Fueling the High-School Runner: The Numbers Everyone Argues About Are the Small Ones

There’s a kid on almost every roster who is flat all season. Times stalled or sliding, always a little tired, picking up the small injuries, never quite bouncing back between workouts. And the reflex — because we’re coaches and training is the lever we know — is to answer it with more training. More mileage, more intensity, more discipline. Sometimes that’s right. Often it’s the exact wrong prescription, because the problem was never the training. The kid isn’t eating enough to cover the training they’re already doing, plus the not-small matter of still growing.

That’s the whole article, really. Almost everything you’ll read online about fueling a young runner argues over the small stuff — the exact grams of protein, the perfectly timed pre-run snack, whether the “anabolic window” is closing. Those are real levers. They’re just small ones, and most of the confident numbers behind them come from studies of adult men in a lab, not fourteen-year-olds. The big lever — the one that actually moves both performance and health — is total energy. Eat enough, consistently, mostly real food, carbohydrate as the backbone. Get that right and the timing details barely matter. Get it wrong and no amount of pre-run banana precision will save the season.

Start here: is the athlete eating enough at all?

Before any question about what or when, there’s the question that outranks all of them: is there enough fuel in the system? Sports scientists have a name for the accounting — energy availability, the energy left to run the body’s basic operations (immune system, bones, hormones, growth) after training’s cost is subtracted. When it drops too low for too long, things break in a specific, well-documented order, and the syndrome has a name: Relative Energy Deficiency in Sport (REDs). The 2023 International Olympic Committee consensus is explicit that it affects both male and female athletes — this is not only a girls’ issue, and the boys on your team are more likely to go unnoticed precisely because everyone assumes it isn’t.¹⁰

There’s a number attached — disruption begins below roughly 30 kcal per kg of fat-free mass per day — but I want to be careful with it, because it will mislead you if you treat it as a target.¹¹ It comes from controlled studies of adult women, it’s expressed in fat-free mass that no coach can measure at practice, and a growing teenager needs energy for growth stacked on top of training, so an adult maintenance floor is arguably too low for them anyway. It’s a reason to pay attention, not a test you administer.

For a runner specifically, the stakes have a name: bone stress injury. The chronic energy shortfall that drives REDs weakens bone at the same time impact loading is pounding it — which is why the athlete who “keeps getting stress fractures” so often turns out to be the under-fueled one, not the unlucky one.¹⁰ If you take one thing from this article, take this: audit whether the athlete is eating enough before you conclude they need to train more.

Protein: enough, spread out, and from food

Protein is where the noise is loudest and the marketing is heaviest, so let’s cut straight to the finding that matters most: most teen athletes already hit their protein target by eating normal food, and do not need a supplement. That is the stated position of the one major guideline written specifically for adolescent athletes.¹ On a team of twenty-two, the number who genuinely need a protein powder is approximately zero. The supplement aisle is selling a solution to a problem your athletes mostly don’t have.

The defensible daily range for athletes is about 1.2–2.0 g per kg of body weight;²³ the adolescent-specific guidance lands modestly higher than the adult baseline — roughly 1.35 g/kg for girls and 1.6 g/kg for boys — and, importantly, that bump exists to cover growth plus training, not to build extra muscle.¹ Treat those numbers as a description of a normal athlete’s plate, not a prescription you hand a kid. Nobody should be running “60 kg × 1.6 = 96, go eat 96 grams.” What it means in practice:

Two myths to retire while we’re here. The anabolic window — the belief that protein must be consumed within 30–60 minutes of finishing or the session is wasted — is badly overstated; total protein across the day and its rough spread matter far more than hitting a stopwatch, and the acute-timing effect has essentially never been studied in teenagers.²³ And the coach-blog warning that extra protein damages a healthy kid’s kidneys or liver has no support in healthy young people.¹ One honest caveat cuts the other way: the precise per-meal numbers come entirely from studies of adult men, and the limited adolescent data suggest teens may actually be more efficient at using dietary protein during puberty — which is one more reason to err toward “enough, from food” rather than chasing a lab-derived gram count.⁴

Carbohydrate before running: fuel, not a threat

Carbohydrate is the fuel a distance runner actually burns at the intensities they train and race. The guidance is unglamorous and it works: a normal carbohydrate-forward meal a few hours before a hard session, and a small, easy-to-digest carb snack closer to it if the athlete wants one.⁶ That’s it. A banana and toast, a bowl of cereal, a bagel — the boring stuff is the correct stuff.

