The 10 most common nutrition mistakes endurance athletes make
Mavr Sports Nutrition Team
Updated September 28, 2026. 8 min read.
Quick answer
Endurance athletes most commonly underfuel, time carbs wrong, neglect hydration, and skip recovery nutrition — fix these by tracking intake against workout demands, starting carbs early, drinking to thirst with electrolytes, and eating protein + carbs within 60 minutes post-workout.
4 key facts
RED-S (Relative Energy Deficiency in Sport) affects up to 50% of female endurance athletes and 25% of male athletes, causing injury and performance decline.
Delaying carbs by even 30 minutes during long efforts can accelerate glycogen depletion and fatigue.
Drinking to thirst, with electrolytes on long sessions, lowers the risk of both dehydration and hyponatremia. Over-drinking is the main cause of hyponatremia.
Skipping post-workout nutrition delays glycogen restoration by hours and increases injury risk.
You train hard. You follow the plan. You take your rest days. And still something is off — your paces have stalled, your legs feel permanently heavy, you catch every cold going around, or small injuries keep flaring up. The natural response is to assume the training is wrong and to add more miles or more intensity, which usually makes things worse.
Very often the real culprit is not your training program at all — it is your nutrition, and specifically a handful of mistakes that are easy to make and easy to miss. None of the ten below are exotic; they are the ordinary, well-intentioned errors that quietly cap the ceiling on otherwise good training. The encouraging part is that each one has a concrete, low-effort fix, and correcting even two or three of them tends to produce a noticeable jump in how you feel and perform.
Endurance athletes consistently make the same nutrition mistakes that quietly sabotage performance. Let's break down the top 10 and how to fix them.
Mistake #1: not eating enough (underfueling)
Underfueling — sometimes called RED-S (Relative Energy Deficiency in Sport) — is the silent performance killer.
When you consistently eat fewer calories than you burn, your body downregulates metabolism, hormones, and immune function. Performance suffers, injury risk rises, and recovery slows.
Persistent fatigue despite adequate sleep
Inability to maintain race weight
Frequent injuries or illness
Declining performance despite hard training
Irregular periods (in female athletes)
Fix: Track your intake for one week and compare it to your training load. If you're consistently below 30 kcal/kg of body weight on high-training weeks, increase calories gradually.
Mistake #2: starting fuel too late
Many athletes wait until they feel tired before eating during training. This is a mistake — by the time you feel fatigue, glycogen stores are already depleted.
The solution: start fueling within the first 30 minutes of any session over 90 minutes.
Mistake #3: over-reliance on water (neglecting electrolytes)
Drinking much more plain water than you sweat during long efforts dilutes blood sodium and raises the risk of hyponatremia.
Include 300–500 mg sodium per liter during exercise
Add electrolytes to at least one bottle per long session
Weigh yourself before and after to understand your sweat rate
Mistake #4: skipping post-workout nutrition
The 60-minute window after training is prime time for glycogen restoration. Skipping it delays recovery by hours.
Target 1.0–1.2 g/kg carbs and 20–30 g protein within 60 minutes of finishing.
The protein part of that window is wider than most people think. A normal meal with 20–40 g of protein within about 2 hours works as well as a shake straight after, and your total daily protein matters more than the exact timing. Carbs are the time-sensitive part, and they matter most when your next hard session is less than a day away.
Mistake #5: ignoring protein distribution
Protein isn't just for bodybuilders. Endurance athletes need 1.2–1.4 g/kg daily, distributed across 4–5 feedings for optimal muscle repair.
Aim for 0.3–0.4 g/kg protein per meal (20–30 g for most athletes)
New gels, new drinks, new foods — race day is not the time for experimentation.
Everything you plan to eat or drink during a race should be tested in at least three long training sessions beforehand.
Those sessions also train your gut. Most athletes can raise how many carbs per hour they tolerate: start at about 30–40 g per hour in long sessions and add about 10 g per hour each week until you reach your race target.
