By Karyn Guidry, Karyn Guidry Fitness
Most athletes think they have a training problem.
But in reality?
They often have a fueling problem.
I see this constantly with hybrid athletes, runners, HYROX competitors, and high-performing individuals:
They are training hard…
But not eating in a way that actually supports performance, recovery, or longevity.
The result often looks like:
- Constant fatigue
- Poor recovery
- Plateaued progress
- Low energy
- Brain fog
- Increased soreness
- Poor race performance
- Hormonal disruption
- Increased injury risk
And one of the most frustrating parts?
Many athletes do not even realize nutrition is the thing holding them back.
If you want to perform like an athlete, you need to fuel like one.
Because no amount of hard training can consistently overcome poor fueling.
Here are the biggest nutrition mistakes affecting performance and what to do instead.
This is by far the most common nutrition mistake I see in athletes.
Many athletes unintentionally undereat while simultaneously trying to:
- Run more
- Lift heavier
- Improve conditioning
- Recover faster
- Stay lean year-round
The problem?
Performance requires energy availability.
Hybrid training, endurance work, strength training, and high-output sessions all place a significant demand on the body because you are asking it to improve multiple systems simultaneously, including:
- Aerobic endurance
- Strength
- Muscular endurance
- Power output
- Recovery capacity
That requires fuel.
When athletes consistently underfuel, the body eventually starts compensating.
Signs You May Be Underfueling
If several of these sound familiar, inadequate energy intake may be affecting performance:
- Constant fatigue
- Poor recovery
- Heavy legs during training
- Brain fog
- Poor sleep quality
- Irritability
- Plateaued progress
- Decreased performance
- Increased cravings
- Hormonal dysfunction
A lot of athletes believe:
"If I eat less, I will get leaner and perform better."
But chronic underfueling often creates the opposite result.
It reduces training quality, slows recovery, limits adaptation, and increases stress on the body.
In many cases, athletes are not underperforming because of poor work ethic.
They are underperforming because they are under-recovered and under-fueled.
What To Do Instead
Eat enough to support your workload.
Performance nutrition is not about eating less.
It is about eating appropriately for the demands of your training.
The goal is not simply to survive training.
The goal is to adapt and improve from it.
One of the biggest misconceptions in fitness is that carbohydrates are bad.
For sedentary individuals, excessive carbohydrate intake can sometimes be problematic.
But for athletes?
Carbohydrates are fuel.
Your body stores carbohydrates as glycogen, which serves as the primary energy source during:
- Running
- Intervals
- HYROX training
- Strength training
- Conditioning sessions
- Higher-intensity exercise
When glycogen availability is low, performance usually suffers.
Low carbohydrate availability can contribute to:
- Early fatigue
- Poor recovery
- Reduced performance
- Low energy
- Increased perceived exertion
In practical terms, workouts feel harder than they should.
Recovery slows.
Performance drops.
And many athletes mistakenly assume they just need to push harder.
Signs You May Need More Carbohydrates
You may benefit from increasing carbohydrate intake if you consistently experience:
- Feeling flat during training
- Difficulty recovering between sessions
- Poor performance later in workouts
- Constant fatigue
- Intense cravings
- Difficulty sustaining intensity
Good Carbohydrate Sources for Athletes
Strong carbohydrate options include:
- Rice
- Potatoes
- Oats
- Fruit
- Rice cakes
- Bagels
- Pasta
- Toast
The most important factors are timing and total intake.
Carbs are not the enemy.
Poor fueling strategies are.
Protein plays an essential role in:
- Recovery
- Muscle repair
- Lean muscle retention
- Performance adaptation
- Body composition
Yet many athletes, especially endurance-focused athletes, underconsume protein without realizing it.
And when protein intake is too low, recovery quality often suffers.
Without enough protein:
- Recovery slows
- Muscle breakdown increases
- Strength progression stalls
- Hunger often increases
- Lean mass becomes harder to maintain
General Protein Recommendations for Athletes
Most active athletes tend to perform well around:
0.7 to 1 gram of protein per pound of bodyweight daily
This will vary slightly depending on training demands, body composition goals, and recovery needs, but it is a strong starting point for most athletes.
Quality Protein Sources
Good protein sources include:
- Chicken
- Lean beef
- Eggs
- Greek yogurt
- Protein powder
- Fish
- Cottage cheese
One of the easiest ways to improve recovery, body composition, and performance is simply becoming more consistent with protein intake.
Hydration affects nearly every aspect of athletic performance.
