What Is RED-S?

Why Eating “Healthy” and Exercising More Can Sometimes Work Against Your Body
By Dr. Stefania Tiveron ND
“I’m eating well. I train five or six days a week. I’m doing everything I’m supposed to do… so why am I exhausted?”
It’s a conversation I have more often than you might expect.
Sometimes the person sitting across from me has stopped getting their menstrual cycle. Sometimes they’re constantly injured, can’t recover between workouts, or feel like their metabolism has “slowed down.” Others are frustrated because they’re eating less, exercising more, and somehow feel worse. Not better.
Many have already searched online. They’ve wondered if it’s their thyroid, hormones, cortisol, iron, or even perimenopause.
Sometimes those questions are worth exploring.
But sometimes, the answer is something much less talked about.
It’s called Relative Energy Deficiency in Sport (RED-S).
Despite its name, RED-S isn’t limited to elite athletes. In fact, many recreational exercisers and health-conscious individuals are at risk without ever realizing it.

It’s Not About Whether You’re Eating “Enough”
One of the biggest misconceptions about RED-S is that it only affects people who are starving themselves or who have an eating disorder.That’s simply not true. Many people with RED-S eat what most of us would consider a healthy diet. They prioritize protein, vegetables, whole foods, and limit processed foods. They genuinely care about their health.
The problem isn’t necessarily the quality of the diet. The problem is that their body’s energy demands have quietly outgrown their energy intake.

Think of your body like a household budget. Every day you have energy coming in through food. That energy has to pay for a surprising number of expenses:
keeping your heart beating
breathing
maintaining body temperature
supporting your immune system
repairing muscles
building (and breaking down) bone
producing hormones
thinking, concentrating, and remembering
regulating mood
digesting food
recovering from exercise
managing everyday life stress

Exercise is just one line on the budget. If there isn’t enough energy left after all of these demands are met, your body has to make decisions about where to cut spending. And that’s exactly what it does. Your Body Isn’t Failing. It’s Adapting. This is one of the most important ideas I hope people understand.

RED-S isn’t a sign that your body is broken. It’s evidence that your body is incredibly intelligent.
From your body’s perspective, ovulation, building muscle, maintaining bone density, and producing optimal levels of thyroid hormone are expensive processes. They’re wonderful when resources are plentiful.
They’re less important when energy is scarce. So your brain begins reallocating resources.
Instead of investing in reproduction, recovery, muscle growth, and long-term health, it shifts toward immediate survival. That explains why RED-S affects so many different body systems at once. Rather than viewing low thyroid hormones, missing periods, recurrent injuries, and fatigue as unrelated problems, I think of them as different expressions of the same underlying adaptation.

Your body isn’t broken. It’s conserving energy.

Why “Eat Less, Move More” Doesn’t Always Work
Most of us have heard some version of this advice: Eat less. Move more.
For some people, a temporary calorie deficit can absolutely support healthy weight loss.
But context matters.

What happens when someone is already exercising five or six days a week, walking 12,000 steps per day, working a demanding job, sleeping six hours per night, and trying to stay in a calorie deficit?
Eventually, the body adapts.
Resting metabolic rate begins to decrease.
Recovery slows.
Hormones shift.
Training adaptations become less effective.
The body becomes more efficient at conserving energy.

Many of my patients describe this as feeling like their metabolism is “broken.” In reality, it isn’t broken at all.
It’s adapting exactly as it was designed to. One thing I often explain in practice is that the body isn’t a calculator. It’s a living, dynamic system whose first priority is survival (not achieving a particular body composition goal). It could care less about our body composition goals. Sometimes the path toward better health, improved performance, or even sustainable fat loss isn’t pushing harder. It’s creating enough physiological safety that the body no longer needs to conserve every available calorie.

Who Can Develop RED-S?
Although RED-S was first described in high-level athletes, it can affect anyone whose energy intake consistently falls short of their energy needs.
That includes:
endurance athletes
recreational runners
CrossFit athletes
strength athletes
dancers
cyclists
adolescents who are still growing
individuals intentionally dieting
people tracking calories or macros
anyone whose training volume has increased without adjusting nutrition

One thing that surprises many people is that recreational athletes may actually be at higher risk than elite athletes.
Elite athletes often have coaches, sports dietitians, and structured recovery plans.
Many recreational exercisers are trying to figure everything out on their own while balancing careers, families, poor sleep, and life stress. Stress matters. Your body doesn’t distinguish between the stress of a difficult workout, a demanding job, poor sleep, or emotional strain. They all increase the body’s overall energy demands.

Why RED-S Can Look Like So Many Different Conditions. One reason RED-S is often missed is because its symptoms overlap with many other health conditions. People may wonder if they have:
hypothyroidism
iron deficiency
adrenal dysfunction
overtraining syndrome
burnout
depression
perimenopause
chronic fatigue

Sometimes those conditions are present. Sometimes they’re contributing. But sometimes they’re actually downstream consequences of low energy availability. That’s why it’s important not to focus on one symptom in isolation.
Instead, we need to ask a better question: Why is the body making these adaptations in the first place?

