AJCN North Carolina Research Campus
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Vogt, J. A
Right arrow Articles by Wolever, T. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Vogt, J. A
Right arrow Articles by Wolever, T. M.
Agricola
Right arrow Articles by Vogt, J. A
Right arrow Articles by Wolever, T. M.
American Journal of Clinical Nutrition, Vol. 80, No. 5, 1254-1261, November 2004
© 2004 American Society for Clinical Nutrition

ORIGINAL RESEARCH COMMUNICATION

L-Rhamnose increases serum propionate after long-term supplementation, but lactulose does not raise serum acetate1,2,3

Janet A Vogt, Katrin B Ishii-Schrade, Paul B Pencharz and Thomas MS Wolever

1 From the University of Toronto (JAV, KBI-S, PBP, and TMSW); St Michael's Hospital, Toronto (TMSW); and The Hospital for Sick Children, Toronto (PBP)

2 Supported by the Heart and Stroke Foundation of Canada and the Natural Sciences and Engineering Research Council. JAV was supported by a joint Heart and Stroke/Medical Research council doctoral research award.

3 Address reprint requests to TMS Wolever, Department of Nutritional Sciences, University of Toronto, 150 College Street, Room 316, Toronto, ON, M5S 3E2 Canada. E-mail: thomas.wolever{at}utoronto.ca.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Background: Acute ingestion of the unabsorbed sugar L-rhamnose in humans raises serum propionate, whereas acute ingestion of lactulose raises serum acetate. It is not known whether short-chain fatty acid concentrations in urine and feces reflect those in blood.

Objective: The objective was to test the effects of oral L-rhamnose and lactulose for 28 d on acetate and propionate concentrations in serum, urine, and feces.

Design: Eleven subjects ingested 25 g L-rhamnose, lactulose, or D-glucose (control) for 28 d in a partially randomized crossover design. One fecal sample, hourly blood samples, and all urine samples were collected over 12 h on the last day of each phase.

Results: The increase in serum propionate was greater after L-rhamnose than after lactulose (P < 0.05). The effect of lactulose on serum acetate was not significant, but lactulose raised the acetate:propionate ratio compared with D-glucose or L-rhamnose in serum (P < 0.005) and urine (P < 0.02). Flatulence was significantly greater after lactulose and L-rhamnose than after D-glucose (P < 0.0001), an effect that lasted 4 wk with lactulose but only 1 wk with L-rhamnose.

Conclusions: This study confirmed that L-rhamnose ingestion over 28 d continues to selectively raise serum propionate in humans. Although serum acetate did not increase significantly after lactulose, the serum acetate:propionate ratio was significantly different after L-rhamnose and lactulose, which suggests that these substrates could be used to examine the role of colonic acetate and propionate production in the effect of dietary fiber on lipid metabolism. Changes in the ratio of urinary acetate to propionate reflected those in serum.

Key Words: Propionate • short-chain fatty acids • colon • humans • fermentation • L-rhamnose • lactulose • feces


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Short-chain fatty acids (SCFAs) are produced by the bacterial fermentation of unabsorbed carbohydrates in the human colon. The 3 main SCFAs—acetic, propionic, and n-butyric acids—occur in a molar ratio of {approx}60:20:20 in the colonic contents and fecal matter (1). As a group, the SCFAs function as systemic energy substrates (2-5), but, in addition, each has its own distinct metabolic role. n-Butyric acid has received much attention as both an energy substrate for colonocytes (6) and a differentiation-inducing antineoplastic agent (7). Acetic acid can be used as a substrate for the synthesis of cholesterol and fatty acids (8), but it has been suggested that propionic acid may play an inhibitory role in these processes (8-12).

The selection of fermentation substrate can affect the relative proportions of the 3 primary SCFAs produced. For example, the unabsorbable sugar L-rhamnose, when fermented in vitro with human feces for 24 h, produced roughly two-thirds the amount of acetic acid and 4 times the amount of propionic acid produced by another unabsorbable sugar, lactulose (13). When human subjects ingested 25 g L-rhamnose, lactulose, or D-glucose on 3 separate occasions, serum propionic acid was significantly higher with L-rhamnose than with lactulose or D-glucose, and the area under the curve for serum acetic acid was significantly greater with lactulose than with D-glucose (14). It remains to be seen whether these changes in serum SCFA concentrations would be maintained with long-term ingestion of the sugars. If so, it could have implications for lipid metabolism in humans.

There are no published studies of the effect of L-rhamnose intake on fecal SCFAs, but one study reported that lactulose increased fecal acetic acid concentrations (15), whereas another study found no change in fecal acetic acid concentrations despite significant increases in total SCFAs, acetic acid, and lactate in the cecum (16). Because fecal and urine sampling is arguably a less invasive means of collecting SCFA data from living humans than is blood sampling, it may be considered more acceptable by potential study participants. Both fecal and urine sampling were conducted in this study to determine whether they could act as proxies for blood sampling.

