Specific types of colonic fermentation may raise low-density-lipoprotein-cholesterol concentrations

Effects of Silage Diet on Meat Quality through Shaping Gut Microbiota in Finishing Pigs

With increasing demand for high-quality pork, development of green and healthy feed for finishing pigs is urgently needed. In this study, the effects and mechanisms of mulberry and paper mulberry silages on growth performance, meat quality, and intestinal health of finishing pigs were explored. Intestinal microbiota were profiled, and microbially produced short-chain fatty acids (SCFAs) were measured. The average daily gain (ADG) and feed conversion rate (FCR) with mulberry and paper mulberry silages were not significantly different from those of the control. Meat quality as measured by pork marbling and fatty acids in the longissimus dorsi was better with mulberry silage. The highest concentration of SCFAs was also with mulberry silage. According to 16S rRNA sequencing, Clostridium_sensu_stricto_1, Terrisporobacter, and Lachnospiraceae, which are important in SCFA production, were biomarkers of mulberry silage. PICRUSt functional analysis of intestinal microbes indicated that galactose metabolism, starch and sucrose metabolism, and carbohydrate digestion and absorption decreased significantly in silage treatments but increased in the control. Correlations between intestinal microbes and SCFAs and fatty acids indicated Clostridium_sensu_stricto_1, Terrisporobacter, and Lachnospiraceae were closely associated with SCFA and fatty acid contents. The results indicated that mulberry silage could increase SCFA content through shaping intestinal microbes to affect the deposition of fatty acids, which laid a solid theoretical foundation for improving pork quality. IMPORTANCE To avoid competition between people and animals for food, it is essential to develop nontraditional feeds. In this study, the effects of the silages of the unconventional feed resources mulberry and paper mulberry on meat quality of finishing pigs were examined. With mulberry silage in the diet, meat quality improved as indicated by meat color, marbling score, and beneficial fatty acids in the longissimus dorsi muscle. Pigs fed mulberry silage had the highest concentrations of short-chain fatty acids (SCFAs), and 16S rRNA sequencing identified Clostridium_sensu_stricto_1, Terrisporobacter, and Lachnospiraceae as biomarkers, which are important in SCFA production. Functions of intestinal microbes in the two silage groups primarily involved amino acid metabolism and SCFA production. Correlations between intestinal microbes and SCFAs and fatty acids indicated that Clostridium_sensu_stricto-1, Terrisporobacter, and Lachnospiraceae were closely associated with SCFA contents in the intestine and fatty acids in the longissimus dorsi.

Cardiometabolic impacts of saturated fatty acids: are they all comparable?

In last decades, a phenomenon named nutrition transition has been observed in many countries around the world. It has been characterised by increased consumption of fat-rich diets, predisposing to cardiometabolic diseases and high prevalence of the obesity. In the dietary recommendations cited to prevent metabolic diseases, there is a consensus to decrease intake of saturated fatty acids (SFA) to less than 10% of total energy intake, as recommended by the Food Safety Authorities. However, fatty acids of different chain lengths may exhibit different cardiometabolic effects. Thus, our major aim was to review the cardiometabolic effects of different classes of SFA according to carbon chain length, i.e. short-, medium- and long-chains. The review emphasises that not all SFA may have harmful cardiometabolic effects since short- and medium-chain SFA can provide beneficial health effects and participate to the prevention of metabolic disorders.

Diet-induced metabolic changes of the human gut microbiome: importance of short-chain fatty acids, methylamines and indoles

The human gut is a home for more than 100 trillion bacteria, far more than all other microbial populations resident on the body's surface. The human gut microbiome is considered as a microbial organ symbiotically operating within the host. It is a collection of different cell lineages that are capable of communicating with each other and the host and has an ability to undergo self-replication for its repair and maintenance. As the gut microbiota is involved in many host processes including growth and development, an imbalance in its ecological composition may lead to disease and dysfunction in the human. Gut microbial degradation of nutrients produces bioactive metabolites that bind target receptors, activating signalling cascades, and modulating host metabolism. This review covers current findings on the nutritional and pharmacological roles of selective gut microbial metabolites, short-chain fatty acids, methylamines and indoles, as well as discussing nutritional interventions to modulate the microbiome.

Prebiotics: Definition, Types, Sources, Mechanisms, and Clinical Applications

Prebiotics are a group of nutrients that are degraded by gut microbiota. Their relationship with human overall health has been an area of increasing interest in recent years. They can feed the intestinal microbiota, and their degradation products are short-chain fatty acids that are released into blood circulation, consequently, affecting not only the gastrointestinal tracts but also other distant organs. Fructo-oligosaccharides and galacto-oligosaccharides are the two important groups of prebiotics with beneficial effects on human health. Since low quantities of fructo-oligosaccharides and galacto-oligosaccharides naturally exist in foods, scientists are attempting to produce prebiotics on an industrial scale. Considering the health benefits of prebiotics and their safety, as well as their production and storage advantages compared to probiotics, they seem to be fascinating candidates for promoting human health condition as a replacement or in association with probiotics. This review discusses different aspects of prebiotics, including their crucial role in human well-being.

Growth performance, lipid metabolism, and health status of grass carp (Ctenopharyngodon idella) fed three different forms of sodium butyrate

Sodium butyrate (SB) can be coated with fatty acid matrix. In this study, the effects of three SB forms, being zero-lipid-coated (SB-A), half-lipid-coated (SB-B), and 2/3 lipid-coated (SB-C) (w/w), on growth, lipid metabolism, and health status of grass carp (Ctenopharyngodon idella) were investigated. The three forms of SB were added to a control diet to form three SB diets, Con., SB-A, SB-B, and SB-C, where the pure SB in each SB diet was kept at the same level (500 mg kg^-1). A total of 216 C. idella (14.10 ± 0.60 g/fish) were allotted into four groups (triplicate per group) and fed the four diets respectively for 56 days, and then fish were sampled and determined. Fish growth was not affected by any of the three forms of SB. Viscerosomatic index, intraperitoneal fat index, and crude lipid of hepatopancreas and muscle were significantly decreased and villus height of intestine and mRNA expression of MyD88 and TLR22 in hepatopancreas were significantly improved in SB diets compared with control (p < 0.05), respectively. MiSeq sequencing of the V3-V4 region of bacterial 16S rRNA gene revealed that SB increased the relative abundances of intestinal healthy bacteria, Fusobacteria and Bacteroides, and the abundances of Cetobacterium decreased in the SB-C group. In conclusion, the present results showed that three forms of SB, without affecting the growth of fish, respectively decreased lipid accumulation and probably have a beneficial effect on health of C. idella.

