Biomedical subjects

G Livesey

Publications and source records attributed to G Livesey.

At least 19 recordsLinked to original sources

PubMed2002

Thermogenesis associated with fermentable carbohydrate in humans, validity of indirect calorimetry, and implications of dietary thermogenesis for energy requirements, food energy and body weight.

BACKGROUND: Animal studies and theory show fermentable carbohydrate (FC) intake causes appreciably thermogenesis, but a similar occurrence in humans is controversial. HYPOTHESES: (a) That indirect calorimetry (IDC) is a valid method to assess thermogenesis during fermentation. (b) That a consistent and rigorous approach to the analysis of published IDC data from human studies will establish a representative thermogenic response to FC. (c) That conventional estimates of food energy and energy requirements can mismatch appreciably, more especially when thermogenesis is ignored. PURPOSE: To derive information and understanding of IDC, thermogenesis and energy balance in relation to food energy and energy requirement estimates. METHODS: (a) The validities of IDC equations that estimate the heat of reaction and carbohydrate utilization were assessed for various types of FCs under various circumstances. (b) Pooled analysis of eight published randomized cross-over studies in humans with elevation of FC intake. Studies were analysed for the first time or reanalysed according to a consistent approach with appropriate corrections for confounders. (c) Some 1500 regular and 'special' diet compositions were examined to assess the extent to which Atwater general food energy factors and updated estimates of energy requirements mismatch due to variation in substrate-associated thermogenesis and substrate-associated faecal+urinary energy losses. Impact of such mismatches on BMI was assessed under conditions of all else being equal. RESULTS: (a) Indirect calorimetry was valid, providing robust estimates of heat production during various types of fermentation; only small correction factors were necessary. By contrast, IDC equations for carbohydrate utilization sometimes applied poorly to FC. (b) A best estimate of thermogenesis in humans due to fermentation, above that due to oral glucose as a reference standard, was 0.39 (s.e.m. 0.14) kJ per kJ net metabolizable energy (NME; P<0.05, n=8 studies, total 72 humans) compared with 0.34 kJ/kJ from theory. Six sources of bias were identified; all had potential to underestimate FC thermogenesis. (c) Mismatches in energy availability and requirement estimates were often marked and translated into long-term differences in body mass index from approximately 20 to 33 kg/m(2) in average-height middle-aged initially obese women, and from approximately 22 to a non-survivable 13 kg/m(2) in initially slim women. CONCLUSIONS: (a) Indirect calorimetry is valid for the present purpose. (b) Thermogenesis in response to FC is real in humans and is comparable to that in animals and in theory. (c) Mismatches between estimates of energy requirements and dietary energy as metabolizable energy means the two expressions are not directly comparable, which has implications for the expression of food energy, energy requirements and the conduct and interpretation of research related to body weight.

Body Weight↗

PubMed2001

A perspective on food energy standards for nutrition labelling.

Food energy values used for nutrition labelling and other purposes are traditionally based on the metabolisable energy (ME) standard, which has recent support from. By reference to current practices and published data, the present review critically examines the ME standard and support for it. Theoretical and experimental evidence on the validity of ME and alternatives are considered. ME and alternatives are applied to 1189 foods to assess outcomes. The potential impact of implementing a better standard in food labelling, documentation of energy requirements and food tables, and its impact on users including consumers, trade and professionals, are also examined. Since 1987 twenty-two expert reviews, reports and regulatory documents have fully or partly dropped the ME standard. The principal reason given is that ME only approximates energy supply by nutrients, particularly fermentable carbohydrates. ME has been replaced by net metabolisable energy (NME), which accounts for the efficiency of fuel utilisation in metabolism. Data collated from modern indirect calorimetry studies in human subjects show NME to be valid and applicable to each source of food energy, not just carbohydrates. NME is robust; two independent approaches give almost identical results (human calorimetry and calculation of free energy or net ATP yield) and these approaches are well supported by studies in animals. By contrast, the theoretical basis of ME is totally flawed. ME incompletely represents the energy balance equation, with substantial energy losses in a missing term. In using NME factors an account is made of frequent over-approximations by the ME system, up to 25 % of the NME for individual foods among 1189 foods in British tables, particularly low-energy-density traditional foods. A new simple general factor system is possible based on NME, yet the minimal experimental methodology is no more than that required for ME. By accounting for unavailable carbohydrate the new factor system appears as specific to foods as the USA's food-specific Atwater system, while it is more representative of energy supply from food components. The NME content of foods is readily calculable as the sum from fat (37 kJ/g), protein (13 kJ/g), available carbohydrate (16 kJ/g), fully-fermentable carbohydrate (8 kJ/g), alcohol (26 kJ/g) and other components. Obstacles to the implementation of NME appear to be subjective and minor. In conclusion, the ME standard is at best an approximate surrogate for NME, and inadequately approximates food energy values for the purpose of informing the consumer about the impact on energy balance of the energy supply for equal intake of individual foods. NME is superior to ME for nutrition labelling and other purposes.

