Quercetin has a wide range of biological properties. The gut microflora can often modulate its biological activity and their potential health effects. There still is a lack of information about gut bacteria involving in this process. The strains of gut microbes from human feces that can transform quercetin were isolated and identified by in vitro fermentation. The results showed that Escherichia coli, Stretococcus lutetiensis, Lactobacillus acidophilus, Weissella confusa, Enterococcus gilvus, Clostridium perfringens and Bacteroides fragilis have the various ability of degrading quercetin. Among them, C. perfringens and B. fragilis were discovered to have the strongest ability of degrading quercetin. Additionally, quercetin can't inhibit the growth of C. perfringens. In conclusion, many species of gut microbiota can degrade quercetin, but their ability are different.

Dietary fiber (DF) can be broken down into short-chain fatty acids (SCFAs) such as acetic, propionic and n-butyric acid by gut microbiota to obtain energy. Therefore, dietary fibers have effects on the balance of gut microbiota and the production of SCFAs. In the four-week feeding, mice were fed with four dietary fibers, including pectin, resistant starch (RS), fructo-oligosaccharide (FOS) and cellulose. The results showed that the mice body-weight gain was the smallest (7.0 ± 2.3 g) when the mixture of RS-FOS-cellulose was ingested, followed by the mixture of RS-cellulose (7.2 ± 3.5 g) and FOS-cellulose (8.3 ± 2.5 g). Ingestion of the mixture of pectin-FOS-cellulose, RS-FOS and RS-FOS-cellulose can respectively increase the diversity of the gut microbiota with 12, 11 and 11 terminal restriction fragments (TRFs) detected (digested by Hha I). The maximum amount of total SCFAs were produced by the mixture of FOS-cellulose (5.504 ± 0.029 μmol mL(-1)), followed by pectin-FOS-cellulose (3.893 ± 0.024 μmol mL(-1)) and pectin-RS-FOS-cellulose (3.309 ± 0.047 μmol mL(-1)). In conclusion, the addition of DFs (pectin, RS, FOS and cellulose), in single or mixture pattern, can exert different effects. An amount of 10.7% of single DF in the diet cannot be conducive to the balance of gut microbiota after ingestion for a long time, however, it can help with body weight loss like the mixtures of DFs in this study; FOS is a very important component in the mixture of DFs for both the balance of the gut microbiota and the production of SCFAs.

Fructooligosaccharides (FOS) are believed to be beneficial to the host growth and its gut health. This article is intended to investigate the different influences of a high-fructooligosaccharide (FOS) diet on the growth and gut microbiota of lean and obese rats. Diet-induced lean and obese rats were fed a high-FOS diet for 8 weeks. Rats' body weight (BW) and feed intake were recorded weekly, and their gut microbiota was analyzed by 16S rDNA sequencing. The results showed that the lean rats gained more BW than the obese ones from the high-FOS diet. In the meanwhile, the gut microbiota in both lean and obese rats was altered by this diet. The abundance of Bacteroidetes was increased significantly (P < 0.05) in the lean rats, while no significant alteration in Firmicutes was observed in all rats after the consumption of a high-FOS diet. In conclusion, this study first reported that the lean rats gained more body weight from a high-FOS diet than the obese ones, and the increase of Bacteroidetes might help rats harvest more energy from the high-FOS diet.

There is controversy over previous findings that a high ratio of Firmicutes to Bacteriodetes helps obese animals harvest energy from the diet. To further investigate the relationship between microbial composition and energy harvest, microbial adaptation to diet and time should be considered. In this study, lean and obese rats were successfully induced with low-fat and high-fat diets. An 8-week high soyabean fibre (HSF)-containing diet was then fed to investigate the interaction between the diet and the rats' gut microbiota, as well as their influence on rats' growth. Rats' body weight (BW) was recorded weekly; their plasma lipids and their gut microbiota at week 11, 15 and 19 were analysed. After the consumption of the HSF diet, BW of lean rats increased significantly (P < 0·05), but no significant alteration in BW was found in obese rats. The average content of plasma cholesterol was lowered and that of TAG was upgraded in both the groups when fed the HSF diet. There was no significant difference observed at each period between lean and obese rats. In the group of lean rats, the diversity of gut microbiota was elevated strongly (P < 0·01), and bacteria from phylum Firmicutes and Bacteroidetes were both increased largely (P < 0·01); however, the bacterial diversity and composition in obese rats were less altered after the HSF diet control. In conclusion, the increased Firmicutes and Bacteriodetes might relate to lean rats' higher BW gain; 'obese microbiota' could not help the hosts harvest more energy from the HSF diet.Key words: Obesity: Soyabean fibre: Energy harvest: Gut microbiota: Bacteroidetes: Firmicutes People's weight and body composition are likely determined by interactions between their genetic makeup and social, cultural, behavioural and environmental factors. There is equilibrium between the amount of energy obtained from food and the amount expended through resting metabolism, thermic effect of food, physical activity and loss via faeces and urine. People's increased intake of energy-dense foods surely contribute to the high prevalence of obesity; however, as the internal regulating system of energy balance is far more complex than that we have imagined, the interaction between diet and obesity should be considered in a larger context (1,2) . Recent evidence suggests that gut microbiota can affect nutrient acquisition and energy regulation; moreover, scientists have also discovered that obese and lean people have different gut microbiota (3) . Changes in gut microbial ecology can cause alteration in the host's efficiency of energy harvest from the diet, leading to significant changes in body weight (BW) and energy balance (4) . Gut microbiota may play an important role in regulating weight, as it has been recently reported that gut bacterial composition is partly responsible for the development of obesity in some people (3) . Turnbaugh et al.(5) believed that the alteration in gut microbial composition is possibly associated with the onset of obesity, and they also indicated that a high ra...

Fructooligosaccharide (FOS) has been reported to increase Lactobacillus and Bifidobacterium populations in animal and human gut. Hence, it has been utilized to regulate the balance of gut microbiota. In this study, we compared the effects of high-FOS (HFOS) diet on normal and obese rats' gut Lactobacillus and Bifidobacterium, with high-soybeanfibers (HSF) diet as control. The results showed that the level of Bifidobacterium population substantially increased at week 4 in groups of rats fed the HFOS diet (P < 0.05), but significantly reduced to a small level at week 8 (P < 0.05); the abundance of Lactobacillus was increased in normal rats (P < 0.05), but decreased in obese rats (P < 0.05). The HSF diet did not promote the growth of Lactobacillus and Bifidobacterium in rats' gut. The findings suggested that Bifidobacterium population could not be maintained at a high level when the rats continuously ingested the HFOS diet for 8 wk; additionally, Lactobacillus population could adapt to a relatively stable level with the consumption of HFOS diet.