Full agreement on the distinction between different types of dietary fiber has not been reached. However, focusing on the IOM's most recent report on the subject, total dietary fiber is defined as the sum of dietary fiber and functional fiber, therefore allowing for the diversity of edible, non-digestible carbohydrates and for flexibility to incorporate new fiber sources developed in the future .
There are large variations in the physical and chemical characteristics of dietary fiber that influence physiological responses in humans differently. Gums, which are hydrophilic polymers with significant water binding capability display unique physicochemical properties that allow them to form viscous solutions or gels when mixed with liquids. Because of these exceptional characteristics, when gums are mixed with food and human digesta in the stomach, a firm soluble polysaccharide/food matrix is formed leading to a delay in gastric emptying which was found to have several effects with possible physiological ramifications including (1) increased sensation of fullness , (2) possible reduction of postprandial blood glucose concentrations, potentially increasing glucose sensitivity , (3) delayed absorption of several nutrients in the small intestine [4, 12], possibly resulting in decreased absorption of energy , (4) interference with the absorption of dietary fat and cholesterol with an overall result of decreased concentrations of blood cholesterol [6, 14], and (5) slower transit time through the small intestine . One study assessed the viscosity of different soluble and insoluble dietary fibers, and found that guar and xanthan gums had the highest viscosities, regardless of concentration and exhibited this characteristic throughout gastric and small intestinal simulation, indicating potential to elicit blood glucose and lipid attenuation .
In addition to the definition for dietary fiber, the amount required to impact health is also debatable. For example, IOM established an Adequate Intake (AI) recommendation for total fiber intake, based on age and sex. For adults 50 years of age and younger, the AI recommendation for total fiber intake is 38 g per day for men and 25 g per day for women, while for adults over 50 years of age, the recommendation is 30 g per day for men and 21 g per day for women. IOM did not set a Tolerable Upper Intake Level (UL) for dietary fiber or functional fiber . On the other hand, FDA bases its recommendation for fiber on caloric intake. The percent daily value (DV) recommended by the FDA for dietary fiber for individuals consuming 2,000 kcal/day is 25 g, and 30 g for those consuming 2,500 kcal/day (21 CFR §101.9(d)(9)). However, it is evident that the intake of dietary fiber in the United States is significantly lower that the recommended amounts, as reflected by intake data from the Continuing Survey of Food Intakes by Individuals (CSFII) (1994–1996, 1998)  – median intakes of dietary fiber ranged from 16.5 to 17.9 g/d for men and 12.1 to 13.8 g/d for women. Based on the AI set for the various age and gender groups, 10 percent or less of a particular group consumed greater than the recommended AI .
PolyGlycopleX (PGX) is a proprietary product composed of three, highly-purified, water-soluble polysaccharides (konjac powder, sodium alginate, and xanthan gum) manufactured with the use of novel technology. The three gums act synergistically to form strong bonds that lead to a level of viscosity that is 3 to 5 times higher than any known individual polysaccharide. The final product is a soluble highly viscous functional fiber that can be used to provide consumers with a supplementary source of fiber in the diet.
Because of its potential use in food and dietary supplements, the present investigation was carried out to evaluate the tolerance to ingestion of 10 g PGX per day, for 21 days, in healthy male and female volunteers. The main objective of the study was to evaluate the overall GI tolerance, while secondary objectives were to evaluate GI signs and symptoms and assess any effects on blood hematology, biochemistry, urine and stool analysis. The protocol was developed to mimic as closely as possible a normal lifestyle and dietary intakes of healthy subjects, who did not go through a "wash out period" prior to being introduced to the test and control products. Instead, a one-week ramp-up period was used to acclimate the subjects to the new products (2.5 g BID). The maximum dose of 10 g PGX per day was selected based on literature values that indicate that the general population probably falls into three categories, with regards to tolerance to dietary fiber: (1) non-sensitive individuals, able to consume ≥ 30 g/day of fiber without experiencing undesirable gastrointestinal effects, (2) sensitive individuals, able to consume 10 g/day of fiber without undesirable gastrointestinal effects, but showing effects at ≥ 20 g/day, and (3) very sensitive individuals, who can experience undesirable gastrointestinal effects at levels of ≤ 10 g/day . Also taken into consideration were the facts that dietary fibers are better tolerated if intake is in the form of solid versus liquid, and in divided versus single doses .