The main objective of this study was to see whether the acute effects of lactulose and L-rhamnose ingestion on serum SCFA concentrations would be maintained after 28 d of dietary supplementation with the sugars. A secondary objective was to determine whether serum SCFA concentrations were reflected in feces and urine. We hypothesized that the ingestion of L-rhamnose would result in significantly higher serum propionic acid concentrations, whereas the ingestion of lactulose would result in significantly higher serum acetic acid concentrations. In addition, we hypothesized lactulose ingestion would increase fecal acetic acid concentrations more so than would the other sugars.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Subjects
Twelve healthy men were recruited from the University of Toronto campus. One subject withdrew after completing the first study period because of work-related reasons. Eleven subjects [age: 25.9 ± 1.7 y; body mass index (in kg/m2): 24.8 ± 0.8] completed all 3 phases. No subjects had used antibiotics within the previous 3 mo or had a history of gastrointestinal problems. Subjects were asked to maintain their usual level of physical activity throughout the 3 study periods.

Diets
During the study periods, the subjects' diets were self-selected. Each subject was provided with a digital electronic scale during each trial and instructed in its correct use. Subjects recorded their 7-d weighed dietary intake during week 2 of the first study period. This record was photocopied and returned to the subjects to use as a template for their dietary intake during week 4 of the first study period. Subjects recorded any deviations made from the template diet during week 4. The resultant 7-d diet record was then used as a control diet during week 4 of the 2 subsequent study periods. The average total daily intake during week 4 is shown for selected nutrients in Table 1Go.


View this table:
[in this window]
[in a new window]
  		TABLE 1 Average total daily intakes during week 41

 
Compliance, assessed on the basis of the changes noted on the week 4 diet records that were returned at the end of each study period and by the number of empty sugar vials returned, was considered satisfactory.

Study design
The study followed a semirandomized crossover design in which all 11 subjects underwent three 28-d study periods. The first group of subjects (n = 9) began the study in May and were randomly assigned to receive either lactulose or L-rhamnose. After a 3-mo washout period, they participated in the D-glucose study period the following September. The day after the end of the D-glucose study period, 7 of these 9 subjects began study period 3, wherein they consumed the remaining unabsorbable sugar. The second group of subjects (n = 2) began the study in September and consumed D-glucose in their first study period. The day after completing the D-glucose study period, they were randomly assigned to receive either lactulose or L-rhamnose for the second study period. After a 6-mo washout period, these subjects and 2 from the first group completed their final study period in May. It was assumed that the lack of a washout period after the D-glucose study period would not significantly affect the baseline measurements in the following study period. Studies were not conducted during the summer or winter months to avoid seasonal effects on serum cholesterol concentrations (17, 18), which were being collected from these subjects as part of a separate protocol.

At the beginning of each study period, the subjects were provided with a 2-wk supply of L-rhamnose (BDH Inc, Toronto), lactulose (Inalco Pharmaceuticals, San Luis Obispo, CA), or D-glucose (Sigma-Aldrich Canada Ltd, Oakville, Canada). Lactulose is a synthetic disaccharide that is 99.0% pure, with lactose (0.5%) and galactose (0.5%) as impurities, and L-rhamnose is 99.7% pure. The sugar was packaged in polystyrene vials containing 8 or 9 g each. Vials were bundled in sets of 3 so that the total weight of sugar for any bundle was 25 g. Subjects were instructed to consume one bundle per day by dissolving the contents of one vial in a hot beverage at breakfast, lunch, and dinner. On day 15 of each phase, subjects reported to the clinic to hand in the empty vials, discuss any symptoms that they were experiencing, and receive the remaining 2-wk supply of sugar and their electronic scale and diet template. On each test day the subjects came to the laboratory at 0730 after an overnight fast. On the first test day, each subject chose 3 meals and 2 snacks from a fixed menu, as reported previously (14). For each subject, the exact amounts and types of foods chosen on the first test day were replicated on the 2 remaining test days. Food portions were weighed in the metabolic diet kitchen adjoining the test room. Fluid intake, in the form of beverages, was limited to 500 mL with meals and 250 mL with snacks. The mean test day food intake for all 11 subjects (not including the contribution of the test sugars) was 3140 kcal, with 63% of energy from carbohydrate, 16% from protein, and 26% from fat. The mean total dietary fiber intake was 42 g, 10 g of which was soluble fiber. Subjects were told to fast until the beginning of the test on the next morning. Test day meals and snacks were eaten in the metabolic kitchen: breakfast at 0800, snack 1 at 1030, lunch at 1300, snack 2 at 1530, and dinner at 1800. Subjects were instructed to completely consume all meals and snacks within 15 min of being served. The test sugar that a subject had been consuming for the preceding 28 d was added to the hot beverage consumed with the test meals (9 g with breakfast and 8 g with lunch and dinner). This study was approved by the Human Subjects Review Committee, Office of Research Services, University of Toronto. All subjects gave written informed consent.

Collection and analysis of samples on the test days
On the test days, a fasting blood sample was taken before ingestion of the 9-g dose of test sugar, with additional blood samples collected at hourly intervals for 12 h. Serum SCFA concentrations were analyzed by gas chromatography as previously described (14).

The first fecal sample passed by each subject on each test day was collected into a plastic bag suspended in a frame under the toilet seat. As much air as possible was excluded from the bag, and then it was stored immediately at –70 °C. On arrival at the clinic on each test day, the subjects were instructed to void their bladders. Any urine passed before ingestion of the test sugar was discarded, and all urine passed after ingestion of the first sugar dose was collected over the 12-h test day. The urine samples from each subject were pooled in separate containers and stored during the test day at 4 °C. At the end of each test day, aliquots were taken and transported on frozen carbon dioxide, along with the fecal samples, to the laboratory where they were stored at –70 °C. Aliquots for creatinine analysis were analyzed for each subject in a single batch in the routine clinical chemistry laboratory, Department of Laboratory Medicine and Pathobiology, St Michael's Hospital, by standard methods (Kodak Ektachem analyzers; Eastman Kodak, Rochester, NY).

