Abstract

Fiber intake has been shown to increase gastrointestinal motility, slow gastric emptying rate, reduce glucose absorption, and body weight, increase insulin sensitivity, and stimulate the hunger-satisfaction effect. Despite the high fiber variety, this set of characteristics is not present in all products. For this reason, this study assessed the physicochemical and structural properties of B. gasipaes nanocellulose and its metabolic effect on glucose regulation, intestinal motility, and orexigenic and anorexigenic hormones related to signals of food consumption and body weight gain/loss. The peach palm (Bactris gasipaes) nanocellulose has a particle size of 44.30 μm, which increases its water balance, oil, and viscosity retention capacity, allowing at a concentration of 12.50 mg/kg to decrease the rate of gastric emptying, with an increase in water retention in feces, reduction in body weight, glucose reduction, and other effects on intestinal markers of inflammation and gastrointestinal hormones. As a conclusion, the consumption of nanocellulose in mice of the BALB/c strain reduces the sense of hunger and stimulates the feeling of satiety, which may have a positive effect in the decrease of metabolic-related diseases.

1. Introduction

Globally known as a raw material for the manufacture of palm heart, Bactris gasipaes Kunth is a palm tree that grows throughout the Amazon region ¹. The economic potential of raw materials like palm heart (B. gasipaes) has changed due to the increasing interest in researching the potential of fruit remains processed as new materials ². Bactris gasipaes is a palm tree that was one of the first domesticated plants in pre-Columbian times ³. It is generally propagated by seeds with a germination period of 38 to 133 days ⁴. In Brazil, mainly in the south, it is known as Pupunha and its cultivation has two important benefits, obtaining palm heart and fruits named coconuts ⁵. During palmitate extraction in 2017, approximately 1.67x10⁶ tons of trash were produced. Nanocellulose is made from this renewable and economical raw material, turning it into a high-value product ^{3, 4, 5, 6}. Cellulose is one of the most prevalent biological materials and it is a naturally occurring polymer that dates back thousands of years. It can be obtained from a broad range of sources, including bacteria, plants, and marine life. It is a nearly limitless, biodegradable organic polymer that makes up almost half of all biological resources found in nature ⁷. The past ten years have seen a significant increase in the use of nanotechnology to help with waste and products involving cellulosic substrates. This is the reason why nanocellulose can be considered functional in many applications. It has been found that this fully polymeric component has been applied and functionalized with an antimicrobial and biodegradable approach in electronic devices ⁸, heavy metal adsorption ⁹, water purification ¹⁰, energy storage ¹¹, and food packaging ¹², applying a biodegradable approach ¹³. However, its use for consumption has not been explored. Dietary fiber is made up of carbohydrate polymers that have three or more monomeric units that are indigestible and non-absorbed by humans ¹⁴. Dietary fiber is now understood to have a larger range of physiological roles than it once did in maintaining health and lowering the risk of disease, as interest in its physiological properties has grown significantly in recent years ¹⁵. Consuming fiber has been linked to impacts on intestinal transit, gastrointestinal content, slowed stomach emptying rate, and enhanced motility. According to new research, there are other benefits including reduced glucose absorption, increased insulin sensitivity, greater postprandial metabolism, enhanced satiety impact, and a decrease in disorders linked to metabolism ¹⁶. The excessive eating of foods high in fat and sugar is a contributing factor to disorders associated to variations in blood glucose levels. Intervention to promote satiety, which is strongly related to food consumption, is one factor that can help decrease the growth rate of these diseases ¹⁷. Certain substances that have been studied for their ability to reduce appetite, such as dietary fiber, have also been studied for how they affect satiety ^{18, 19}, in humans ^{20, 21, 22}, and rodents ^{23, 24}. According to ²⁵, gastrointestinal hormones such as ghrelin, cholecystokinin (CCK), YY3-36 peptide, and glucagon-like peptide 1 (GLP-1) are secreted. As a result of this secretion, gastric distension is modulated along with alterations in intestinal motility. Increased intake of fiber has a positive impact on some physiological processes. For instance, some studies demonstrate that fiber consumption in mice can improve gut health ²⁶, maintain a unique microbiota ²⁴, and reduce blood glucose concentrations and body mass ²⁷. Consumption of 15 g/day for 4 months was associated with reduced fasting glucose levels, a 10% decrease in energy intake, and a body mass reduction of 1.9 kg ²⁸. For this reason, this study assessed the physicochemical and structural properties of B. gasipaes nanocellulose and its metabolic effect on glucose regulation, intestinal motility, and orexigenic and anorexigenic hormones related to signals of food consumption and body weight gain/loss in male BALB/c mice.