Animals↗

PubMed2001

Tolerance of low-digestible carbohydrates: a general view.

The tolerance of low-digestible carbohydrates (LDCs) may be measured as the potential to cause abdominal symptoms and laxation. Tolerance of any one LDC is determined by its concentration in the food product eaten, the amount of the food product eaten, the frequency of eating the food and the consumption of other foods (increasing tolerance) and water decreasing tolerance). Added to these, individuals vary considerably in their response to low-digestible carbohydrates in the reporting of gastrointestinal symptoms. A precise maximum no-response dose is sometimes difficult to obtain because some dose--response curves are distinctly sigmoidal. Food regulators hoping to set a trigger level at which laxation may occur have been unable to take account of all these factors because the necessary information matrices are not available for any one LDC. Nevertheless analysis of the data shows consistent trends and for circumstances when food is consumed throughout the day it now seems feasible to assign specific tolerances to specific low-digestible carbohydrates, especially the polyols for which most is known. The method by which the no-effect dose or laxative threshold is expressed is critical to its application to individual foods.

Adaptation, Physiological↗

PubMed2000

Evidence for altered control of glucose disposal after total colectomy.

Colonic fermentation of organic matter to short-chain fatty acids has been implicated in the improvement in insulin sensitivity achieved by feeding diets rich in complex carbohydrates. The present study assessed the potential role of the colon in determining postprandial glucose kinetics. Metabolic responses to a complex-carbohydrate test meal were determined in conjunction with a primed continuous infusion of D-[6,6-2H]glucose in a group of ileostomists and sex-matched controls. Glucose disposal (GD) was computed using Steele's (1959) non-steady-state kinetics on a single compartment model. Insulin sensitivity was derived using cumulative GD as the dependent variable, and time and the integrated insulin concentration as independent variables. The ileostomist group had a significantly higher postprandial plasma insulin concentration ( P = 0.034) compared with the control group, but no difference in the plasma glucose concentration. Total GD was similar in each group, although the insulin-dependent GD was substantially lower in the ileostomists (0.46 v. 0.13 mg glucose/min per pmol, P = 0.015). The ileostomist group also showed a 50% lower rate of glucose oxidation in the postprandial period (p = 0.005), although the rate of non-oxidative GD was not significantly affected. The present study indicates that loss of the colon is associated with several characteristics of the insulin resistance syndrome, and favours a view that the colon has a role in the control of postprandial glucose.

Adult↗

PubMed1999

The influence of the colon on postprandial glucagon-like peptide 1 (7-36) amide concentration in man.