Fecal samples were weighed and then each sample was submersed in a plastic bag of bactericidal solution made of 0.05 g CuSO4 per g feces suspended in 0.4–0.5 mL per g feces of doubly distilled deionized water. After all air was excluded from the bag, it was sealed and the sample was allowed to thaw at {approx}10 °C. After thorough manual homogenization, aliquots were stored at –70 °C for the measurement of SCFAs and the percentage of moisture. To prepare samples for gas chromatographic determination of SCFAs, an aliquot of the homogenate was thawed and spun at 20 000 x g for 10 min, and the supernatant fraction was diluted with doubly distilled deionized water to a final dilution of 200-fold and then analyzed for SCFAs following the same protocol as that used for the serum samples. Feces were also analyzed for the percentage of moisture and dry weight. Urine samples were prepared as per the serum protocol, and the ratio of urinary SCFA concentrations to urinary creatinine concentrations was calculated to decrease the contribution of sample collection problems to variance in the data.

Symptoms and bowel habits
During each trial, the subjects kept a symptom record. They were told to contact the study coordinator (JAV) if they experienced symptoms severe enough to interfere with usual daily activities. At 2 wk, they were asked about symptoms and reminded to keep the record. At 4 wk, if a record was not handed in, the subject was interviewed regarding symptoms. The symptom record of one subject from the L-rhamnose trial was not available, so the symptom data for this subject was excluded from the analysis. Otherwise, any subject that did not hand in a report stated that they had not experienced noticeable symptoms during that trial. In this case, zeroes were recorded in the database. The following symptoms were reported: flatulence, abdominal pain, abdominal bloating, and diarrhea. Symptoms were coded as follows: 0 = none, 1 = just noticeable, 2 = mild, 3 = moderate, and 4 = severe. The median rating for each symptom from weeks 1 to 4 was calculated for each subject and trial. Subjects recorded all bowel movements during days 22 through 28 (week 4) of each trial, rating the ease of movement, stool consistency, and symptoms such as flatulence, abdominal pain, and abdominal bloating. Ease of movement was coded on a scale of 0–6, with 0 being easy to pass and 6 being difficult to pass. Stool consistency was rated on a scale of 0–6, with 0 being watery, 2 being soft, 4 being formed, and 6 being very hard. The remaining symptoms were rated on a scale of 0–6, with 0 being none, 2 being mild, 4 being moderate, and 6 being severe. For each subject and trial, statistical analysis was performed on the median rating for each symptom and the total number of bowel movements during week 4.

Dietary analysis
Diets were analyzed by using information from the US Department of Agriculture (19), which was supplemented with additional data on foods analyzed in our department for protein, total fat, and dietary fiber with the use of Association of Official Analytic Chemists methods (20) and fatty acids by gas chromatography (21). Additional data on dietary fiber were obtained from the tables of Anderson and Bridges (22).

Statistics:
Hourly serum SCFA concentrations and weekly median symptom scores were analyzed as a three-factor analysis of variance (ANOVA) with repeated measures on all factors (time, sugar, and subject) (23). The error term to test a main effect in this model was specified as the effect x subject interaction. For symptom scores, the weekly medians were converted to ranks within subjects before the statistical analyses were performed. If the interaction between time and sugar was significant, ANOVA was performed at each time point to assess the effect of sugar, with a Bonferroni correction.

Four summary measures were calculated for serum SCFAs. The total area under the curve (TAUC) was calculated by adding one-half the value of the serum concentrations at times 0 h (fasting) and 12 h to the serum concentrations from hours one through 11. The mean concentration across 12 h (mean 0–12) was calculated by dividing the TAUC by 12. The incremental area under the curve (IAUC) was calculated by subtracting the fasting value from the mean 0–12 value and then multiplying by 12. The peak rise was defined as the peak concentration in serum minus the fasting concentration.

Differences in the mean 0–12, TAUC, IAUC, and fecal and urine outcomes were assessed for the effect of sugar by using the SAS procedure for mixed models. Because the study covered an 8–12-mo period, rather than assuming a constant correlation and variance for observations within one patient, the residual covariance matrix was structured by trial period to allow for the possibility that the correlation might vary with different pairs of study periods (24). On the basis of Akaike's and Schwarz's information criteria, and after comparison with fixed-effects models, compound symmetry provided an adequate fit for the data. To correct for small sample considerations, the df values were adjusted by using the method of Kenward and Roger (25).

The median scores from the bowel-habit questionnaire and the total number of bowel movements during week 4 were ranked within subject and assessed by Friedman's ANOVA on ranks (26). All statistical procedures were performed by using version 8.1 of SAS (SAS Institute, Cary, NC). The SCFA results are expressed as mean ± SEMs, and the symptom results are expressed as median values. Unless otherwise indicated, the means reported are those generated by the fixed-effects approach, and differences between means are considered significant at P < 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Eleven subjects completed the 3 treatment periods. Fasting concentrations of serum SCFAs and breath gases did not differ significantly between treatments. The treatment effects on serum, urine, and fecal variables and symptoms are reported in Tables 2–4GoGoGo) and Figures 1Go and 2Go.


