If you’re here because your kid is training hard, but something feels “off,” you’re not alone. A lot of us have watched a young athlete get slower, more tired, or more injured… even while doing “all the right things.” One big reason can be RED-S—when a kid’s food intake does not match what their body burns in sports and growth. And here’s the tricky part: RED-S can happen in boys and girls, and it often shows up in athletes who look totally “normal” on the outside.
This guide will help you spot early warning signs, understand what’s really going on, and know what to do next—without turning food into a fight.
1) What RED-S is (and why parents should care)
RED-S in plain English
RED-S stands for Relative Energy Deficiency in Sport. It’s a big medical term for a simple problem:
Your athlete doesn’t have enough fuel left over after training to run their body well.
That “fuel gap” is called low energy availability. Energy availability means:
Food energy in minus exercise energy out = what’s left for growth, hormones, bones, and recovery.
According to the American Academy of Orthopaedic Surgeons (AAOS), RED-S can affect many body systems—not just weight or periods—and it can raise injury risk, especially bone stress injuries like stress fractures. (AAOS RED-S overview: https://orthoinfo.aaos.org/en/diseases--conditions/relative-energy-deficiency-in-sport-reds/)
Why it matters in youth sports
Kids are not small adults. They need energy for:
- Practice and games
- Growth spurts
- Brain development
- Puberty and hormones
- Building strong bones for life
So when fuel is low, the body starts “saving energy” by turning down things that don’t feel urgent—like bone building, hormone function, and recovery. That’s where performance drops and injuries creep in.
RED-S is not just an “underweight” problem
This is important: RED-S can happen at any body size. Some athletes restrict food. Others are just super busy and under-eat by accident. Some train so much that normal meals don’t keep up.
The National Eating Disorders Association (NEDA) also points out that RED-S can overlap with disordered eating, but it can also happen without a diagnosed eating disorder. (NEDA RED-S resource: https://www.nationaleatingdisorders.org/relative-energy-deficiency-in-sport-red-s/)
2) Background: RED-S, low energy availability, and disordered eating athletes
Low energy availability: the “math” behind RED-S
Let’s break it down with a simple example.
- Your 14-year-old burns about 2,200 calories/day just living (school, walking, normal body function).
- Practice adds 500 calories on a hard day (this can vary a lot by sport and body size).
- Total need that day might be around 2,700 calories.
If they only eat 1,900 calories (skipping breakfast, small lunch, “clean eating,” no snacks), they’re short by 800 calories.
That’s low energy availability. Not for one day—but if it becomes a pattern, the body adapts in ways that hurt health and performance.
RED-S vs “female athlete triad”
You may have heard of the “female athlete triad” (low energy, missed periods, low bone density). RED-S is the newer, broader idea. It includes:
- Boys and girls
- More body systems (immune system, heart, mood, digestion)
- Performance effects (slower times, poor recovery)
Where disordered eating fits in
Disordered eating athletes can include a wide range of behaviors, like:
- Skipping meals to “stay lean”
- Cutting food groups (carbs, fats) out of fear
- Using extra workouts to “earn” food
- Feeling guilty after eating
- Obsessive tracking or weighing
Not every athlete with RED-S has disordered eating. But RED-S and disordered eating often travel together, especially in sports with weight, leanness, or aesthetics pressure (distance running, gymnastics, dance, wrestling, cheer, figure skating).
3) Main Content 1: Early warning signs (often before weight changes)
The signs parents actually notice first
Most parents don’t notice “low energy availability.” We notice the results:
Performance + recovery
- Gets tired faster than usual
- Slower sprint times, worse endurance
- Can’t hit normal training numbers
- “Always sore”
- Needs more days to recover
Injuries
- Repeated overuse injuries (shin pain, foot pain, hip pain)
- Tendon pain that won’t calm down
- Stress fractures or “bone stress injuries” (big red flag)
If stress fractures are on the table, it’s worth reading our deeper guide on stress fractures in young athletes and recovery timelines. Stress fractures are one of the classic RED-S warning signs.
Illness + energy
- More colds than teammates
- Gets sick and stays sick longer
- Looks wiped out after school before practice even starts
Mood + focus
- More irritable or anxious
- Low mood
- Trouble focusing in class
- “Not themselves”
Sleep
- Trouble falling asleep
- Waking up hungry at night
- Sleep doesn’t feel refreshing
Menstrual changes are a late sign (not an early one)
For girls, missed or irregular periods can be part of RED-S—but it’s often later in the process. So if a coach says, “She still has her period, so she’s fine,” that’s not a safe rule.