Glucagon-like peptide (7-36) amide (GLP-1) is an incretin hormone of the enteroinsular axis released rapidly after meals despite the fact that GLP-1 secreting cells (L-cells) occur predominantly in the distal gut. The importance of these colonic L-cells for postprandial GLP-1 was determined in healthy control subjects and in ileostomy patients with minimal small bowel resection (<5 cm). Subjects were fed a high complex carbohydrate test meal (15.3 g starch) followed by two carbohydrate-free, high fat test meals (25 g and 48.7 g fat respectively). Circulating levels of glucose, insulin, glucagon, glucose insulinotrophic peptide (GIP) and GLP-1 were measured over a 9-h postprandial period. For both subject groups the complex carbohydrate test meal failed to elicit a rise in either GIP or GLP-1. However, both hormones were elevated after the fat load although the GLP-1 concentration was significantly reduced in the ileostomist group when compared with controls (P=0.02). Associated with this reduction in circulating GLP-1 was an elevation in glucagon concentration (P=0.012) and a secondary rise in the plasma glucose concentration (P=0.006). These results suggest that the loss of colonic endocrine tissue is an important determinant in the postprandial GLP-1 concentration. Ileostomists should not be assumed to have normal enteroinsular function as the colon appears to have an important role in postprandial metabolism.

Analysis of Variance↗

PubMed1998

Energy balance and thermogenesis in rats consuming nonstarch polysaccharides of various fermentabilities.

BACKGROUND: The equivalents of dietary protein, fat, and available carbohydrate as fuels for maintenance (kJ apparent metabolizable energy/kJ maintenance requirement) are known from classical experiments and are similar across species; that for nonstarch polysaccharide (NSP) is undetermined. OBJECTIVES: Our objectives were to determine the energy equivalent of NSP and the thermic responses to NSP. DESIGN: In a randomized block design, 120 rats were treated in groups of 10 for 28 d with a basal diet (control) supplemented with starch and 10 different NSP treatments in amounts between 38 and 92 g/kg basal diet. Cellulose and starch were references. Thermic responses, deduced from body-composition changes and modeling of energy disposition, and energy and substrate excretion were determined. RESULTS: NSP had fermentabilities between 0.01 and 0.93 g/g intake. Fermentability, partial digestible energy, and net metabolizable energy values of NSP were closely related. Generally, 51% of apparent metabolizable energy from NSP (fermentable gross energy) met maintenance requirements. Diet (energy)-induced thermogenesis (DIT) was evident from whole diets. Fermentable NSP supplied net metabolizable energy and caused DIT. After DIT and fermentation were accounted for, NSP-induced thermogenesis was generally -2+/-4% (x+/-SEM) of gross NSP energy, except for an outlying pectic preparation, which was 33% (P< 0.1). CONCLUSIONS: The energy equivalent of NSP was 196 (100/51) kJ/kJ, compared with 128, 105, and 100 for protein, fat, and glucose, respectively, from the classical experiments. With the exception of pectic NSP, NSP does not induce thermogenesis in excess of that associated with DIT and fermentation.

Animals↗

PubMed1998

Energy expenditure and net substrate utilization in men ingesting usual and high amounts of nonstarch polysaccharide.

BACKGROUND: Diets intrinsically high in nonstarch polysaccharides (NSPs) are frequently advised for body weight regulation and health, but the consequences for energy expenditure and fuel selection are undetermined. OBJECTIVE: We determined whether energy expenditure and fuel selection differ when men consume a diet intrinsically higher in NSP than a usual mixed diet. DESIGN: A randomized crossover design was used in which 12 healthy men were fed a maintenance diet for approximately 3 wk in a metabolic suite. By judicial choice of food exchanges, the usual- and high-NSP diets were similar in protein, fat, and carbohydrate contents. Twenty-four-hour, indirect, open-circuit calorimetry was performed, including measurements of total hydrogen gas and methane. Participants were weight stable (within 2 kg for 3 wk), entered an 11-m3 calorimetry chamber for 36 h with measurements taken in the last 24 h, and underwent a strictly controlled program of moderate physical activity (1.3 x basal metabolic rate). RESULTS: The mean total 24-h energy expenditure and percentages from protein, fat, and carbohydrate metabolism were 10 MJ/d and 16%, 35%, and 48%, respectively. Differences (mean+/-SEM) between the 2 diets were only -0.005+/-0.130 MJ/d, -0.3+/-1.3%, -0.2+/-2.0%, and 0.6+/-2.2%, respectively, and were nonsignificant (P> 0.2). CONCLUSIONS: There was no thermogenic response to the high-NSP diet, which would be advantageous for body weight control, and no short-term influence on body composition, as may be judged from a lack of change in protein, fat, or carbohydrate metabolism.

