1. Introduction
Obesity is one of the major current public health problems owing to lifestyle changes and an increase in hypercaloric diet availability. An imbalance between energy intake and energy expenditure can engender obesity and its associated comorbidities including diabetes, insulin resistance, and cardiovascular diseases. Deterioration in gut bacterial profiles was associated with high-fat dietary patterns, resulting in the occurrence and development of gastrointestinal diseases [
1,
2].
Many interventional studies have suggested that adequate consumption of dietary fibers, such as fructooligosaccharide (FOS) and resistant maltodextrin (RMD), could reduce body fat accumulation and body weight [
3], and also help improve bowel functions and intestinal health [
4,
5]. The beneficial physiological functions of FOS and RMD included protection against colorectal diseases, immunomodulatory effect, management of diabetes mellitus and obesity, and improvement of serum lipids’ concentrations and mineral absorption [
6,
7,
8]. A sufficient intake of FOS and RMD, as prebiotics, might also improve stool quality (e.g., pH, SCFA, frequency, microflora, and consistency), lower the risks of gastroenteritis and infections, and maintain general well-being [
9,
10,
11].
The combination of FOS and RMD at a ratio of 3:7 has been reported to show a satisfied hypolipidemic potential [
12]. Our previous in vivo preliminary study [
13] also demonstrated that rats fed a mixture of FOS and RMD (namely FOS-RMD mixture) at a ratio of 1:2 (FOS 0.48 g/kg bw and RMD 0.97 g/kg bw) for eight weeks was effective in lowering body fat accumulation.
Based on the associations between high fat dietary pattern and deterioration of certain fecal parameters, as well as the ability of dietary fibers in reducing body fat accumulation and promoting probiotic growth, it was believed that the administration of FOS and RMD might confer a concreted solution to the obesity and deteriorated fecal bacteria profiles resulted from high fat consumption. In the present study, animals were fed high-fat diets with an inclusion of a mixture of FOS and RMD. The changes in body fat accumulation, intestinal microbial growth, and different fecal parameters were determined and compared.
2. Results and Discussion
A summary of the total food intake, body weight, total energy intake, and feed efficiency ratio is shown in
Table 1. The total food intake, which was a sum of the total amount of base diet and sample given, in the normal control (1915.9 g) was significantly (
p < 0.05) higher than those of high fat (HF) (1624.6 g), HF1X (1640.6 g), and HF2X (1651.3 g) groups. No apparent differences in food intake among the three diet groups (HF, HFX1, and HFX2) were observed. Although the normal control (NC) group had the most total food intake, it had significantly (
p < 0.05) lower total energy intakes (6418.3 kcal) than those of the animals fed the three high fat diets (6891.9–6969.5 kcal).
After the acclimation period, the rats’ initial weights did not differ among the four diet groups. As for the weight changes, all three high fat groups (262.3–302.0 g) presented a markedly (
p < 0.05) higher weight gain than the normal diet group (199.5 g), indicating the effectiveness of high fat diet in inducing obesity. The inclusion of the FOS-RMD sample into the high fat diets resulted in the least (
p < 0.05) weight gain for the HF2X group (262.3 g). A negative association between the weight gain and the amount of sample intake was observed in
Table 1. Adequate intake of dietary fibers, such as FOS and RMD, has been reported to be capable of suppressing the weight increase even with high dietary energy consumption [
14,
15].
As compared with the feed efficiency of the NC group, the results revealed that the high fat dietary formula used in this study would render a significant (p < 0.05) increase in feed efficiency up to 152–181% higher. An incorporation of the FOS-RMD mixture at a high dose (HF2X) into the high fat diet would in turn lead to a remarkable (p < 0.05) decrease in feed efficiency (−16.0%) versus the HF group.
A comparison of the relative weights of total visceral fat, total non-visceral fat, and total body fat among the four diet groups is presented in
Table 2. There were no substantial differences in the levels of epididymal and perirenal fats. However, a significant (
p < 0.05) decline in the mesenteric fat in the HF2X group (2.31 g/100 g) compared to the HF group (2.97 g/100 g) was observed. In summary, the total visceral fat accumulation in rats from the HF (11.25 g/100 g), HF1X (9.84 g/100 g), and HF2X (9.29 g/100 g) groups were significantly (
p < 0.05) higher than those fed the NC diet (4.75 g/100 g). Again, this indicated that the high fat diet was capable of inducing obesity in rats effectively. A significant (
p < 0.05) reduction in total visceral fat in HF2X group (−17.4%) was noted against the HF group. As for the non-visceral fat levels, an incorporation of the FOS-RMD mixture in high fat diet at different doses also led to significant (
p < 0.05) reductions in both the HF1X (−17.5%) and HF2X (−20.3%) groups.
