Investigation of the Effects of a High Fibre Diet Challenge on Colonic Microbiota, Metabolic Profiles and Health Outcomes across Generations

膳食纤维是存在于水果、蔬菜、谷物或豆类中的多糖。膳食纤维不能被人类消化酶消化，因此它们完好无损地到达大肠，在那里它们被肠道微生物区系发酵成短链脂肪酸和气体。短链脂肪酸被吸收到血液中，并有一系列的作用，如结肠细胞的能量来源或调节血脂水平等。它们的产生是肠道微生物群发酵膳食纤维能力的替代。膳食纤维是健康生活方式的重要组成部分，因为它们的摄入量增加与健康相关，例如降低心脏病、2型糖尿病或结直肠癌的风险。尽管膳食纤维对健康有好处，但大多数人每天的平均膳食纤维摄入量远低于推荐的每天30克。这背后的一个原因是西方化饮食模式的出现，其特点是增加了动物来源的蛋白质和脂肪、糖的摄入量，减少了富含膳食纤维的食物的消费。有证据表明，这些饮食习惯已经影响了肠道微生物群的组成和发酵纤维的能力。事实上，一项人类研究表明，从一个摄入富含纤维食物的社会迁移到一个西方化饮食模式很常见的社会，采用后一种饮食习惯会导致肠道微生物区系多样性的迅速丧失，特别是能够发酵复杂纤维的物种以及体重指数的增加。此外，一项小鼠研究表明，4代以上低膳食纤维饮食会导致70%的肠道微生物区系物种灭绝，而高纤维饮食不能取代丧失的物种。据我们所知，考虑到目前的饮食习惯，在老鼠身上观察到的东西对不同世代的人类是否有效的信息很少。该项目的目的是通过研究同一家庭(母亲和女儿或祖母、母亲和女儿)2代或3代(母亲和女儿、母亲和女儿)对一系列膳食纤维(菊粉、果胶、β-葡聚糖和纤维素)的直接联系的健康个体的肠道微生物区系组成、功能和健康结果，来阐明这些未知因素。为了实现这项研究的目标，将开展两个项目：使用人类粪便样本的批量发酵研究(非NHS研究)和人类双盲随机交叉临床试验(NHS研究)。第一个项目包括在厌氧条件下培养24小时内含有一系列膳食纤维的粪便样本，并检查肠道微生物区系组成和代谢物产生。第二个项目将让人类志愿者在4周内每天服用膳食纤维或安慰剂补充剂，并检查它们对肠道微生物区系组成、功能和健康结果(葡萄糖、胰岛素、肠道激素、脂肪和炎症标记物水平)的影响。在这个项目中已经获得的技能包括：为两个项目编写方案和伦理，第一个项目已经获得伦理批准并完成了样本收集，项目管理，分析参与者的食物日记，提取DNA用于肠道微生物区系测序，样品制备和使用气相色谱-质谱仪(GC-MS)进行分析，用于代谢物分析和数据分析。预计在这一项目中将获得的未来技能包括：获得临床试验的伦理批准、临床试验的管理、肠道微生物组遗传数据的分析、核磁共振设备的使用和分析由其产生的数据、血液样本的准备和分析以测量血糖、胰岛素、胃肠激素、血脂和炎症标志物水平，以及提高使用GC-MS和统计软件(R和MatLab)的能力。

Dietary fibres are polysaccharides present in fruit, vegetables, grains or legumes. Dietary fibres cannot be digested by human digestive enzymes and therefore they reach the large intestine intact where they are fermented into short-chain fatty acids and gases by the gut microbiota. Short-chain fatty acids are absorbed into the bloodstream, and have a range of effects, such as energy source for colonocytes or regulation of lipid levels among others. Their production is a proxy for how capable the gut microbiota is to ferment dietary fibres.Dietary fibres are an important component of a healthy lifestyle as their increased intake is associated with good health such as lower risks of heart disease, type 2 diabetes or colorectal cancer. Despite their health benefits, the average daily intake of dietary fibres of most individuals is way below the recommended 30g a day. One reason behind this is the advent of Westernised dietary patterns characterised by increased intake of animal-derived proteins and fats, sugars and reduced consumption of dietary fibre-rich foods. Evidence suggests that these dietary habits have affected the gut microbiota composition and ability to ferment fibres. Indeed, a human study has indicated that migration from a society where intake of fibre-rich foods is common to a society where Westernised dietary patterns are common and adopting the latter dietary habits leads to rapid loss of gut microbiota diversity, especially species capable of fermenting complex fibres as well as increased body-mass index. In addition, a mice study has indicated that diets low in dietary fibres over 4 generations lead to extinction of 70% of gut microbiota species and that high fibre diets cannot replace the lost species. To our knowledge, there is little information on whether what has been observed in mice is valid to humans from different generations given the current dietary habits. The aim of this project is to elucidate these unknowns by examining the gut microbiota composition and function and health outcomes of healthy individuals in direct link from 2 or 3 generations from the same family (mother and daughter or grandmother, mother and daughter) in response to a range of dietary fibres (inulin, pectin, beta-glucan and cellulose). Two projects will be carried out to achieve this study's aims: a batch fermentation study using human stool samples (non-NHS study) and a human double-blinded, randomised cross-over clinical trial (NHS study). The first project involved incubating stool samples with a range of dietary fibres over 24h in anaerobic conditions and examination of gut microbiota composition and metabolites production. The second project will involve human volunteers taking dietary fibres or placebo supplements daily over 4 weeks and examination of their impact on gut microbiota composition, function and health outcomes (glucose, insulin, gut hormone, lipid and inflammatory marker levels). Skills already gained during this project are: writing the protocols and ethics for both projects, for the first project ethical approval has been obtained and samples collection has been finalised, project management, analysis of participants' food diaries, DNA extraction for gut microbiota sequencing, samples preparation and analysis using gas-chromatography coupled with mass-spectrometry (GC-MS) for metabolites analysis and data analysis. Future skills expected to be gained during this are project are: obtaining ethical approval for the clinical trial, its management, analysis of gut microbiome genetic data, utilization of nuclear magnetic resonance equipment and analysing the data generated by it, preparation and analysis of blood samples to measure glucose, insulin, gut hormone, lipid and inflammatory marker levels and improved competence in using GC-MS and statistical software (R and Matlab).