimally in Sled Dogs Before and After Short Bouts of Exercise

Although emerging data suggests a greater influence of gluconeogenic precursors, endurance sled dogs have long appeared to rely heavily on fatty acid oxidation for sustained energy production. However, much of the research investigating lipid utilization during exercise in sled dogs has been carried out with dogs subjected to extended bouts of endurance exercise. Less is known about changes in fatty acid composition in endurance training sled dogs subjected to short bouts of exercise, and fewer data define how fatty acid composition may change in distinct lipid fractions. As such, the study objective was to assess whether short bouts of submaximal exercise would affect fatty acid profiles of serum lipid fractions in endurance training sled dogs. Fifteen privately-owned Siberian huskies were used (8 females: 4 intact, 4 spayed; 7 males: 2 intact, 5 neutered), with an average age of 4.6 ± 2.5 years and body weight of 24.8 ± 4.2 kg. Throughout the diet acclimation and remainder of the study, all dogs were fed a dry extruded diet that met or exceeded all AAFCO nutrient recommendations. Dogs were weighed weekly and fed to maintain baseline body weight. A 12-week exercise regimen was designed to incorporate weekly increases in running distance, but weather played a role in setting the daily distance. On weeks 2, 5, and 11, an exercise challenge was implemented whereby dogs would run 4 km at 15 km/h in teams of 4. Pre- and post-exercise blood samples were taken, and gas chromatography was used to evaluate fatty acid profiles of all identified serum lipid fractions (cholesterol ester, diacylglycerol, free fatty acid, phospholipids, triglyceride). Data were analyzed using PROC MIXED of SAS, with dog as a random effect and week and sampling time point as fixed effects. Composition of oleic (18:1n9), linoleic (18:2n6), and alpha-linolenic (18:3n3) acids in the free fatty acid fraction decreased by ~9, 10, and 60%, respectively, following exercise (P ≤ 0.05). The results presented herein suggest that aside from a degree of depletion of these 18-carbon unsaturated fatty acids, short bouts of submaximal exercise do not induce considerable changes to sled dog fatty acid profiles.

Measurement of fasted state gastric antral motility before and after a standard bioavailability and bioequivalence 240 mL drink of water: Validation of MRI method against concomitant perfused manometry in healthy participants

Objective

The gastrointestinal environment in which drug products need to disintegrate before the drug can dissolve and be absorbed has not been studied in detail due to limitations, especially invasiveness of existing techniques. Minimal in vivo data is available on undisturbed gastrointestinal motility to improve relevance of predictive dissolution models and in silico tools such as physiologically-based pharmacokinetic models. Recent advances in magnetic resonance imaging methods could provide novel data and insights that can be used as a reference to validate and, if necessary, optimize these models. The conventional method for measuring gastrointestinal motility is via a manometric technique involving intubation. Nevertheless, it is feasible to measure gastrointestinal motility with magnetic resonance imaging. The aim of this study was is to develop and validate a magnetic resonance imaging method using the most recent semi-automated analysis method against concomitant perfused manometry method.

Material and methods

Eighteen healthy fasted participants were recruited for this study. The participants were intubated with a water-perfused manometry catheter. Subsequently, stomach motility was assessed by cine-MRI acquired at intervals, of 3.5min sets, at coronal oblique planes through the abdomen and by simultaneous water perfused manometry, before and after administration of a standard bioavailability / bioequivalence 8 ounces (~240mL) drink of water. The magnetic resonance imaging motility images were analysed using Spatio-Temporal Motility analysis STMM techniques. The area under the curve of the gastric motility contractions was calculated for each set and compared between techniques. The study visit was then repeated one week later.

Results

Data from 15 participants was analysed. There was a good correlation between the MRI antral motility plots area under the curve and corresponding perfused manometry motility area under the curve (r = 0.860) during both antral contractions and quiescence.