Distant Site Effects of Ingested Prebiotics

The gut microbiome is being more widely recognized for its association with positive health outcomes, including those distant to the gastrointestinal system. This has given the ability to maintain and restore microbial homeostasis a new significance. Prebiotic compounds are appealing for this purpose as they are generally food-grade substances only degraded by microbes, such as bifidobacteria and lactobacilli, from which beneficial short-chain fatty acids are produced. Saccharides such as inulin and other fructo-oligosaccharides, galactooligosaccharides, and polydextrose have been widely used to improve gastrointestinal outcomes, but they appear to also influence distant sites. This review examined the effects of prebiotics on bone strength, neural and cognitive processes, immune functioning, skin, and serum lipid profile. The mode of action is in part affected by intestinal permeability and by fermentation products reaching target cells. As the types of prebiotics available diversify, so too will our understanding of the range of microbes able to degrade them, and the extent to which body sites can be impacted by their consumption.

The role of probiotics on each component of the metabolic syndrome and other cardiovascular risks

INTRODUCTION

Probiotics are defined as live microorganisms that when administered in adequate amounts confer health benefits to the host. The consumption of probiotics has gained increasing recognition from the scientific community due to the promising effects on metabolic health through gut microbiota modulation.

AREAS COVERED

This article presents a review of scientific studies investigating probiotic species and their effects on different risk factors of the metabolic syndrome (MetS). This article also presents a summary of the major mechanisms involved with gut microbiota and the components of the MetS and raises the key issues to be considered by scientists in search of probiotics species for treatment of patients suffering from this metabolic disorder.

EXPERT OPINION

Probiotics may confer numerous health benefits to the host through positive gut microbiota modulation. The strain selection is the most important factor for determining health effects. Further studies may consider gut microbiota as a novel target for prevention and management of MetS components and other cardiovascular risks.

Comparison of acarbose and voglibose in diabetes patients who are inadequately controlled with basal insulin treatment: randomized, parallel, open-label, active-controlled study

We studied the efficacy and safety of acarbose in comparison with voglibose in type 2 diabetes patients whose blood glucose levels were inadequately controlled with basal insulin alone or in combination with metformin (or a sulfonylurea). This study was a 24-week prospective, open-label, randomized, active-controlled multi-center study. Participants were randomized to receive either acarbose (n=59, 300 mg/day) or voglibose (n=62, 0.9 mg/day). The mean HbA1c at week 24 was significantly decreased approximately 0.7% from baseline in both acarbose (from 8.43% ± 0.71% to 7.71% ± 0.93%) and voglibose groups (from 8.38% ± 0.73% to 7.68% ± 0.94%). The mean fasting plasma glucose level and self-monitoring of blood glucose data from 1 hr before and after each meal were significantly decreased at week 24 in comparison to baseline in both groups. The levels 1 hr after dinner at week 24 were significantly decreased in the acarbose group (from 233.54 ± 69.38 to 176.80 ± 46.63 mg/dL) compared with the voglibose group (from 224.18 ± 70.07 to 193.01 ± 55.39 mg/dL). In conclusion, both acarbose and voglibose are efficacious and safe in patients with type 2 diabetes who are inadequately controlled with basal insulin. (ClinicalTrials.gov number, NCT00970528).

Dietary roles of non-starch polysaccharides in human nutrition: a review

Nonstarch polysaccharides (NSPs) occur naturally in many foods. The physiochemical and biological properties of these compounds correspond to dietary fiber. Nonstarch polysaccharides show various physiological effects in the small and large intestine and therefore have important health implications for humans. The remarkable properties of dietary NSPs are water dispersibility, viscosity effect, bulk, and fermentibility into short chain fatty acids (SCFAs). These features may lead to diminished risk of serious diet related diseases which are major problems in Western countries and are emerging in developing countries with greater affluence. These conditions include coronary heart disease, colo-rectal cancer, inflammatory bowel disease, breast cancer, tumor formation, mineral related abnormalities, and disordered laxation. Insoluble NSPs (cellulose and hemicellulose) are effective laxatives whereas soluble NSPs (especially mixed-link β-glucans) lower plasma cholesterol levels and help to normalize blood glucose and insulin levels, making these kinds of polysaccharides a part of dietary plans to treat cardiovascular diseases and Type 2 diabetes. Moreover, a major proportion of dietary NSPs escapes the small intestine nearly intact, and is fermented into SCFAs by commensal microflora present in the colon and cecum and promotes normal laxation. Short chain fatty acids have a number of health promoting effects and are particularly effective in promoting large bowel function. Certain NSPs through their fermented products may promote the growth of specific beneficial colonic bacteria which offer a prebiotic effect. Various modes of action of NSPs as therapeutic agent have been proposed in the present review. In addition, NSPs based films and coatings for packaging and wrapping are of commercial interest because they are compatible with several types of food products. However, much of the physiological and nutritional impact of NSPs and the mechanism involved is not fully understood and even the recommendation on the dose of different dietary NSPs intake among different age groups needs to be studied.

Intravenous acetate elicits a greater free fatty acid rebound in normal than hyperinsulinaemic humans

Background/Objectives

Colonic fermentation of dietary fiber may improve insulin sensitivity via the metabolic effects of short chain fatty acids (SCFA) in reducing free fatty acids (FFA). The main objectives of this study were to compare peripheral uptake of acetate (AC) in participants with normal (< 40pmol/L, NI) and high (≥ 40pmol/L, HI) plasma-insulin and the ability of AC to reduce FFA in both groups.

Subject/Methods

Overnight fasted NI (n = 9) and HI (n = 9) participants were given an intravenous (IV) infusion of 140 mmol/L sodium acetate at 3 different rates over 90 minutes. The total amount of AC infused was 51.85 mmols.

Results

Acetate clearance in NI participants was not significantly different than that in HI participants (2.11 ± 0.23 vs 2.09 ± 0.24 ml/min). FFA fell in both groups, but rebounded to a greater extent in NI than HI participants (time × group interaction, P = 0.001). Significant correlations between insulin resistance (IR) indices (HOMA-IR, Matsuda and Insulinogenic Index) vs FFA rebound during IV AC infusion were also observed.

Conclusions

These findings suggest that AC uptake is similar in both groups. Participants with lower plasma insulin and lower IR indices had a greater FFA rebound. These results support the hypothesis that increasing AC concentrations in the systemic circulation may reduce lipolysis and plasma FFA concentrations and thus improve insulin sensitivity. More in-depth studies are needed to look at the effects of SCFA on FFA metabolism in insulin resistant participants.

Digestive and physiologic effects of a wheat bran extract, arabino-xylan-oligosaccharide, in breakfast cereal

OBJECTIVE

We assessed whether a wheat bran extract containing arabino-xylan-oligosaccharide (AXOS) elicited a prebiotic effect and influenced other physiologic parameters when consumed in ready-to-eat cereal at two dose levels.

