Fuelling Strategy for a 70.3 Triathlon: Everything You Need
A middle-distance triathlon is long enough to be won or lost on nutrition and short enough that most people never quite take it seriously. Four to seven hours of continuous work — 1.9km swim, 90km bike, 21.1km run — sits in an awkward window. It's too long to get away with a couple of gels and a swig of water, but not so long that you can slow down, eat a sandwich and still call it a good day. Get the fuelling right and the last 10km of the run feels like a run. Get it wrong and it becomes a shuffle punctuated by walking the aid stations.
The frustrating thing is that most 70.3 fuelling failures are not exotic. They're arithmetic errors. People guess at how much they're taking in, they take on board far less than they think, and the deficit only shows up at around the 3.5-hour mark when there's nothing left to give. What follows is a practical fuelling strategy for a 70.3 triathlon built around numbers you can actually calculate the week before your race, rather than vague advice to "eat little and often".
Start With the Maths, Not With the Products
Your body stores roughly 400–500g of carbohydrate in muscle and liver glycogen if you're well fed — call it 1,600–2,000 kcal. At middle-distance race intensity you'll burn somewhere between 600 and 900 kcal per hour. Even with a full tank you're running on empty by hour three unless you're topping up.
The target most athletes should aim for is 60–90g of carbohydrate per hour. That range isn't arbitrary. Glucose is absorbed through the SGLT1 transporter in the gut wall, which saturates at around 60g per hour — take more glucose than that and the surplus sits in your gut sloshing about, which is precisely how people end up doubled over at the second-to-last aid station. Fructose uses a completely separate transporter (GLUT5), so combining the two lets you push total absorption up towards 90–100g per hour. This is why the glucose-to-fructose ratio on a label matters more than the flavour.
Work out your own number:
- Sub-5 hour athletes: aim for 80–90g/hr, mostly on the bike
- 5–6 hours: 70–80g/hr
- 6+ hours: 60–70g/hr, with more real food tolerated at lower intensity
Multiply your target by your projected bike split, then by your run split, and you have a total gram figure. A 5:30 athlete at 75g/hr needs roughly 410g of carbohydrate across the race. Now go and count what's actually in your bento box. Most people discover they've packed about half of what they need.
The Bike Is Where the Race Is Fuelled
The single most useful principle in middle-distance racing: you eat on the bike to run well. The bike is the only leg where your gut is stable, your breathing is controlled and your hands are free. Gastric emptying drops sharply once you start running — the mechanical jostling plus the higher relative intensity of the run means blood is diverted away from the digestive system. Anything you plan to absorb in the first 30 minutes of the run has to already be on board before you rack the bike.
Practically, that means front-loading. Take your first feed within 15 minutes of leaving T1, while your heart rate is settling and the adrenaline of the swim is washing out. Then eat on a fixed schedule rather than by feel. A 15-minute timer on your bike computer beats hunger cues every time, because by the time you feel like eating you're already 20g behind.
Aim to be finished with solid or chewable fuel by about 10km from the end of the bike leg. The final stretch should be liquid carbohydrate and fluid only, so you arrive at T2 with a settled stomach and a full tank rather than a lump of half-digested bar.
Building Your Fuelling Strategy for a 70.3 Triathlon Hour by Hour
Here's a template for a 5:30 athlete targeting roughly 75g/hr. Adjust the volumes to your own split times, but keep the shape.
- Three hours before the start: 1.5–2g of carbohydrate per kg of body weight. For a 70kg athlete that's around 120g — porridge with honey and a banana, plus 500ml of fluid. Nothing new, nothing high in fibre.
- 15 minutes before: 20–25g of fast carbohydrate. Chews or a small gel. This tops up liver glycogen without triggering a meaningful insulin response by the time the gun goes.
- Swim (approx. 35 min): nothing. You can't, and you don't need to.
- Bike, hours 1–3 (approx. 2:50): 80–90g/hr. Split it across a concentrated bottle mix and chewable fuel every 15 minutes. This is where you bank the calories.
- Last 15 minutes of the bike: fluid and electrolytes only, plus a final 20g hit of carbohydrate you can swallow easily.
- Run (approx. 2:00): 50–70g/hr, taken in smaller, more frequent doses — 15–20g every 20 minutes with water at aid stations.
On fluid and sodium: 500–750ml per hour is a sensible starting point on the bike, more in heat. Sweat sodium concentration varies enormously between individuals — anywhere from 300 to over 1,500mg per litre — so blanket advice is close to useless. If you're a heavy, salty sweater (white marks on your kit, gritty skin), you're likely at the upper end and should be taking 700–1,000mg of sodium per hour. If you're not, 400–600mg/hr is plenty.
Train the Gut, Not Just the Legs
The ability to absorb 90g of carbohydrate per hour is trainable. Repeated exposure upregulates intestinal transporter expression — studies have shown meaningful increases in exogenous carbohydrate oxidation after just two to four weeks of high-carbohydrate training feeds. You cannot decide on race morning to double your intake and expect your gut to cooperate.
Build it into your long sessions. Once a week, do your long ride at your exact race intake, with your exact race products. Then do at least three brick sessions where you run for 30–40 minutes off the bike having eaten properly, so you learn what your stomach does under running load. If something disagrees with you, you want to find that out in a car park 15 minutes from home, not 60km into a race.
What We Use at FTP Endurance Fuel
We built our pastilles around the problem of hitting a high hourly carbohydrate target without wrecking your stomach. They use a 1:1 glucose-to-fructose ratio, so you're working with both transporter pathways rather than hammering one — which is what allows you to push towards the higher end of the range without the gut distress that comes from a glucose-only approach.
The practical reason we use chewable fuel on the bike is control. A pastille is a known quantity: you can count them, you can eat them one at a time with a hand on the bars, and there's no sticky wrapper to stuff back in your trisuit. Our Mixed Fruit Pastilles rotate flavours through a long ride, which matters more than people expect at hour three when everything sweet has started tasting the same. The Tart Cherry Pastilles add anthocyanins — the compounds that give the fruit its dark colour and which have been shown to blunt oxidative stress and reduce markers of muscle damage — which is why plenty of our customers use them for the days either side of a race as well as during it.
A 70.3 rewards the athlete who did the boring preparation. Write your fuelling plan down, tape it to your top tube, practise it twice on long rides and then execute it without improvising on the day. If you want to test what works for your stomach before committing to a full bag, our Taster Pack is the sensible place to start — and once you've settled on a flavour, the bundles will see you through a full race build.
