Why Your Running Buddy's Fueling Plan Won't Work for You

You're eight weeks out from your fall marathon. You've been trawling Reddit threads, scrolling through Strava posts, and saving Instagram carousels that break down someone's "exact race-day nutrition plan." Three gels before halfway, a caffeine gel at mile 18, 500 ml per hour of electrolyte drink. Sounds solid. Sounds like a plan.

Here's the problem: it's not YOUR plan.

That fueling strategy was built — consciously or not — around someone else's body weight, sweat rate, finishing time, and stomach. Copying it is like wearing someone else's shoes for 42 kilometres. They might be the right brand, but they're the wrong size.

The four variables that make fueling personal

Every fueling plan is shaped by four things. Change any one of them and the plan changes with it.

1. Body weight

Your carbohydrate needs during a marathon scale with your body mass. A 60 kg runner and a 90 kg runner burning the same relative effort are burning different absolute amounts of glycogen. The heavier runner depletes faster, needs more fuel per hour, and hits the wall sooner if they under-fuel.

Most gel-timing guides ignore this completely. "Take one gel every 45 minutes" treats every body the same way. It's a starting point, not a plan.

2. Sweat rate

You lose fluid and electrolytes through sweat, but how much varies enormously between individuals. Some runners lose 400 ml per hour in mild conditions. Others lose 1.8 litres per hour in the same conditions. The difference isn't fitness — it's physiology.

Your sweat rate determines how much you need to drink, how much sodium you need to replace, and whether your hydration plan can keep up with your losses. And it changes with temperature, humidity, fitness, and acclimatisation. The plan that kept you comfortable in April training will under-serve you in August heat — and over-serve you in October coolness.

You can estimate your sweat rate at home by weighing yourself before and after a run (without clothes, accounting for fluid consumed). It's not perfect, but it's a hundred times better than guessing.

3. Pace and duration

This is the variable people underestimate most. A 3:00 marathoner and a 4:30 marathoner aren't running the same race from a fueling perspective.

The faster runner is working at a higher intensity, burning a higher percentage of carbohydrate relative to fat, and has less time to absorb fuel through the gut. The slower runner is on their feet for 90 more minutes, needs more total fuel, but can absorb it more gradually and may tolerate solid food better than gels.

Here's the counterintuitive part: slower marathoners often need MORE total carbohydrate than faster ones, not less. They're out there longer. Their glycogen stores don't last forever either. But most fueling guides are written by and for sub-3:30 runners, leaving the 4:00–5:00 crowd dangerously under-fuelled.

4. Gut tolerance

Your gut is a muscle in the fueling equation. It can be trained to absorb more carbohydrate per hour — but only through deliberate practice. The current sports science consensus suggests most athletes can handle 60–90 grams of carbohydrate per hour with training, and some can push to 90–120 g/hr using dual-transport carbohydrates (glucose + fructose).

But your running buddy who comfortably takes four gels per hour didn't start there. They built up over months. If you copy their race-day plan without their gut training history, you'll spend miles 18 to 26 looking for a portable toilet instead of a finish line.

The "I followed their plan and bonked anyway" problem

This scenario plays out thousands of times every autumn marathon season. An athlete copies a plan from someone who:

• Weighs 15 kg less than them
• Finishes 45 minutes faster
• Sweats half as much
• Has been practising with gels for two years

The borrowed plan delivers too few carbs per hour for the heavier, slower runner. The fluid intake is too low for their sweat rate. The gel timing doesn't account for their pace or the fact that they'll be on course for an extra hour.

By mile 18, they're in glycogen debt. By mile 22, they're walking. And the frustrating part is they think they had a plan. They did — it was just someone else's.

Why generic advice keeps failing

It's not just running buddies. The internet is full of fueling advice that reads as definitive but is actually just one person's experience disguised as universal truth.

"Take a gel every 45 minutes." For who? At what pace? At what body weight? In what conditions?

"Drink 500 ml per hour." Based on whose sweat rate? In what temperature? With what sodium concentration?

"Carb load with pasta the night before." How much pasta? Based on what body weight? And does that account for the 72-hour carb loading window that actually works, or just one big dinner?

These aren't bad starting points. But they're ranges, not plans. And when your marathon goes wrong at mile 20, "somewhere in the range" is cold comfort.

How to build a plan from YOUR data

Here's what a truly personalised fueling plan accounts for:

Your body weight determines your baseline carbohydrate needs per hour. Heavier runners need more fuel. This is simple maths, but most plans skip it.

Your sweat rate (measured across different conditions) determines your fluid and sodium needs. This changes with the seasons — test it in the conditions closest to your race.

Your goal pace and expected finishing time determine how long you'll be fueling, what intensity you're working at, and how much total carbohydrate you need across the entire race.

Your gut training history determines your carbohydrate ceiling per hour. If you haven't practised with gels on long runs, start at 30–40 g/hr and build up. Don't copy someone else's 90 g/hr plan on race morning.

Race-day conditions — temperature, humidity, altitude — shift everything. A plan built for a 12°C October morning needs adjusting if race day is 22°C and humid.

Put these together and you get a plan that tells you exactly how many grams of carbohydrate per hour, how many millilitres of fluid per hour, how much sodium, and when to take each gel or drink — based on your numbers, not averages.

Your watch has the data. You just need something to use it.

If you train with an Apple Watch or Garmin and log runs on Strava, you're already generating the data you need. Heart rate across different paces. Training load over time. Historical workout data that reveals how your body responds to different efforts and conditions.

The problem isn't data collection — your watch does that beautifully. The problem is translation. Your Garmin can show you that you ran for 2:45 at an average heart rate of 155 bpm and burned an estimated 2,400 calories. What it can't do is tell you to take a gel at kilometre 14 and drink 350 ml between kilometres 20 and 25.

Sweatr connects to your Apple Watch, Garmin, and Strava data, combines it with your body weight and sweat rate profile, and builds a fueling plan that's calculated for you. Not for your running buddy. Not for the person who posted on Reddit. For you.

When race day conditions change — hotter than expected, hillier than trained for — the plan adapts because it's built from variables, not fixed rules.

Build your plan now, not the night before

If your fall marathon is eight weeks away, this is the window. You have three to four long runs left to test your fueling strategy. That's three to four chances to find out whether your gut can handle your target carb intake, whether your fluid plan keeps up with your sweat rate, and whether the products you've chosen actually work at race effort.

Don't waste those long runs testing someone else's plan. Build one from your own data, practise it under fatigue, and arrive at the start line knowing — not hoping — that your nutrition will hold.

Your running buddy's plan worked for your running buddy. Yours should work for you.