METHODS

This double-blind, randomized, controlled, crossover trial evaluated the effects of consuming AXOS at 0 (control), 2.2, or 4.8 g/d as part of ready-to-eat cereal for 3 wk in 55 healthy men and women. Fecal microbial levels, postprandial serum ferulic acid concentrations, and other physiologic parameters were assessed at the beginning and end of each condition.

RESULTS

The median bifidobacteria content of stool samples (log₁₀/grams of dry weight [DW]) was found to be higher in the subjects consuming the 4.8-g/d dose (10.03) than in those consuming 2.2 g/d (9.93) and control (9.84, P < 0.001). No significant changes in the populations of other fecal microbes were observed, indicating a selective increase in fecal bifidobacteria. Postprandial ferulic acid was measured at 120 min at the start and end of each 3-wk treatment period in subjects at least 50 y old (n = 37) and increased in a dose-dependent manner (end-of-treatment values 0.007, 0.050, and 0.069 μg/mL for the control, AXOS 2.2 g/d, and AXOS 4.8 g/d conditions, respectively, P for trend < 0.001).

CONCLUSION

These results indicate that AXOS has prebiotic properties, selectively increasing fecal bifidobacteria, and increases postprandial ferulic acid concentrations in a dose-dependent manner in healthy men and women.

Is the gut microbiota a new factor contributing to obesity and its metabolic disorders?

The gut microbiota refers to the trillions of microorganisms residing in the intestine and is integral in multiple physiological processes of the host. Recent research has shown that gut bacteria play a role in metabolic disorders such as obesity, diabetes, and cardiovascular diseases. The mechanisms by which the gut microbiota affects metabolic diseases are by two major routes: (1) the innate immune response to the structural components of bacteria (e.g., lipopolysaccharide) resulting in inflammation and (2) bacterial metabolites of dietary compounds (e.g., SCFA from fiber), which have biological activities that regulate host functions. Gut microbiota has evolved with humans as a mutualistic partner, but dysbiosis in a form of altered gut metagenome and collected microbial activities, in combination with classic genetic and environmental factors, may promote the development of metabolic disorders. This paper reviews the available literature about the gut microbiota and aforementioned metabolic disorders and reveals the gaps in knowledge for future study.

Inulin increases short-term markers for colonic fermentation similarly in healthy and hyperinsulinaemic humans

Background/Objectives

Colonic fermentation of dietary fibre produces short-chain fatty-acids (SCFA) acetate, propionate and butyrate, which may protect against type 2 diabetes by reducing serum free-fatty acids (FFA). Since hyperinsulinemia is associated with insulin resistance and increased diabetes risk, the main objective was to compare markers of colonic fermentation after acute inulin ingestion in subjects with normal (< 40pmol/L, NI) and high (≥ 40pmol/L, HI) plasma-insulin.

Subjects/Methods

Overnight fasted NI (n = 9) and HI (n = 9) subjects were studied for 4 h on 2 separate days after consuming 300 ml drinks containing 75 g glucose (Glucose) or 75 g glucose plus 24 g inulin (Inulin) using a randomized, single-blind, cross-over design.

Results

Inulin elicited a higher breath hydrogen and methane AUC but the increases in SCFA responses were not statistically significant. Overall mean serum-acetate over the 4 h study period was higher in NI than HI subjects (44.3±6.9 vs 22.5±3.7 μmol/L, p = 0.001). The rate of rebound of FFA was reduced by Inulin, with FFA at 4hr being less after Inulin than Glucose, regardless of insulin status (0.310±0.028 vs 0.432±0.042 mEq/L, p = 0.008).

Conclusions

This suggests that inulin increases short-term markers for colonic fermentation but a longer study period may be necessary to observe differences in SCFA production. The reason for the lower serum-acetate in HI is unclear but may be due to reduced absorption, increased clearance or decreased endogenous production. This suggests the need to compare acetate kinetics in normal and hyperinsulinemic subjects.

The effect of Linola and W92/72 transgenic flax seeds on the rabbit caecal fermentation--in vitro study

The effect of W92/72 transgenic flax seeds taken from a variety of Linola on the production of SCFA, ammonia and methane by bacteria inhabiting rabbit caecum was studied. The in vitro method was used where caecal contents from rabbits was incubated with W92/72 transgenic or Linola flax seeds, or without any additives (control samples). The total concentration of SCFA was higher in samples with the addition of flax seeds than in the control samples. The increase in concentrations of acetic, propionic and butyric acids was the highest in samples with Linola seeds added. A higher percentage of propionic and butyric acids was observed in the contents incubated with addition of flax seeds as compared to the control samples. This increase was the result of a percentage decrease in acetic acid. No differences were observed in the concentration of ammonia between fermented samples. Moreover, the addition of flax seeds resulted in slight decrease of pH in incubated samples. In gas samples, the methane level was higher in samples with flax seeds added, although the highest level was found in samples with transgenic seeds. In addition, gas pressure was significantly higher in samples with flax seeds added as compared to control samples, and this may indicate a higher intensity of microbiological fermentation processes. These studies suggest that neither Linola nor W92/72 flax seeds have any unfavorable effect on the caecal microflora activity of rabbits. A beneficial influence of flax seeds on the microbiological fermentation process in rabbit caecum was observed, based on an increase in percentage ratio of propionic acid in samples with flax seeds added.

Antihypertensive properties of plant-based prebiotics

Hypertension is one of the major risk factors for cardiovascular disease. Although various drugs for its treatment have been synthesized, the occurring side effects have generated the need for natural interventions for the treatment and prevention of hypertension. Dietary intervention such as the administration of prebiotics has been seen as a highly acceptable approach. Prebiotics are indigestible food ingredients that bypass digestion and reach the lower gut as substrates for indigenous microflora. Most of the prebiotics used as food adjuncts, such as inulin, fructooligosaccharides, dietary fiber and gums, are derived from plants. Experimental evidence from recent studies has suggested that prebiotics are capable of reducing and preventing hypertension. This paper will discuss some of the mechanisms involved, the evidence generated from both in-vitro experiments and in-vivo trials and some controversial findings that are raised.

Carbohydrate digestibility and metabolic effects

There is a history of interest in the metabolic effects of alterations in small intestinal digestion and colonic fermentation of carbohydrate. It is believed that the rate of digestion of carbohydrate determines the place and form in which carbohydrate is absorbed. Slowly absorbed or lente carbohydrate sources may reduce postprandial glucose surges and the need for insulin with important implications for lowering coronary heart disease risk and reducing diabetes incidence. Carbohydrates that are not digested in the small intestine will enter the colon, and those that are fermentable will be salvaged as short-chain fatty acids in the colon and at the same time may stimulate colonic microflora, such as bifidobacteria. This process may have metabolic effects in the gut and throughout the host, possibly related to short-chain fatty acid products, although these effects are less well documented. One important aspect of colonic fermentation is the stimulation of certain populations of the colonic microflora, which may assist in the biotransformation of bioactive food components including the cleaving of plant phenolics from their glycone to produce the more rapidly absorbed aglycone. However, human studies have been limited. Therefore, further studies are required to explore these important aspects of metabolism related to the rate of carbohydrate absorption and fermentation and their implications in health and disease.