Mistake #7: poor pre-race meal timing
Eating too close to the start can cause gut distress. Eating too early means starting depleted.
The sweet spot: eat your pre-race meal 3–4 hours before the start, targeting 1–4 g carbs per kg.
A related timing mistake is eating "healthy" foods too close to a session. Fiber and fat slow down how fast your stomach empties, and some foods ferment in the gut and cause gas. In the 2–3 hours before training, keep these small or skip them:
High-fiber cereals, whole-grain breads, and beans
Broccoli, cauliflower, kale, and other cruciferous or raw vegetables
Chia seeds and flaxseed
Nuts, avocado, and other high-fat foods
Large smoothies or big glasses of fruit juice
You do not need to cut these foods out. Just move them: simple, low-fiber carbs before training, fast carbs during, carbs plus protein after, and fiber, healthy fats, and vegetables the rest of the day.
Mistake #8: getting hydration wrong (too little or too much)
Start sessions well hydrated. Waiting until you are very thirsty on a long, hot session can leave you short.
During exercise, drink to thirst and sip steadily, and use a sweat rate test to learn how much you actually lose.
Drinking too much is also a mistake. Over-drinking during long events can cause exercise-associated hyponatremia (low blood sodium), which is more dangerous than mild dehydration. During exercise, drink to thirst rather than forcing a schedule, and never drink more than you sweat. A sweat rate test tells you where that limit is.
Mistake #9: cutting carbs too early in taper
Taper means reduced training volume, not reduced carb needs. Your body still needs fuel to absorb training adaptations.
Maintain carb intake while reducing volume — this is the time to top off glycogen stores, not deplete them.
Also, one big pasta dinner the night before is not carb loading. Topping off glycogen takes 2–3 days of higher carbs, roughly 7–10 g per kg of body weight per day, spread across every meal. Cramming it into one dinner mostly leaves you bloated on race morning.
Mistake #10: ignoring individual differences
What works for your training partner might not work for you. Sweat rate, gut tolerance, and carb needs vary significantly between athletes.
Don't copy professional athletes' nutrition strategies. Experiment to find what works for your unique body.
The gaps between athletes are big. These are typical ranges:
Sweat rate
Typical range0.5–2.5 L per hour
What it changesHow much you drink
Sweat sodium
Typical range20–80 mmol/L
What it changesHow much sodium you add
Carb tolerance
Typical range30–90 g per hour
What it changesHow many carbs you take in long sessions
Factor
Typical range
What it changes
Sweat rate
0.5–2.5 L per hour
How much you drink
Sweat sodium
20–80 mmol/L
How much sodium you add
Carb tolerance
30–90 g per hour
How many carbs you take in long sessions
You can build a simple profile from three numbers: your sweat rate from a weigh-in before and after a run, the carbs per hour you can take without stomach trouble, and whether you are a salty sweater. White, gritty marks on your kit are a rough hint, not a measurement.
Copy how pros plan, not what they eat: carbs matched to each session, a race plan tested in training, and a set recovery routine. Generic guidelines are a fine starting point for beginners and short, easy sessions. Personalizing matters more as your races get longer.
The myths behind these mistakes
Many of these mistakes start with advice that gets repeated in running clubs and forums. Here is what to do instead.
One big pasta dinner is carb loading
Raise carbs over the 2–3 days before the race (see Mistake #9)
Eat the same amount every day
Fuel the session, not the calendar: eat more on long and hard days and less on rest days
Fasted running burns more fat
Fine for easy runs under 60 minutes, but it hurts intervals, tempo runs, and long runs, and does not lead to more fat loss over time
You need a protein shake within 30 minutes
A normal meal with protein within about 2 hours works; carbs are the timing priority
You need gels for every run
Only needed for runs over about 90 minutes, or when you are deliberately training your gut
More protein is always better
Hit the daily target in Mistake #5; for endurance athletes, carbs are usually the bigger gap
Drink as much as you can during races
Drink to thirst, and use a sweat rate test so you never drink more than you sweat
Myth
What to do instead
One big pasta dinner is carb loading
Raise carbs over the 2–3 days before the race (see Mistake #9)
Eat the same amount every day
Fuel the session, not the calendar: eat more on long and hard days and less on rest days
Fasted running burns more fat
Fine for easy runs under 60 minutes, but it hurts intervals, tempo runs, and long runs, and does not lead to more fat loss over time
You need a protein shake within 30 minutes
A normal meal with protein within about 2 hours works; carbs are the timing priority
You need gels for every run
Only needed for runs over about 90 minutes, or when you are deliberately training your gut
More protein is always better
Hit the daily target in Mistake #5; for endurance athletes, carbs are usually the bigger gap
Drink as much as you can during races
Drink to thirst, and use a sweat rate test so you never drink more than you sweat
Fix the two that matter most first
Do not try to fix all ten at once — you will last a week. Instead, start with the two mistakes that cause the most damage for the least effort to correct: under-fueling overall, and skipping the post-workout window. For a fortnight, simply make sure you are eating enough to match your training (use the warning signs above as your gauge, not a calorie app) and that every hard session is followed within an hour by carbs plus 20-30g of protein. Those two changes alone resolve a surprising share of the fatigue, plateaus, and frequent illness that send athletes looking for answers. Once they are habits, work down the rest of the list one at a time.
Setting daily targets from your workload and reminding you of the recovery window is part of what a tool like Mavr does, so the mistakes are harder to make. But the two-fix starting point above needs no app — it is just a matter of deciding to eat enough and to refuel promptly.
Frequently asked questions (FAQ)
How do I know if I'm underfueling?
Track your intake for a week and compare to training load. Signs include persistent fatigue, declining performance, frequent illness, and inability to maintain weight.
What should I eat immediately after a workout?
Aim for 1.0–1.2 g/kg carbs and 20–30 g protein within 60 minutes. Examples: chocolate milk, Greek yogurt with granola, or a smoothie with fruit and protein powder.
How much sodium do I need during exercise?
Most athletes need 400–800 mg per hour, depending on sweat rate and conditions. Weigh yourself before and after training to personalize your needs.
Is it okay to try new foods during a race?
No. Test all race-day nutrition in at least three training sessions first. Race day is for executing a proven plan, not experimenting.
Does Mavr help with nutrition mistakes?
Yes. Mavr sets your carb and calorie targets from your training and times meals and recovery snacks around your workouts, so you can compare what you eat with what your training asks for.
Can I drink too much water while running?
Yes. Drinking far more than you sweat can cause exercise-associated hyponatremia (low blood sodium), which can be dangerous. Drink to thirst during exercise instead of forcing a schedule, and use a sweat rate test to learn your upper limit.
Is fasted running bad?
Not for easy runs under 60 minutes. For intervals, tempo runs, and long runs, running fasted makes the session harder and does not lead to more fat loss over time. Fuel your hard sessions.
Should I eat differently on training days and rest days?
Yes. Eat more carbs and calories on long and hard days and less on rest and easy days. Your daily intake should follow your training load instead of staying flat all week.
Can I eat fiber before exercise?
Small amounts of lower-fiber fruit are fine. Avoid large servings of high-fiber foods, beans, seeds, and cruciferous vegetables in the 2–3 hours before training, and eat them later in the day.
Can I still lose body fat while fueling well?
Yes. Fuel your key sessions properly, then eat a little less on lighter days. A modest deficit on easy days works better than underfueling hard training all week.
General guidance for healthy adults, not medical advice. Talk to a doctor or registered dietitian if you have a health condition, take medicines or have special dietary needs.
Mavr Sports Nutrition Team. The Mavr sports-nutrition team translates peer-reviewed endurance research (Jeukendrup, Burke, the ISSN) into daily fueling for runners and triathletes.