Besides this, total body fat was presented as a sum of total visceral fat and total non-visceral fat. Opposing the HF group (67.65 g/100 g) that had the highest body fat, the feeding of FOS-RMD mixture could effectively (
p < 0.05) lower the total body fat in HF1X (23.76 g/100 g) and HF2X (22.72 g/100 g) diets by −15.5% and −19.2%, respectively. Other authors have also revealed the potential of FOS and RMD in hurdling intestinal fat absorption and mitigating the fat tissue accumulation even though these dietary fibers were administered separately [
16]. In this study, an administration of either 2% or 5% of FOS-RMD mixture has contributed to a reduction of fat accumulation in the rats fed different high fat diets.
It was reported that RMD might disturb the uptake of lipid and promote lipid excretion by inhibiting the decomposition of micelles as well as the release of fatty acids from micelles in the small intestine [
17]. FOS could directly inhibit the absorption of non-esterified fatty acids or monoglycerides in the small intestine [
18]. These findings reinforced our observations in the present study regarding the ability of both the RMD and FOS on alleviating body fat accumulation, at least in part through the mechanism of lowering the dietary lipid absorption and metabolism.
According to
Table 3, fecal weight in the NC group was notably (
p < 0.05) higher than those of the three high fat diet groups, among which no apparent fecal weight changes were observed. This could be possibly attributed to the fact that the NC group had the most total food intake. A mild ascending trend in fecal fat excretion was noted among the three high fat groups on the order of HF (159.5 mg/day) < HF1X (165.0 mg/day) < HF2X (174.5 mg/day). As previously reported by Jun et al. [
19], there was a positive relationship between reduced dietary fat absorption and elevated fecal fat output.
Table 4 shows the changes in the bacterial counts of
Escherichia coli,
Clostridium perfringens, and
Bifidobacterium spp. in different fecal samples. There were no apparent changes in the fecal
E. coli count (4.73–5.99 log CFU/g) among the four diet groups.
C. perfringens is known to be harmful by producing toxins that are active in the human gastrointestinal tract [
20]. A significant (
p < 0.05) increase in the fecal
C. perfringens counts in HF group (5.75 log CFU/g) was observed, showing that high fat consumption might induce a higher growth of
C. perfringens in the large intestine.
High dietary fat consumption was also found to retard the growth of the
Bifidobacterium spp. and result in a decrease of this desirable intestinal strain by −23.8% (
Table 4). The provision of a FOS-RMD mixture at a high dose could in turn enhance the growth of
Bifidobacterium spp. by increasing the count from 6.20 log CFU/g (HF) to 8.33 log CFU/g (HF2X). FOS is an indigestible oligosaccharide or dietary fiber that might improve the host health by stimulating the growth or activity of large bowel bacteria, such as
Bifidobacterium and
Lactobacillus spp. [
9]. To sum up briefly, our results revealed the potential of the FOS-RMD mixture in lowering body fat accumulation and meanwhile improving the growth of intestinal
Bifidobacterium spp. effectively.
Table 5 presents the SCFA analyses of fecal samples collected from the animals fed the four different diets. High fat consumption resulted in a drastic (
p < 0.05) reduction of total SCFAs and acetic acid in the fecal samples from 164.1 and 99.1 μmol/g, respectively (NC) to 132.4 and 74.8 μmol/g, respectively (HF). The inclusion of FOS-RMD mixture in the high fat dietary formula, especially at a high dose (HF2X), effectively (
p < 0.05) elevated the levels of acetic acid, propionic acid, and butyric acid to 152.0 μmol/g (203.2%), 55.9 μmol/g (182.1%), and 50.8 μmol/g (188.8%), respectively, hence increasing (
p < 0.05) the total SCFA level up to 258.7 μmol/g (195.4%).
In agreement with the findings from Jakobsdottir et al. [
21], high fat consumption could cause a reduction in the intestinal total SCFAs. It was inferred that both the FOS and RMD, which were fermented mainly by the increased
Bifidobacterium spp. count (as shown in
Table 4), would give rise to the production of SCFAs, such as acetic acid, propionic acid, butyric acid, and other SCFAs [
22,
23]. These SCFAs were the key metabolites that reflected the fundamental roles of dietary fibers and gut microbiota in enhancing the intestinal health [
24]. To encapsulate the results in both
Table 4 and
Table 5, the counts of intestinal harmful and beneficial bacteria would decline and escalate, respectively, as the amount of sample intake increased.