Effect of Dietary Rhodobacter capsulatus on Egg-Yolk Cholesterol and Laying Hen Performance

The present study was conducted to investigate the effects of dietary Rhodobacter capsulatus on the laying hen. A total of forty 23-wk-old Hy-Line Brown laying hens were randomly assigned into 4 treatment groups (10 laying hens/group) and fed diets supplemented with 0 (control), 0.01, 0.02, and 0.04% R. capsulatus during the 60-d feeding period. Dietary supplementation of R. capsulatus (0.04%) reduced (P < 0.05) cholesterol and triglycerides concentration in serum (15 and 11%), as well as in egg-yolk (13 and 16%) over a 60-d feeding period. Cholesterol and triglycerides concentrations in serum as well as egg-yolk were changed linearly in accordance with increasing levels of dietary R. capsulatus. Supplementation of R. capsulatus in diets increased high-density lipoprotein cholesterol level and decreased (P < 0.05) atherogenic index in serum. Yolk color was improved (P < 0.05) in the group fed the 0.04% R. capsulatus supplemented diet compared with the control group. Hepatic cholesterol and triglycerides were reduced (P < 0.05) by 0.04% R. capsulatus. Moreover, the supplementation of R. capsulatus in layer diets did not appear to cause any adverse effects on egg production, shell weight, shell thickness, Haugh unit, yolk index, and feed conversion efficiency compared with the same parameters for the control laying hens. It is postulated that known and unknown factors are present in R. capsulatus presumably responsible for the hypocholesterolemic effect on laying hens. Therefore, the dietary supplementation of R. capsulatus may lead to the development of low-cholesterol chicken eggs as demanded by health-conscious consumers.

Short-chain fatty acid formation in the hindgut of rats fed oligosaccharides varying in monomeric composition, degree of polymerisation and solubility

The contents of short-chain fatty acids were investigated in rats fed lactitol, lactulose and four fructo-oligosaccharides of different degree of polymerisation and solubility. Fructo-oligosaccharides with a low degree of polymerisation (2–8) generated the highest levels of butyric acid all along the hindgut, whereas fructo-oligosaccharides with a high degree of polymerisation (10–60) generated the highest levels of propionic acid. These specific differences were also generally reflected in the caecal pools and molar proportions of short-chain fatty acids. The lower solubility of the fructo-oligosaccharides was related to a lower degree of caecal fermentation. Lactulose and lactitol yielded high proportions of acetic acid and low proportions of butyric acid. It is concluded that both the degree of polymerisation and the solubility may affect short-chain fatty acid formation, whereas the fructose contentper seseem to be of less importance. This may be of interest when designing foods with specific health effects.

L-rhamnose and lactulose decrease serum triacylglycerols and their rates of synthesis, but do not affect serum cholesterol concentrations in men

Colonic short-chain fatty acids (SCFA) may affect hepatic lipid metabolism. Lactulose increases colonic acetate production, whereas L-rhamnose increases propionate. To test the effects of oral L-rhamnose and lactulose for 28 d on fasting concentrations and hepatic synthesis of lipids in humans, 18 men were administered 25 g/d of L-rhamnose, lactulose, or d-glucose for 4 wk in a partially randomized crossover design, with blood collected from fasting subjects on the first and last day of each period. Cholesterol and triacylglycerol (TG) synthesis rates were determined using deuterated water uptake rate over the last 24 h of each period. Postprandial blood lipids, and glucose and insulin were assessed in 11 subjects on d 28. Fasting serum cholesterol was unchanged; however, when expressed as a percentage change, TG were decreased, relative to baseline (P < 0.04), by L-rhamnose (-10%) and lactulose (-10%), compared with D-glucose, which increased serum TG (+11%). Net TG-fatty acid (TGFA) synthesis on d 28 was lower with L-rhamnose (2.42 +/- 0.38 g/d) and lactulose (2.62 +/- 0.35 g/d) than with D-glucose (2.96 +/- 0.31 g/d, P < 0.01). We conclude that these results do not support a primary role for propionate in the cholesterol-lowering effect of soluble fiber. However, both lactulose and L-rhamnose lowered serum TG (expressed as a percentage change) and TGFA synthesis, compared with d-glucose, which increased them. Although these data are consistent with inhibition of TGFA synthesis by SCFA, other aspects of the metabolism of these sugars cannot be ruled out as putative agents of their TG-lowering effects.

Colonic health: fermentation and short chain fatty acids

Interest has been recently rekindled in short chain fatty acids (SCFAs) with the emergence of prebiotics and probiotics aimed at improving colonic and systemic health. Dietary carbohydrates, specifically resistant starches and dietary fiber, are substrates for fermentation that produce SCFAs, primarily acetate, propionate, and butyrate, as end products. The rate and amount of SCFA production depends on the species and amounts of microflora present in the colon, the substrate source and gut transit time. SCFAs are readily absorbed. Butyrate is the major energy source for colonocytes. Propionate is largely taken up by the liver. Acetate enters the peripheral circulation to be metabolized by peripheral tissues. Specific SCFA may reduce the risk of developing gastrointestinal disorders, cancer, and cardiovascular disease. Acetate is the principal SCFA in the colon, and after absorption it has been shown to increase cholesterol synthesis. However, propionate, a gluconeogenerator, has been shown to inhibit cholesterol synthesis. Therefore, substrates that can decrease the acetate: propionate ratio may reduce serum lipids and possibly cardiovascular disease risk. Butyrate has been studied for its role in nourishing the colonic mucosa and in the prevention of cancer of the colon, by promoting cell differentiation, cell-cycle arrest and apoptosis of transformed colonocytes; inhibiting the enzyme histone deacetylase and decreasing the transformation of primary to secondary bile acids as a result of colonic acidification. Therefore, a greater increase in SCFA production and potentially a greater delivery of SCFA, specifically butyrate, to the distal colon may result in a protective effect. Butyrate irrigation (enema) has also been suggested in the treatment of colitis. More human studies are now needed, especially, given the diverse nature of carbohydrate substrates and the SCFA patterns resulting from their fermentation. Short-term and long-term human studies are particularly required on SCFAs in relation to markers of cancer risk. These studies will be key to the success of dietary recommendations to maximize colonic disease prevention.