2. Materials and Methods

The nanocellulose was obtained from agro-industrial waste of B. gasipaes, by Talita Slapack Franco from the University of Paraná, Brazil. The extraction methodology was described and carried out by ⁶. The chicory inulin was obtained from Sigma-Aldrich^® - I2255, with CAS Number: 9005-80-5 (Darmstadt, Germany).

Inulin and Nanocellulose sample water absorption capacity (WHC) was evaluated using the method described by ²⁹, with some modifications. Each sample (0.01 g) was mixed homogeneously with 1 mL of distilled water at room temperature (25 °C) for 2 hours, and then the suspension was centrifuged at 2500 rpm for 10 minutes. Finally, the supernatant was discarded and WHC was calculated using the following equation:

Where m₀ is the weight of the centrifuge tube; m₁ is the mass of the centrifuge tube and the dry sample, and m₂ is the weight of the centrifuge tube and the moisturized sample.

Oil absorption capacity (OAC) was determined using ²⁹ method, in which 0.01 g of sample was homogeneously mixed with 1 mL of soybean oil at room temperature (25°C) for 2 hours. Subsequently, the suspension was centrifugated at 2500 rpm for 10 minutes and the OAC was calculated using the following equation:

Where m₀ is the weight of the centrifuge tube, m₁ is the mass of the centrifuge tube and the dry sample, and m₂ is the weight of the centrifugal tube and the moisturized sample.

Inulin and nanocellulose sample at 2% were prepared, and viscosity was determined at 25 °C with a digital rotary viscosimeter (Brookfield DV1, Middleboro, MA, USA) with a No. 3 needle, at 100 rpm. The values obtained were expressed in centipoise (cP) ³⁰.

Samples were analyzed using a Scanning Electron Microscopy (SEM) (EVO 18, ZEISS, Germany, at 15 kV). Before observation, samples were dehydrated for 24 hours at 60 °C and then metalized with gold and mounted on a support. Micrographs were taken with increases of 500 to 2000 x. Particle size was calculated using the ImageJ software (Image Processing and Analysis in Java, NIH, Bethesda, Maryland, USA).

FT-IR spectra samples were performed on a Fourier-transformed full-reflection infrared spectrometer (FT-IR, Nicolet, Waltham, MA, USA). Each sample was dehydrated at 60 °C for 48 h. Samples were mixed with potassium bromide (KBr) (1:100 p/p), and FT-IR spectra between 400 and 4000 cm^-1 were obtained with a resolution of 4 cm^-1. Area Under the Curve (AUC) analysis was performed to determine the increase in absorption bands. Data obtained was analyzed with the OriginPro 8 software (OriginLab Corp., Northampton, MA, USA).

Experiments were performed using 60 male BALB/c mice (20 - 25 g body weight) obtained from Center for Biomedical Research of the West-Mexican Institute of Social Security. Animals were housed in groups of 15 mice/cage and were maintained in standard laboratory conditions (room temperature 25 ± 1.0 °C; humidity 55-65% and 12-h light/12-h dark cycle) with food and water provided ad libitum. Mice were handled according to Mexican Federal Regulations for the Care and Use of Laboratory Animals ³¹ (Mexican Ministry of Health). This protocol was submitted to CUCEI-UDG Ethics Committee (CICUAL-02/2022).