AAOS notes that RED-S affects hormones and bone health. Waiting for menstrual changes can mean you’re waiting until the body has been under-fueled for a while. (AAOS: https://orthoinfo.aaos.org/en/diseases--conditions/relative-energy-deficiency-in-sport-reds/)
Boys can have RED-S too (and it’s easy to miss)
Boys don’t have an obvious monthly signal. Signs can look like:
- Lower morning energy
- Drop in strength gains
- More injuries
- Low mood
- Less interest in food
- Slower growth or delayed puberty (sometimes)
If your son is training hard and “eating like a bird,” it’s worth paying attention.
4) Main Content 2: How RED-S happens in real youth sports life
Scenario A: The “busy kid” who under-eats by accident
This is super common in middle school and early high school.
A day might look like:
- 6:30am: out the door, no breakfast
- 10:30am: small snack
- 12:00pm: quick lunch (maybe 500 calories)
- 3:30pm: practice
- 6:30pm: dinner
- 9:00pm: too tired, skips evening snack
They aren’t trying to restrict. They’re just busy. But the body still gets the same message: not enough fuel.
If your athlete is also dealing with lots of training load (how much total work they do), check our guide on overuse injuries and how much sports is too much. Under-fueling plus high training is a common combo behind RED-S.
Scenario B: The “clean eating” trap
Some athletes start cutting:
- Carbs (“carbs make you slow”)
- Fats (“fat makes you fat”)
- Full meals (“I’ll just snack”)
But athletes need carbs for training fuel and fats for hormones and growth. When those drop, RED-S risk goes up.
Scenario C: Weight pressure (even if nobody says “lose weight”)
Sometimes the pressure is subtle:
- Comments about “leaning out”
- Team weigh-ins
- Uniform fit
- Social media “what I eat in a day”
- Comparing bodies in the locker room
This is where disordered eating athletes can develop. The athlete may still eat “healthy” foods, but not enough total energy.
Scenario D: Making weight sports and “cutting”
Wrestling, rowing, some martial arts, and even certain track events can bring weight pressure. Rapid weight cuts are risky for hydration, growth, and mental health. RED-S can show up when cutting becomes a season-long pattern.
If your athlete’s sport includes weigh-ins, you’ll want a plan with a sports medicine doctor and a sports dietitian (RD). The goal is performance and safety, not just a number.
5) Practical Examples (with real numbers and “what would you do?”)
Example 1: 12-year-old travel soccer player (busy + growth spurt)
Athlete: 12 years old, practices 3x/week + weekend games
Training day estimate:
- Daily needs (normal day): ~1,800–2,000 calories
- Practice adds: ~300–500 calories
- Total: ~2,200–2,500 calories
What they’re actually eating (common pattern):
- Breakfast: skipped (0)
- Lunch: sandwich + chips (600)
- Pre-practice snack: none (0)
- Dinner: chicken + veggies (600)
- Total: 1,200 calories
Fuel gap: 2,300 needed − 1,200 eaten = 1,100 calories short
What you might see:
- “Legs feel heavy”
- More ankle and knee pain
- Can’t recover by the next practice
Fix (simple, not perfect):
- Add breakfast: yogurt + granola + banana (~450)
- Add pre-practice snack: bagel + peanut butter (~350)
- Add bedtime snack: cereal + milk (~300)
That’s about 1,100 extra calories—which matches the gap. Often, symptoms improve fast when fueling improves.
For snack ideas, our best game day snacks for young athletes list is a lifesaver in the car.
Example 2: 15-year-old runner with recurring shin pain (classic RED-S pattern)
Athlete: 15, runs 35 miles/week
Signs:
- Shin pain that keeps coming back
- Resting heart rate creeping up
- Mood more anxious
- “Healthy eating,” but small portions
Common food issue: low carbs + low total intake
They may be eating lots of salads and protein, but not enough starch.
Why this matters: Bone stress injuries are strongly linked to low energy availability. AAOS specifically calls out bone health risks in RED-S. (AAOS: https://orthoinfo.aaos.org/en/diseases--conditions/relative-energy-deficiency-in-sport-reds/)
Parent move: Don’t just buy new shoes and hope. Ask for a sports medicine evaluation and a nutrition plan. Also consider reading our shin splints in kids guide to understand the injury side—then zoom out to the fueling side.