View this table:
[in this window]
[in a new window]
  		TABLE 2 Total and incremental areas under the curve for serum short-chain fatty acids1

 

View this table:
[in this window]
[in a new window]
  		TABLE 3 Short-chain fatty acid (SCFA) concentrations in feces and urine1

 

View this table:
[in this window]
[in a new window]
  		TABLE 4 Results of the bowel-habit questionnaire1

 


View larger version (24K):
[in this window]
[in a new window]
  		FIGURE 1. Mean (±SEM) concentrations of serum acetate, serum propionate, and serum butyrate in 11 subjects that took 25 g L-rhamnose •, lactulose {circ}, or D-glucose {blacktriangleup} for 28 d, with measurements on day 28. Meals (larger arrows) were consumed at 0, 5, and 10 h; smaller arrows indicate the times at which snacks were eaten. Treatments were assessed by repeated-measures ANOVA. Time x treatment interaction, P < 0.005 for propionate. *Significantly greater than lactulose, P < 0.05 (Bonferroni-corrected).

 


View larger version (19K):
[in this window]
[in a new window]
  		FIGURE 2. Median scores for flatulence in weeks 1, 2, 3, and 4 for 7 subjects who ingested 25 g/d of L-rhamnose (Rha; {blacksquare}), lactulose (Lac; {square}), or D-glucose (Glu; {cjs2112}). Flatulence was coded as follows: 0 = none, 1 = just noticeable, 2 = mild, 3 = moderate, and 4 = severe. Treatments were assessed by Friedman's ANOVA on ranks. There was a significant time x treatment interaction (P < 0.05). Bars with different letters are significantly different (Bonferroni-corrected): a, b, and c (P < 0.02); d and e (P < 0.0005).

 
The mean 0–12 h concentration of acetic acid did not differ significantly between lactulose (93.3 ± 12.3), L-rhamnose (84.4 ± 8.7), and D-glucose (75.7 ± 8.4), and there was no significant effect of sugar on TAUC, IAUC (Table 2Go), or hourly serum acetic acid concentrations (Figure 1Go). The mean 0–12 h concentration and TAUC for propionic acid were higher with L-rhamnose than with lactulose, but D-glucose did not differ significantly (Figure 1Go, Table 2Go, respectively), whereas the IAUC for propionic acid was higher with L-rhamnose than with D-glucose and lactulose (Table 2Go). There was a significant interaction between treatment and time for the hourly serum propionic acid concentrations (P < 0.005). From 6 h through 8 h, serum propionic acid was higher with L-rhamnose than with lactulose (Figure 1Go). L-Rhamnose caused an increase in serum propionic acid from fasting concentrations that was greater than that elicited by either lactulose or D-glucose for every subject. The mean peak rise with L-rhamnose was 3.6 ± 0.3 µmol/L, which was significantly higher (P < 0.0005) than with lactulose (1.6 ± 0.3) and D-glucose (1.3 ± 0.2). The peak rises for individual subjects with L-rhamnose ranged from 1.8 to 5.3 µmol/L. The mean 0–12 concentration of n-butyric acid did not differ significantly between L-rhamnose, lactulose, and D-glucose (Figure 1Go), and there was no effect of sugar on IAUC and TAUC (Table 2Go) or on the day profile (Figure 1Go). The serum acetic acid:propionic acid ratio, based on the mean 0–12 h concentration, was higher (P < 0.0005) with lactulose (26.3 ± 2.0) than with D-glucose (19.3 ± 1.1) or L-rhamnose (17.7 ± 1.3).

There were no significant effects of sugar on fecal SCFA concentrations (Table 3Go), and fecal percentage moisture did not differ significantly between L-rhamnose (75.6 ± 1.6), lactulose (73.2 ± 2.5), and D-glucose (72.8 ± 1.7). There were no significant effects of sugar on individual urine SCFA concentrations corrected for creatinine (Table 3Go). The urine acetic acid:propionic acid ratio was higher (P < 0.02) with lactulose (37.1 ± 4.7) than with D-glucose (25.1 ± 2.6) or L-rhamnose (17.7 ± 1.3).

There were no significant effects of sugar on the frequency of bowel movements or symptoms assessed with the bowel-habit questionnaire (Table 4Go). Less than one-half of the subjects reported any occurrences of abdominal bloating, abdominal pain, or diarrhea on the side effects records for any given study period, so these data were not analyzed. However, an analysis of data from 7 subjects who reported flatulence while taking lactulose and L-rhamnose showed a significant treatment effect on flatulence (P < 0.0001) and a significant interaction between time and treatment (P < 0.05; Figure 2Go).


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
This study has shown that the ability of 25 g L-rhamnose to raise serum propionic acid acutely in humans persists when subjects supplement their diet with 25 g for 28 d. However, the ability of lactulose to increase serum acetic acid acutely does not persist over 28 d. Because of their opposing roles in lipid metabolism, the ratio of acetic acid to propionic acid in the portal circulation may play a role in regulating lipid metabolism. Lactulose raised the peripheral acetic acid:propionic acid ratio in comparison with either L-rhamnose or D-glucose.

The fasting serum acetic acid concentration tended to be highest with lactulose, but the IAUC tended to be higher with L-rhamnose; thus, the TAUC for acetic acid showed no treatment effect. In a previous crossover study, when 22 subjects followed the same 12-h test day protocol without a pretreatment phase (14), the IAUCs for serum acetic acid with both D-glucose (–255.5) and L-rhamnose (–130.6) were similar to those reported in this study. However, the IAUC for acetic acid with lactulose dropped from –74.1 in the previous study to –189.8 in this study. This attenuation of the serum acetic acid response suggests that either adaptation to lactulose occurred or that this study may have lacked power to detect a significant effect.

Colonic bacteria can adapt to lactulose ingestion. Ingestion of 3 g lactulose/d for 14 d increased bifidobacteria to 47.4% of the fecal microflora, from 8.3% at baseline (27). The primary metabolites of lactulose metabolism by bifidobacteria are lactate and acetic acid (16, 28). Ingestion of 20 g lactulose twice daily for 8 d increased cecal concentrations of lactic and acetic acids and fecal ß-galactosidase activity. It was suggested that in 1 wk, cecal bacteria became more efficient at digesting lactulose (16). We found no data on the effect of lactulose ingestion on microflora and SCFAs for a longer period.

Acetate, present at much higher concentrations in peripheral blood than either propionic acid or n-butyric acid (29-31), is quickly oxidized (32). Cytosolic acetyl-CoA synthetase in adipose and mammary gland tissues enables them to use acetic acid for lipogenesis, whereas mitochondrial acetyl-CoA synthetase in muscles, kidneys, and heart enables those tissues to burn acetic acid as a fuel (33). In rats, increased SCFA absorption can induce cytosolic acetyl-CoA synthetase (33). If this enzyme was induced, acetic acid produced from chronic lactulose intake may have been used systemically to a greater extent than occurred in the acute study of these sugars (14). However, lactate can inhibit lipogenesis from acetic acid in perfused rat liver (34). Lactate was not measured in this study, so we can only speculate as to the effect that higher SCFA production may have had on systemic acetic acid use under these conditions.

Colonic fermentation is considered the major source of SCFAs (31, 35), the rate of which varies diurnally and peaks after feeding (36). Acetic acid and propionic acid are also produced endogenously, from fat (31, 37) and amino acid (38) oxidation, respectively. The decrease in fasting acetic acid concentrations after the breakfast meal was likely due to the inhibition of fat oxidation by insulin secretion and was observed previously (14, 37). Fasting propionic acid concentrations did not change significantly after breakfast, as was observed in the acute study of these sugars (14). However, in another study, propionic acid displayed a decrease similar to that of acetic acid after breakfast (37). Assuming a mouth-to-cecum transit time of 90–120 min (30) and suppression of endogenous acetic acid production by insulin secretion due to feeding every 2.5 h, the increases in serum acetic acid at 3 h with lactulose and 4 h with L-rhamnose were likely due to the colonic fermentation of these sugars.

Eleven men took part in this study, as opposed to 10 males and 12 females in the acute study of these sugars (14). Analysis of the acute acetic acid data for males and females as 2 separate groups showed a nonsignificant trend in both groups; the mean IAUC for lactulose was highest and that for D-glucose was lowest. High between-subject variability may make a sample of 10 to11 too small to find a significant difference.

Our secondary aim was to determine whether changes in fecal and urine SCFA concentrations would reflect changes in serum. However, neither fecal nor urine concentrations of acetic acid, propionic acid, or n-butyric acid showed the same treatment effects seen in serum, even though lactulose intake in humans has been shown to affect fecal acetic acid concentrations (15). A review of the effect of dietary fiber on fecal SCFAs concluded that most human studies show no effect (39). At least 95% of colonic SCFAs are absorbed (40), so provided the colonic transit rate is not accelerated (41-43), the fraction of SCFAs in feces does not necessarily correspond to their intracolonic production (44). Changes in transit rate can affect the proportion of SCFAs produced by altering the nature of substrates flowing to the colon (43). For instance, a quicker transit rate causes digestible starch to be less efficiently absorbed in the small intestine, thus increasing propionic acid and n-butyric acid production (45-48). One subject reported diarrhea initially with L-rhamnose and could only tolerate 17 g/d. The colonic transit rate was not measured, but the frequency of his bowel movements increased from 1/d with glucose to 2/d with L-rhamnose. Fecal concentrations of acetic acid, propionic acid, and n-butyric acid increased from 41:21:4 to 92:57:34, respectively. On the other hand, an inverse relation between fecal acetic acid concentrations and absorption of rectally infused acetic acid (49) suggests that low fecal acetic acid concentrations reflect high absorption rates and vice versa. As in other studies of fecal SCFAs (50, 51), the fecal data from the current study showed a high between-subject variation. Such variation impairs the ability to show significant effects. Finally, most reports of fecal SCFAs are based on a 24–72-h collection (16, 52, 53) or longer (47, 54-57), whereas our data were from one fecal sample. However, other investigators have reported fecal SCFA concentrations from single samples at the end of an intervention (58, 59).

Lactulose raised the acetic acid:propionic acid ratio in serum and urine. The liver extracts 90% of propionic acid, as opposed to 75% of acetic acid, during a single pass (60, 61), so the portal acetic acid:propionic acid ratio can be assumed to be 40% that of the peripheral acetic acid:propionic acid ratio. The urine concentrations of SCFAs measured after ingestion of D-glucose are similar to those reported for fasting urine acetic acid, propionic acid, and n-butyric acid (77.4, 4.3, and 3.3 µmol/L, respectively) in 41 healthy subjects (62). Infusion of 4 mmol sodium acetate/kg body wt has been shown to increase the fractional excretion of acetic acid in urine, which suggests that when blood acetic acid concentrations increase, the filtered load may exceed the capacity for renal reabsorption (63). The serum acetic acid:propionic acid ratio in men, adjusted for age and body mass index, was positively correlated with serum total and LDL-cholesterol concentrations (64). Thus, the relation between the acetic acid:propionic acid ratio in serum and urine in men may be of interest.