According to bibliographic references, dietary fiber consumption parameters were established, where the use of three concentrations: 3.12 mg/kg, 6.25 mg/ kg, and 12.50 mg/kg were considered, to assess and determine which showed the best dose-response. For nanocellulose preparation, different concentrations were weighed and it was dissolved in purified water, due to its low solubility characteristic, an emulsion was carried out with the help of an IKA Ultra-Turrax T50 Digital Homogenizer (Staufen, Germany) at a speed of 10,000 rpm. This homogenization ensured that different concentrations samples could pass through feeding canula.

Gastrointestinal motility was carried out by counting feces discharged each time. BALB/c mice were administered with the corresponding nanocellulose dose using a feeding canula and immediately were placed in individual cages, without a sawdust layer, for two hours, where they were continuously observed so that each of the discharges would be immediately removed to prevent contamination with urine. The feces were placed in previously tared Eppendorf tubes. Once the time had elapsed and all pellets had been recovered, they were weighed again and placed in a stove at 66°C for 24 h. After 24 h, tubes with samples were to determine the dry weight of feces and estimate the water percentage ³².

To determine the nanocellulose influence on blood glucose levels, this effect was evaluated through a Glucose Tolerance Curve, in a first phase (acute dose) and a second phase (chronic dose for 60 days). In second phase, basal glucose and body weight was determined weekly. The glucose tolerance curve was performed by placing BALB/c mice in 4 h fasting, where food was removed from the cages and water intake ad libitum was left. After fasting period, glucose concentration was measured by using a digital hand glucometer, Contour^® TS (Bayer HealthCare LLC, Mishawaka, IN, USA) in blood samples collected from the tail vein. Once the basal glucose was taken, the corresponding nanocellulose concentration was orally administered (v. o.) by gavage-feeding, a 30-minute period was allowed to pass and blood glucose level was taken again, taking into account the zero time (t₀) and administrating an oral dextrose load of 2g/kg of mouse weight, followed by measurements at intervals of 15, 30, 60 and 120 min ³³. Basal glucose was measured weekly during the eight weeks of phase two, from the tail vein. The body weight was monitored with support of a manual scale (LABESSA), and the measurements were carried out every week, placing the mouse on the base plate and recording the weight score.

Quantification of gastrointestinal hormones and peptides was carried out through a Millipore MILLIPLEX^® (Darmstadt, Germany) MMHE-44K expanded panel by using blood serum. The test was carried out according to manufacturer's instructions, whereas a first step pearls were activated with immobilized antibodies of ghrelin, glucagon, insulin, GLP-1, leptin and resistin. The spheres were shaken with a vortex for 30 s, then 150 μL of each of them was placed in a vial to bring to a final volume of 30 mL with the diluent. Quality controls and hormone standards were prepared, in which 250 μL of deionized water was placed, gently shaken and left to rest for 10 min. For the process of immunoassay, 200 μL of tampon solution was placed in the microplate, and then, the plate was sealed and shaken for 10 min at room temperature. Once the tampon was decanted, 10 μl of matrix solution with the pearls were added along with 10 μL buffer, 10 μL of each of the standards, 25 μL controls. Curves of standards and corresponding samples were sealed on the board, covered from light, and left shaking throughout the night at 4 °C.

After incubation, stitches were carefully removed, and contents were washed with tampon solution three times, and water remains were absorbed using absorbent towels. Subsequently, 50 μL of antibodies were added, sealed and shaken at temperature room for one hour. After this period, 50 μL of streptavidin phycoerythrin were added. Contents were sealed and shaken for 30 minutes. Finally, the contents were removed and washed three times, and 150 μL of vanilla fluid were added to the entire plate and shaken for 5 minutes. Once this procedure was complete, the plate was read.

For characterization and structure, data was expressed as the average ± standard deviation. Statistical significance results were analyzed using the Student t-test or variance analysis. Significant differences between experimental groups were expressed like *P ≤ 0.05, **P ≥ 0.01, *** P ≤ 0.001, ****P ≥ 0.0001 whereas not significant differences were expressed as (ns). For biological determinations, a unifactorial design was used where controlled factor was treatment received by mouse, and variable responses were gastrointestinal motility, hormone concentration, gastropeptides, glucose tolerance, basal glucose, and body weight. For statistical analysis, GraphPad Prism^® software version 8.0 was used (GraphPad Software, Inc., La Jolla, CA, USA).

