Fueling the Mission: How to Eat While Training for Your First 50K
- Justin Biays
- Apr 24
- 11 min read
You want to train like a serious athlete? Start eating like one.
Most first-time ultrarunners are under-fueled — not under-trained. They hit their long runs, strength sessions, even some cross-training. They warm up well, execute their runs as written, and take their recovery seriously.
But their performance flatlines, their recovery tanks, and their energy crashes. Why?
Because they’re trying to train for a 50K on leftover fuel.
This article is your guide to fixing that. We’re not talking about elite-level sports nutrition or precision nutrient tracking. We’re talking about eating enough, eating smart, and eating with purpose for the everyday athlete with a life outside of running - who still wants to chase excellence. (If you are signed up for your first ultra race, check out this article, From Registration to Race Day for a more comprehensive guide.)
Because if your training is the spark, your fuel is the flame; And without it, nothing burns.
We recommend reading this article all the way through so you can understand the full purpose + practicalities, but you can also jump to a section:
Daily Nutrition: You Can’t Train on Empty
Let’s get one thing clear: calories are not the enemy. If you’re running, lifting, and trying to prep for an ultra, you need to eat like you give a damn about performance — not just weight loss, body comp, or even maintenance.
At Dark Horse Athlete, we tell our runners to build their daily nutrition like they build their training blocks: intentional, progressive, and repeatable.
Calorie Balance
Calories in = energy out = recovery, performance, and adaptation.
We all know that calories balance matters for weight loss or weight gain. Generally speaking, eating more calories than you burn causes weight gain, and consuming less than you burn causes weight loss; but the game of endurance sports is a different beast entirely.
When you under-eat as an endurance athlete, your body isn’t just going to lose a little weight; your body slows down, your recovery sucks, and your training sessions start to suffer. Long-term under-fueling leads to hormonal dysfunction, muscle loss, poor sleep, and increased injury risk. That’s not even touching on the fact that you are going to lose as much (or more) muscle mass as fat mass, and likely feel like sh*t most of the time...just to name a few side effects outside of your actual running output.
However, this doesn’t mean that you need to track and count every gram of your intake, nor do you have to upend every nutrition habit you currently have.
But you do need to match your intake to your output. Here’s how:
Macronutrient Targets (General Guidelines)
Calorie balance is important, but by accounting first for macronutrients, we essentially hit two bird with one stone. Whether you’re an athlete or not, there are some general guidelines to macro intake that help us optimize health, wellbeing, and body composition. These guidelines become even more important when we are training extensively or have any sort of performance goals we’re looking to meet.
Protein: 0.8–1.0g per pound of bodyweight
Repairs muscle tissue, supports recovery
Carbs: 1.5–3.0g per pound depending on training volume
Primary fuel for running and lifting
Fats: 0.3–0.5g per pound
Supports hormone function, energy density, and satiety
This sounds like a lot of math initially, but if we consume 3–5 balanced meals per day and add a few snacks around training windows, we can land closer to our needs than we may think.
Prioritize real, whole foods 80–90% of the time — lean proteins, fruits, vegetables, whole grains, healthy fats. This will get you close. Track for a week or so, adjust and tweak as necessary. The goal here isn’t perfection, but ranges and inputting enough fuel more than anything.
The rest? Do what works for your body and lifestyle.
How to Eat Differently on Strength vs. Run Days
Your fueling doesn’t need to be the same every day — because your training isn’t the same every day. What you do in the gym vs. what you do on the trail places different demands on your body.
Once you’ve got some of your foundational nutrition habits down, here’s how we recommend adjusting your intake:
On Strength Training Days
Carb Needs: Moderate. You're not burning through as much glycogen as a long run, but you still need carbs to support power output and recovery.
Protein: Priority. Focus on a consistent protein intake to rebuild muscle tissue.
Fat: Can be slightly higher if total calorie demand is lower than on run days.
Sample Adjustments:
Stick to whole food meals.
You likely don’t need intra-workout carbs unless the session exceeds 75 minutes.
Prioritize a post-workout protein + carb meal to recover faster and reduce soreness.
(If you don't have strength training days in your programming, this is a massive misstep. Check out this article, "Stronger = Farther" on how + why to implement them in your own training.)
On Running Days
Carb Needs: Higher. Whether it’s intervals, a threshold run, or a long run — your body is tapping into glycogen stores heavily.
Protein: Still essential — especially for long runs that create muscle breakdown.
Fat: Keep lower around training windows for better digestion.
Sample Adjustments:
Add more carbs at breakfast before your run.
Use intra-run fuel for sessions over 75–90 minutes.
Replenish aggressively post-run with carbs and protein.
Hydrate and replace electrolytes more intentionally.
On Long Run Days
Eat like it’s race day. Use this as your chance to practice fueling strategy, hydration, and pacing.
Front-load and back-load carbs to stay ahead of fatigue.