All the subjects enrolled in the trial completed the study. There were no serious adverse events and the adverse events reported were of a mild to moderate nature, and specific to GI discomfort (e.g., flatulence, bloating, intestinal rumbling, or abdominal pain). FDA defines a serious adverse event as "an adverse event that results in death, a life-threatening experience, inpatient hospitalization, a persistent or significant disability or incapacity, or a congenital anomaly or birth defect; or requires, based on reasonable medical judgment, a medical or surgical intervention to prevent an outcome described above" (Section 761(a)(2) of the FD&C Act (21 U.S.C. 379aa-1(a)(2)). An adverse event is defined as "any health-related event associated with the use of a dietary supplement that is adverse" (Section 761(a)(1) of the FD&C Act (21 U.S.C. 379aa-1(a)(1)). The intensity of abdominal pain and nausea were somewhat higher, but not statistically significant in the test (PGX) than in the control group, as reported in subjects' diaries. However, this was not reflected by VAS assessment. The GI complaints experienced by the subjects in this study including flatulence, bloating, abdominal distension and rumbling are well described in the literature , and are accepted occurrences with dietary intake of fruits and vegetables, and fiber in general .
There are limited studies to suggest that chronic high intakes of dietary fiber can cause gastrointestinal distress. The ingestion of wheat bran at levels up to 40 g/day did not result in significant increases in GI distress compared to placebo . However, flatulence did increase with increased intake of dietary fiber in general , and with gums that led to moderate to severe degrees of flatulence in a trial in which 4 to 12 g/day of a hydrolyzed guar gum were provided to 16 elderly patients .
In the present study, none of the subjects experienced diarrhea (diarrhea is defined as an abnormally frequent discharge of semisolid or fluid fecal matter from the bowel, while laxation is a bowel movement ); however, the consistency of stools was softer in the test than control group at V2, although the difference was not statistically significant. The softer stools correlate with the results from the stool analysis that showed that the dry matter (%) was statistically higher in the control than in the test (PGX) group at V2. The stool softness difference was no longer present at the V3 visit, and corresponds to those documented by the IOM report indicating that viscous fiber generally has little effect on fecal bulk or laxation .
Statistical analysis showed no differences between test and control group with regard to urinalysis or hematological values. Although the authors believe that PGX is a fermentable fiber, the stool analysis for SCFA showed no differences between test and control groups. SCFA are highly labile and it is possible that the amount of time that lapsed between sample collection to the time of analysis was too long, possibly affecting the over all results.
The biochemical parameters were evaluated at baseline, V2 and V3 and showed no differences between test and control group, except for statistically significant decreases in total cholesterol, and LDL cholesterol at V2 and V3, and for GGTP and uric acid at V2.
PGX's effects on decreasing total and LDL cholesterol levels in the study concur with similar reports in the literature describing the effects viscous dietary fiber has on lowering serum cholesterol levels . Noteworthy is the fact that not all dietary fibers decrease serum cholesterol concentration, or at least not to the same extent, with viscous fibers being most successful. Behall  examined the effects a low- and high-fiber diet had on plasma cholesterol concentrations. The high-fiber diet of an average of 19.5 g/day was further divided into non-viscous fiber (cellulose), and viscous fiber (carboxymethylcellulose gum, karaya gum, or locust bean gum). Results showed that diets containing viscous dietary fiber led to significantly lower plasma cholesterol concentrations. Jenkins et al.  reported the hypocholesterolemic effect of guar gum in the mid 1970s, followed in the 1980s by other studies that showed a significant reduction in serum cholesterol concentrations of between 11 and 16 percent [23–25]. Anderson et al  demonstrated that when 20 hypercholesterolemic men were randomly assigned to either a wheat bran or oat bran diet, a significant decrease in serum total cholesterol concentration of 12.8 percent was noted only after 21 days; however, this effect was not seen in the wheat bran group.
Two meta-analyses evaluating the effects of viscous fiber arrived at the same conclusions. One meta-analysis of 20 trials that used high doses of the viscous fiber oat bran, showed that the reductions in serum cholesterol concentrations ranged from 0.1 to 2.5 percent/g of intake , while another, evaluating the effects of oat bran, pectin, psyllium and guar gum on blood lipid concentrations showed that 2 to 10 g/day of viscous fiber were associated with small but significant decreases in total and LDL cholesterol concentrations .
IOM also concluded that viscous dietary and functional fibers reduce both total and LDL cholesterol concentrations, and possibly serum triglycerides in a dose-dependent manner, although the report acknowledges that only few studies report dose-response data. Further, the report indicates that these relatively small-scale intervention trials using viscous functional fibers have reported substantial cholesterol-lowering effects and therefore, probably have protective effects against coronary heart disease (CHD) .