Effect of antibiotics as cholesterol-lowering agents

Antibiotics were once proposed as hypercholesterolemic agents although the mechanism is unclear, despite broad implications, including providing an alternative approach to cholesterol reduction, with potential relevance for current trials of antibiotics to reduce cardiovascular disease, and possible confounding of routine diagnostic cholesterol measurements. The effect on serum lipids of antibiotics against aerobes and anaerobes, together with possible mechanisms, was therefore explored. Twenty-two men and women took antibiotics for 10 days (either ciprofloxacin for 13 subjects or metronidazole for 10 subjects), with 10 days control in random order separated by 2-week washout periods. Subjects maintained low-fat diets throughout the study. Blood samples and blood pressure were obtained on days 0 and 10 of each phase with 3-day fecal collections and 12-hour breath gas collections at the end of each phase. The results indicated that metronidazole markedly reduced low-density lipoprotein cholesterol (-14.0 +/- 4.0%, P = .006), oxidized low-density lipoprotein (-23.0 +/- 5.1%, P = .002), and the apolipoprotein B/A-I ratio (-18.0 +/- 2.8%, P < .001), whereas the reduction with ciprofloxacin was less pronounced (apolipoprotein B/A-I, -5.0 +/- 1.8%, P = .017). Neither antibiotic altered C-reactive protein or blood pressure. The low-density lipoprotein cholesterol reduction related to an increase in bifidobacteria (r = -0.46, P = .029), but not to markers of colonic fermentation. We conclude that antibiotics can reduce serum lipids acutely. These effects may confound diagnostic measurements but indicate possible links between colonic microflora and blood lipids and the need to study ways of altering colonic microflora by nonantibiotic means as a potential therapeutic option.

L-Rhamnose increases serum propionate in humans

BACKGROUND

Acetic and propionic acids are produced by colonic bacterial fermentation of unabsorbed carbohydrates and are absorbed into the portal circulation. From there, they travel to the liver, where acetate is a lipogenic substrate and propionate can inhibit lipogenesis. The extent to which peripheral blood short-chain fatty acid concentrations reflect differences in colonic fermentation is uncertain. The unabsorbed sugar lactulose produces mainly acetate when fermented in vitro, whereas L-rhamnose yields propionate.

OBJECTIVE

The objective of the study was to ascertain whether ingestion of L-rhamnose and lactulose would have different acute effects on peripheral acetate and propionate concentrations and on breath hydrogen and methane concentrations.

DESIGN

Twenty-two subjects were fed 25 g L-rhamnose, lactulose, or glucose on 3 separate occasions in a randomized crossover design. Blood and breath samples were collected hourly for 12 h.

RESULTS

Serum propionate was significantly higher with ingestion of L-rhamnose than with that of lactulose or glucose (P < 0.001). The area under the curve for serum acetate was significantly higher with ingestion of lactulose than with that of glucose (P < 0.03). The ratio of serum acetate to propionate was significantly higher with ingestion of lactulose than with that of glucose or L-rhamnose (P < 0.01). Breath hydrogen was significantly higher with ingestion of lactulose than with that of L-rhamnose or glucose (P < 0.0001).

CONCLUSIONS

The selective increases in serum acetate and propionate concentrations in humans were obtained by feeding specific fermentable substrates. Presumably, these changes in serum concentrations reflect changes in colonic production. Selective alteration of colonic fermentation products could yield a new mechanism for modifying blood lipids.

Applications of inulin and oligofructose in health and nutrition

Inulin and oligofructose belong to a class of carbohydrates known as fructans. The main sources of inulin and oligofructose that are used in the food industry are chicory and Jerusalem artichoke. Inulin and oligofructose are considered as functional food ingredients since they affect the physiological and biochemical processes in rats and human beings, resulting in better health and reduction in the risk of many diseases. Experimental studies have shown their use as bifidogenic agents, stimulating the immune system of the body, decreasing the pathogenic bacteria in the intestine, relieving constipation, decreasing the risk of osteoporosis by increasing mineral absorption, especially of calcium, reducing the risk of atherosclerosis by lowering the synthesis of triglycerides and fatty acids in the liver and decreasing their level in serum. These fructans modulate the hormonal level of insulin and glucagon, thereby regulating carbohydrate and lipid metabolism by lowering the blood glucose levels; they are also effective in lowering the blood urea and uric acid levels, thereby maintaining the nitrogen balance. Inulin and oligofructose also reduce the incidence of colon cancer. The biochemical basis of these beneficial effects of inulin and oligofructose have been discussed. Oligofructose are non cariogenic as they are not used by Streptococcus mutans to form acids and insoluble glucans that are the main culprits in dental caries. Because of the large number of health promoting functions of inulin and oligofructose, these have wide applications in various types of foods like confectionery, fruit preparations, milk desserts, yogurt and fresh cheese, baked goods, chocolate, ice cream and sauces. Inulin can also be used for the preparation of fructose syrups.

Modulation of lipid synthesis, apolipoprotein biogenesis, and lipoprotein assembly by butyrate

Short-chain fatty acids (SCFAs) are potent modulators of the growth, function, and differentiation of intestinal epithelia. In addition, high-fiber diets may protect against the development of atherosclerosis because of their cholesterol-lowering effects due, in large part, to SCFA production, liver sterol metabolism, and bile acid excretion. Although the small gut plays a major role in dietary fat transport and contributes substantially to plasma cholesterol and lipoprotein homeostasis, the impact of SCFAs on intestinal lipid handling remains unknown. In the present study, the modulation of lipid synthesis, apolipoprotein biogenesis, and lipoprotein secretion by butyrate was investigated in Caco-2 cells plated on permeable polycarbonate filters, which permit separate access to the upper and lower compartments of the monolayers. Highly differentiated and polarized cells (20 days of culture) were incubated for 20 h with 20 mM butyrate in the apical medium. In the presence of [14C]oleic acid, butyrate led to a significant reduction of secreted, labeled triglycerides (27%; P < 0.01) and phospholipids (25%; P < 0.05). Similarly, butyrate significantly decreased the incorporation of [14C]acetate into exported cholesteryl ester (49%; P < 0.005). As expected from these results, with [14C]oleic acid as a precursor, butyrate significantly (P < 0.05) diminished the delivery of radiolabeled chylomicrons and very low-density lipoproteins. In parallel, [35S]methionine pulse labeling of Caco-2 cells revealed the concomitant inhibitory effect of butyrate on the synthesis of apolipoproteins B-48 (28%; P < 0.05) and A-I (32%; P < 0.01). Collectively, our data indicate that butyrate may influence lipid metabolism in Caco-2 cells, thus suggesting a potential regulation of intestinal fat absorption and circulating lipoprotein concentrations.

Do colonic short-chain fatty acids contribute to the long-term adaptation of blood lipids in subjects with type 2 diabetes consuming a high-fiber diet?

BACKGROUND

We recently obtained evidence of long-term adaptation of blood lipids to changes in intakes of carbohydrate and fiber in subjects with type 2 diabetes.

OBJECTIVE

We determined the effect of increased carbohydrate and fiber intakes on serum short-chain fatty acids (SCFAs) and the relation between changes in serum acetate and changes in blood lipids.

DESIGN

Subjects with type 2 diabetes (n = 62) were randomly assigned to receive approximately 10% of energy from low-fiber breakfast cereal (LF diet), high-fiber breakfast cereal (HF diet), or monounsaturated fatty acids (MUFA diet) for 6 mo.

RESULTS

Carbohydrate intakes were higher in the LF and HF groups than in the MUFA group (54% compared with 43%), and more fiber was consumed by the HF group (approximately 50 g/d) than by the LF or MUFA group (approximately 23 g/d). Fasting serum SCFAs did not change significantly over the first 3 mo. Between 3 and 6 mo, serum acetate tended (NS) to decrease in the LF group (from 69 +/- 4 to 59 +/- 5 micromol/L) and increase in the HF group (from 100 +/- 18 to 107 +/- 17 micromol/L), with no significant change in the MUFA group. Serum butyrate did not change significantly in the LF or MUFA group but increased in the HF group (from 2.5 +/- 0.5 to 3.1 +/- 0.6 micromol/L; P < 0.001). Changes in serum acetate from 0 to 3 mo were not related to changes in lipids. However, changes in serum acetate from 3 to 6 mo were positively related to changes in the ratio of total to HDL cholesterol (P = 0.041) and in fasting (P = 0.013) and postprandial (P = 0.016) triacylglycerols.

CONCLUSIONS

In subjects with type 2 diabetes, changes in serum SCFAs in response to changes in carbohydrate and fiber intakes took many months to occur, and the changes in serum acetate were significantly related to the long-term adaptive changes in blood lipids.

Dietary fructans, but not cellulose, decrease triglyceride accumulation in the liver of obese Zucker fa/fa rats

This study was designed to compare the effects of dietary supplementation with nondigestible carbohydrates, differing in fermentability by colonic bacteria, on hepatic steatosis in growing obese Zucker rats. Male Zucker fa/fa rats were divided into three groups: a control group that received the basal diet, a fructan group that received 10 g highly fermented Synergy 1/100 g diet and a cellulose group that received 10 g poorly fermented Vivapur Microcrystalline cellulose/100 g diet. Rats consuming fructan had a lower energy intake, a lower body weight and less triacylglycerol accumulation in the liver as assessed in vivo by nuclear magnetic resonance (NMR) spectroscopy, and ex vivo by biochemical and histochemical analysis compared with the control and/or cellulose groups. The high fermentation of fructans compared with cellulose was reflected by greater cecal contents and by a twofold greater propionate concentration in the portal vein of rats fed fructan compared with those fed cellulose. By measuring the capacity of hepatocytes isolated from liver of Zucker rats to synthesize triglycerides or total lipids from different precursors, we showed that propionate, at the concentrations measured in the portal vein of rats treated with fructan, selectively decreased the incorporation of acetate into total lipids, a phenomenon that could contribute, along with the lower energy intake, to less triglyceride accumulation in the liver of obese Zucker rats fed dietary fructans.

Comparison of high- and low-glycemic-index breakfast cereals with monounsaturated fat in the long-term dietary management of type 2 diabetes

BACKGROUND

Results of 6-wk studies suggest that high-carbohydrate diets are deleterious for people with type 2 diabetes.

OBJECTIVE

Our objective was to see whether long-term replacement of dietary monounsaturated fatty acids (MUFAs) with carbohydrate from breakfast cereals with either a high or a low glycemic index (GI) affected blood glucose and lipids in subjects with type 2 diabetes.

DESIGN

Subjects with type 2 diabetes (n = 91) were randomly assigned to receive approximately 10% of energy from a low-GI breakfast cereal, a high-GI cereal, or oil or margarine containing MUFA for 6 mo. Eating breakfast cereal was prohibited for subjects in the MUFA group.

RESULTS

Seventy-two subjects completed the trial. The subjects who received cereals consumed approximately 10% more energy from carbohydrate than did the subjects in the MUFA group. Changes in glycated hemoglobin, body weight, and fasting cholesterol and triacylglycerol did not differ significantly among groups. HDL cholesterol increased by approximately 10% in the MUFA group compared with subjects who consumed either high- or low-GI cereals (P = 0.002). The ratio of total to HDL cholesterol was higher in the subjects who consumed the high-GI cereal than in the MUFA group at 3 mo but not at 6 mo (diet x time interaction, P = 0.041). During 8-h metabolic profiles, mean plasma insulin was higher and mean free fatty acids were lower in the 2 cereal groups than in the MUFA group (P < 0.05).

CONCLUSIONS

A 10% increase in carbohydrate intake associated with breakfast cereal consumption had no deleterious effects on glycemic control or blood lipids over 6 mo in subjects with type 2 diabetes. The increase in plasma insulin and the reduction in free fatty acids associated with higher carbohydrate intake may reduce the rate of progression of diabetes.

Consumption of fermented and nonfermented dairy products: effects on cholesterol concentrations and metabolism

The objective of this article was to review existing literature concerning the effects and mechanisms of action of fermented dairy products on serum cholesterol concentrations. Although not without exception, existing evidence from animal and human studies suggests a moderate cholesterol-lowering action of fermented dairy products. Mechanistically, fermented milk has been shown to cause an increase in human gut bacterial content. These bacteria, once resident in the large intestine, are believed to ferment food-derived indigestible carbohydrates. Such fermentation causes increased production of short-chain fatty acids, which decreases circulatory cholesterol concentrations either by inhibiting hepatic cholesterol synthesis or by redistributing cholesterol from plasma to the liver. Furthermore, increased bacterial activity in the large intestine results in enhanced bile acid deconjugation. Deconjugated bile acids are not well absorbed by the gut mucosa and are excreted. Consequently, cholesterol, being a precursor of bile acids, is utilized to a greater extent for de novo bile acid synthesis. These actions combined are proposed as contributing mechanisms to the association of fermented milk consumption with decreased circulating cholesterol concentrations.

