Dietary Fibre
Brief description
Dietary fibre is the non-digestible part of plants that you eat but is not broken down by the small intestine. It is processed by bacteria in the large intestine and is essential good optimal gut health.
Fibre can be categorised by its physical characteristics, including its solubility, viscosity and how well it is broken down (fermentability).
Soluble fibre: oats, peas, beans, apples, citrus fruit, carrots, barley psyllium.
Insoluble fibre: whole-wheat flour, wheat bran, nuts, beans, cauliflower, green beans, potatoes,
Prebiotics: types of carbohydrates only our gut bacteria can feed upon examples include: onion, garlic, asparagus and banana.
Dietary fibre can increase the beneficial bacterial in your gut, which can improve your immune system. Foods higher in fibre are usually lower in energy density – meaning they have less kilojoules per gram of food. They often are bulkier and more filling. Soluble fibres form a thick gel which slows down the emptying from the stomach -keeping you fuller for longer.
Fibre also slows the absorption of sugars from the gut, meaning small glucose spikes after a meal. This can be good for reducing the risk of diabetes.
Evidence base
Mortality from any cause, heart (CVD), and cancer: A meta-analysis of 64 studies examining 3,512,828 subjects looked at the relationship between dietary fibre intake and mortality from the above outcomes. Higher consumption of total dietary fibre significantly reduces the risk of all-cause mortality by 23% (HR:0.77; 95%CI (0.73,0.82); heart-related mortality by 26% (HR:0.74; 95%CI (0.71,0.77)); and cancer-mortality by 22% (HR:0.78; 95%CI (0.68,0.87)).
Insoluble fibre tended to be more effective than soluble fibre in reducing the risk of CVD and Cancer mortality(1). Other systematic reviews reinforced these findings(2, 3).
Blood Pressure: A meta-analysis of 83 trials (n=5,985) participants found that soluble fibre significantly decreased systolic blood pressure (SBP) (WMD: -1.36 mmHg, 95% CI: -2.13 to -0.60, P < 0.001; I2 = 47.1%, P < 0.001), as well as diastolic blood pressure (DBP) (WMD: -0.72 mmHg, 95% CI: -1.26 to -0.18, P = 0.009; I2 = 45.4%, P < 0.001).
For every 5g/d increment in soluble fibre, there was a 0.54mmHg (p=0.001) reduction in SBP and 0.28mmHg reduction in DBP (p=0.007). The SBP decreased proportionally up to 20g/d of soluble fibre with a mean difference of -1.79mmHg(4). Other studies reinforced these conclusions(3, 5).
Cholesterol: Findings from 181 RCTs (n=14,505 participants) demonstrated for every 5g/day soluble fibre supplementation, there was a reduction in LDL (MD: -5.57 mg/dl, 95% CI: -7.44, -3.69) and total cholesterol (TC) MD: -6.11 mg/dL, 95% CI: -7.61, -4.61). Furthermore, increasing soluble fibre intake was also associated with a reduction in Apolipoprotein B (MD: -44.99 mg/L, 95% CI: -62.87, -27.12)(6). Other studies reinforced these conclusions(3, 5).
Body weight: A meta-analysis examined soluble fibre supplementation vs placebo in overweight or obese populations (mean trial duration: 17 weeks, mean dietary fibre 11g/day). Researcher concluded dietary fibre supplementation was able to reduce body weight after at least 12 weeks vs control (MD −1.25 kg, 95% CI −2.24, −0.25; p = 0.01; I2 = 0%; 27 RCTs; 1428 participants). BMI, waist circumference and fasting blood insulin also significantly decreased(7) and was confirmed in other meta-analyses(5).
Recommended serving & duration.
Adults – 30g/day
16-18yrs – 30/day
11-16yrs – 25g/day
5-11yrs – 20g/day
2-5yrs – 15g/day
Read more about fibre: https://www.nutrition.org.uk/nutritional-information/fibre/
Safety & tolerability
Without good hydration, excess fibre may cause abdominal discomfort, bloating and gas.
References
Ramezani F, Pourghazi F, Eslami M, Gholami M, Mohammadian Khonsari N, Ejtahed HS, et al. Dietary fiber intake and all-cause and cause-specific mortality: An updated systematic review and meta-analysis of prospective cohort studies. Clin Nutr. 2024;43(1):65-83.
Yao F, Ma J, Cui Y, Huang C, Lu R, Hu F, et al. Dietary intake of total vegetable, fruit, cereal, soluble and insoluble fiber and risk of all-cause, cardiovascular, and cancer mortality: systematic review and dose-response meta-analysis of prospective cohort studies. Front Nutr. 2023;10:1153165.
Reynolds AN, Akerman A, Kumar S, Diep Pham HT, Coffey S, Mann J. Dietary fibre in hypertension and cardiovascular disease management: systematic review and meta-analyses. BMC Med. 2022;20(1):139.
Ghavami A, Banpouri S, Ziaei R, Talebi S, Vajdi M, Nattagh-Eshtivani E, et al. Effect of soluble fiber on blood pressure in adults: a systematic review and dose-response meta-analysis of randomized controlled trials. Nutr J. 2023;22(1):51.
Lee DPS, Peng A, Taniasuri F, Tan D, Kim JE. Impact of fiber-fortified food consumption on anthropometric measurements and cardiometabolic outcomes: A systematic review, meta-analyses, and meta-regressions of randomized controlled trials. Crit Rev Food Sci Nutr. 2023;63(26):8301-19.
Ghavami A, Ziaei R, Talebi S, Barghchi H, Nattagh-Eshtivani E, Moradi S, et al. Soluble Fiber Supplementation and Serum Lipid Profile: A Systematic Review and Dose-Response Meta-Analysis of Randomized Controlled Trials. Adv Nutr. 2023;14(3):465-74.
Huwiler VV, Schönenberger KA, Segesser von Brunegg A, Reber E, Mühlebach S, Stanga Z, et al. Prolonged Isolated Soluble Dietary Fibre Supplementation in Overweight and Obese Patients: A Systematic Review with Meta-Analysis of Randomised Controlled Trials. Nutrients. 2022;14(13).