Adult↗

PubMed1998

Metabolizable energy of high non-starch polysaccharide-maintenance and weight-reducing diets in men: experimental appraisal of assessment systems.

We have examined the reliability of several food energy assessment systems for healthy men. The predictions of metabolizable energies were compared with determinations made in energy balance studies with three maintenance diets (12 MJ/d); one of the diets was moderate in non-starch polysaccharide (NSP; 2.1% of gross energy) and two were higher in NSP (3.5-4.6% of gross energy). A fourth diet was a submaintenance (6 MJ/d) high NSP (7% gross energy) diet. Discrepancies between the different food energy assessment systems and the determined metabolizable energy values ranged between 0 and 15%. With the maintenance diets, the Atwater specific factor system had errors generally within 6% of the determined value and a limit of agreement (bias +2SD) for diets of 10%. This accuracy compares with errors of 2% for both the originally published assessment of this system and a more recent general formula; both systems were without bias with increasing NSP content of the diets but the latter had limits of agreement within 3%. In contrast, the Atwater general, the European general and a recent FDA general formula showed increasing bias with increasing NSP intake. All of the general energy assessment systems overpredicted metabolizable energy from the high NSP submaintenance diet, which shows that even the least biased and most reliable energy assessment system that we identified applies to maintenance diets only; thus a correction has to be made for submaintenance diets.

Adult↗

PubMed1998

Splanchnic retention of intraduodenal and intrajejunal glucose in healthy adults.

Estimates of the spanchnic retention and appearance in the systemic circulation of orally administered glucose vary among laboratories even after recently identified sources of error have been accounted for [Livesey, G., P. D. G. Wilson, J. R. Dainty, J. C. Brown, R. M. Faulks, M. A. Roe, T. A. Newman, J. Eagles, F. A. Mellon, and R. Greenwood. Am. J. Physiol. 275 (Endocrinol. Metab. 38): E717-E728, 1998]. We questioned whether, in healthy humans, D-glucose delivered intraluminally to the midjejunum appeared systemically as extensively as that delivered intraduodenally. Subjects were infused over a period of 90 min with 50 g of glucose in 1 liter of isotonic saline (incorporating 0.5 g D-[13C6]glucose) per 70 kg of body weight. Infusions were via enteral tubes terminating approximately 15 and 100 cm postpylorus. The systemic appearance of glucose was monitored by means of a primed-continuous intravenous infusion of D-[6,6-2H2]glucose. Whereas 98 +/- 2% (n = 7) of the duodenally infused glucose appeared in the systemic circulation, only 35 +/- 9% (n = 7) of midjejunally infused glucose did so, implying that 65 +/- 9% was retained in the splanchnic bed. Either glucose was less efficiently absorbed at the midintestinal site or hepatic glucose sequestration was increased 10-fold, or both. The proximal intestine plays a key role in the delivery of glucose to the systemic circulation, and the distal intestine potentially delivers more glucose to the liver.

Adult↗

PubMed1998

Simultaneous time-varying systemic appearance of oral and hepatic glucose in adults monitored with stable isotopes.

The rates (and extent) of appearance of glucose in arterialized plasma from an oral glucose load and from liver (RaO, RaH) can be estimated in humans using radioisotopes, but estimates vary among laboratories. We investigated the use of stable isotopes and undertook 22 primed intravenous infusions of D-[6,6-2H2]glucose with an oral load including D-[13C6]glucose in healthy humans. The effective glucose pool volume (VS) had a lower limit of 230 ml/kg body weight (cf. 130 ml/kg commonly assumed). This VS in Steele's one-compartment model of glucose kinetics gave a systemic appearance from a 50-g oral glucose load per 70 kg body weight of 96 +/- 3% of that ingested, which compared with a theoretical value of approximately 95%. Mari's two-compartment model gave 100 +/- 3%. The two models gave practically identical RaO and RaH at each point in time and a plateau in the cumulative RaO when absorption was complete. Less than 3% of 13C was recycled to [13C3]glucose, suggesting that recycling errors were practically negligible in this study. Causes of variation among laboratories are identified. We conclude that stable isotopes provide a reliable and safe alternative to radioactive isotopes in these studies.