Viscous and nonviscous fibres, nonabsorbable and low glycaemic index carbohydrates, blood lipids and coronary heart disease

Viscous fibres such as guar, glucomannans, pectins, oat betaglucan and psyllium continue to be seen as hypocholesterolaemic. Nevertheless, in large cohort studies, ironically it is the insoluble cereal fibre that has been demonstrated to relate negatively to cardiovascular disease and diabetes, despite an absence of effect on fasting lipids or postprandial glycaemia. In general, resistant or nonabsorbable starch is lipid neutral, whereas some nonabsorbable sugars or oligosaccharides may raise serum cholesterol, possibly through providing more acetate after colonic fermentation by colonic microflora. On the other hand, fructo-oligosaccharides appear to reduce serum triglycerides for reasons that are not entirely clear. Of possibly greater recent interest have been the carbohydrates that are not so much resistant to absorption, but rather are slowly absorbed. They possess some of the features of dietary fibre in providing a substrate for colonic bacterial fermentation. In the small intestine, however, they form lente or sustained release carbohydrate. In the form of low glycaemic index foods, lente carbohydrate consumption has been shown to relate to improved blood lipid profiles in hyperlipidaemic individuals and improved glycaemic control in diabetes. In larger cohort studies, low glycaemic index foods or low glycaemic load diets have been associated with higher HDL-cholesterol levels and reduced incidence of diabetes and cardiovascular disease.

Inulin, oligofructose and intestinal function

Inulin and oligofructose have attracted much attention recently as nonabsorbable carbohydrates with prebiotic properties. When inulin and oligofructose were added to a controlled diet, significant increases were noted in colonic bifidobacterial populations, and it has been proposed that these changes promote both colonic and systemic health through modification of the intestinal microflora. Inulin and oligofructose are rapidly and completely fermented by the colonic microflora with the production of acetate and other short-chain fatty acids. As with lactulose, they may also result in the growth of the fecal biomass, and in doing so, entrap ammonia for bacterial protein synthesis or conversion to the ammonium ion. As with dietary fiber and other nonabsorbable carbohydrates, there is also interest in inulin and oligofructose from the standpoint of inhibition of colonic carcinogenesis, blood cholesterol reduction, immune stimulation and enhanced vitamin synthesis. In these areas, the influence of their molecular weight is also an issue, with the longer chain length providing a more sustained fermentation pattern. More human studies are now required, including studies on the long-term effects of inulin and oligofructose consumption on colonic health, in particular on markers of cancer risk such as reduction in colonic polyp recurrence.

Colonic bacterial activity and serum lipid risk factors for cardiovascular disease

Antibiotics are being proposed for the treatment of cardiovascular disease. In the past, antibiotics were advocated for the control of hypercholesterolemia. We have therefore investigated the relation between colonic bacterial activity and serum lipids. In a four-phase randomized crossover study, we fed a different starch supplement during each 2-week phase to 24 healthy subjects. In two phases, supplements containing resistant starches were fed that reach the colon and are largely fermented by colonic bacteria. Fecal starch recovery therefore reflects the metabolic activity of colonic microflora. The control treatments were conventional starches. Blood lipid levels were obtained at the start and 4-day fecal collections at the end of each phase. Resistant starch supplements increased fecal starch excretion by 3.8 +/- 1.2 g/d more than conventional starches (P = .006). Mean starch excretion was related positively to pretreatment serum high-density lipoprotein (HDL) cholesterol (r = -.57, P = .003) and negatively to low-density lipoprotein (LDL) cholesterol (r = -.57, P = .004), apolipoprotein B:AI (r = -.56, P = .005), and fecal output of fusobacteria (r = -.73, P = .003) and bacteroides (r = -.72, P = .003). The ratio of fusobacteria to total anaerobes was also related to pretreatment LDL cholesterol (r = .56, P = .037). Differences in starch excretion between healthy subjects, as a measure of bacterial activity, accounted for 32% of the variation in pretreatment LDL cholesterol. The activity of colonic microflora therefore appears to influence serum lipid levels. Alterations of bacterial number and activity may provide an additional strategy to control serum lipid risk factors for cardiovascular disease.

A novel source of wheat fiber and protein: effects on fecal bulk and serum lipids

BACKGROUND

Wheat fiber is a laxative and wheat protein may affect blood lipids.

OBJECTIVE

We therefore tested the effects on laxation and serum lipid metabolism of a novel source of wheat fiber and protein produced by the amylolytic digestion of starch from wheat.

DESIGN

Twenty-four healthy men and women consumed 3 different test cereals in random order, each for 2 wk. The test supplement and the positive control, American Association of Cereal Chemists wheat bran supplement, both provided the same amount of fiber (21 g/d) and the negative control supplement provided 1.7 g fiber/d.

RESULTS

The test supplement and the positive control supplement increased fecal bulk similarly (239.5+/-19 and 216.7+/-19 g/d, respectively) and significantly more than did the negative control supplement (165.6+/-16 g/d, P < 0.010). Compared with the negative and positive control supplements, the week 2 value of the test supplement for the ratio of total to HDL cholesterol was significantly reduced (P = 0.046).

CONCLUSION

We conclude that the product of amylolytic digestion of starch from wheat flakes, which is high in wheat fiber and protein, has a fecal bulking effect similar to that of wheat bran and may have a beneficial effect on serum lipids.

Consumption of fructooligosaccharides does not favorably affect blood glucose and serum lipid concentrations in patients with type 2 diabetes

BACKGROUND

Fructooligosaccharides have been claimed to lower fasting glycemia and serum total cholesterol concentrations, possibly via effects of short-chain fatty acids produced during fermentation.

OBJECTIVE

We studied the effects of fructooligosaccharides on blood glucose, serum lipids, and serum acetate in 20 patients with type 2 diabetes.

DESIGN

In a randomized, single-blind, crossover design, patients consumed either glucose as a placebo (4 g/d) or fructooligosaccharides (15 g/d) for 20 d each. Average daily intakes of energy, macronutrients, and dietary fiber were similar with both treatments.

RESULTS

Compliance, expressed as the proportion of supplements not returned, was near 100% during both treatments. Fructooligosaccharides did not significantly affect fasting concentrations (mmol/L) of serum total cholesterol (95% CI: -0.07, 0.48), HDL cholesterol (-0.04, 0.04), LDL cholesterol (-0.06, 0.34), serum triacylglycerols (-0.21, 0.44), serum free fatty acids (-0.08, 0.04), serum acetate (-0.01, 0.01), or blood glucose (-0.37, 0.40).

CONCLUSIONS

We conclude that 20 d of dietary supplementation with fructooligosaccharides had no major effect on blood glucose, serum lipids, or serum acetate in patients with type 2 diabetes. This lack of effect was not due to changes in dietary intake, insufficient statistical power, or noncompliance of the patients.