3. Results

In Figure 1A, nanocellulose WHC was observed at 35.30 ± 1.80 g/g, while inulin was 0.50 ± 0.20 g/g. This property is defined as the sum of free water vs. the united water in the fiber matrix, and is influenced by the hydrogen bonds, the dipolar hydrophilic groups of compounds involved, and the structural morphology ³⁴. Regarding the OAC, it was shown (Figure 1B) that nanocellulose had values significantly higher than inulin, with values of 30.50 ± 3.00 and 6.50 ± 0.50 g/g respectively.

Inulin and nanocellulose viscosity tests were carried out and values obtained were 9 and 10 cP respectively (Figure 1C), with a slightly significant difference (*P ≤ 0.05) between groups.

Inulin and nanocellulose sample micrographs obtained are shown in Figure 2. With regards to inulin samples (Figure 2A-C), smaller spherical particles were observed mainly at 500x and 1000x. The surface of these was mostly observed smooth with protrusions in some of them. This same morphology has been reported by some authors such as ³⁵, mentioning that average particle size of this material is 47.30 μm, similar to one obtained in this work (44.30 μm).

Figure 3 shows the FT-IR spectrum of inulin and nanocellulose samples. This graph describes the transmission band displacement of different functional groups.

IR spectroscopy provides a very valuable method to quickly and easily recognize the presence of functional groups, due to the atomic vibrations of covalent bonds in an organic molecule, generating different bands or absorption peaks and providing information about the structure of the chemical compound ³⁶.

Different nanocellulose concentrations (3.12, 6.25 and 12.50 mg/kg) were evaluated in the preliminary phase. The positive control inulin concentrations were 6.25, 12.50 and 25.00 mg/kg. It was observed that, in the acute dose of inulin assessment, concentration increase was proportional to the increase of evacuations over a two-hour period, as well as in the weight of these, but inversely proportional to water percentage (Figure 4). Number of stools in nanocellulose sample was greater than a lower acute dose and it decreased as the concentration increased, as well as their weight ratio. Although there were fewer discharges, the water concentration was higher in relation to the amount of nanocellulose consumed. It has been documented that after dietary fiber consumption, a laxative effect occurs by increasing its volume in the gastrointestinal system, decreasing the transit time, and thus, increasing the number of evacuations. A characteristic that can be observed in case of inulin, as concentration increases, there is a laxative effect that increases feces amount. With regards to nanocellulose, although stool number is lower, no intestinal obstruction can be observed as a result of a constipatory effect given at a concentration of 12.50 mg/kg, since its water concentration is significantly higher than the control and the higher concentrations of inulin.

The evaluation of different concentrations was aimed at being able to determine the chronic trial ideal dose; it was observed that best response was presented at a concentration of 12.50 mg/kg of inulin and nanocellulose at the gastrointestinal level, as it produced no laxative effect, intestinal obstruction while maintaining a significant water concentration. The evaluation effects occurred after chronic consumption, by administering inulin and nanocellulose at the previously established dose (12.50 mg/kg), for 60 days. It was also noted that there is no significant difference in the number of discharges (Figure 5A) and in the feces weight (Figure 5B) related to nanocellulose consumption in relation with control. It was also corroborated that there are no laxative or obstructive effects after intake, compared with water percentage contained in the feces, and that there is a significant increase in comparison with the control (Figure 5C).

Nanocellulose chronic consumption showed that weekly basal glucose levels were constant; a significant difference was observed in the last week in reducing their values in contrast to control. This behavior was similar to the one observed when administering inulin (Figure 6A). In several studies it is mentioned that dietary fiber consumption promotes glucose levels, and a reduction in body weight. In this study, it was confirmed that nanocellulose administration-maintained body weight consistently for the first five weeks; whereas from the sixth week, a decrease of 1.25 g below the initial weight was observed (Figure 6B). In the case of inulin, a significant decrease from the positive control was shown from the sixth week, where finally, in the eighth week the weight was 2.40 g below the initial value (Figure 6B).

