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Head-to-head evidence comparison — which supplement is right for you?
Galactooligosaccharides vs Iodine: Iodine has the stronger overall evidence (8.5 vs 5/10); the best pick depends on your goals. Take the 60-second quiz for a pick tailored to your goals.
Iodine wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Probably helps
2 of 4 studies with measurable effects showed benefit.
Top outcomes
Verdict
Mixed evidence
4 of 11 studies with measurable effects showed benefit.
Top outcomes
3.5-5.5 g/day. Going higher is not supported: in the one IBS trial, 3.5 g/d improved more symptoms than 7 g/d, and in stressed students 2.5 g lowered cold-or-flu symptom scores across all stress levels while 5 g helped only at lower stress
With meals, Split across two servings if a single dose causes gas
Trans-galactooligosaccharide (B-GOS) powder, the form used in the trials
150-300mcg for maintenance; higher only if deficient under supervision
Any time with food
Potassium iodide (most common and studied)
1-2 weeks
8 weeks
n/a
n/a
4-12 weeks
4-8 weeks
Prebiotics in irritable bowel syndrome and other functional bowel disorders in adults: a systematic review and meta-analysis of randomized controlled trials.
Am J Clin Nutr (2019) · Meta analysis · n=729
Global response was NULL: 52/97 (54%) responded on prebiotic versus 59/94 (63%) on placebo (OR 0.62; 95% CI 0.07, 5.69; P=0.67)
Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis.
Am J Clin Nutr (2018) · Meta analysis · n=2099
Fibre raised Bifidobacterium spp. overall (SMD 0.64; 95% CI 0.42, 0.86; P<0.00001) and Lactobacillus spp. (SMD 0.22; 0.03, 0.41; P=0.02)
Clinical trial: the effects of a trans-galactooligosaccharide prebiotic on faecal microbiota and symptoms in irritable bowel syndrome.
Aliment Pharmacol Ther (2009) · Rct · n=44
44 patients with Rome II positive IBS completed a 12-week single-centre trial of 3.5 g/d prebiotic, 7 g/d prebiotic, or 7 g/d placebo
Maternal Iodine Status and Birth Outcomes: A Systematic Literature Review and Meta-Analysis
Nutrients (2023) · Meta analysis · n=42269
Birth weight was similar between UIC ≥ 150 μg/L and <150 μg/L (difference = 30 g, 95% CI −22 to 83, p = 0.3, n = 13, I2 = 89%) with no evidence of linear trend (4 g per 50 μg/L, −3 to 10, p = 0.2, n = 12, I2 = 80%).
Iodine fortification of foods and condiments, other than salt, for preventing iodine deficiency disorders
The Cochrane database of systematic reviews (2019) · Meta analysis · n=4317
This is equivalent to an increase of 38.32 µg/L (95% CI 24.03 to 52.61 µg/L).
Systematic review and meta-analysis of iodine nutrition in modern vegan and vegetarian diets
The British journal of nutrition (2023) · Meta analysis · n=4421
Vegan diets had the poorest iodine intake (17·3 µg/d) and were strongly associated with lower iodine intake (P = < 0·001) compared with omnivorous diets.
Based on meta-analyses showing urinary iodine concentration increases with supplementation. Effects only meaningful in iodine-deficient populations. Excessive intake (>300mcg) may increase thyroid cancer risk. Most studies used potassium iodide; kelp-derived forms have variable bioavailability.
AI-estimated from published studies. Interpret as directional guidance.
Iodine has a higher evidence score (8.5/10 vs 5/10) and wins in 2 of 3 categories.
No known interactions between Galactooligosaccharides and Iodine have been documented in our database. However, always consult a healthcare provider before combining supplements.
Selenium helps; iodine can WORSEN Hashimoto’s. The honest take on "thyroid support".
What’s safe while nursing, the truth about milk-supply herbs, and what to avoid (it passes into milk).
Commonly recommended vs ask-your-clinician vs avoid — a general, safety-first overview.
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.