During week 1, the subjects reported more flatulence with the unabsorbable sugars than with D-glucose, a finding that was similar to the results reported in the acute study (14). In the current study, whereas lactulose caused moderate flatulence throughout the 4 wk, flatulence with L-rhamnose decreased from mild to just noticeable, which suggested that, at 25 g/d, L-rhamnose was better tolerated. This finding suggests a potential role for L-rhamnose as a more easily tolerated alternative to lactulose in certain long-term clinical applications.

We conclude that consumption of L-rhamnose over 28 d continues to selectively raise serum propionic acid in men, whereas the selective raising of serum acetic acid by lactulose did not persist, perhaps because the colonic microflora adapted or because of a lack of statistical power. The combined effects on acetic acid and propionic acid resulted in a significant difference between L-rhamnose and lactulose with respect to the serum acetic acid:propionic acid ratio. Because these 2 SCFAs purportedly play opposing roles in lipid metabolism, L-rhamnose and lactulose are appropriate substrates to test the hypothesis that the hypocholesterolemic effect of dietary fiber may be mediated by colonic SCFAs.


   ACKNOWLEDGMENTS
 
We thank Gina Kim, Alexis Ratsch, Kirvan Rivera-Rufner, Svetlana Ristovski-Slijepcevic, and Mary Ann Ryan for their excellent technical assistance.

TMSW obtained the funding for this research, was involved in the design of the study, reviewed the draft, and contributed comments on the final manuscript. JAV was involved in the conception and design of the study, collected and analyzed the data, and wrote the manuscript. KBI-S helped with the collection and analysis of the samples, set up the methodology for the analysis of fecal and urine SCFAs, and reviewed the draft of the manuscript. PBP reviewed the draft and contributed comments for the final manuscript. None of the authors had a conflict of interest, either financial or personal, with the financial sponsor of this work.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