This effect was evaluated through glucose quantification, determining the values obtained over a period of time and calculating the area under the curve. It was noted that there was no significant difference between the first and second phases of the experiment. In case of acute administration of nanocellulose and after two months of consumption of this, no changes were observed in postprandial glucose levels, which suggests that there is no direct interaction at the gastrointestinal level that demonstrates an increase of glucose level in the blood that generates an amortization after glucose load, whose peak occurred at 15 min and that gradually decreased over time (Figure 7C). Unlike in acute inulin intake case, the maximum glucose level appeared up to 30 min, which generated a blood sugar peak for a longer time, decreasing through chronic consumption, because in the second phase of the experiment the glucose peak was observed at 15 min and decreased over time as it was shown in the group of nanocellulose (Figure 7B).

Nanocellulose consumption effect on peripheral detectors in system describes variable changes where central receptors are activated and send signals that activate the release of mediators that mitigate the signals related to hunger or satiety (Figure 8). Ghrelin is an orexigenic hormone that sends appetite signal and its level is mitigated directly depending on the consumption of food, in the case of nanocellulose ingestion, from its basal state to its postprandial state, it increases this expression, but not significantly (Figure 8A). This suggests that the intake of this type of fiber can maintain the levels of ghrelin to reduce the amount of food in a meal. This effect will allow glycogen use that is found as a reserve in the body, through pancreas glucagon generation, the release of this hormone promotes amino acid capture which serve as a substrate for gluconeogenesis, thus showing that their postprandial levels increase not significantly after the consumption of nanocellulose (Figure 8B). Glucagon, although it does not modify the transcription levels of this enzyme, it increases the release of glycerol by the adipocyte, serving as a substrate for gluconeogenesis ³⁷, thus confirming that a release sustained of glucagon in the system stimulates the metabolism of stored lipids, thereby producing a reduction in weight (Figure 6B). Glucagon and glucose release lead to insulin secretion, this phenomenon is called incretin effect to which it is attributed the fact that oral glucose leads the release of incretins ³⁸.

Insulin and glucagon are released by pancreatic islets and play an essential role in homeostasis regulation and carbohydrate metabolism. Arterial blood passes through the nucleus of the islet to be enriched by insulin from the β cells and then reaches the α cells, where insulin can regulate the secretion of glucagon ³⁷. Insulin showed a significant increase after nanocellulose consumption and dextrose load (Figure 8C) compared to baseline and controls, indicating a balance between insulin and glucagon secretion that keeps plasma glucose levels within a narrow physiological range, thus showing a decrease in blood sugar levels and areas below the curve (Figure 7). GLP-1 stimulates insulin secretion at high glucose concentrations in the postprandial state by 16.5% (Figure 8D), regulating glucagon secretion (Figure 8B), and generating increased insulin sensitivity (Figure 8D). We can also observe an increase in leptin postprandial expression by 24% (Figure 8E), which will have an anorexigenic effect by decreasing neuropeptide Y expression, increased energy expenditure, an insulin sensitizing effect, oxidation of free fatty acids, reduction in the accumulation of ectopic fat in non-fat tissues ³⁹, and activation of resistin production ⁴⁰, which is decreased after nanocellulose consumption, showing a decrease of 32.0% in its expression during post prandial state (Figure 8F), thus linking the increase in insulin expression to 38% (Figure 8C). The ratio of these three hormones will produce increased insulin sensitivity (Figure 8C), glucose metabolism (Figure 6A), and weight maintenance (Figure 6B). Taking into account these results in conjunction with low levels of resistin (Figure 8F), increased expression of insulin (Figure 8C) and leptin (Figure 8E), as well as existing backgrounds, it is noted that chronic consumption promotes weight loss (Figure 6B) and increases insulin sensitivity.

The importance of knowing the response of nanocellulose characteristics will establish which fibers from various sources can be used for consumption, also to consider the relationship between the intake amount and its beneficial effects with the aim of understanding its behavior in the lipid profile, weight loss, blood glucose levels, serum concentrations of ghrelin, GLP-1, glucagon, insulin, leptin, and resistin in favor of satiety modulation and reduction of food intake in metabolic diseases reduction.