The claim genuinely worth dismantling — because parents believe it hard and pass it to their kids — is the “sugar before a race makes you crash.” This is the reactive-hypoglycemia fear, and the evidence does not support it. A review of the actual studies called the advice to avoid pre-exercise carbohydrate “unfounded”: yes, a transient dip in blood sugar can occur at the start of exercise in some people, but it is usually symptom-free, self-corrects within minutes, and across controlled trials does not hurt — and often helps — performance.⁵ Note the “for most”: a minority of athletes genuinely feel a bit shaky, and if one of yours does, that’s real for them and worth adjusting. But it is not a reason to send the whole team to the line under-fueled.

Breakfast: real value, wrong reasons

Breakfast matters — but almost everything said about why is the weak part, and the strong reason goes unmentioned.

Retire first: “breakfast kickstarts your metabolism / it’s non-negotiable for everyone.” The best evidence we have — randomized trials that actually assigned people to eat breakfast or skip it — found breakfast does not raise resting metabolic rate, and that people don’t fully make up the calories later.⁹ It’s a fine meal. It is not a metabolic switch.

Now the reason that actually holds up, and it’s the one nobody puts on the poster: breakfast helps the school day. This is the single place in all of youth sports nutrition where the evidence is genuinely built on children and adolescents rather than borrowed from adults — eating breakfast produces a short-term, same-morning benefit to attention and memory, strongest in kids whose baseline nutrition is shaky.⁷ Most of your athletes’ day is spent in a classroom, not on a course. That’s the argument that lands with a teenager and a parent both.

The training angle is smaller and more conditional. Before a long or hard morning session (over about an hour), eating first tends to help; before a short, easy run, the fed-versus-fasted difference is minor, and a kid who heads out for an easy dawn jog without eating is very unlikely to have hurt anything.⁸ “Something is better than nothing” is a good default, not an iron law.

Iron — the one runner-specific flag, handled carefully

Iron deserves its own note because iron deficiency is genuinely common in adolescent female endurance runners and their needs are elevated — a real concern, not a myth.¹² You’ll see a striking statistic recycled everywhere: that 34% of high-school girls in cross-country were iron-deficient. It traces to a single, small study from 1989 — worth knowing, not worth quoting as if it were today’s prevalence.¹³ The modern, defensible version is simpler: low iron is common in female distance runners, it mimics under-fueling almost exactly (flat, tired, times off), and it’s worth ruling out.

The sentence that matters most

The through-line of everything above is a safeguarding one, and it deserves to be said plainly rather than buried in a fueling tip. In both distance running and — even more — in appearance-sensitive sports, the athlete at risk is usually the conscientious one who is quietly eating too little, sometimes on purpose, sometimes just because the fuel never caught up with the training. A coach is the first person positioned to notice. A coach is also emphatically not the person to diagnose it, and must never, under any circumstances, tell a high-school athlete to lose weight or lean out. So here is the script, because a worried coach with no words tends to either say nothing or say the wrong thing:

Don’t coach the body. Coach what the body can do. The question is never “should you weigh less” — it’s “are you eating enough to match what we’re asking of you?”

That framing keeps the conversation about capacity — recovery, energy, holding pace at the end of a race — and hands the medical question to the people qualified for it.

What’s genuinely unsettled

What this means for your athletes

Not a meal plan — you know your roster. What the evidence makes actionable: