From 60 to 120 grams per hour — the in-race carbohydrate ceiling has moved
The textbook 60 g/hr ceiling was set by glucose-only transporter saturation. Glucose + fructose and gut training have since doubled what elite runners can absorb and oxidise.
The 60 g/hr "ceiling" written into generations of sports-nutrition textbooks reflected the saturation of intestinal SGLT1 glucose transporters at roughly 1 g of glucose per minute. For decades, going above that simply pooled carbohydrate in the gut, invited GI distress, and did not increase exogenous oxidation. Then Asker Jeukendrup's group demonstrated (MSSE, 2004; Currell & Jeukendrup, MSSE, 2008) that combining glucose and fructose in roughly a 2:1 ratio engages SGLT1 and GLUT5 simultaneously, raising absorption and oxidation to ~1.75 g/min — approximately 105 g/hr — with better GI comfort.
The ceiling kept moving. Work by Tim King (MSSE, 2022) and Jernej Podlogar and colleagues (IJSPP, 2022), and Viribay et al.'s mountain-ultramarathoner studies (Nutrients, 2020), demonstrated ergogenic benefit at 90–120 g/hr in gut-trained athletes, with reduced muscle damage markers and faster recovery. Commercial products followed the science: Maurten's hydrogel 320 and 160, SIS Beta Fuel, Precision PF 90, and Neversecond C30 are engineered to deliver 80–120 g/hr.
The operative word is "gut-trained". This is not a static, one-size capacity — it is an adaptation. Recreational runners who jump from 30 g/hr straight to 90 g/hr will puke. Costa et al. (Alimentary Pharmacology & Therapeutics, 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.
Practical protocol for a marathon goal of ~90 g/hr. Weeks −8 to −6: long runs with 30–40 g/hr (one gel every 30 min). Weeks −5 to −4: 50–60 g/hr (one gel every 20 min). Weeks −3 to −2: 70–90 g/hr (one gel every 15–18 min plus sports drink). Race week: full dress rehearsal on the last long run, using the exact products planned for race day. The most common race-day failure is introducing an unfamiliar fuel at the start line; the second most common is stopping practising in the final 3 weeks because "the training is done".
Glucose-to-fructose ratio matters. Most modern endurance products formulate 0.8:1 or 1:1 glucose:fructose (closer to the transporter optimum for higher intakes) rather than the older 2:1 pure glucose bias. At very high intakes (>90 g/hr), the fructose component becomes more important; at lower intakes (30–60 g/hr), single-source glucose gels work fine.