Conclusion

Non-invasive dynamic magnetic resonance imaging of gastric antral motility coupled with recently developed, semi-automated magnetic resonance imaging data processing techniques correlated well with simultaneous, ‘gold standard’ water perfused manometry. This will be particularly helpful for research purposes related to oral absorption where the absorption of a drug is highly depending on the underlying gastrointestinal processes such as gastric emptying, gastrointestinal motility and availability of residual fluid volumes.

Clinical trial

This trial was registered at ClinicalTrials.gov as NCT03191045.

Rheological characterization of an in vitro model for salmonid chyme to quantify changes in feed composition

BACKGROUND

Developments in the production of aquacultural salmonid feeds in the last 20 years have led to extruded diets with extremely low water content and a shift from mainly marine fish based ingredients towards plant content. These changes expose the industry to the vagaries of the highly dynamic plant protein market. Resulting variations in the precise composition of aqua feeds may carry unpredictable consequences for water quality, since some plant ingredients cause undesirable reductions in the mechanical stability of faeces. Dietary supplements known as binders that enhance the stability of faeces have the potential to mitigate these issues, but may also bring negative effects.

OBJECTIVE AND METHODS

The present study employs an in vitro model to perform the first fundamental rheological characterization of salmonid chyme, and a factorial experiment designed to investigate the impacts of the presence of rheologically active substances.

RESULTS

The highest mean viscosity values were measured for a treatment containing a 2:1 ratio of tara gum:xanthan gum, resulting in chyme four times more viscous than a control formulation containing the same amount of water. Shear resistance was quantified by analyses of slopes fitting the frequency sweep measurements.

CONCLUSIONS

These data open a new statistical approach to monitoring the consequences of market-driven changes in aqua feed composition and their impacts on the nutrition, health or performance of farmed fish.

Re-evaluation of the mechanisms of dietary fibre and implications for macronutrient bioaccessibility, digestion and postprandial metabolism

The positive effects of dietary fibre on health are now widely recognised; however, our understanding of the mechanisms involved in producing such benefits remains unclear. There are even uncertainties about how dietary fibre in plant foods should be defined and analysed. This review attempts to clarify the confusion regarding the mechanisms of action of dietary fibre and deals with current knowledge on the wide variety of dietary fibre materials, comprising mainly of NSP that are not digested by enzymes of the gastrointestinal (GI) tract. These non-digestible materials range from intact cell walls of plant tissues to individual polysaccharide solutions often used in mechanistic studies. We discuss how the structure and properties of fibre are affected during food processing and how this can impact on nutrient digestibility. Dietary fibre can have multiple effects on GI function, including GI transit time and increased digesta viscosity, thereby affecting flow and mixing behaviour. Moreover, cell wall encapsulation influences macronutrient digestibility through limited access to digestive enzymes and/or substrate and product release. Moreover, encapsulation of starch can limit the extent of gelatinisation during hydrothermal processing of plant foods. Emphasis is placed on the effects of diverse forms of fibre on rates and extents of starch and lipid digestion, and how it is important that a better understanding of such interactions with respect to the physiology and biochemistry of digestion is needed. In conclusion, we point to areas of further investigation that are expected to contribute to realisation of the full potential of dietary fibre on health and well-being of humans.

Rheological and microstructural properties of porcine gastric digesta and diets containing pectin or mango powder

Hydrated polysaccharides and their assemblies are known to modulate gastric emptying rate due to their capacity to change the structural and rheological properties of gastric contents (digesta). In the present study, we investigated the rheological and microstructural properties of gastric digesta from pigs fed with diets incorporating mango powder or pectin, and compared results with those from hydrated diets of the same water content, in order to investigate the origins for rheological changes in the pig stomach. All of the hydrated diets and gastric digesta were particle-dominated suspensions, generally showing weak gel or more solid-like behavior with the storage modulus (G') always greater than loss modulus (G") under small deformation oscillatory measurements, and with small deformation viscosity greater than steady shear viscosity (i.e. non-Cox-Merz superposition). Although significant rheological differences were observed between the hydrated diets, rheological parameters for gastric digesta were similar for all diets, indicative of a rheological homeostasis in the pig stomach. Whilst the addition of gastric mucin (20mg/mL) to control and mango diets altered the rheology to match the gastric digesta rheology, the effect of mucin on the pectin-containing diet was negligible. The viscous effect of pectin also hindered the action of alpha amylase as observed from relatively less damaged starch granules in pectin digesta compared to mango and control digesta. Based on the experimental findings that the rheology of gastric digesta differs from hydrated diets of the same water content, the current study revealed composition-dependent complex behavior of gastric digesta in vivo, suggesting that the rheology of food products or ingredients may not necessarily reflect the rheological effect when ingested.

