How to Pick the Right Gels and Electrolytes for Your Race

You are eight weeks out from your race. You have a training plan. You have your kit sorted. And then you open a browser tab to figure out what to actually eat and drink during the race — and you are immediately drowning in options.

Maurten or SiS? LMNT or Precision Hydration? Caffeinated or not? Liquid or solid? Isotonic gel or the kind you need to wash down with water?

Every brand says theirs is the best. Every runner you know swears by something different. And the more you read, the less certain you feel.

This is the part of race prep that trips up more athletes than pacing, training load, or shoe choice. Not because the science is complicated, but because nobody gives you a framework for making the decision personal.

That is what this article is for.

Why "best gel" lists are mostly useless

Every year, magazines and websites publish "best gels for marathon" roundups ranked by taste tests and editor opinions. They are fine for discovering what exists, but useless for telling you what will work for your body on your race day.

Here is why: the gel that fuels a 2:45 marathoner running in cool conditions with a low sweat rate is a terrible recommendation for a 4:30 marathoner running a warm spring race who sweats heavily and has a sensitive stomach.

The variables that determine your ideal fueling products are personal:

• Your sweat rate — how much fluid and sodium you lose per hour
• Your race distance and expected finishing time — which determines total carbohydrate needs
• Your stomach tolerance — how well your gut handles concentrated carbohydrates under race effort
• The conditions — heat and humidity amplify fluid and electrolyte losses
• Your training history — whether your gut is adapted to processing fuel at race pace

A product roundup cannot account for any of these. A framework can.

Step 1: Know your carbohydrate target

Before you can choose a product, you need to know how much carbohydrate you need per hour. This is non-negotiable for any race over 90 minutes.

The general guidelines are:

• 60-90 minutes (half marathon for many runners): 30-60g carbohydrate per hour
• 90 minutes to 3 hours (fast marathons, Olympic triathlons): 60-80g per hour
• 3-5 hours (most marathon finishers): 60-90g per hour, sustained
• 5+ hours (ultras, long-course triathlon): 80-100g per hour for trained guts

These ranges are wide on purpose. Where you land within them depends on your body weight, your pace, and how well you have trained your gut to absorb fuel at effort.

The critical point most athletes miss: a 5-hour marathoner needs more total carbohydrate across the race than a 3-hour marathoner, not less. Slower does not mean less fuel. It means more time on your feet, more glycogen depletion, and more opportunities for things to go wrong if you under-fuel.

Step 2: Know your sodium number

This is where most race nutrition falls apart. Generic electrolyte advice says "take some sodium" and leaves it there. But athletes lose anywhere from 400mg to 1,800mg of sodium per litre of sweat — a nearly fourfold difference.

If you are a light sweater with low sodium concentration, a high-sodium electrolyte tablet might give you stomach issues for no benefit. If you are a heavy, salty sweater, a standard sports drink will leave you wildly under-replaced.

Signs you are probably a heavy sodium loser:

• White salt stains on your kit after long runs
• You crave salty food after training
• You cramp despite being well hydrated
• You feel worse, not better, when you drink more water without electrolytes

The most precise way to know your sodium loss rate is a sweat test — services like Precision Fuel & Hydration offer them, or you can estimate with a structured DIY method. But the gold standard is using actual data from your wearable and training history to calculate it, which is exactly what Sweatr does when it builds your hydration plan.

Step 3: Match the product format to your race

Not all fuel formats are equal for all situations. Here is a practical breakdown:

Gels

Best for: Running events where you cannot carry much and need fast carbs. Watch out for: Many gels require water to absorb properly. If you take a concentrated gel without water, it sits in your stomach and pulls fluid from your bloodstream — the opposite of hydrating.

Isotonic gels (Maurten, SiS GO Isotonic) do not need water. This is a genuine advantage during running races where aid station timing is unpredictable.

Standard gels (GU, Clif, Spring) are cheaper and come in more flavours, but you must take them with 200-300ml of water.

Electrolyte drinks

Best for: Cycling and triathlon bike legs where you carry bottles. Also useful as a pre-race sodium loading tool. Key decision: Concentration. Hypotonic drinks absorb faster but deliver less sodium per sip. Hypertonic drinks deliver more fuel but can cause GI distress.