Example 3: 16-year-old volleyball player trying to “lean out”
Athlete: 16, club volleyball 4 days/week + lifting 2 days/week
Behavior changes:
- Skips team snacks
- Cuts out carbs at dinner
- Watches food videos, tracks calories
- Gets dizzy standing up sometimes
This is where disordered eating athletes can start. Even if weight hasn’t changed, RED-S risk can be high.
What helps:
- Talk about performance: “Fuel helps jumping and recovery.”
- Remove body talk at home (even “good weight loss” talk).
- Get help early. NEDA recommends professional support when RED-S or eating concerns are present. (NEDA: https://www.nationaleatingdisorders.org/relative-energy-deficiency-in-sport-red-s/)
Example 4: 13-year-old baseball player who “never seems hungry”
Athlete: 13, afternoon practice in heat
Pattern:
- Small lunch
- Practice
- Doesn’t want dinner
- Drinks lots of water but low food
Sometimes heavy training and heat blunt appetite. But the body still needs energy.
Quick win plan:
- Liquid calories can help: chocolate milk, smoothies, drinkable yogurt
- Add a recovery snack within 30–60 minutes after practice
If heat is part of it, pair this with our youth athlete hydration guide so you’re not mixing up dehydration and under-fueling.
6) Common mistakes and misconceptions (that keep RED-S going)
- “RED-S only happens to thin kids.” Nope. It’s about energy balance, not a look.
- “My kid eats healthy, so they’re fine.” Healthy foods are great. But total calories still matter.
- “Missing periods is the first sign.” It’s usually a later sign. Don’t wait for it.
- “More conditioning will fix the performance drop.” If the problem is low energy availability, more work often makes it worse.
- “This is just teen moodiness.” Sometimes it is. But fatigue + injuries + illness patterns deserve a closer look.
- “We’ll handle it at home.” Fueling changes help, but RED-S and disordered eating athletes often need a team approach.
7) Step-by-step: What parents and coaches should do next
Step 1: Start with a calm, performance-based talk
Pick a neutral time (not right after a game).
Try:
- “I’ve noticed you’re more tired and sore lately.”
- “I’m not mad. I want you to feel good.”
- “Can we look at your schedule and meals together?”
Avoid:
- “Are you starving yourself?”
- “You’re too skinny / you’re gaining weight.”
- Any comments about body shape.
Step 2: Do a simple 3-day “fuel and training” check
No judgment. Just data.
For 3 days, write down:
- Practice length and intensity (easy/moderate/hard)
- Meals + snacks (rough portions are fine)
- Sleep hours
- Any pain, fatigue, mood
You’re looking for patterns like:
- Long gaps with no food (6+ hours)
- No pre-practice snack
- No post-practice recovery snack
- Low breakfast intake
Step 3: Add “bookend” snacks around training
This is one of the easiest fixes.
- 1–2 hours before practice: carbs + a little protein
Examples: bagel + peanut butter, granola bar + milk, turkey sandwich - Within 60 minutes after: carbs + protein
Examples: chocolate milk, yogurt + fruit, rice bowl with chicken
This supports recovery and helps close the low energy availability gap.
For more structure, use our youth athlete meal plan guide.
Step 4: Get medical help sooner than you think
If you see signs like stress fractures, dizziness, fainting, rapid weight change, or obsessive food rules, bring in pros.
Look for:
- Sports medicine doctor (or pediatrician who knows athletes)
- Registered Dietitian (RD) with sports experience
- Mental health support if food anxiety or restriction is present
AAOS recommends medical evaluation for RED-S because it affects bone and overall health. (AAOS: https://orthoinfo.aaos.org/en/diseases--conditions/relative-energy-deficiency-in-sport-reds/)
Step 5: Adjust training load if needed (temporary is okay)
Sometimes the body needs a short reset:
- Reduce extra conditioning
- Add rest days
- Prioritize sleep
If you need help thinking through rest and recovery, our youth athlete recovery tips can guide you.
8) Key Takeaways / Bottom Line
RED-S (relative energy deficiency in sport) is what happens when a young athlete’s training and growth needs outpace their food intake. The core issue is low energy availability, and it can show up in boys and girls, often without obvious weight loss. Early signs are usually fatigue, poor recovery, more illness, and repeat overuse injuries—while menstrual changes in girls can be a late signal.
If you suspect RED-S or disordered eating athletes behaviors, focus on fueling for performance, not body shape. Track a few days, add smart snacks, and get help from sports medicine and a sports dietitian early. It’s not about blame. It’s about getting your kid healthy, strong, and enjoying their sport again.