4. Discussion

Studies have suggested that the physicochemical properties of dietary fiber, such as WHC, OAC, and WSC, are closely related to its physiological functions ⁴¹. WHC has some relationship with irregular, loose, and porous surfaces of fiber. When the contact area and the hydrophilic groups increase, water can be retained in the hydrophile space of the fiber structure, which will improve WHC. Fiber presents adequate levels of WHC, improving human health with a lubricating effect after water absorption, which can promote intestinal peristalsis and motility, and therefore, it can increase defecation and elimination of carcinogens. Additionally, dietary fiber increases fecal volume after absorbing water, which can reduce food intake. Glucose can adhere to the structural network of dietary fiber reducing contact with the human intestinal tract, which can prevent diabetes ⁴². The nanocellulose evaluated in this study had a greater swelling capacity (55.87 mL/g) in relation to these physiological parameters than inulin (39.80 mL/g). Cellulose is an insoluble polysaccharide connected by glucose through β (1-4) glycosidic bonds and belongs to a linear molecule ³⁴. The adjacent cellulose chains have a stable fibrous structure through hydrogen bonds, which causes cellulose to have WHC and oil retention OAC ⁴³. Nanocellulose has the same potential application as cellulose, however, by showing a reduction in its size, it has an increase in its contact area, improving its mechanical, thermal, and rheological properties ⁶, which suggests that it also has a good physiological application as dietary fiber.

Inulin is an abundant storage fructooligosaccharide, obtained from different sources such as chicory root, dahlia, cereals, garlic, bananas, and onions ⁴⁴. It consists mainly of 1,2-[3-d-fructofuranose] linked to a terminal fraction of glucose, which makes inulin resistant to hydrolysis by gastrointestinal enzymes due to its C-2 anomere β configuration but can be fermented in the large intestine ^{45, 46, 47}. Chicory inulin can be composed of several fructose units, ranging from 2 to 60 (polymerization degree [DP]). DP depends on the species, climatic and physical plant conditions ⁴⁸. Fiber OAC is mainly related to particle size, specific surface area, porosity, and reaction to temperature.

Dietary fiber can absorb lipids and reduce excessive calorie intake in the body, which can prevent obesity development. When fiber structure becomes loose and porous, more superficial functional groups are exposed, so this characteristic can improve its lipids and glucose interaction ³⁴. Viscosity and its physicochemical properties are related, referring to some polysaccharides ability to thicken and form gels when mixed with water, affecting directly the physiological properties of fiber in the organism, such as glucose and lipid concentration and modulation, and gastric emptying and transit time reduction in the small intestine ⁴⁹. In low concentrations, insoluble components of dietary fiber, such as cellulose, have a low viscosity capacity in aqueous solutions; however, this behavior can be improved by increasing substance concentration. According to ⁴⁹, the cellulose viscosity (Solka floc) ranged from 6 cP to 0.50% at a concentration 2% higher. In the same research, a soluble fiber named Guar rubber, showed values of 962 cP in a low concentration (0.50%). Michelin et al., 2020 ⁵⁰ mention that nanocellulose particles can immobilize a high amount of water on their internal and external surfaces, creating a highly viscous aquatic system. In this study, the viscosity values of Chicory inulin were at a 2% concentration. This behavior was observed similarly by Shoaib et al. in 2016, reporting values of 1.65 cP in 5% inulin solutions dissolved in water at 10 °C. This viscosity value was reversed by increasing the inulin concentration up to 30% reporting a value of 100 cP ⁴⁸.

Particle size is an important dietary fiber parameter, due to its influence on human body function, relating with physicochemical properties such as WHC, OAC ⁵¹, WSC and viscosity. In nanocellulose images shown in Figure 2D-F, it is possible to observe a filament-type structure that corresponds to the dietary fiber expected morphology, presenting a similarity with nanocellulose micrography of unprocessed dietary fiber by ⁶. Furthermore, 2D micrography reveals the pores existence. He et al., 2022 ³⁴ indicate that dietary fiber porosity is associated with significant physicochemical properties like OAC, so the feature seen in nanocellulose micrography may be connected to values found for this property in the current study. The nanocellulose had an average particle size of 326.02 μm. Regarding infrared spectroscopy, spikes between bands of 2950–2800 cm^-1 refer to a vibratory stretching of saturated aliphatic structures belonging to cellulose and hemicellulose.