Acute effects of pea protein and hull fibre alone and combined on blood glucose, appetite, and food intake in healthy young men--a randomized crossover trial

Whether pulse components can be used as value-added ingredients in foods formulated for blood glucose (BG) and food intake (FI) control requires investigation. The objective of this study was to examine of the effects of pea components on FI at an ad libitum meal, as well as appetite and BG responses before and after the meal. In a repeated-measures crossover trial, men (n = 15) randomly consumed (i) pea hull fibre (7 g), (ii) pea protein (10 g), (iii) pea protein (10 g) plus hull fibre (7 g), (iv) yellow peas (406 g), and (v) control. Pea hull fibre and protein were served with tomato sauce and noodles, while yellow peas were served with tomato sauce. Control was noodles and tomato sauce. FI was measured at a pizza meal (135 min). Appetite and BG were measured pre-pizza (0-135 min) and post-pizza (155-215 min). Protein plus fibre and yellow peas led to lower pre-pizza BG area under the curve compared with fibre and control. At 30 min, BG was lower after protein plus fibre and yellow peas compared with fibre and control, whereas at 45 and 75 min, protein plus fibre and yellow peas led to lower BG compared with fibre (p < 0.05). Following the pizza meal (155 min), yellow peas led to lower BG compared with fibre (p < 0.05). No differences were observed in FI or appetite. This trial supports the use of pea components as value-added ingredients in foods designed to improve glycemic control.

The effects of biopolymer encapsulation on total lipids and cholesterol in egg yolk during in vitro human digestion

The purpose of this study was to examine the effect of biopolymer encapsulation on the digestion of total lipids and cholesterol in egg yolk using an in vitro human digestion model. Egg yolks were encapsulated with 1% cellulose, pectin, or chitosan. The samples were then passed through an in vitro human digestion model that simulated the composition of mouth saliva, stomach acid, and the intestinal juice of the small intestine by using a dialysis tubing system. The change in digestion of total lipids was monitored by confocal fluorescence microscopy. The digestion rate of total lipids and cholesterol in all egg yolk samples dramatically increased after in vitro human digestion. The digestion rate of total lipids and cholesterol in egg yolks encapsulated with chitosan or pectin was reduced compared to the digestion rate of total lipids and cholesterol in other egg yolk samples. Egg yolks encapsulated with pectin or chitosan had lower free fatty acid content, and lipid oxidation values than samples without biopolymer encapsulation. Moreover, the lipase activity decreased, after in vitro digestion, in egg yolks encapsulated with biopolymers. These results improve our understanding of the effects of digestion on total lipids and cholesterol in egg yolk within the gastrointestinal tract.

Effects of dietary conjugated linoleic acid and biopolymer encapsulation on lipid metabolism in mice

Forty mice were randomly divided into four groups on the basis of the diet to be fed as follows: 5% (low) fat diet (T1: LF); 20% (high) fat diet (T2: HF); 20% fat containing 1% conjugated linoleic acid (CLA) (T3: HFC); and 20% fat containing 1% CLA with 0.5% biopolymers (T4: HFCB). The high-fat with CLA diet groups (HFC and HFCB) and the low-fat diet group (LF) tended to have lower body weights and total adipose tissue weights than those of the high-fat diet group (HF). Serum leptin and triglyceride were significantly lower in the high fat with CLA-fed groups (HFC and HFCB) and the low-fat diet group (LF) than those in the high-fat diet group (HF). It is noteworthy that the high-fat with CLA and biopolymers group (HFCB) showed the lowest serum triglyceride and cholesterol concentrations. In the high-fat-fed group (HF), voluntary travel distance as a measure of physical activity decreased after three weeks of feeding. However, the CLA-fed groups showed increased physical activity. The groups fed high-fat diets supplemented with CLA alone and with CLA and biopolymers had higher viscosity of small intestinal contents than that in the low- and high-fat dietary groups.