Administration, Oral↗

PubMed1996

Effects of the type and level of dietary fibre supplements on nitrogen retention and excretion patterns.

The hypothesis was tested that fermentable dietary fibre (DF) sources elevate faecal N excretion at the expense of urinary N without affecting N retention. DF that substantially increase fermentation (pectin, sugarbeet and soya bran) or are poorly fermented (crystalline cellulose and maize bran) were fed as supplements to a basal DF-free diet at three dose levels: 0, 50 and 100 g supplement/kg basal diet. The diets were fed to juvenile male Wistar rats for 2 weeks before a 7 d period when faeces and urine were collected. Faecal excretion of N was significantly increased, dose-dependently, by all DF supplements and was positively correlated to faecal bulking. Urinary excretion of N was lower at the high doses of the DF supplements but reached significance only with the highly fermentable (0.68) sugarbeet-supplemented diets. Regression analysis showed that the major part (0.75) of the increase in faecal N excretion due to DF supplementation was balanced by a reduction in urinary excretion; N retention was therefore, at the dose levels used, only affected to a small extent. Only in the maize-bran-supplemented diets were the reductions in N retention significant. The shift in N excretion from urine to faeces can be explained largely by the degree of microbial fermentation in the large intestine caused by the addition of DF supplements and emphasizes the modifying role that certain DF supplements may have on the enterohepatic cycle of N. Possible implications of these findings for patients with liver or renal failure or for conditions when the intake of dietary protein is marginal are discussed.

Animals↗

PubMed1996

D-tagatose is a bulk sweetener with zero energy determined in rats.

The ketohexose D-tagatose is readily oxidized but contributes poorly to lipid deposition. We therefore examined whether this sugar contributes to energy requirements by determining its net metabolizable energy value in rats. All substrate-induced energy losses from D-tagatose, with sucrose as reference standard, were determined as a single value accounting for the sum of the energy losses to feces, urine, gaseous hydrogen and methane and substrate-induced thermogenesis. A randomized parallel design involving two treatment periods (adaptation to D-tagatose and subsequent energy balance) and two control groups (to control for treatment effects in each period) was used. Rats consumed 1.8 g test carbohydrate daily as a supplement to a basal diet for a 40- or 41-d balance period after prior adaptation for 21 d. Growth, protein and lipid deposition were unaffected by supplementary gross energy intake from D-tagatose compared with an unsupplemented control, but sucrose significantly (P < 0.05) increased all three. Based on the changes induced in protein and fat gain during the balance period it was calculated that D-tagatose contributed -3 +/- 14% of its heat of combustion to net metabolizable energy, and therefore this ketohexose effectively has a zero energy value. D-Tagatose would potentially be helpful in body weight control, especially in diabetic subjects because of its antidiabetogenic effects.

Animals↗

PubMed1996

Circadian patterns of total 24-h hydrogen and methane excretion in humans ingesting nonstarch polysaccharide (NSP) diets and the implications for indirect calorimetric and D2 18O methodologies.

OBJECTIVES: To quantify the relationship between substrate fermentation and total 24-h H2 and CH4 excretion on mixed diets and to assess errors incurred in the calculation of energy expenditure and fuel selection by the exclusion of these gases from standard calculations. DESIGN AND SUBJECTS: Twelve healthy, lean men were studied over two consecutive dietary periods of 3 weeks. Measurements of total H2 and CH4 excretion were made during 24h within a whole body calorimeter. Subjects were fed a diet containing 16 g or 38 g of nonstarch polysaccharide (NSP) and 16 g or 19 g resistant starch (RS). Colonic fermentation was measured by balance techniques during the two dietary treatments. RESULTS: There was an inverse non-linear relationship between H2 and CH4 excretion on both diets (r2 = 0.53; P < 0.001), but absolute excretion did not increase significantly as the intake of NSP and RS (from 28 +/- 3 and 48 +/- 4 g/day) increased. No relationship was found between daytime and 24-h measurements of H2 and CH4. H2 and CH4 excretion introduces an error of less than 0.2% and 1% in calculations of energy expenditure and CO2 production from the standard human equations used in indirect calorimetric (IC) and doubly labelled water (DLW) methodologies respectively, and less than 2% in fuel utilisation calculated as % non-protein energy expenditure from IC. CONCLUSIONS: This study provides evidence that neither daytime nor total 24-h rates of H2 or CH4 excretion accurately predict degree of fermentation of NSP+RS in either individual subjects or groups of subjects, probably because of changes in the stochiometry of the fermentation process.