The presence of stretches around 850 – 900 cm^-1 can be attributed with the -CH glycoside bonds and also with deformation caused by -OH groups vibration associated to glycosidic bonds between anhydroglucose units in cellulose molecules ⁵². Some authors refer to the presence of a peak in a region close to 1739 cm^-1, mainly related to acetyl and uronic vibrations ^{53, 54}. Bands present between 1730 - 1734 cm^-1 are related to absorption in a xylene axial deformation, the main carbohydrate present in hemicelluloses ⁶.

Table 1. FT-IR analysis of inulin and nanocellulose. The stretch present between 3402 - 3413 cm^-1 indicates hydrophilic characteristics of both samples. The presence of lignin in the nanocellulose sample (19.48 ± 0.40) obtained from the working group ⁶, is observed in an absorption range of 3410 - 3460 cm^-1. Area Under the Curve (AUC) was carried out to know the difference between the different absorption peaks. The 1059 cm^-1 nanocellulose peak was taken as a reference, where its furano- and piran-type characteristic rings are present in inulin and cellulose structures. The greatest stretching was mainly observed at peaks 3402 and 3413 cm^-1 with increases of 5 and 3 times in that enlargement, corresponding to inulin and cellulose respectively. A gel-forming fiber consumption significantly increases the chimo viscosity in the upper intestine. WHC allows a gastrointestinal action level and does not generate constipation or laxative effect, which reduces contact with digestive enzymes and delays absorption, causing a greater fraction of nutrients to be supplied to the distal regions of the small intestine ⁶². The presence of fiber, as an added ingredient in foods or as an integral part of the structure of edible plants, has a beneficial effect. A lot of evidence relates fiber intake with intestinal health, in the physiology of the upper gastrointestinal system, as it plays a key role in nutrition, increasing gastric secretions and improving bowel motility, through increased luminal volume, luminal viscosity, and possible binding with other nutrients ⁶³. In this work, nanocellulose consumption reported a significant difference in water retention in feces; the number of the discharge does not make a difference, reducing contact without causing constipation or laxative effect (Figure 5C). Gastrointestinal administration of nanocellulose at a concentration of 12.50 mg/kg shows a decrease in gastric emptying, as there was no significant difference in discharges or increase number in fecal weight (Figure 5). Fiber consumption has been shown to have a beneficial effect and plays a key role on the diet, but this will depend on the fiber type, the amount consumed and the intake time; for example, fiber from cereals, Psyllium, inulin, among others, act in a different way, which has been demonstrated through a study, where a comparison of the use of these fibers in the development of type 2 diabetes mellitus was performed, observing a significant difference in their reduction while consuming each of them ⁶⁴. It is shown that dietary fiber-enriched diets improve insulin sensitivity and glucose tolerance in subjects with both slim and obese diabetes. Systematic reviews and meta-analyses indicate that increased dietary fiber intake reduces cardiovascular risk disease, type 2 diabetes, obesity, and metabolic syndrome ^{65, 66}. Prebiotic and gel-forming fibers confer multiple metabolic benefits, including reduction in weight gain, and fat mass, which appear to be beyond the fiber-induced pituitary tract ⁶⁷. Through the ingestion of nanocellulose, there is a decrease in body weight (Figure 6B), basal blood glucose levels (Figure 6A) and a delay in glucose absorption (Figure 7). Fibers such as those found in oat leaf, form a viscous solution in the small intestine, which reduces the contact and mixing of macronutrients with digestive enzymes, and this delays glucose absorption, which consequently reduces postprandial glycemia and insulin levels ⁶⁸. Psyllium shows glycemic control in patients with a developing type 2 diabetes mellitus risk ⁶⁹. Inulin influences reducing the lipid profile and blood glucose levels ⁷⁰. In a study with different inulin and cellulose concentrations, a dose-dependent relationship with improved glucose tolerance was shown ³³. In the homeostatic regulation, the body sends out signals to inform the need for food