The GGTP levels were statistically lower in the PGX group compared to controls. While the exact mechanism that led to this decrease is not fully understood, especially because the other liver enzymes were not altered, it is the belief of the investigators that this decrease is beneficial, as elevation in GGTP is used to assess possible damage to the liver or the biliary system.
Elevated levels of uric acid are associated with gout and recently have been considered important markers for hypertension, cardiovascular disease and metabolic syndrome . While most studies have focused on hyperuricemic states caused by either over production or under excretion of uric cid, as well as by excessive intake of ribonucleic acid (RNA), few studies have been devoted to hypourecemia, or the effects of maintaining low uric acid levels in otherwise healthy individuals . Specifically, the effect of dietary fiber on serum uric acid levels has been only minimally investigated. Koguchi et al.  have shown that feeding rats a diet high in viscous fiber (e.g., xanthan gum) they were able to alter metabolic processes that contribute to hyperurecemia by lowering serum uric acid levels, reducing RNA digestion and increasing RNA excretion in the feces , a mechanism that probably also explains the statistically lower levels of serum uric acid identified in this clinical study at the V2 visit.
Lastly, the serum levels of several fat- and water soluble vitamins were assessed during the study. Vitamin D was measured because PGX demonstrates specific physical properties including high viscosity and solubility and, there was concern for possible sequestration of fat soluble vitamins and therefore vitamin malabsorption. Consequently, vitamin A, D, E and K levels were monitored during the study. Vitamin C and B levels were followed as an assessment of the potential of PGX to result in generalized malabsorption. Results showed that there were no differences observed in the levels of vitamin A, B1, B6, B12, E, and K between test and control group, except for statistically higher levels of plasma vitamin D (1,25-dihydroxyvitamin D) and C. Vitamin D is a fat soluble vitamin found only in few foods and produced endogenously with exposure to sunlight. The vitamin D ingested or produced is inactive (25-hydroxyvitamin D [25(OH)D] (calcidiol)) and undergoes activation through a two-step hydroxylation process in the liver and kidneys to form 1,25-dihydroxyvitamin D [1,25(OH)2D] (calcitriol). According to the National Institutes of Health/Office of Dietary Supplements (NIH/ODS), circulating 1,25(OH)2D is generally not a good indicator of vitamin D status, because it has a short half-life of 15 hours and serum concentrations are closely regulated by calcium, phosphate and parathyroid hormone. Further, levels of 1,25(OH)2D do not decrease until vitamin D deficiency is severe . Adequate levels of vitamin D are essential for bone and overall health. However, it has been determined that 41 percent of American men and 53 percent of American women have levels of vitamin D below what is considered optimum. A recent study found that a low serum level of 25-hydroxyvitamin D could be independently associated with a significantly increased risk of all-cause mortality. According to the authors, if these findings are confirmed in future clinical studies, vitamin D supplementation should be studied as a way to reduce mortality risk .
Interestingly, optimal serum concentrations of 25(OH)D have not been established [34, 35] and are likely to vary at each stage of life. NIH considers a concentration of <50 nmol/L 25(OH)D generally inadequate. In 2007, a controversial editorial was published contending that supplemental intakes of 400 International Units (IU)/day of vitamin D increase 25(OH)D concentrations by only 2.8–4.8 ng/mL (7–12 nmol/L) and that daily intakes of approximately 1,700 IU are needed to raise these concentrations from 20 to 32 ng/mL (50 to 80 nmol/L) . The exact mechanism leading to higher levels of serum 1,25(OH)2D in our study is not completely understood, or interpreted as a good indicator of vitamin D status. However, based on evidence that subnormal levels of vitamin D can impact bone and overall health, and that according to some investigators, current recommendations for supplementation of the US population is approximately 4-fold lower than it should be, it is likely that consumers could benefit from increased levels of serum vitamin D to provided the necessary health benefits.
The exact mechanism causing increase in the serum vitamin C levels in the test group is not completely understood; however, as a water soluble vitamin, the somewhat higher levels are not anticipated to have any detrimental effects in otherwise healthy subjects.
The effects of the intervention on dietary intakes were not measured in this clinical trial, because the focus of the study was on assessing GI tolerance. However, this intentional omission could be interpreted as a limitation of the study, which the authors plan in addressing in future clinical trials.