Don’t skip your post-run recovery meal — ever.
Bottom line: Strength days build your chassis. Running days stress your engine. Both deserve different fueling strategies. Dialing in your intake based on the work you’re doing is the next step from “eating clean” to fueling like an athlete.
Fueling Around Training: Before, During, After
You wouldn’t go into a training session without a plan — so why go into one without fuel?
Here’s the thing: Nutrient timing is crucial for athletic performance because it aligns the intake of essential nutrients, particularly carbohydrates and proteins, with the body’s metabolic needs during different phases of exercise and recovery.
Proper nutrient timing ensures that athletes have the necessary fuel for optimal performance during exercise, reduces the risk of muscle breakdown, and accelerates post-exercise recovery.
Yes, overall intake matters most. But timing matters, too.
You can check out a more comprehensive guide on nutrient timing for performance in general in this article.
Here’s how to fuel the work of endurance sport training:
Pre-Workout Fuel (60–90 min before)
Goal: top off glycogen, stabilize energy, and avoid digestive issues.
Simple carb + light protein
Keep fat and fiber low
Examples:
Banana + whey protein
Toast with jam + egg whites
White rice + turkey breast
During Training (For Runs > 75–90 Minutes)
This is where most beginners screw it up. They try to “grind it out” without fueling mid-run — and end up bonking or dragging through the second half.
Carbs: 30–60g per hour
Hydration: 16–24 oz of fluid per hour
Electrolytes: 300–600mg of sodium per hour
Examples:
Carb gels (GU, Spring, Maurten, etc.)
Carb drink mixes (Tailwind, Skratch, etc.)
Real food (bananas, dates, pretzels, PB packs)
Electrolyte tabs or sports drinks
You have to practice this in training — don’t wait until race day to see what your stomach handles.
Post-Workout Fuel (Within 30–60 minutes)
Goal: jump-start recovery, replenish glycogen, support muscle repair.
Protein: 25–40g
Carbs: 40–80g
Low fat to speed digestion
Examples:
Whey protein + banana
Chocolate milk
Rice + lean protein
Oats + protein powder and berries
Keep in mind that these are general guidelines.
Factors like the athlete’s training state, the sport’s specific demands, the environment (i.e. temperature & humidity), as well as individual preferences and digestion can all influence optimal intake and timing.
But these benchmarks are a great place to start, test, and adjust as needed.
Long Run Fueling: Practice Like You’ll Race
Long runs are where you test more than your legs — you test your fueling strategy. If you plan to run your 50K with gels, then guess what? You need to train with gels. If you prefer real food, great — but you’d better find what actually digests well after 2 hours on the move.
You really do not want to be the person who has to DNF a race because your digestion is a disaster from trying a new race-day fueling strategy.
What to Practice:
Carb intake: 30–60g/hour (some athletes push 90g, but don’t start there)
Fluid intake: 16–24 oz/hour
Electrolyte replacement: ~300–600mg sodium/hour
Timing: Take your first fuel early (~30–45 min in), not after you start to fade
Format: Practice drinking, chewing, or swallowing while running or hiking
Fuel types to consider:
Carb gels
Carb drink mixes
Real food: bananas, rice cakes, baby food pouches, nut butter packets
Salt tabs (especially useful in heat or humid conditions)
You are going to find that some things work better than others for you than your running buddies. Some gel you try may make a run miserable. You might find you hate carb drink mixes but love baby food pouches and pickle juice.
There are tons of extremely specific fueling strategies out there simply because everyone is different - physiologically, psychologically, and in their preferences. Try out new things on shorter-mid-distance runs and slowly implement them into your longer runs. It may take some trial & error to figure out, but don’t wait until race day to “see what works.”
Train your gut just like you train your legs.
Hydration & Electrolytes: The Overlooked Performance Killers
Dehydration and electrolyte imbalance can tank a run faster than a bad pair of shoes. And no, just “drinking more water” doesn’t fix the problem.
You know how you have a remote control for your TV? It needs batteries to work. Think of electrolytes like the batteries for your body. They help send messages from your brain to your muscles so they can work optimally. Electrolytes are minerals—you might have heard of some of them, like sodium, potassium, and calcium. You can find them in lots of foods and drinks, like bananas, oranges, and even in sports drinks.
During endurance sports, you lose water, sodium, potassium, and magnesium through sweat — and if you don’t replace them, you risk cramps, nausea, dizziness, and in severe cases, hyponatremia. It's important to strike a balance, so here are some rules of thumb for ideal hydration:
General Guidelines:
Fluids: 16–24 oz per hour on long runs
Sodium: 300–600mg per hour (can go higher in hot/humid conditions)
Don’t wait until you’re thirsty — sip early and consistently
Alternate water with an electrolyte-enhanced drink mix or salt tabs
Monitor your sweat rate, weigh yourself before and after runs, and track how you feel.