Suppressive effect of cellulose on osmotic diarrhea caused by maltitol in healthy female subjects

Using a single-group time-series design, we determined that osmotic diarrhea caused by maltitol ingestion was suppressed by the addition of not only soluble but also insoluble dietary fiber in healthy humans. We then clarified that cellulose delayed gastric emptying in rats. Twenty-seven healthy volunteers ingested maltitol step-wise at doses of 15, 20, 25, 30, 35, 40 and 45 g from small to large amounts. Within that range of ingested amounts, 22 out of 27 subjects experienced osmotic diarrhea from maltitol ingestion, and the minimal dose level of maltitol that induced osmotic diarrhea (MMD) was established for each subject. When 5 g of cellulose was added to the MMD, osmotic diarrhea was suppressed in 13 out of 19 subjects (68.4%), while partially hydrolyzed alginate-Na (PHA-Na), a soluble dietary fiber, suppressed osmotic diarrhea in 10 out of 20 subjects (50.0%). When a mixed solution of cellulose and maltitol was administered to rats, the gastric emptying of maltitol was significantly delayed at 30 and 60 min after administration (p=0.019, p=0.013), respectively. PHA-Na also significantly delayed gastric emptying at 30 min (p=0.013). In conclusion, cellulose can suppress the osmotic diarrhea caused by maltitol ingestion in humans and delay the gastric emptying of maltitol in rats. A new physiological property of cellulose was clarified in this study.

Disintegration of solid foods in human stomach

Knowledge of the disintegration of solid foods in human stomach is essential to assess the bioavailability of nutrients in the gastrointestinal (GI) tract. A comprehensive review of food gastric digestion, focusing on disintegration of solid foods, is presented. Most of the research reviewed in this paper is contained in the medical, pharmaceutical, food, and nutritional literature. Stomach physiology is briefly introduced, including composition and rheological properties of gastric contents, stomach wall motility in fed/fasted states, and hydrodynamic and mechanical forces that act on the ingested food. In vivo and in vitro methods used for studying food and drug digestion in GI are summarized. Stomach emptying rate, which controls the rate of absorption of nutrients, is highly related to the disintegration of foods. This topic is highlighted with focus on the important mechanisms and the influence of chemical and physical properties of foods. Future research in this area is identified to increase our fundamental understanding of the food digestion process in the stomach as related to the food composition, material properties such as texture and microstructure, and chemical characteristics. This information is necessary to develop new guidelines for seeking innovative processing methods to manufacture foods specifically targeted for health.

African plant foods rich in non-starch polysaccharides reduce postprandial blood glucose and insulin concentrations in healthy human subjects

The effects of two vegetable flours, prepared from the African plants Detarium senegalense Gmelin, a legume, and Cissus rotundifolia, a shrub, on postprandial blood glucose and insulin concentrations in human subjects, were investigated. Chemical analysis indicated that these flours contained significant amounts of NSP. The detarium in particular was found to be a rich source of water-soluble NSP (SNSP). The flours were incorporated into two types of breakfast meal, a stew meal and a wheat bread meal, containing 50 g and 70 g available carbohydrate respectively. Both meals also contained 10–12g NSP, the major fraction of which was SNSP. Control and fibre-rich meals were consumed on separate days in randomized order by two different groups of subjects (n 5, stew meals; n 10, bread meals). Venous blood samples were taken at fasting (0 min) and postprandially at 30 min intervals for 2·5 h and the plasma analysed for glucose and insulin. Compared with the controls, detarium and cissus meals elicited significant reductions (P < 0·006) in plasma glucose levels at most postprandial time points and for area-under-the-curve (AUC) values (AUC reductions 38–62%). Significant reductions (P < 0·002) in plasma insulin levels at various postprandial time points and for AUC values were also seen after detarium and cissus breads (AUC reductions 43 and 36% respectively), but not after the fibre-rich stew meals. SNSP and starch are possibly the main, but not the only, components responsible for the glucose- and insulin-lowering effects of cissus flour. The main SNSP fraction of detarium, identified as a high-molecular-weight xyloglucan, is likely to be a primary factor in determining the physiological activity of detarium flour.

Selected gelling agents in canned dog food affect nutrient digestibilities and fecal characteristics of ileal cannulated dogs

Little is known about the effects of gelling agents in canned dog food on nutrient digestibilities and fecal characteristics. Dogs were fed canned diets with either no gelling agent (control) or one of three gelling agents, wheat starch, a guar gum/carrageenan mixture (50:50), and a locust bean meal (LBM)/carrageenan mixture (50:50) incorporated at two levels (0.2 and 0.5% of the diet on a wet weight basis). Six dogs were fed each diet in a 6 x 7 Youden square design. Dogs fed diets containing gelling agents had higher ileal digestibilities of OM (P = 0.05), fat (P < 0.01), GE (P = 0.02), and total amino acids (P = 0.04) and lower (P < 0.01) total tract DM digestibilities when compared to dogs fed the control diet. Fecal output by dogs fed the control diet, expressed on both an as-is (73.4 g/d) and DM (45.6 g/d) basis, was lower (P < 0.01) than for dogs fed gelling agent-containing diets (mean 102.3 g/d as-is and 57.6 g/d DM). Dogs fed the control diet also had lower (P < 0.01) fecal DM percentages and higher (P = 0.02) fecal scores than dogs fed gelling agent-containing diets.

Effect of thickening agents, based on soluble dietary fiber, on the availability of calcium, iron, and zinc from infant formulas

Although it is accepted that dietary fiber probably is not needed in the diets of infants younger than 1 y, babies suffering from regurgitation are often fed with infant formulas thickened with considerable amounts of fiber. The effect of increasing amounts of alginic acid, locust-bean gum, and guar gum was studied from casein and whey-based infant formulas. A dialysis in vitro method with preliminary intraluminal digestion, adapted to the conditions of infants younger than 6 mo, was used. Human milk was used as the reference standard. Elemental contents of samples and dialysates were determined by atomic absorption spectrometry. Soluble dietary fiber inhibited mineral availability more in casein than in whey-based formulas. Mineral availabilities from casein- and whey-based formulas supplemented with 0.42 g of locust-bean gum/100 mL were 9.4% (0.7) and 10.4% (0.6) for calcium (P < 0.05), 0.32% (0.08) and 1.45% (0.17) for iron (P < 0.05), and 3.2% (0.2) and 5.6% (0.5) for zinc (P < 0.05), respectively. Calcium availability from the whey formula decreased in the presence of each fiber source, especially guar gum and alginic acid. Supplementing 2 g of alginic acid-based agents per 100 mL depressed calcium availability from 13.3% (1.2) to 5.3% (0.3; P < 0.05). With respect to iron and zinc, availabilities increased from 1.28% (0.28) to 6.05% (0.96; P < 0.05) and from 6.7% (0.6) to 10.2% (1.0), respectively, with the addition of 2 g of alginic acid (P < 0.05). Both gums lowered iron and zinc availabilities, and guar gum affected iron availability more severely than locust-bean gum did. Iron availabilities were 1.45% (0.17) from formula thickened with locust-bean gum (0.42 g/100 mL) and 0.92% (0.15) from formula thickened with guar gum (P < 0.05). Adding thickening agents based on soluble dietary fiber to traditional infant formulas probably affects calcium, iron, and zinc availability in various ways.

Effect of meal viscosity and nutrients on satiety, intragastric dilution, and emptying assessed by MRI

The relationship between the intragastric distribution, dilution, and emptying of meals and satiety was studied using noninvasive magnetic resonance imaging techniques in 12 healthy subjects with four polysaccharide test meals of varying viscosity and nutrient content as follows: 1) low-viscosity nonnutrient, 2) low-viscosity nutrient, 3) high-viscosity nonnutrient, and 4) high-viscosity nutrient. Increasing the nutrient content of the high-viscosity meal delayed gastric emptying from 46 +/- 9 to 76 +/- 6 min (P < 0.004), whereas increasing viscosity had a smaller effect. The volume of secretions within the stomach 60 min after ingestion was higher for the high-viscosity nutrient meal (P < 0.04). A simple model to calculate the total volume of secretion added to the test meal is presented. Color-coded dilution map images showed the heterogeneous process of progressive gastric dilution of high-viscosity meals, whereas low-viscosity meals were uniformly diluted. Fullness was found to be linearly related to total gastric volumes for the nutrient meals (R(2) = 0.98) and logarithmically related for the nonnutrient meals (R(2) = 0.96). Fullness was higher for high- compared with low-viscosity meals (P < 0.02), and with the nutrient meals this was associated with greater antral volumes (P < 0.05).

Assessment of antral grinding of a model solid meal with echo-planar imaging

Mathematical modeling of how physical factors alter gastric emptying is limited by lack of precise measures of the forces exerted on gastric contents. We have produced agar gel beads (diameter 1.27 cm) with a range of fracture strengths (0.15-0.90 N) and assessed their breakdown by measuring their half-residence time (RT(1/2)) using magnetic resonance imaging. Beads were ingested either with a high (HV)- or low (LV)-viscosity liquid nutrient meal. With the LV meal, RT(1/2) was similar for bead strengths ranging from 0.15 to 0.65 N but increased from 22 +/- 2 min (bead strength <0.65 N) to 65 +/- 12 min for bead strengths >0.65 N. With the HV meal, emptying of the harder beads was accelerated. The sense of fullness after ingesting the LV meal correlated linearly (correlation coefficient = 0.99) with gastric volume and was independently increased by the harder beads, which were associated with an increased antral diameter. We conclude that the maximum force exerted by the gastric antrum is close to 0.65 N and that gastric sieving is impaired by HV meals.

Dilutions of low- vs. high-fat diets on intakes and gastric volumes in rats

Rats adapt to changes in dietary energy to maintain nearly constant energy intakes. This regulation indicates that animals sense and respond to nutrient content. We sought to determine whether this response was affected by the fat content of the diet. Our second goal was to determine how energy dilution affected intragastric volumes. Rats were randomized to high (18% w/w) and low fat (4.5% w/w) as the energy density of the diet was altered from 2.0 to 3.5 kcal/g. Average energy intake during 7-h feeds rose steeply (P<.01) when density was increased from 2.0 to 3.0 kcal/g, but modestly as density increased from 3.0 to 3.5 kcal/g. In other rats on 18% vs. 32% fat diets, energy intakes increased significantly (P<.01) as density of the diet was raised from 3.5 to 4.5 kcal/g. During diets at 2.0 and 2.5 kcal/g, animals on 18% fat ate fewer kilocalories than those on 4.5% fat; but over 3.0-4.5 kcal/g, energy intake was similar regardless of fat concentration (4.5-32%). Gastric contents after 7-h feeds increased with grams of food ingested similarly for high- and low-fat diets. We concluded that in rats: (a) compensation to energy dilution or concentration was inexact but (b) was about equal for high- vs. low-fat diets; thus, high fat was as well sensed as high carbohydrate; (c) compensations for energy densities were made despite varied gastric volumes; thus, rats learned to override the stimulus of gastric stretch and to sense energy via extra gastric mechanisms.

Low levels of viscous hydrocolloids lower plasma cholesterol in rats primarily by impairing cholesterol absorption

Hydrocolloids have been proposed as cholesterol-lowering agents, but their viscosity limits their use in human nutrition. A low level (1 %) of hydrocolloids (guar gum, (GG); xanthan gum, (XG); and konjac mannan) was investigated in rats fed 0.2 g/100 g cholesterol diets. Food intake and body weight gain were not altered by the diets. Bile flow and cholesterol bile flux were not modified by diet, whereas the bile acid flux was greater in rats fed hydrocolloid diets. The cecal pool of bile acids was greater than control rats only in rats fed the XG diet (+71%, P<0.001). The fecal excretion of neutral sterols was stimulated in rats fed the hydrocolloid diets; cholesterol apparent digestibility (60% in controls) was reduced to 30-36% in rats fed hydrocolloids. Bile acid fecal excretion was not altered by diet treatment. As a result, apparent steroid balance was about +40 micromol/d in controls and only +10 to +20 micromol/d in rats fed hydrocolloids. Both plasma cholesterol and triglycerides were significantly lower than controls in rats fed XG, but only cholesterol was lower in rats fed the GG diet. These effects were essentially found in the d <1.040 kg/L fraction. Liver cholesterol content was significantly lower than in controls in rats fed the GG or XG diets. Liver HMG CoA reductase was not affected by the hydrocolloid diets. In conclusion, a low percentage of viscous hydrocolloids lowers plasma cholesterol in cholesterol-fed rats. Inhibition of intestinal cholesterol absorption may be the primary mechanism.

The nutritional requirements of exercising dogs

The nutrient requirements of canine athletes are unique. Dogs have a greater capacity for fat oxidation than humans both at rest and during exercise. In dogs undertaking endurance exercise, such as sled dogs, high fat (>50% of energy) diets increase stamina and maximize energy production, and high protein (>30% of energy) diets prevent training-induced anemia. Nutrient requirements differ, however, for sprint racing dogs, such as greyhounds. Greyhounds run faster when fed moderately increased dietary fat but run more slowly when dietary protein is increased. Sled dogs have similar energy requirements to other breeds at rest in a thermoneutral environment ( approximately 550W0.75 kJ/d where W is body weight in kg) but may require as much as 4200W0.75 kJ/d during a race. The energy requirement of greyhounds in training, however, is only approximately 600W0.75 kJ/d. There is little information, however, concerning the vitamin, mineral or other nutrient requirements of athletic dogs; most sled dogs and greyhounds are fed "homemade" recipes. These recipes usually include raw meat and represent a health risk. More studies are required to improve the health and performance of working and racing dogs.

The cholesterol-lowering effect of guar gum is not the result of a simple diversion of bile acids toward fecal excretion

The effects of partially hydrolyzed, nonviscous, guar gum (PHGG) on cholesterol metabolism and digestive balance have been compared with those of native guar gum (GUAR) in rats adapted to 0.4% cholesterol diets. Both types of guar gum elicited acidic fermentations in the large intestine, but only GUAR effectively lowered plasma cholesterol (P < 0.001), chiefly in the triglyceride-rich lipoprotein fraction. The biliary bile acid excretion was significantly enhanced in rats fed GUAR (P < 0.05), as well as the intestinal and cecal bile acid pool (P < 0.001). In rats fed GUAR and to a lesser extent in those fed PHGG, the fecal excretion of bile acids and neutral sterol was higher than in controls (P < 0.01). The digestive balance (cholesterol intake-steroid excretion) was positive in control rats (+47 mumol/d), whereas it was negative in rats fed GUAR (-20 mumol/d), which could involve a higher rate of endogenous cholesterol synthesis. In rats fed PHGG, the steroid balance remained slightly positive. Liver 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was very low (22 pmol/min/mg protein), owing to cholesterol supplementation, in control rats or in rats fed PHGG, whereas it was markedly higher (+463%) in rats fed GUAR. In conclusion, even if PHGG does alter some parameters of the enterohepatic cycle of cholesterol and bile acids, its effects are not sufficient to elicit a significant cholesterol-lowering effect. The intestinal (ileal or cecal) reabsorption of bile acids was not reduced, but rather increased, by GUAR; nevertheless the intestinal capacities of reabsorption were overwhelmed by the enlargement of the digestive pool of bile acids. In the present model, induction of HMG-CoA reductase probably takes place in the presence of elevated portal bile acid concentrations.

Fecal losses of sterols and bile acids induced by feeding rats guar gum are due to greater pool size and liver bile acid secretion

The effect of dietary guar gum (GG, 7.5%) on lipid metabolism and on bile acid secretion and reabsorption was investigated in rats adapted to cholesterol-free or 0.3% cholesterol diets. Compared with controls (fiber-free/cholesterol-free), rats fed cholesterol had significantly elevated plasma and liver cholesterol and triglyceride. In these rats, GG had a potent plasma cholesterol-lowering effect and also counteracted the liver accumulation of triglyceride and cholesterol esters. Fecal excretion of sterols, the major route of cholesterol elimination, was markedly enhanced by GG, especially in rats fed the cholesterol-containing diet (P < 0.001). The biliary bile acid flux into the small intestine was enhanced by dietary cholesterol (+30%) or GG (+52%) or both (P < 0.001). The fecal excretion of bile acids was significantly elevated by GG alone (+74%) and by dietary cholesterol (+190%). Small intestine reabsorption of bile acids appears to be significantly enhanced by GG, which also enhanced the transfer of bile acids into the large intestine, hence a greater fecal loss of steroids, although bile acid reabsorption was very effective in the cecum. GG feeding induced liver hydroxymethyl-glutaryl coenzyme A (HMG CoA) reductase, even in cholesterol-fed rats, as well as cholesterol 7 alpha-hydroxylase (P < 0.001). The cholesterol-lowering effect of GG thus appears to be mediated by an accelerated fecal excretion of steroids and a rise in the intestinal pool and biliary production of bile acids. Although liver HMG CoA reductase and cholesterol 7 alpha-hydroxylase are induced in parallel, this is not sufficient to compensate for fecal steroid losses.

Pharmacology of dietary fibre

"Dietary fibre" includes a range of relatively poorly digested food substances mainly composed of non-starch polysaccharides. Pectins and gums are multi-branched hydrophilic substances, forming viscous solutions that delay gastric emptying and nutrient absorption from the small bowel. They are used to delay gastric emptying and improve glycemic control in diabetes, as well as to alleviate constipation. Other fibres, including cellulose and lignins, are insoluble and have little effect on gastric emptying and small bowel transit. They markedly accelerate colonic transit and are frequently used as laxatives. Other important, less well-characterised effects of fibre include lowering of blood cholesterol, increase in satiety and possibly reduction in colon neoplasia.

Insulin resistance in Mexican Americans--a precursor to obesity and diabetes?

Mexican Americans appear to have a strong genetic predisposition to insulin resistance, android obesity, and type II diabetes, apparently as a function of Native American genetic heritage. Theoretical considerations suggest that insulin resistance may be a primary factor that plays a causative role in the induction of both obesity and diabetes. Measures which promote optimal insulin sensitivity--chromium picolinate, brewer's yeast, soluble fiber supplements, metformin, very-low-fat diet, exercise training--may have value for preventing, treating, or retarding the onset of obesity and diabetes, and merit clinical evaluation in this regard. Correction of insulin resistance may also lessen cardiovascular risk, in part by reducing LDL cholesterol and improving risk factors associated with Syndrome X. These comments are likely to be valid for other Native American groups at high risk for diabetes.

The effect of ingestion of guar gum on ileostomy effluent

Randomized, paired studies were carried out on five healthy volunteers equipped with terminal ileostomies to investigate the effect of incorporating 15 g of the viscous polysaccharide guar gum in the normal diet on the volume, weight, composition and physical properties of ileostomy effluent. Subjects ate an identical diet during two 5 d study periods, which were separated by 2 d. Outputs of fat, protein, sodium, potassium, dry weight and water were all increased during guar gum administration, but outputs of carbohydrate, calcium and phosphorus were not significantly altered. Mouth-to-stoma transit was not significantly affected and, surprisingly, the viscosity of the ileostomy effluent was reduced by guar gum. These results show that it is not always possible to predict what will happen to small intestinal function when guar gum is added to the diet from experiments carried out when guar gum is administered alone or with glucose. While our findings show that guar gum will reduce fat absorption, the mechanisms involved are more sophisticated than hitherto envisaged.