Gut training — how to tolerate 90 g/hr without the pukies
The gut is trainable. Here is the 4–8 week progressive protocol that takes recreational runners from 30 g/hr to 90–120 g/hr without GI distress.
Runners' trots are near-universal: 30–90% of runners experience exercise-induced GI symptoms (de Oliveira et al., Sports Medicine, 2014). The mechanisms are mechanical (jostling at foot-strike), ischaemic (up to 80% splanchnic blood-flow reduction during hard running), neuroendocrine (sympathetic activation), and nutritional (high-fibre, FODMAP, fat, or hypertonic pre-run intake).
The good news: the gut is a trainable tissue. Costa et al. (APT, 2017) and Miall et al. (SJMSS, 2018) demonstrated that 2–4 weeks of progressive carbohydrate intake during training runs — starting at 30 g/hr and increasing 10–15 g per week — meaningfully raises tolerance and reduces symptoms. Gut training works at two levels: intestinal transporter upregulation (SGLT1, GLUT5 density) and gastric emptying adaptation to carbohydrate-rich boluses.
Protocol for a recreational marathoner aiming at 90 g/hr:
Week −8: 30 g/hr on long runs. Practice one gel every 30 min. Note GI response. Week −7: 40 g/hr. One gel every 22 min, or gel + half-strength sports drink. Week −6: 50 g/hr. One gel every 18 min. Week −5: 60 g/hr. Gels + sports drink, rehearse the mix. Week −4: 70 g/hr. Full sports drink + gels. Test your planned race products. Week −3: 80 g/hr. Final progressions in heat. Week −2: 90 g/hr. One dress rehearsal on a long run at marathon pace. Week −1: Lower volume, but one short run with race products to confirm tolerance.
Rules of gut training: rehearse the exact product and timing you will use in the race; increase one variable at a time; practise in conditions (heat, pace) that resemble race day; never introduce a new product in the final 3 weeks.
FODMAP reduction for 24–48 hours pre-race (Lis et al., MSSE, 2018) is a legitimate evidence-based intervention for runners with recurrent GI distress. Temporarily reduce wheat, onions, garlic, legumes, apples, stone fruit, and sugar alcohols. This is a race-specific tool, not a long-term dietary pattern — the fibres that feed your gut microbiome are valuable in normal training.
Probiotics with runner-specific evidence: Lactobacillus acidophilus, Bifidobacterium animalis subsp. lactis, Lactobacillus rhamnosus GG. Supplementation begun 4 weeks pre-race shows strongest effect on reducing GI distress (Pugh et al., Eur J Appl Physiol, 2019) and upper-respiratory infection incidence (West et al., Clin Nutr, 2014).