Much like the calorie and carb fueling individualization we discussed in the previous section, the exact way in which you intake your electrolytes may vary from person to person. Test this too.
Hydration is personal — but ignoring it isn’t an option.
The Most Common Mistakes We See
You can have the perfect training plan, the best shoes, and elite-level genetics — but if you’re screwing up your fueling, none of those things even matter. These are the mistakes we see over and over again from beginner ultrarunners. Fix them, and you immediately put yourself ahead of the pack.
1. Under-eating — Especially on Long Run Days
This is the number one killer of progress. Athletes will eat light all week, then crush a two-hour long run on Saturday and still treat food like a cheat code they have to “earn.” That mindset doesn't belong here.
You burned 1,500+ calories on that run.
You have another training session in 24–48 hours.
You need to rebuild, not restrict.
Training without enough fuel is like trying to build a house with no lumber. You need raw materials — and calories are the material your body uses to recover and adapt.
2. No Post-Run Fuel
You finish your run. You shower. You get busy. You forget to eat.
Big mistake.
Your body is in a prime window to absorb and utilize nutrients within the first 30–60 minutes post-run. Skip that window, and:
Muscle protein synthesis slows down
Glycogen replenishment is delayed
Recovery takes longer
Fatigue starts to compound across the week
This doesn’t need to be complicated. A quick shake with carbs and protein. A real meal an hour later. Done.
3. Trying New Fuel on Race Day
This one never ends well. That's why this is the third time we're mentioning it.
Don’t roll up to the starting line with an untested gel brand, a new sports drink, or “that bar your buddy swears by” — unless you’ve already practiced with it in training.
Race-day gut issues are real. Vomiting, GI distress, cramping — all because you didn’t respect your fueling strategy.
Your stomach has to be trained, just like your legs. You don’t want surprises after mile 20.
4. Skipping Carbs Out of Fear of “Weight Gain”
Let’s be blunt: carbs are not your enemy. They’re your fuel.
If you’re training for a 50K — especially with a hybrid plan that includes both running and lifting — your body needs carbohydrates to:
Restore glycogen
Fuel anaerobic and aerobic output
Prevent muscle breakdown
Support recovery
The fear of weight gain from carbs is rooted in misinformation. If you’re eating high-quality, performance-based meals and matching your intake to your output, carbs won’t make you fat — they’ll keep you in the game.
5. Not Drinking Enough — or Only Drinking Water
Most beginners underestimate how much fluid and sodium they lose — especially on long runs or hot days. The result? They either don’t drink enough at all or they drink only water. Neither is sufficient.
Plain water can actually dilute your blood sodium levels and lead to hyponatremia — a potentially dangerous condition that causes nausea, confusion, cramping, or worse.
If you're running longer than an hour, especially in heat:
Bring a hydration pack or bottles
Add electrolytes to your fluids
Don’t wait until you’re thirsty to start sipping
Train your hydration strategy the same way you train your fueling.
6. Eating “Clean” but Not Eating Enough
Clean eating sounds great on paper — but if it means you're under-fueled, it's still a problem. If you're only eating salads, grilled chicken, and steamed broccoli, you're likely falling short on:
Carbs
Calories
Total volume
There's a difference between eating for aesthetics and eating for performance. One might keep you lean. The other helps you run 31 miles without breaking.
If your “clean eating” leads to energy crashes, poor sleep, or delayed recovery — it's time to reassess.
7. Fueling Only on Run Days — Not Strength Days
Another mistake we see: runners eat well around long runs but treat strength days like they’re optional in terms of nutrition.
Wrong.
Your strength training sessions:
Break down muscle tissue
Deplete glycogen (especially with volume work)
Require protein and carbs to recover
If you're skipping meals or undereating on lift days, you're leaving gains on the table and slowing your overall progress.
The Fix: Eat Like It Matters
These aren’t little slip-ups. These are habits that tank training blocks and crush race-day confidence. The fix isn't complicated — it’s discipline and awareness:
Fuel long runs like they’re race day
Rehydrate and refeed after every hard session
Respect strength days like you do run days
Practice your plan before you compete
Your body isn’t just logging miles. It’s adapting. Feed it what it needs.
Final Thoughts: Train Like an Athlete, Eat Like an Athlete
Fueling isn’t about chasing macros; It’s about preparing your body to handle real work. You can’t train hard and recover fast if you’re underfed, under-hydrated, or running on fumes.
Treat food like gear: it’s a tool. Use it strategically and it’ll elevate your training, your recovery, and your race-day performance. It may take some time to figure it out, and that’s okay.
Eat enough. Eat consistently. Eat with purpose.
You’re not just running — you’re becoming something more. And your fuel is part of the mission.
If you want 50k programming ready-to-go for you, check out our 20 Week 50k prep program. That’s how we build athletes who can not only run 50K — but come back wanting more.
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Stop training in circles. Start recovering like it matters. Perform like it counts.
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