International Journal of Molecular Medical Science, 2025, Vol.15, No.2, 98-106 http://medscipublisher.com/index.php/ijmms 103 variety of health benefits (Zhai et al., 2018; Vinelli et al., 2022). Combining these two methods can more comprehensively demonstrate the impact of fiber on the intestinal microbiota and its metabolic activities. 6.3 Evaluation criteria: diversity of intestinal flora, levels of metabolites, changes in health parameters, etc Evaluating the impact of dietary fiber on intestinal health usually starts from the following aspects. First is the diversity of the microbiota, which is measured by the α -diversity index to assess the richness and evenness of the community. Studies have shown that dietary fiber can enhance the diversity of the microbiota, but the effect varies depending on the type and dosage of fiber (So et al., 2018; Lin et al., 2020). The second is the level of metabolites, especially the concentration of SCFAs. An increase in SCFAs indicates active microbial fermentation, which is usually associated with improved intestinal health and metabolism. For instance, dietary fiber intervention is associated with an increase in butyrate concentration in feces, and butyric acid has anti-inflammatory effects (Liu et al., 2021; Vinelli et al., 2022). These indicators jointly provide a basis for evaluating the efficacy of dietary fiber. 7 Existing problems and challenges 7.1 Safety and tolerability issues of compound dietary fiber preparations Whether compound dietary fiber preparations are safe and can be adapted to by humans is something to pay attention to, especially since different fibers have different effects on the intestines. Fibers such as inulin have a good effect on the microbiota, but their effect in producing short-chain fatty acids (SCFA) varies, which may cause some people to suddenly have an uncomfortable stomach (Vinelli et al., 2022). In addition, new fibers such as bacterial cellulose and konjac glucomanase are beneficial to the flora and fatty acid metabolism. However, whether they are safe for long-term use and whether humans can adapt to them still need to be confirmed by more studies (Zhai et al., 2018). Individual differences also increase the difficulty of safety assessment. The type of fiber, the amount used and the composition of each person's microbiota may all affect the effect. For instance, some research reports indicate that Bifidobacterium and Lactobacillus increase after fiber supplementation, but other studies show no significant changes. This suggests that fiber intervention programs need to be tailored to individuals (So et al., 2018; Liu et al., 2020). 7.2 Optimize the complexity of component ratios and individual differences Soluble and insoluble fibers have different effects on the microbiota and metabolism, and it is very complex to find the optimal ratio. Studies have shown that different fiber ratios can change the microbiota structure and SCFAs levels (Zhang et al., 2023). Moreover, each person responds differently to the same ratio, which is related to their specific microbiota and metabolic status (Li et al., 2023). The challenge lies in finding a ratio that suits the majority of people while also taking into account individual differences. Some combinations can increase probiotics and SCFAs, but the effects of others are not obvious. Therefore, it may be necessary to customize personalized fiber supplementation plans for different groups of people (Cronin et al., 2021; Liu et al., 2021). 7.3 Clinical applicationchallenges: dose selection, long-term efficacy and sustainability Clinically, it is difficult to determine the optimal dose of fiber because there is no unified standard yet. Although high-dose fiber can improve the intestinal barrier and reduce inflammation, it may also cause side effects such as gastrointestinal discomfort (Liu et al., 2021). Furthermore, the effects of long-term and excessive intake of fiber on the intestines and overall health remain unclear, and further research is needed to formulate safe dose recommendations (Lin et al., 2020). Sustainability is also a major problem. The production and procurement of fibers need to take environmental impacts into account to ensure long-term supply and reasonable prices. Developing supplements that are both effective and have a good taste can help improve compliance. Meanwhile, enhancing fiber activity by using new methods such as fermentation and nanotechnology is the future direction, but its feasibility still needs to be further verified (Tian et al., 2023).
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