Dietary fructans

Fructan is a general term used for any carbohydrate in which one or more fructosyl-fructose link constitutes the majority of osidic bonds. This review focuses on the fate of inulin-type fructans (namely native chicory inulin, oligofructose produced by the partial enzymatic hydrolysis of chicory inulin, and synthetic fructans produced by enzymatic synthesis from sucrose) in the gastrointestinal tract, as well as on their systemic physiological effects on mineral absorption, carbohydrate and lipid metabolism, hormone balance, and nitrogen homeostasis. The scientific evidence for the functional claims of inulin-type fructans is discussed, as well as their potential application in risk reduction of disease, namely constipation, infectious diarrhea, cancer, osteoporosis, atherosclerotic cardiovascular disease, obesity, and non-insulin dependent diabetes.

Functional food science and substrate metabolism

The present review addresses the role of food constituents in the aetiology of metabolic conditions and chronic diseases, mostly related to energy metabolism and substrate regulation, such as obesity and non-insulin-dependent diabetes mellitus. Second, attention is paid to malnutrition, a major cause of mortality and morbidity in developing countries, which may be a cause of concern in Europe because of the increasing number of elderly people in the population. Finally, the role of diet during exercise, a condition of enormous substrate demands, is evaluated. Based on a critical evaluation of the existing knowledge in the literature, implications for future research in relation to functional foods are discussed.

Increased serum cholesterol in healthy human methane producers is confounded by age

It has been theorized that colonic production and absorption of short-chain fatty acids (SCFA) is different in methane producers (MP) compared with nonproducers (MNP). Because colonic SCFA may influence systemic lipid metabolism, blood lipids may differ in MP and MNP. To compare serum lipids and SCFA in fasting MP and MNP, we measured breath gases, serum lipids and SCFA in 167 healthy subjects and excluded subjects with abnormal blood lipids. The 66 MP were significantly older than the 63 MNP (49.5 +/- 16.0 vs. 39.6 +/- 17.0 y, P = 0.0009), and breath methane concentrations were weakly correlated with age in MP (r = 0.268, P = 0.03). Mean serum cholesterol was significantly higher in MP compared with MNP, but the differences were not significant after adjusting for age. No significant differences were observed in serum SCFA between the two groups. This study has shown that breath methane increases with age, which may be due to age-related increases in transit time and carbohydrate malabsorption. These results provide no conclusive link between colonic events and serum lipids in MP because, with age, methane production increased as did serum cholesterol. More research is required before any definite conclusions can be drawn.

Time of day and glucose tolerance status affect serum short-chain fatty acid concentrations in humans

Short-chain fatty acids (SCFA) are derived from endogenous (metabolism of fat, carbohydrate, and amino acids) and exogenous (colonic fermentation) sources. To see how time of day and glucose tolerance status influenced serum SCFA concentrations, we determined serum SCFA throughout the day in 22 subjects with impaired glucose tolerance (IGT) and 10 young and eight middle-aged normal controls. On 1 day, insulin sensitivity was assessed as the steady-state plasma glucose (SSPG) level achieved during intravenous infusion of glucose insulin, and somatostatin. On another day, plasma glucose and insulin and serum SCFA levels were measured 12 times over 12 hours with subjects eating a standard diet. SSPG in young controls (5.5 +/- 1.1 mmol/L) was less than in middle-aged controls (9.3 +/- 1.6 mmol/L), which in turn was less than in IGT subjects (13.7 +/- 0.6 mmol/L; P < .01). Mean plasma glucose in IGT subjects was greater than in normal controls, and mean plasma insulin in IGT subjects was higher than in young controls but similar to the levels in middle-aged controls. Mean 12-hour serum acetate in young controls (143 +/- 13 mumol/L) was greater than in middle-aged controls (104 +/- 11 mumol/L) and IGT subjects (113 +/- 5 mumol/L; P < .05). Mean 12-hour serum propionate in young controls (3.8 +/- 0.5 mumol/L) was less than in IGT subjects (5.4 +/- 0.3 mumol/L; P < .01), with middle-aged controls being intermediate (4.6 +/- 0.3 mumol/L). Both young (1.6 +/- 0.3 mumol/L) and middle-aged (1.0 +/- 0.2) controls had lower mean butyrate than IGT subjects (3.1 +/- 0.4 mumol/L; P < .05). Levels of all three SCFA varied significantly during the day, tending to decrease after breakfast and increase transiently after lunch and dinner. It is concluded that both time of day and glucose tolerance status affect serum SCFA levels in nondiabetic humans. The results suggest that serum acetate is derived primarily from colonic fermentation, serum butyrate primarily from endogenous fatty acid metabolism, and serum propionate from both exogenous and endogenous sources.

Metabolic effects of non-absorbable carbohydrates

Food components which are incompletely absorbed in the small intestine or not absorbed at all but are delivered to the colon have been part of the diet throughout the course of human evolution. Our great ape cousins may derive 30% or more of their dietary calories from colonic uptake of short-chain fatty acids (SCFAs) generated in the colon. The metabolic effects of dietary carbohydrate entering the colon are many and include laxation, the growth of the fecal biomass, nitrogen entrapment and SCFA generation. These SCFAs in turn may nourish mucosal cells, spare glutamine utilization, enhance hepatic gluconeogenesis and lipogenesis and possibly influence renal handling of uric acid. The health implications are significant in terms of modifying risk factors for disease and disease prevention and justify interest in the metabolic effects of non-absorbable sugars such as lactulose.

One-year acarbose treatment raises fasting serum acetate in diabetic patients

alpha-Glucosidase inhibitors such as acarbose improve blood glucose control in diabetes by delaying or reducing carbohydrate absorption. The fermentation of malabsorbed carbohydrate in the colon is associated with the production of gas, leading to flatulence, and short chain fatty acids such as acetate, which may have systemic effects. To see if acarbose raised fasting serum acetate in diabetic patients, we studied 85 subjects selected from the 267 who had completed a 1-year, double-blind, placebo-controlled, parallel design study of the effects of acarbose in the treatment of diabetes. At baseline, there was no significant difference between the 44 subjects subsequently randomized to placebo and the 41 randomized to acarbose, respectively, in fasting serum acetate (80 +/- 5 vs 71 +/- 4 mumoll-1) or glycosylated haemoglobin (HbA1C; 7.2 +/- 0.3 vs 7.4 +/- 0.3%). Compared to placebo, acarbose treatment significantly increased fasting serum acetate by 11 +/- 4 vs 2 +/- 3 mumoll-1 (p < 0.02) and reduced HbA1C by -0.59 +/- 0.16 vs -0.13 +/- 0.20% (p < 0.02). Acarbose treatment had no significant effect on serum cholesterol or non-esterified fatty acids, but was associated with a significant increase in flatulence. There was no relationship between changes in serum acetate and changes in HbA1C, serum cholesterol or symptoms. We conclude, in subjects with diabetes who tolerate therapy for a 1-year period, that acarbose treatment increases serum acetate. The magnitude of change in acetate was unrelated to side-effects or changes in blood glucose control or serum lipids.