Adult↗

PubMed1996

Is the rat a suitable model for humans on studies of cereal digestion?

OBJECTIVES: To compare the extent of starch digestion from barley flake and flour in humans and rat. Is the rat a useful model? DESIGN: Four healthy male ileostomy volunteers consumed, in random order, flapjacks containing flaked barley on one occasion and barley flour on another. Ileostomy fluid was collected for analysis of starch and nonstrach polysaccharide (NSP) hourly for 12 h. The ratio of starch to NSP in ileostomy fluid was compared with that in the terminal ileum of eight randomly selected male rats consuming the flaked barley flapjack and another eight rats consuming the barley flour flapjack. RESULTS: After consuming flaked barley the terminal ileal starch-NSP ratio was 20 times lower in rats than in ileostomists and was 0.04 (s.e.m. 0.006) g/g compared with 0.89 (s.e.m. 0.05) g/g respectively. By contrast the starch-NSP ratio was very low after consuming the barley flour in both species; however the ratio was still lower in rats than in ileostomists and was 0.02 (s.e.m. 0.01) g/g compared with 0.05 (s.e.m. 0.01) g/g respectively. Using the NSP as an indigestible marker, starch from barley flake that resisted small intestinal digestion was calculated to be 0.7 (s.e.m. 0.02)% in rats compared with a higher value of 17 (s.e.m. 1)% in ileostomists. CONCLUSION: The cell walls of barley flake limit the extent of starch digestion in humans but in rats this appears not to be a limiting factor. In the present instance it was not possible to extrapolate results from rats to humans.

Adult↗

PubMed1995

Determination of digestible energy values and fermentabilities of dietary fibre supplements: a European interlaboratory study in vivo.

The performance of methods to determine energy conversion factors for dietary fibre (DF) supplements and fermentability (D) values of their non-starch polysaccharides (NSP) was investigated. Heats of combustion, digestible energy (DE) and D values were determined on five DF supplements in five European laboratories on five separate occasions. In each instance the DF supplements were fed to juvenile male Wistar rats at two doses, 50 and 100 g/kg basal diet, for 3 weeks with food and faeces collected in the 3rd week. Among-laboratory variations in heats of combustion (delta Hc) were < 2%. DE values (kJ/g dry weight) at the upper and lower doses respectively were: 10.4 and 9.9 for a high-methoxyl apple pectin, 9.5 and 9.4 for a sugar-beet DF supplement, 12.2 and 12.7 for soyabean DF supplement, 3.8 and 4.0 for maize bran, and 0.3 and 0.3 for Solka-floc cellulose. Variations among laboratories, among occasions and among animals were < 1, < 2 and < 2.5 kJ/g respectively. The among-occasion: among-laboratory variance ratio for DE was 0.5, suggesting the method performed equally well in all laboratories. There was no evidence of learning of fatigue or fatigue in the performance of the method. D values were also independent of dose and at the high and lower doses were: pectin 0.92 and 0.95, sugar-beet NSP 0.68 and 0.68, soyabean NSP 0.86 and 0.88, maize bran 0.17 and 0.18, cellulose 0.07 and 0.06. Among-laboratory variance tended to increase with decreasing fermentability and ranged from 0.03 to 0.18. The DE and D data were not significantly different from a previously proposed relationship DE = 0.7 x delta Hc x D, where delta Hc is the heat of combustion of the supplement. We conclude that while the among-laboratory variation in the D of difficult-to-ferment NSP is too large for the reliable prediction of energy value the method for the direction determination of DE is both reproducible and repeatable, that DE is independent of dosage of DF supplement up to 100 g/kg diet, and that it is safe to discriminate between energy values with a precision of 3 kJ/g. The conversion of both DE and D to net metabolizable energy for the purpose of food labelling, tables and databases is described.

