Can an increase in consumption of dietary fibre improve gut flora profile, bowel habit and sense of wellbeing in healthy adults?

INTERVENTION: 25 healthy volunteers (no pre‐existing gastrointestinal disorders) will be recruited into a single‐blinded, randomised, cross‐over design study of 12 weeks in duration. They will each follow the following three dietary treatments for 3 weeks with a 1 week break between each treatment and 1 week baseline period prior to commencing the first study diet . The three treatments will be consistent with the Australian Dietary Guidelines in terms of recommended foods and serves of foods and will differ only in relation to the types of carbohydrate containing foods (including grains, legumes, fruits and vegetables) provided to modify intake of naturally occurring indigestible oligosaccharides (which have known prebiotic effects), in the following amounts: 1. Low prebiotic diet ( 4g oligosaccharides/day) 2. Moderate prebiotic diet ( 8g oligosaccharides/day) 3. High prebiotic diet ( 12g oligosaccharides/day) The majority of food will be provided to participants for this study and will be prepared in Monash University's commercial kitchen by their research chef. Menu planning will include beef and lamb as recommended in the 'Australian Dietary Guidelines' i.e. 130g every second day (200g uncooked meat). Sample study meal plan for one day: Low prebiotic diet‐ Breakfast: Cereal (flakes of corn, puffed oats, puffed rice, rice bran, dried cranberries, almonds, sunflower seeds) with milk + tea and/or coffee + orange juice + yoghurt. Snack: Banana Lunch: Sourdough spelt bread sandwich with ham, cheese and salad + tea and/or coffee + yoghurt with strawberries Snack: Mix of macadamia, Brazil nuts and pecans Dinner: Beef curry (with small amount of onion and garlic) served with rice, vegetables and pita bread. Moderate prebiotic diet‐ Breakfast: Cereal (flakes of wheat, rolled oats, dried apple, wheat bran, cashews, sunflower seeds) with milk + tea and/or coffee + apple juice + yoghurt. Snack: Nectarine Lunch: Wholemeal bread sandwich with ham, cheese and salad (including beetroot) + tea and/or coffee + yoghurt with peaches Snack: Mix of cashew nuts and almonds Dinner: Beef curry (with moderate amounts of onion and garlic) served with lentil curry, rice, vegetables and pita bread. High prebiotic diet‐ Breakfast: Cereal (flakes of amaranth, lupin flakes, wheat bran, dried mango, pistachio nuts) with milk + tea and/or coffee + apple juice + yoghurt. Snack: Watermelon Lunch: Rye bread sandwich with ham, cheese and salad (including beetroot and asparagus) + tea and/or coffee + yoghurt with mango Snack: Mix of cashew and pistachio nuts Dinner: Beef curry (with large amounts of onion and garlic) served with lentil curry, rice, vegetables and naan bread. Evaluation of dietary adherence: This will be checked via direct questioning, via daily diaries into which any food consumed in addition to that supplied will be entered and via assessment of uneaten food. Breath hydrogen/methane testing will also evaluate adherence. Hourly breath samples for hydrogen and methane testing will be collected over a one‐day period to assess the degree of fermentation occurring with each diet. CONDITION: gut health sense of wellbeing ; ; INCLUSION CRITERIA: ‐ Generally healthy adults with no pre‐existing gastrointestinal conditions (e.g. Irritable bowel syndrome, coeliac disease, Crohn's disease or Ulcerative colitis) PRIMARY OUTCOME: Changes in regional gut transit time and luminal pH from mouth to anus measured using a SmartPill device. Detection and characterisation of gut microbial changes as reflected in collected faecal samples. Analysis will include use of real‐time PCR to compare the absolute and relative abundance of bacteria. SECONDARY OUTCOME: Changes in faecal calprotectin concentration measured by commercially available ELISA (Buhlman) as a quantitative marker of intestinal inflammation. Changes in breath hydrogen and methane levels as assessed using a QuinTron breath track Analyser instrument. Changes in cognitive function assessed by Subtle Cognitive Impairment Test (SCIT). Changes in faecal levels of short chain fatty acids, including butyrate measured using gas‐liquid chromatography. Changes in faecal water content measured by weighing faecal sample before and after freeze‐drying. Changes in gastrointestinal symptoms (including bloating, wind, abdominal pain and fatigue) assessed using a 100mm visual analogue scale. Changes in levels of faecal ammonia and phenols measured by high‐performance liquid chromatography. Changes in levels of fatigue measured using the 40 item Daily Fatigue Impact Scale (D‐FIS). Changes in psychological state assessed using the 80 item State‐Trait‐Personality Inventory (STPI) and 21 item Depression Anxiety Stress Scale (DASS 21). Changes in stool frequency/consistency assessed using the Bristol stool chart and recorded on a 4‐point (frequency) and 7‐point (consistency) likert scale.