Chews, blocks, and real food

Best for: Ultra-distance events where flavour fatigue is real. Also useful for athletes who cannot stomach the texture of gels. Watch out for: Slower absorption. Fine for a 10-hour ultra. Risky for a 3-hour marathon where absorption speed matters.

Step 4: The gut tolerance test

You have your carb target, your sodium number, and a product format. Now you need to find out whether your body actually agrees with your choices. This happens in training, not on race day.

The protocol is simple:

1. Start 8-10 weeks before race day. This gives your gut time to adapt.
2. Use your chosen products on your long run every week. Same brands, same quantities, same timing you plan for race day.
3. Simulate race conditions. Take fuel at race pace, not easy pace. Your gut behaves differently under effort because blood flow diverts away from your digestive system and toward your muscles.
4. Increase gradually. If your target is 80g carbs per hour, start at 40-50g and build up over 4-6 weeks.
5. Log what works and what does not. Note which products caused bloating, nausea, or energy dips. This data is the difference between a good race and a bad one.

If a product makes you feel sick at race pace during training, it will make you feel worse on race day when adrenaline, nerves, and the stakes are higher.

Step 5: Build your race-day fueling kit

Once you know what works, build the kit:

For a marathon:

• Pre-race: breakfast 3-4 hours before, with a gel or sports drink 15 minutes before the start
• During: one gel every 25-35 minutes depending on your per-hour target, alternating with electrolyte intake at aid stations
• Carry: enough gels to cover your expected finish time plus one spare. A race belt or shorts with pockets makes this manageable

For a triathlon:

• Bike: electrolyte drink in bottles plus gels taped to the top tube. This is where you do most of your fueling — the run leg is harder on the stomach
• Run: gels only, minimal volume. Your gut tolerance drops after T2
• Carry: flask of concentrated electrolyte for the run if the course does not provide your preferred brand

For an ultra:

• Variety is survival. Pack gels, chews, real food (rice cakes, potatoes, PB&J), and multiple electrolyte options. Flavour fatigue is real after 6+ hours
• Plan by checkpoints, not by time. Know what each aid station offers and fill gaps with what you carry

The real problem: you should not have to figure this out manually

Everything above is doable. But it requires you to research products, calculate carb targets from your body weight and pace, estimate sodium needs without a lab test, cross-reference formats with your event, and track gut tolerance across weeks of training.

Most athletes — especially first-timers — do not do this. They grab whatever gel the expo was handing out, take it when it feels right, and hope for the best. Some get lucky. Many bonk, cramp, or spend the final miles with a stomach that has given up.

Sweatr exists to close this gap. It pulls your training data from your Apple Watch, Garmin, or Strava, calculates your personalised carbohydrate and fluid needs per hour, and maps those numbers to a curated product library of gels, electrolytes, and drinks. You get a race-day plan that tells you exactly what to take, when, and how much — built from your data, not someone else's average.

No spreadsheets. No guesswork. No discovering at mile 20 that you chose wrong.

A quick-reference decision framework

| Factor | Question to answer | Where to find your number | |--------|-------------------|--------------------------| | Carb target | How many grams per hour? | Body weight + race duration + training adaptation | | Sodium needs | Light or heavy sweater? Salty or dilute? | Sweat test, wearable data, or observation (salt stains, cramp history) | | Format | Gel, drink, chew, or real food? | Match to your sport, stomach, and race logistics | | Gut tolerance | Does this product work at race pace? | 8-10 weeks of training rehearsal | | Caffeine | Do you want it, and when? | Personal tolerance — test in training. Best saved for the second half of the race |

What to do this week

If your race is more than 6 weeks away, you have time to get this right. Here is your action plan:

1. Calculate your carb-per-hour target based on your expected finishing time.
2. Assess your sodium profile — check your kit for salt stains after your next long run.
3. Pick 2-3 products to test based on your format needs.
4. Start gut training this weekend on your long run.
5. Or skip the manual work — download Sweatr and let it build your personalised plan from your wearable data in minutes.

Your race-day nutrition should be the most rehearsed part of your race. Start treating it that way.