Animals↗

PubMed1995

Influence of the physical form of barley grain on the digestion of its starch in the human small intestine and implications for health.

It has been suggested that incomplete digestion of cereal starch explains the low energy values of certain cereals of large particle size. We used human subjects with ileostomies to investigate the digestion of barley and to determine whether the physical form of barley affects stomal excretion of starch, glucooligosaccharides, nitrogen, fat, and calculated energy. Only 2 +/- 1% of starch remained undigested after finely milled barley was eaten, but after flaked barley was eaten 17 +/- 1% resisted digestion, partly as oligosaccharides (G1-G10) but largely as intact unpitted starch granules bound by intact cell walls. The calculated energy excretion from the stoma was three times higher after flaked than after milled barley [51.5 decreasing to 15.3 kJ/g nonstarch polysaccharide (NSP, P < 0.001]. NSP, starch, and fat made almost equal contributions to the higher energy excretion. It is concluded that possibly the botanical source of cereals and certainly processing, other than retrogradation of the starch, are important determinants of starch digestibility and energy value. Possible clinical implications are introduced.

Adult↗

PubMed1995

Metabolizable energy of macronutrients.

I describe recent advances in assessing the amount of energy available from diets of varied composition. Empirical models of food energy prediction have grown in preference to factorial models over the past 20 y and knowledge of the quantitative aspects of energy salvage in the colon have modified our thoughts on how to best calculate food energy values. In contrast, food regulatory practices have been limited mostly to changes in the way in which carbohydrate is defined or measured and there has been little change in the basic approach to energy evaluation or the energy conversion factors used with food components. The empirical systems have advantages over factorial models of food energy assessment and it is proposed that such empirical systems should be used in food regulations, food tables and databases, and in nutritional studies in which knowledge of metabolizable energy intake is desirable but cannot be determined directly.

Dietary Carbohydrates↗

PubMed1995

Whole body metabolism is not restricted to D-sugars because energy metabolism of L-sugars fits a computational model in rats.

Can L-sugars contribute to whole body energy metabolism? Energy balance studies were undertaken in rats fed L-sugars at a rate of 10 g/100 g basal diet. Partial metabolizable energy values (MEVp) during the last 28 of 56 d while consuming the L-sugar diets showed that L-glucose contributed no energy (0.3 +/- 0.9 kJ/g, P > 0.5, mean +/- SEM), whereas L-fructose and L-glucose contributed 6.9 +/- 0.9 (P < 0.001) and 8.8 +/- 1.8 (P < 0.001) kJ/g, respectively. Over periods from 0 to 28 and 0 to 56 d of L-sugar treatment, measurements were made of energy intake, the average lean mass of animals, fat and lean mass deposition. Using these measurements and a computational model, estimates were made of each supplement's net metabolizable energy value for maintenance (NEVs). These estimates confirmed the supply of energy from L-fructose, with NEVs of 5.6 +/- 3.2 (P < 0.32) and 6.1 +/- 1.7 (P < 0.01) kJ/g over 28 and 56 d, respectively, and L-gulose with NEVs of 10.2 +/- 3.4 (P < 0.01) and 11.4 +/- 1.8 (P < 0.001) kJ/g over 28 and 56 d, respectively. A lack of energy supply from L-glucose was confirmed with NEVs of -2.6 +/- 3.2 (P > 0.5) and 0.0 +/- 1.6 (P > 0.5) kJ/g over 28 and 56 d, respectively. As reference substrates, sucrose and cellulose gave expected energy values in all determinations. Methods comparison analysis showed no differences between MEVp and NEVS. The assimilation of energy from L-fructose and L-gulose is probably via large bowl microorganisms. These observations show that L-gulose and L-fructose contribute to whole body energy metabolism while L-glucose does not.

Animals↗