Yet many athletes are chronically underhydrated without realizing it.
Even mild dehydration can negatively affect:
- Endurance
- Strength output
- Recovery
- Focus and concentration
- Heart rate response
- Muscle contractions
And for hybrid athletes, runners, and HYROX competitors who sweat heavily or train for longer durations, hydration becomes even more important.
Signs You May Be Underhydrated
Common signs include:
- Headaches
- Fatigue
- Muscle cramps
- Dizziness
- Poor recovery
- Elevated heart rate during training
- Low energy
One of the biggest mistakes athletes make is thinking hydration simply means drinking more water.
But hydration is not just water intake.
It is fluid and electrolyte balance.
Why Electrolytes Matter
Electrolytes, especially sodium, play an important role in:
- Fluid balance
- Muscle function
- Performance output
- Nerve signaling
- Recovery
Athletes who sweat heavily, train outdoors, or complete long sessions often benefit from additional electrolytes to support performance and recovery.
Hydration is one of the simplest performance tools available.
Yet it is one of the most overlooked.
Many athletes train:
- Fasted
- Underfed
- After skipping meals
- With only caffeine
And while occasional fasted training may work for some lower-intensity sessions, high-intensity performance usually suffers without proper fuel.
Without adequate pre-training nutrition:
- Energy output drops
- Performance declines
- Recovery worsens
- Cortisol increases
- Sessions feel harder than they should
A lot of athletes assume training hungry improves fat loss.
But if fueling is too low, training quality usually suffers.
And when training quality suffers, long-term progress often slows.
Pre-Workout Nutrition Does Not Have To Be Complicated
Simple pre-training meals often work best.
Examples include:
- Banana + protein shake
- Rice cakes + honey
- Oatmeal + fruit
- Bagel + peanut butter
- Greek yogurt + granola
The goal is simple:
Provide accessible fuel for performance without creating digestive discomfort.
You do not need perfection.
You need consistency.
Supplements can absolutely support performance.
But they cannot replace:
- Sleep
- Hydration
- Consistent nutrition
- Structured training
- Recovery
Too many athletes spend time searching for:
- The best fat burner
- The best pre-workout
- The best recovery supplement
- The next performance shortcut
While ignoring the fundamentals that actually move performance forward.
This is one of the biggest mindset shifts athletes need to make:
Supplements should support a strong foundation, not replace one.
The basics still matter most:
- Protein intake
- Carbohydrate availability
- Hydration
- Electrolytes
- Recovery
- Sleep
Performance nutrition starts with consistency, not complexity.
Post-workout nutrition plays a major role in recovery quality.
After training, your body needs:
- Protein for muscle repair
- Carbohydrates to replenish glycogen
- Fluids and electrolytes for recovery
Athletes who regularly skip post-workout nutrition often experience:
- Slower recovery
- Increased soreness
- Reduced performance in future sessions
- Increased cravings later in the day
The goal is not perfection.
The goal is helping your body recover well enough to perform again.
Simple Post-Workout Meal Ideas
Recovery nutrition does not have to be complicated.
Simple options include:
- Protein shake + fruit
- Rice bowl + lean protein
- Greek yogurt + granola
- Sandwich + electrolytes
- Lean protein with rice or potatoes
Small improvements in recovery nutrition often create big improvements in performance consistency.
This is one of the biggest mistakes I see in performance-focused athletes.
Many athletes stay in a calorie deficit year-round because they are afraid of gaining weight.
But staying in a deficit too long often negatively impacts:
- Hormones
- Recovery
- Strength
- Endurance
- Sleep quality
- Energy availability
- Overall performance
You cannot expect peak athletic performance while chronically depriving your body of fuel.
There are seasons for:
- Performance
- Maintenance
- Fat loss
- Recovery
Trying to stay extremely lean year-round usually comes at a cost.
And that cost is often performance.
What To Do Instead
Match nutrition to your goal.
There are periods where body composition becomes the priority.
And there are periods where performance should lead.
The best athletes understand when to push and when to support recovery.
The biggest nutrition mistake athletes make is viewing food only through the lens of body composition.
Nutrition is not just about aesthetics.
Food is:
- Recovery
- Fuel
- Performance support
- Adaptation
- Longevity
The athletes who consistently perform at a high level usually do a few things very well:
- Fuel appropriately
- Hydrate intentionally
- Prioritize recovery
- Eat enough protein
- Time carbohydrates strategically
- Match nutrition to workload
If you want to train like an athlete…
You need to eat like one.