  1. Cummings JH. Short chain fatty acids in the human colon. Gut 1981;22:763-79.[Free Full Text]
  2. McNeil NI. The contribution of the large intestine to energy supplies in man. Am J Clin Nutr 1984;39:338-42.[Abstract/Free Full Text]
  3. Grossklaus R. Energy gap? Nutr Res 1983;3:595-604.
  4. Wisker E, Feldheim W. Energy value of fermentation. In: Binder H, Cummings J, Soergel K, eds. Falk Symposium 73: short chain fatty acids. London: Kluwer Academic Publishers, 1994:20-8.
  5. Livesey G, Elia M. Short-chain fatty acids as an energy source in the colon: metabolism and clinical implications. In: Cumming J, Rombeau JL, Sakata T, eds. Physiological and clinical aspects of short-chain fatty acids. Cambridge, United Kingdom: Cambridge University Press, 1995:427-81.
  6. Roediger WE. Role of anaerobic bacteria in the metabolic welfare of the colonic mucosa in man. Gut 1980;21:793-8.[Abstract/Free Full Text]
  7. Kim YS, Gum J, Ho S, Deng G. Colonocyte differentiation and proliferation: overview and the butyrate-induced transcriptional regulation of oncodevelopmental placental-like alkaline phosphatase gene in colon cancer cells. In: Binder H, Cummings J, Soergel K, eds. Falk Symposium 73: short chain fatty acids. London: Kluwer Academic Publishers, 1994:119-34.
  8. Nishina PM, Freedland RA. Effects of propionate on lipid biosynthesis in isolated rat hepatocytes. J Nutr 1990;120:668-73.
  9. Wright RS, Anderson JW, Bridges SR. Propionate inhibits hepatocyte lipid synthesis. Proc Soc Exp Biol Med 1990;195:26-9.[Abstract]
  10. Chen WJ, Anderson JW, Jennings D. Propionate may mediate the hypocholesterolemic effects of certain soluble plant fibers in cholesterol-fed rats. Proc Soc Exp Biol Med 1984;175:215-8.[Abstract]
  11. Hara H, Haga S, Aoyama Y, Kiriyama S. Short-chain fatty acids suppress cholesterol synthesis in rat liver and intestine. J Nutr 1999;129:942-8.[Abstract/Free Full Text]
  12. Hara H, Haga S, Kasai T, Kiriyama S. Fermentation products of sugar-beet fiber by cecal bacteria lower plasma cholesterol concentration in rats. J Nutr 1998;128:688-93.[Abstract/Free Full Text]
  13. Fernandes J, Rao AV, Wolever TM. Different substrates and methane producing status affect short-chain fatty acid profiles produced by In vitro fermentation of human feces. J Nutr 2000;130:1932-6.[Abstract/Free Full Text]
  14. Vogt JA, Pencharz PB, Wolever TMS. L-Rhamnose increases serum propionate in humans. Am J Clin Nutr 2004;80:89-94.[Abstract/Free Full Text]
  15. Ballongue J, Schumann C, Quignon P. Effects of lactulose and lactitol on colonic microflora and enzymatic activity. Scand J Gastroenterol Suppl 1997;222:41-4.[Medline]
  16. Florent C, Flourie B, Leblond A, Rautureau M, Bernier JJ, Rambaud JC. Influence of chronic lactulose ingestion on the colonic metabolism of lactulose in man (an in vivo study). J Clin Invest 1985;75:608-13.
  17. Gordon DJ, Trost DC, Hyde J, et al. Seasonal cholesterol cycles: the Lipid Research Clinics Coronary Primary Prevention Trial placebo group. Circulation 1987;76:1224-31.[Abstract/Free Full Text]
  18. Robinson D, Bevan EA, Hinohara S, Takahashi T. Seasonal variation in serum cholesterol levels—evidence from the UK and Japan. Atherosclerosis 1992;95:15-24.[Medline]
  19. The Agricultural Research Service. Composition of foods. Agriculture handbook no. 8. Washington, DC: US Department of Agriculture, 1992.
  20. Association of Official Analytical Chemists. AOAC official methods of analysis. Washington, DC: Association of Official Analytical Chemists, 1980.
  21. Jenkins D, Wolever T, Rao A, et al. Effect on blood lipids of very high intakes of fiber in diets low in saturated fat and cholesterol. N Engl J Med 1993;329:21-6.[Abstract/Free Full Text]
  22. Anderson JW, Bridges SR. Dietary fiber content of selected foods. Am J Clin Nutr 1988;47:440-7.[Abstract/Free Full Text]
  23. Cody RP, Smith JK. Applied statistics and the SAS programming language. 3rd ed. New York: North-Holland, 1991.
  24. Brown H, Prescott R. Applied mixed models in medicine. New York: J Wiley & Sons, 1999.
  25. Jones B, Kenward MG. Design and analysis of cross-over trials. 2nd ed. Boca Raton, FL: Chapman & Hall/CRC, 2003.
  26. Zar JH. Biostatistical analysis. 2nd ed. Englewood Cliffs, NJ: Prentice-Hall, 1984.
  27. Terada A, Hara H, Kataoka M, Misuoka T. Effect of lactulose on the composition and metabolic activity of the human faecal flora. Microbial Ecol Health Dis 1992;5:43-50.
  28. Ito Y, Moriwaki H, Muto Y, Kato N, Watanabe K, Ueno K. Effect of lactulose on short-chain fatty acids and lactate production and on the growth of faecal flora, with special reference to Clostridium difficile. J Med Microbiol 1997;46:80-4.[Abstract]
  29. Cummings JH, Pomare EW, Branch WJ, Naylor CP, Macfarlane GT. Short chain fatty acids in human large intestine, portal, hepatic and venous blood. Gut 1987;28:1221-7.[Abstract/Free Full Text]
  30. Pomare EW, Branch WJ, Cummings JH. Carbohydrate fermentation in the human colon and its relation to acetate concentrations in venous blood. J Clin Invest 1985;75:1448-54.
  31. Scheppach W, Pomare EW, Elia M, Cummings JH. The contribution of the large intestine to blood acetate in man. Clin Sci (Lond) 1991;80:177-82.[Medline]
  32. Skutches CL, Holroyde CP, Myers RN, Paul P, Reichard GA. Plasma acetate turnover and oxidation. J Clin Invest 1979;64:708-13.
  33. Remesy C, Demigne C, Morand C. Metabolism of short-chain fatty acids in the liver. In: Cummings J, Rombeau JL, Sakata T, eds. Physiological and clinical aspects of short-chain fatty acids. Cambridge, United Kingdom: Cambridge University Press, 1995:171-90.
  34. Snoswell AM, Trimble RP, Fishlock RC, Storer GB, Topping DL. Metabolic effects of acetate in perfused rat liver. Studies on ketogenesis, glucose output, lactate uptake and lipogenesis. Biochim Biophys Acta 1982;716:290-7.[Medline]
  35. Ballard FJ. Supply and utilization of acetate in mammals. Am J Clin Nutr 1972;25:773-9.[Medline]
  36. Flourie B, Leblond A, Florent C, Rautureau M, Bisalli A, Rambaud JC. Starch malabsorption and breath gas excretion in healthy humans consuming low- and high-starch diets. Gastroenterology 1988;95:356-63.[Medline]
