Fiber Supplement

Fiber

Dietary fiber

Evidence TierAWADA NOT PROHIBITED

tuneTypical Dose

5-15 g/day

watchEffect Window

Days-to-weeks for bowel effects, weeks for cardiometabolic effects.

check_circleCompliance

WADA NOT PROHIBITED

Overview

Clinical Summary

Fiber reliably supports bowel regularity and can improve LDL cholesterol when dosed consistently

The strongest evidence supports viscous fibers such as psyllium for constipation and LDL lowering, with modest additional glycemic and blood-pressure support in selected groups. Start low, increase gradually, and pair with hydration to reduce gas and bloating.

Increases stool bulk and viscosity, modulates glucose/cholesterol absorption, and supports SCFA generation.

Outcomes

What This Is Expected To Influence

Primary Outcomes

  • Improved bowel regularity
  • LDL cholesterol reduction

Secondary Outcomes

  • Modest glycemic support
  • Small blood-pressure support

Safety

Contraindications and Interactions

Contraindications

  • Bowel obstruction risk
  • Severe dysphagia
  • Severe active GI disease without supervision

Side effects

  • Bloating
  • Gas
  • Abdominal fullness

Interactions

  • Potential delayed absorption of some oral medications

Avoid if

  • Inadequate fluid intake
  • Severe obstructive GI symptoms

Evidence

Study-level References

fiber-SRC-001Systematic review and meta-analysis of RCTs.
Sourceopen_in_new

Jovanovski E, et al. Effect of psyllium (Plantago ovata) fiber on LDL cholesterol and alternative lipid targets: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr. 2018;108(5):922-932. doi:10.1093/ajcn/nqy115. PMID:30239559.

Population: Adults across lipid/cardiometabolic risk strata.

Dose protocol: Psyllium and related viscous fibers, mostly 4-12 weeks.

Key findings: Significant LDL reduction.

Notes: Some heterogeneity by dose/form and background diet.

Paper content

Significant LDL reduction.

fiber-SRC-002Systematic review and meta-analysis.
Sourceopen_in_new

de Vries J, et al. Effects of beta-Fructans Fiber on Bowel Function: A Systematic Review and Meta-Analysis. Nutrients. 2019;11(1):91. doi:10.3390/nu11010091. PMID:30621208.

Population: Healthy and symptomatic cohorts.

Dose protocol: Beta-fructans across multiple doses and durations.

Key findings: Improvement in bowel movement frequency and stool outcomes.

Notes: Heterogeneity in chain length and study design.

Paper content

Improvement in bowel movement frequency and stool outcomes.

fiber-SRC-003Meta-analysis.
Sourceopen_in_new

Gibb RD, et al. Psyllium fiber improves glycemic control proportional to loss of glycemic control: a meta-analysis of data in euglycemic subjects, patients at risk of type 2 diabetes mellitus, and patients being treated for type 2 diabetes mellitus. Am J Clin Nutr. 2015;102(6):1604-1614. doi:10.3945/ajcn.115.106989. PMID:26561625.

Population: Euglycemia to treated type 2 diabetes populations.

Dose protocol: Psyllium supplementation protocols.

Key findings: Modest glycemic improvement, larger in poorer baseline control.

Notes: Mixed baseline control and concurrent therapy differences.

Paper content

Modest glycemic improvement, larger in poorer baseline control.

fiber-SRC-004Systematic review and meta-analysis of RCTs.
Sourceopen_in_new

Clark CCT, et al. The effect of psyllium supplementation on blood pressure: a systematic review and meta-analysis of randomized controlled trials. Korean J Intern Med. 2020;35(6):1385-1399. doi:10.3904/kjim.2019.049. PMID:32066221.

Population: Adults with varied cardiometabolic profiles.

Dose protocol: Psyllium over several weeks.

Key findings: Small but significant BP lowering.

Notes: Moderate heterogeneity.

Paper content

Small but significant BP lowering.

fiber-SRC-005Randomized placebo-controlled trial.
Sourceopen_in_new

Noureddin S, et al. Effects of psyllium vs placebo on constipation, weight, glycemia, and lipids in type 2 diabetes with chronic constipation. Complement Ther Med. 2018;40:1-7. doi:10.1016/j.ctim.2018.07.004. PMID:30219432.

Population: Adults with type 2 diabetes and chronic constipation.

Dose protocol: Psyllium intervention vs placebo.

Key findings: Improved constipation with supportive cardiometabolic directionality.

Notes: Single-population trial limits generalizability.

Paper content

Improved constipation with supportive cardiometabolic directionality.

fiber-SRC-006Prospective cohort study.
Sourceopen_in_new

Fields BC, Traweek RS, Jiang K, et al. High dietary fiber is associated with improved outcomes in patients with melanoma and sarcoma treated with immunotherapy regardless of gut microbiome dysbiosis and social vulnerability. Cancer. 2026;132(6):e70335. doi:10.1002/cncr.70335. PMID:41832741.

Population: Patients with melanoma or sarcoma receiving immune checkpoint blockade therapy.

Dose protocol: Prospective cohort of 153 cancer patients assessing dietary fiber intake and immunotherapy outcomes

Key findings: Higher dietary fiber associated with improved immunotherapy response and superior overall survival. Favorable microbiome composition linked to fiber intake.

Notes: Observational design. Supports emerging fiber-microbiome-immune axis hypothesis.

Paper content

This prospective cohort study of 153 patients with melanoma or sarcoma receiving immune checkpoint blockade found that higher dietary fiber intake was associated with improved immunotherapy response and superior overall survival. Higher fiber intake was also associated with favorable microbiome composition, including increased Bifidobacterium longum abundance. The association persisted regardless of social vulnerability index or baseline microbiome dysbiosis. The study supports dietary fiber as a potentially modifiable factor in cancer immunotherapy outcomes, though as an observational design it cannot establish causation.

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