The Impact of Broad Bean Hull on Blood Glucose Control and Gut Health

Overview

This study aims to assess the effects of broad bean hull (BBH) consumption on blood glucose and gut health. Broad bean (Vicia faba) is widely cultivated in Scotland, with the UK being the most significant European producer. The seed coat (hull or testa) is removed during broad bean processing. This is a significant secondary product that is largely discarded. Preliminary work showed that this material is comparable to wheat bran and is rich in fibre (49%) and protein (18%). Additionally, it showed a rich phytochemical profile and lower fat and carbohydrate content than wheat bran. Experiments also showed that BBH inhibited the activity of alpha-amylase and alpha-glucosidase enzymes, suggesting anti-diabetic properties. Overall, these results showed that BBH is a secondary crop product having potential as a functional food for humans. Therefore, the objective of this study is to assess in vivo in humans the physiological and functional effects of BBH. Using an acute phase randomised controlled crossover design, the study will assess how consuming BBH fortified breads affects plasma glucose and gut health. The study will recruit 18 volunteers, normal-overweight, aged 18-75 years, who habitually consume low amounts of fruits and vegetables (≤3 portions/day). The volunteers will attend two identical stand-alone intervention sessions lasting three days each following the screening. The order of the intervention sessions will be randomised. On the day before each intervention session, the participants will provide a baseline faecal sample and have a continuous glucose monitoring sensor (CGMS) attached. They will be also be given a standardised dinner. On the next morning, following a 10-12 hr fast, an indwelling antecubital cannula will be inserted, and a blood sample will be taken for measuring baseline levels of metabolites. The volunteers will be given a standardised portion of the BBH or control bread to consume, and further blood samples taken for the subsequent four hours. Breath samples will also be taken at the same time points for measuring gastric emptying. The volunteers will be provided with all the meals for the rest of the day and the subsequent two days. These will include two portions per day of either the BBH or control bread. The meals will be standardised for energy and macronutrients. The volunteers will be instructed to return to the Human Nutrition Unit on the fourth morning and provide a second faecal sample and remove the CGMS. Blood samples will be analysed for systemic bioavailability and metabolism of test meal components, glucose regulatory hormones and breath samples for quantifying gastric emptying. The faecal samples will be analysed for gut bioavailability and metabolism of test meal components, microbial counts, composition, and water content.

The study aims to confirm in vivo the effects of consuming broad bean hull on blood glucose control and gut health. Although in vitro evidence is promising, its benefits remain confirmed in vivo in humans. No studies have previously attempted to assess the impact of broad bean hull consumption on glycaemic and gut health outcomes in humans. Therefore, this study will be novel and provide useful information on the potential of using BBH as a functional food for human health. From a health perspective, it is essential to establish the bioavailability and metabolism of dietary constituents in humans. Certain metabolites are absorbed early in the gastrointestinal tract, whereas others are transported to the colon, where they are extensively metabolised by the gut microbiota. This study will characterise the bioactive metabolites present in the plasma and faecal samples obtained. This will inform on their availability to the systemic circulation and their excretion profiles. Using targeted quantitative analysis (LC-MS and GC-MS), metabolites and their in vivo concentrations will be measured. The principal metabolites analysed will be those produced by the phenylpropanoid pathway and protein and carbohydrate metabolism products. These will include derivatives and metabolites of the simple phenols, benzoic acids, phenolic acids, phenylacetic acids, phenypropionic acids, phenylpyruvic acids, phenyllactic acids, mandellic acids, phenolic dimers, acetophenones, benzaldehydes, cinnamaldehydes, benzyl alcohols, cinnamyl alcohols, indoles, isoflavones, coumarins, chalcones, flavanones, flavones, flavonols, anthocyanidins. Furthermore, short-chain fatty acids will be analysed in the participants' faecal samples. It has been shown that many of these compounds are bioactive and exhibit anti-oxidant and anti-inflammatory activity at in vivo concentrations. Therefore, these studies will provide important information on bioavailability and metabolism and correlate the indices with health biomarkers. In addition, compounds such as the carcinogenic heterocyclic amines, genotoxic nitrosamines, indoles, polyamines, bile acids, and other protein metabolites considered detrimental to human health will also be measured. It is likely, the carbohydrate and phytochemical content of plant proteins may also protect against the formation of these toxic and potentially carcinogenic protein by-products.