A 70.3 (Middle Distance: 1.9km swim / 90km bike / 21.1km run) takes most age-group athletes somewhere between 5 and 8 hours — long enough that nutrition strategy stops being a minor detail and becomes one of the two or three biggest factors in whether your race goes well or falls apart in the run. This is general, well-established sports-nutrition guidance, not a specific product recommendation or medical advice — if you have a condition affecting diet or hydration, get individual guidance rather than following generic guidance.
The big picture: what actually goes wrong
The two most common nutrition failures at 70.3 distance are under-fueling (running out of usable energy in the final third of the race, often described as "the wheels coming off") and under-hydrating/under-salting (leading to cramping, nausea, or a genuine bonk, distinct from simple fatigue). Both are largely preventable with a plan you've actually rehearsed in training — not one you're improvising on race day.
How much carbohydrate do you actually need?
A widely-cited general guideline for endurance events over roughly 2-3 hours is 60-90 grams of carbohydrate per hour, once you're past the first 60-90 minutes (early race effort typically runs on existing glycogen without needing external fuel yet). This is a range, not a fixed target — some athletes' guts tolerate the higher end well with practice; others do better nearer 60g/hour. The only reliable way to know where you sit is testing it in training, not guessing on race day.
| Leg | Typical duration | Fueling approach |
|---|---|---|
| Swim (1.9km) | 30-60 min | No fueling needed — this is short enough to run on existing glycogen. |
| Bike (90km) | 2.5-4+ hours | The easiest leg to fuel — bottles, gels and solid food are all realistic here. Most of your total race carbohydrate intake should happen on the bike. |
| Run (21.1km) | 1.5-3+ hours | The hardest leg to fuel — running jostles the stomach more than cycling, and you're already fatigued. Rely on what you practiced, favor easily-digestible sources, and use on-course aid stations if you've tested that specific product before. |
Hydration and sodium
Fluid needs vary hugely by individual sweat rate, body size, and race-day heat — there's no single correct number of liters per hour that applies to everyone. What matters more than a precise target is drinking consistently throughout the bike and run (rather than large volumes infrequently) and replacing sodium lost through sweat, especially in warm conditions or for genuinely heavy sweaters.
A practical sweat-rate check
Weigh yourself before and after a long training session of known duration, without drinking anything during it. The weight lost is roughly your sweat loss for that duration and conditions — a useful, individual reference point that's far more accurate than a generic rule of thumb.
Sodium matters because sweat isn't just water — it carries electrolytes with it, and replacing water alone over many hours in warm conditions can, in rare cases, lead to hyponatremia (dangerously low blood sodium from drinking too much plain water without replacing salt). Most commercial sports drinks and electrolyte tablets are designed around this, which is why race nutrition plans lean on them rather than water alone for anything beyond an hour or so.
Building your own race nutrition plan
- 1 Start with a general target (e.g. 70g carbohydrate/hour, adjust from there) rather than either extreme.
- 2 Choose 2-3 fuel sources you already tolerate well — gels, chews, sports drink, real food (bananas, rice cakes) — rather than relying on a single source for the entire race.
- 3 Practice your exact race-day plan on at least 2-3 long training sessions beforehand, at race effort, not just at an easy training pace where digestion is less stressed.
- 4 Know what your specific race provides on-course (check the race's own information) and decide in advance whether you're relying on it or carrying your own — mixing an unfamiliar on-course product into your plan on race day is a common, avoidable mistake.
- 5 Have a simple backup plan for GI distress — a slower intake rate, plain water for a stretch, or switching fuel sources — rather than no plan at all if something isn't sitting well.
The one rule that matters more than any specific number
Nothing new on race day — not a new gel brand, not a new sports drink, not a new solid-food snack, even if it's what the race itself hands out on course and looks appealing in the moment. Every single thing you plan to consume during a 70.3 should already have been tested, more than once, during a long training session at genuine race effort. GI distress mid-race ends more athletes' days than pacing mistakes or lack of fitness.