  37. Wolever TM, Josse RG, Leiter LA, Chiasson JL. Time of day and glucose tolerance status affect serum short-chain fatty acid concentrations in humans. Metabolism 1997;46:805-11.[Medline]
  38. Walter JH, Thompson GN, Leonard JV, Heatherington CS, Bartlett K. Measurement of propionate turnover in vivo using sodium [2H5]propionate and sodium [13C]propionate. Clin Chim Acta 1989;182:141-50.[Medline]
  39. Fleming SE. Influence of dietary fiber on the production, absorption, or excretion of short chain fatty acids in humans. In: Spiller GA, ed. CRC handbook of dietary fiber in human nutrition. 2nd ed. Boca Raton, FL: CRC Press, 1993:387-412.
  40. Topping DL, Clifton PM. Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides. Physiol Rev 2001;81:1031-64.[Abstract/Free Full Text]
  41. Lewis SJ, Heaton KW. Increasing butyrate concentration in the distal colon by accelerating intestinal transit. Gut 1997;41:245-51.[Abstract/Free Full Text]
  42. El Oufir L, Flourie B, Bruley des Varannes S, et al. Relations between transit time, fermentation products, and hydrogen consuming flora in healthy humans. Gut 1996;38:870-7.[Abstract/Free Full Text]
  43. El Oufir L, Barry JL, Flourie B, et al. Relationships between transit time in man and in vitro fermentation of dietary fiber by fecal bacteria. Eur J Clin Nutr 2000;54:603-9.[Medline]
  44. Cummings JH. The large intestine in nutrition and disease. 1997. Internet: http://www.danoneinstitute.org/danone_institutes_initiatives/books.php (accessed August 2004).
  45. Chapman RW, Sillery JK, Graham MM, Saunders DR. Absorption of starch by healthy ileostomates: effect of transit time and of carbohydrate load. Am J Clin Nutr 1985;41:1244-8.[Abstract/Free Full Text]
  46. Holgate AM, Read NW. Relationship between small bowel transit time and absorption of a solid meal. Influence of metoclopramide, magnesium sulfate, and lactulose. Dig Dis Sci 1983;28:812-9.[Medline]
  47. Scheppach W, Fabian C, Sachs M, Kasper H. The effect of starch malabsorption on fecal short-chain fatty acid excretion in man. Scand J Gastroenterol 1988;23:755-9.[Medline]
  48. Macfarlane GT, Englyst HN. Starch utilization by the human large intestinal microflora. J Appl Bacteriol 1986;60:195-201.[Medline]
  49. Vogt JA, Wolever TM. Fecal acetate is inversely related to acetate absorption from the human rectum and distal colon. J Nutr 2003;133:3145-8.[Abstract/Free Full Text]
  50. Kruse HP, Kleessen B, Blaut M. Effects of inulin on faecal bifidobacteria in human subjects. Br J Nutr 1999;82:375-82.[Medline]
  51. Schwiertz A, Lehmann U, Jacobasch G, Blaut M. Influence of resistant starch on the SCFA production and cell counts of butyrate-producing Eubacterium spp. in the human intestine. J Appl Microbiol 2002;93:157-62.[Medline]
  52. Holt PR, Atillasoy E, Lindenbaum J, et al. Effects of acarbose on fecal nutrients, colonic pH, and short-chain fatty acids and rectal proliferative indices. Metabolism 1996;45:1179-87.[Medline]
  53. van Munster IP, Tangerman A, Nagengast FM. Effect of resistant starch on colonic fermentation, bile acid metabolism, and mucosal proliferation. Dig Dis Sci 1994;39:834-42.[Medline]
  54. Cherbut C, Aube AC, Mekki N, Dubois C, Lairon D, Barry JL. Digestive and metabolic effects of potato and maize fibres in human subjects. Br J Nutr 1997;77:33-46.[Medline]
  55. Gibson GR, Beatty ER, Wang X, Cummings JH. Selective stimulation of bifidobacteria in the human colon by oligofructose and inulin. Gastroenterology 1995;108:975-82.[Medline]
  56. Spiller GA, Story JA, Furumoto EJ, Chezem JC, Spiller M. Effect of tartaric acid and dietary fibre from sun-dried raisins on colonic function and on bile acid and volatile fatty acid excretion in healthy adults. Br J Nutr 2003;90:803-7.[Medline]
  57. Tomlin J, Read NW. The effect of resistant starch on colon function in humans. Br J Nutr 1990;64:589-95.[Medline]
  58. Kawaguchi M, Tashiro Y, Adachi T, Tamura Z. Changes in intestinal condition, fecal microflora and composition of rectal gas after administration of fructooligosaccharide and lactulose at different doses. Bifidobacteria Microflora 1993;12:57-67.
  59. Noakes M, Clifton PM, Nestel PJ, Le Leu R, McIntosh G. Effect of high-amylose starch and oat bran on metabolic variables and bowel function in subjects with hypertriglyceridemia. Am J Clin Nutr 1996;64:944-51.[Abstract/Free Full Text]
  60. Dankert J, Zijlstra JB, Wolthers BG. Volatile fatty acids in human peripheral and portal blood: quantitative determination vacuum distillation and gas chromatography. Clin Chim Acta 1981;110:301-7.[Medline]
  61. Peters SG, Pomare EW, Fisher CA. Portal and peripheral blood short chain fatty acid concentrations after caecal lactulose instillation at surgery. Gut 1992;33:1249-52.[Abstract/Free Full Text]
  62. Perry TL, Hansen S, Diamond S, Bullis B, Mok C, Melancon SB. Volatile fatty acids in normal human physiological fluids. Clin Chim Acta 1970;29:369-74.[Medline]
  63. Richards RH, Vreman HJ, Zager P, Feldman C, Blaschke T, Weiner MW. Acetate metabolism in normal human subjects. Am J Kidney Dis 1982;2:47-57.[Medline]
  64. Wolever TM, Fernandes J, Rao AV. Serum acetate:propionate ratio is related to serum cholesterol in men but not women. J Nutr 1996;126:2790-7.
Received for publication March 19, 2004. Accepted for publication July 9, 2004.




This article has been cited by other articles:


Home page
 J. Nutr.Home page
J. A. Vogt, K. B. Ishii-Schrade, P. B. Pencharz, P. J. H. Jones, and T. M. S. Wolever
L-Rhamnose and Lactulose Decrease Serum Triacylglycerols and Their Rates of Synthesis, but Do Not Affect Serum Cholesterol Concentrations in Men
J. Nutr., August 1, 2006; 136(8): 2160 - 2166.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Vogt, J. A
Right arrow Articles by Wolever, T. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Vogt, J. A
Right arrow Articles by Wolever, T. M.
Agricola
Right arrow Articles by Vogt, J. A
Right arrow Articles by Wolever, T. M.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS