A Half-Ironman (70.3) Nutrition Plan

Racing a 70.3 requires some nutritional planning.

An athlete eats in transition as part of her 70.3 nutrition plan.

(Photo: Jill Brady/Getty Images)

Updated June 26, 2025 05:47AM

A successful 70.3 race comes down to two things: preparation and nutrition. Following a well-designed training plan will provide the race readiness and confidence you need to toe the starting line, but a solid 70.3 nutrition plan will get you across the finish. After all, your body is your most important piece of equipment – it’s the engine that makes it all happen. If you’re not properly fueled, then the most aero bike and the world’s best training plan won’t help you.

But what should you eat during a half-iron or 70.3 race? The market is saturated with options for fueling for a 70.3 – everything from gels and chews, to bars and sports beverages. If you ask 100 triathletes what they eat and drink during a half-Ironman, you’ll likely get 100 different yet successful 70.3 fueling plans. What works for your training buddy won’t necessarily work for you. That provides even more reason to test-drive your fuel plan in training, so on race day you’ve established an ironclad plan that will go the distance.

As you experiment with different strategies in your 70.3 nutrition plan, follow these general guidelines.

Fueling guidelines for half Ironman (70.3)

Half-iron distance events typically last between 4.5 and 8.5 hours, depending on one’s athletic ability. That’s a long time for the body to swim, bike, and run! When our glycogen stores are full, the body has enough energy stored in the muscles and liver to fuel activity for 1-2 hours of easy to moderate effort intensity.

The body relies on both carbohydrate and fat for fuel, but the intensity of the effort dictates the percentage of carbs and fat used. The easier the effort, the longer glycogen stores will last, and the harder the effort, the faster it runs empty. Because carbohydrate stores are limited and needed to convert fat to glucose, we must consume easy-to-digest carbs throughout a 70.3 to avoid depleting glycogen stores, thus “hitting the wall” or “bonking.”

To sum it up – the longer the triathlon, the more critical fueling becomes to sustain aerobic capacity, meet metabolic demands, and ultimately lead to a successful performance, one worthy of your hard-earned fitness.

Key points:

Consume 60-90+g carb/hr (240-360 calories) from multiple carb sources such as glucose, fructose, and maltodextrin mixtures. Consuming a combination of carbs is best since they are absorbed through different mechanisms and break down into glucose at different rates, decreasing the risk of gastrointestinal (GI) distress.
Properly formulated sports drinks, energy gels, sports chews, and low-fat and fiber sports bars are effective fuel sources.
The body’s gastrointestinal absorption rate is higher on the bike due to lower heart rates, so aim to fuel at the middle to top of the recommended carb range. If you want to include semi-solids or solid food such as boiled salted potatoes, well-formulated sports bars, or peanut butter crackers, do so in the middle of the ride with the last 60-90 minutes using designated sports fuel/beverage only. Switching to carb-only sports fuel allows solids to clear the gut by the time you hit T2, warding off GI upset on the run.
Fueling on the bike can be tricky as your priority is riding safely and staying clear of other competitors. Ensure that you can access your fuel easily while navigating the bike. Bento box and tri kit pockets are common and easily accessible fuel storage locations. Be sure to open the package before the ride/race and break into small bite sizes for convenience and safety – in the case of a bar or pack of crackers.
On the run, since heart rates are higher, fueling should be in the low to middle of the carb range. Opt for liquids, diluted gels, or bite-size gummies instead of solids – and go with tried and true easy-to-digest formulations.
Fuel and hydrate early and often. One of the pitfalls athletes face is waiting an hour or two into the race to begin fueling with the mindset that they don’t need it yet. Just as the body is the freshest early in the race, the same goes for the GI system. Take advantage of the situation and start right out of the gate. Waiting too long to fuel and hydrate increases the chance of dehydration, which increases gastrointestinal problems (cramping, vomiting, diarrhea).

Hydration guidelines for half Ironman (70.3)

A triathlete takes water from an aid station as part of a 70.3 nutrition plan. — (Photo: Jurij Kodrun/Getty Images)

Dehydration, defined for our purposes as a fluid deficit of >2% body weight during exercise, is the most common cause of early fatigue and poor performance in endurance sports. Most athletes focus on avoiding “the bonk” and over fuel in racing, but these efforts are misplaced. It’s possible, albeit not fun, to rebound from a bonk, but not dehydration. Once dehydration has set in, there is no coming back during the race. Dehydration increases core body temperature, heart rate, and perceived exertion – all of which wreck performance.

Plain water can be a decent thirst quencher, but not an effective hydrator. The reason being is that sodium facilitates the absorption of fluids. Without sodium, water seeps into the extracellular compartments, leaving you bloated, puffy, and gaining weight.

A properly formulated sports drink that contains additional sodium to meet both fluid and energy (carbs) needs is ideal. Keep in mind that fluid and sodium needs are unique and can be determined through a sweat and sodium rate test and training sessions. However, many studies prove that endurance athletes with high sweat rates and high sweat-sodium concentration sustain significant sodium losses.

Key points:

Drink early and often right out of T1 and consume 20-32+oz (600-960ml) per hour, depending on heat, humidity, individual sweat rate, intensity, etc. Fluid needs are highly individual. Therefore, this fluid range is a general range.
One gulp of fluid = 1 oz. Shoot for 4-8 oz (120-240ml) every 10-15 min on the bike and 3-4+ oz (90-120ml) at each run aid station. Taking short, intentional walk breaks at run aid stations to get in 3-5 good gulps will set you up for a stronger finish than banking time early in the run by skipping aid stations.
Do not depend on thirst to guide your hydration strategy. Instead, drink according to your plan and schedule.
A good indication of being adequately hydrated for a successful run off the bike is the need to urinate once every 2.5 hours on the bike. This translates to needing to once on the bike or if the ride is <3 hours, holding off for the porta-potty in T2.
Hyponatremia, or low blood sodium levels, occurs when fluid intake exceeds sweat and urine loss or fluid replacement lacks sufficient sodium. Weight gain during training and racing is a warning sign of overconsumption or the inability to absorb fluids and occurs more often with endurance athletes who rely on plain water to meet fluid needs.
*500-1000+mg sodium per hour is a general range, but it is highly individual. The best way to determine sodium loss is to have a sweat sodium test for both the bike and run since sweat rates and sodium loss vary between the bike and run.

Should I take in caffeine during a 70.3?

According to numerous research studies, low to moderate doses of caffeine enhance performance. Caffeine is a drug that serves as an ergogenic aid by stimulating the central nervous system, which increases our pain threshold and decreases the perception of effort. The recommended dosage is 2-3mg/kg body weight.

For a 70.3 triathlon, it’s best to wait until the second half of the bike leg to begin using caffeine to delay the onset of fatigue more effectively. The best approach is to find the lowest dosage effective for you and that has been established successfully in training. Despite contrary belief, more caffeine is not better, as serious side effects such as increased heart rate, tremors, and anxiety can occur.

To improve race day caffeine effectiveness, decrease caffeine intake by ½ your regular consumption 3-4 days beforehand.

Caffeine can exacerbate GI issues, especially in those who are not daily consumers. If you don’t typically take in caffeine, be sure to test drive during training if you want to use it on race day.

Final 70.3 fueling tips

Establish a fuel/hydration plan, test it out in training, and stick to YOUR plan on race day. Remember the golden rule: Nothing new on race day!!

Test drive your plan in simulated race day training sessions (long bike/bricks, long runs) at race-like efforts and weather conditions.

Rehearse race day fueling with the same diligence you bring to training. Just as you are training your body to perform for the 70.3 distance, the gut must also be trained to process your chosen fuel at race-like intensities for the duration.

It’s important to execute steady pacing from the start, a smooth effort you can build on. Going too hard too early will shut down the gut, causing bloating and a sloshy stomach, sabotaging your race right out of the gate.

Despite dedicated efforts in training to establish the right race day fuel plan, be prepared to quickly pivot to a plan B. Anything can happen on race day, and you don’t want a nutritional mishap or curveball to throw you off your game. Curveballs are things like bottles projected off your bike by hitting a pothole or a pack of gummies slipping right out of sweaty hands before you have a chance to eat. Familiarize yourself with the sports fuel served on the course and give that a run-through in training, so it’s not new on race day, just in case you need to lean on Plan B.

More 70.3 training resources

Looking for more resources to dial in your 70.3 plan? Check out these top-ranked resources for half-iron/70.3 training and racing:

Susan Kitchen is a Sports Certified Registered Dietitian, USA Triathlon and Ironman Certified Coach, accomplished endurance athlete, and published author. She is the owner of Race Smart, an endurance coaching and performance nutrition company that works with athletes across the globe as they strive toward optimal health, fitness, and performance.

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