consumption through hunger sensation by ghrelin release, being the only orexigenic intestinal peptide or hunger sensation producer, which is secreted by Gr stomach cells in the state of fasting and is inhibited in the postprandial state by light nutrients ingested and hormones of the small intestine in order to generate a satiety effect ⁷¹. It has also been shown that incorporating fibers such as dextrin, maize fiber, poly-dextrose and resistant starch reduces food intake in a subsequent test meal ⁷². This food intake effect can be explained in part because fiber intake suppresses the postprandial ghrelin response ⁷³. Prebiotic and gel-forming fibers have been considered to promote satiety through increased secretion of lower intestinal satiety hormones ⁷⁴. (In addition, increased intake of prebiotic fibers, such as inulin, stimulates the release of saturation-inducing intestinal peptides such as cholecystokinin (CCK), tyrosine peptide (PYY) and glucagon-like peptide 1 (GLP-1) in rodents and in humans ⁷⁵. Consumption of dietary fiber can reduce postprandial glucose through GLP-1 mitigation by antagonizing the GLP1 receptor in the gate vein, its action is mediated to a lesser extent by GLP1 receptors located in the periportal neural system ⁷⁶. In the consumption of nanocellulose, there is a non-significant increase in ghrelin (Figure 8), glucagon, GLP-1, and leptin, a significant increase in insulin, and a significant reduction in resistin levels. In transgenic mice with overexpression of the glucagon receptor in the β cells, an increase in glucose-dependent insulin secretion was observed, as well as an improvement in carbohydrate tolerance, suggesting that glucagon improves the function of pancreatic beta cells ⁷⁷. Fiber-enriched meals have been considered to decrease glucose and ghrelin levels, as well as insulin and GLP-1 stimulation ⁷⁸. The incretin hormones action such as glucagon-1-like peptide (GLP-1) and gastric inhibitor polypeptide (GIP) exert an important influence on the postprandial glucose rate through their static actions of glucagon and tropical insulin, respectively ⁷⁹. The role of β-glucan in the release of intestinal hormones and the effect on satiety, after ingestion of pasta fortified with 6% β-glucan in healthy overweight individuals, has been analyzed. The modification of serum concentrations of orexigenic peptide ghrelin and anorexigenic active form of GLP-1, GLP-2, CCK and PYY, showed a relative increase of the above factors during the postprandial state ⁷⁹. Traditionally it was thought that the main function of adipose tissue was to serve as a temporary storage for energy in the form of triacylglycerol, but fat tissue is now recognized as the largest endocrine organ in the human body ⁸⁰. Fat tissue is known to express and secret a variety of products known as adipokines, which include leptin, adiponectin, resistin, and visfatin ⁸¹. Prebiotic and gel-forming fibers confer multiple metabolic benefits, including reduced circulating lipids, leptin, and insulin resistance, which appear to be beyond the fiber-produced hunger and satiety ratio ⁸². Consumption of oatmeal β-glucan is linked to the reduction of risk factors associated with diabetes and obesity by reducing glycemic response and serum low-density lipoprotein levels ⁸³.

5. Conclusions

The results indicate that nanocellulose shows better physicochemical properties of water, oil and viscosity retention capacity than inulin, which can be contrasted with the presence of pores on its surface visualized by SEM. Therefore, consumption of 12.5 mg/Kg of nanocellulose for two months increases gastrointestinal evacuation without producing a laxative effect. Glucose metabolism improved during chronic consumption of nanocellulose, decreasing the area under the curve for the control, as well as the reduction in body weight reflected by the activation of orexigenic and anorexigenic signals. In the future, it is planned to evaluate the effect of nanocellulose in highly fermentative portions of the colon to evaluate other possible metabolites such as short-chain fatty acids, as well as determine the structure of the intestinal barrier and its permeability before nanocellulose consumption.

Conflict of Interest

All authors declare no conflicts of interest.

ACKNOWLEDGEMENTS

This research work was supported by National Council of Sciences and Technology (CONAHCYT 546742).

References