Fuel The
Hybrid
Professional

The reason most people don't fuel properly isn't laziness — it's that nobody explained the gut physiology clearly enough to make it feel urgent. So here it is. Your small intestine has two separate transport proteins for absorbing carbohydrate into your bloodstream. One handles glucose and maxes out at around 60 grams per hour. The other handles fructose and can process an additional 30 grams per hour. If you're only using glucose — which is what most single-source gels and energy drinks deliver — you are physiologically capped at 60 grams per hour regardless of how many gels you take. Take more and you don't absorb the extra; you just create the conditions for GI distress at mile 22.

Elite athletes using dual-source nutrition — products combining glucose and fructose in roughly a 2:1 ratio — can push absorption to 90 grams per hour. This has been demonstrated in multiple peer-reviewed studies, and it's why SiS Beta Fuel exists in its specific formulation. The 1:0.8 maltodextrin-to-fructose ratio was engineered specifically to hit that upper absorption threshold without triggering gastric distress.

The practical implication for a 3-hour marathon runner is meaningful. At 60 grams per hour, you replace roughly 180 grams of carbohydrate over the race. At 90 grams per hour, you replace 270 grams. Your stored glycogen handles the remainder at the lower rate — just barely, if you started fully loaded. At the higher rate, you run with a buffer. That buffer is what keeps you moving in the final 10 kilometres. It's substrate availability, not willpower.

The starting point: if you haven't been using dual-source carbohydrate in training, don't jump to 90 grams per hour on race day. Your gut needs time to adapt. Start at 60 grams per hour on your next long run and build by 15 grams every 2–3 weeks. Test under the same conditions you'll face on race day — same temperature, same hydration, same pace. And start fuelling at 20 minutes in, not when you feel you need to. By then, you're already behind.

The problem isn't that Irish runners are poorly informed. It's that the products available to them in Irish retail are genuinely limited. Walk into most sports shops and you'll find Kinetica and SiS, maybe High5 if you're lucky. The international gel market is far broader, and the products that dominate elite and serious age-group racing worldwide — GU, OTE, Precision Fuel — are largely absent from Irish shelves. When someone grabs "whatever's available," they're not making a bad choice from a full range. They're making the only choice they know exists.

The second problem is testing. Taking a gel you've never used at mile 10 of a marathon is a genuine gamble. Some products sit perfectly well at race pace. Others cause bloating, nausea, or something the endurance world politely calls GI distress. Whether a specific gel works for your stomach isn't something you can predict from the label. You can only learn it by testing under race conditions.

The fix is simple but requires intention: decide on your products at least eight weeks before your race. Test one product per long training run. Note how your stomach responded, how the texture felt at pace, whether you'd take another one an hour later. By race week, you should know exactly which product you'll use, exactly when you'll take it, and exactly how your body will respond — because you've done it six times.

The runners who have the worst race-day nutrition experiences aren't undertrained. They're the ones who treated nutrition as an afterthought and got surprised at mile 20. The wall is almost always a fuelling failure, not a fitness failure. And fuelling failures are entirely preventable — they just require treating your nutrition with the same seriousness you gave your training plan.

The HPA axis is your body's central stress response system. When you encounter a stressor — a difficult meeting, a tight deadline, a hostile question from a board member — your hypothalamus signals your pituitary gland, which signals your adrenal glands to release cortisol. Cortisol is useful in short bursts. The problem is chronic, sustained cortisol elevation — the kind that comes from a high-pressure career with no meaningful physical outlet — progressively impairs the prefrontal cortex: the part of the brain responsible for complex reasoning, impulse control, and long-term decision making.

Endurance training — sustained aerobic exercise at moderate to hard intensity — has a demonstrable recalibration effect on the HPA axis. Regular training reduces baseline cortisol levels, improves the speed of the cortisol clearance response, and increases the threshold at which the system activates. People who run long distances regularly are better at managing sustained pressure without the physiological degradation that chronic cortisol causes. They recover faster between stressors. Their capacity for complex thought under difficult conditions is maintained.

This is why the CEOs in the Limbach and Sonnenburg study weren't running marathons to stay trim. They were — consciously or not — maintaining the physiological infrastructure that makes sustained high performance possible. The marathon isn't the goal. It's the training artefact of a discipline that produces a neurologically and hormonally more capable executive.

The practical implication for anyone reading this who holds a demanding job and trains seriously is this: you're not indulging a hobby. You're doing maintenance on the system that makes your professional output possible. The 6am run isn't something you're squeezing in around your career. It's part of why your career is going as well as it is. We think that's worth fuelling properly.