The Hormones That Change—and Why

When energy availability stays low for weeks or months, several hormonal systems begin changing together.
The reproductive system is often one of the first. In females, estrogen, progesterone, LH, and FSH levels shift, leading to irregular or absent menstrual cycles. This isn’t because the ovaries suddenly stop working. It’s because the brain has decided that reproduction isn’t a priority while energy is limited. Many people are surprised to learn that estrogen does much more than regulate the menstrual cycle. It also supports:

bone density
cardiovascular health
brain function
mood
muscle recovery
connective tissue health

That’s one reason why an absent menstrual cycle should never be dismissed as a normal consequence of training.
The thyroid also adapts. One hormone in particular, Free T3 (the active thyroid hormone), often decreases.
This is sometimes called low T3 syndrome. Unlike primary hypothyroidism, the thyroid gland itself isn’t necessarily diseased. Instead, the body intentionally slows metabolism to conserve energy. As energy availability improves, this adaptation often reverses. Other hormonal adaptations may include: Altered cortisol patterns, reflecting activation of the body’s stress response. Changes in appetite-regulating hormones, including lower leptin and alterations in ghrelin, which can increase hunger and signal to the brain that energy is scarce. Changes in gut hormones involved in digestion, satiety, and energy regulation, which may influence appetite, gastrointestinal function, and how the body responds to food. Disrupted growth hormone and IGF-1 signaling, reducing the body’s ability to build and repair muscle and bone.
Lower testosterone levels, which can contribute to reduced libido, slower recovery, and decreased muscle protein synthesis.

Together, these hormonal changes affect far more than athletic performance. They influence how you feel day to day—your energy, mood, recovery, appetite, digestion, body composition, and even your ability to adapt to training.
Although these changes can feel alarming, they’re best understood as coordinated survival adaptations rather than signs that the body is permanently damaged. In many cases, these changes improve once adequate energy availability is restored.

It’s Not Just Female Athletes
Missing periods are one of the clearest warning signs in females, but RED-S affects males too. Men may notice:
reduced libido
declining performance
slower recovery
recurrent injuries
persistent fatigue
Because there isn’t an obvious marker like the menstrual cycle, RED-S in males often goes unrecognized for longer.

How I Think About RED-S in Practice
When I suspect RED-S, I’m rarely looking for one abnormal lab value. I’m trying to understand the whole picture.
That conversation often includes questions about:
training volume and intensity
recent increases in exercise
recovery habits
sleep quality
stress levels
menstrual history
injuries
digestive symptoms
eating patterns
food fears or rigid food rules
body image
energy throughout the day
fueling before and after workouts

Lab work can be helpful, but laboratory values are only one piece of the puzzle. One important thing to understand is that “normal” doesn’t always mean “optimal.” Someone with RED-S may have hormone levels that technically fall within laboratory reference ranges while still being meaningfully suppressed relative to what we’d expect for their age, symptoms, and physiology. Clinical context matters. The goal isn’t simply to treat a lab value.
It’s to understand why the body is responding the way it is.

Can Supplements Fix RED-S?

As a naturopathic doctor, this is a question I hear frequently.
Supplements certainly have a role in supporting recovery when appropriate.
If someone is deficient in iron, vitamin D, calcium, or vitamin B12, correcting those deficiencies can improve health and support the recovery process. But supplements cannot replace adequate energy intake. No combination of vitamins, minerals, herbs, or adaptogens can convince the body that food scarcity has ended if it continues to receive insufficient fuel. In other words, supplements may support recovery. They don’t replace it.
The foundation is always restoring adequate energy availability.

Recovery Isn’t About Doing Less—It’s About Giving Your Body More. For many people, recovery involves a mindset shift.
Instead of asking:
“How can I burn more?”
The question becomes:
“How can I support my body so it can adapt, recover, and perform the way I want it to?”
That often includes:
eating enough to match training demands
prioritizing healthy carbohydrates around exercise
allowing adequate recovery between sessions
improving sleep
reducing unnecessary training volume when appropriate
addressing stress outside the gym
working with healthcare professionals who understand both sports performance and overall health

Many patients are understandably anxious about eating more or training less. Yet one of the most rewarding parts of caring for people with RED-S is watching that fear gradually give way to renewed energy, stronger performance, better recovery, and often a healthier relationship with food and exercise.

The Bottom Line
One of the biggest lessons RED-S teaches us is that the body is remarkably intelligent.
When energy becomes scarce, it doesn’t stop working. It starts prioritizing.
The symptoms that develop aren’t signs that your body is failing. They’re signs that it’s trying to protect you.
The encouraging news is that these adaptations are often reversible.
With adequate fueling, thoughtful training, and individualized care, many people can restore hormone function, improve recovery, strengthen bone health, and return to doing the activities they love.
If you’re training hard but finding that your energy, recovery, performance, or hormones aren’t keeping pace, it may be worth asking a different question.
Not “What’s wrong with my body?” But rather,
“Is my body getting everything it needs to do everything I’m asking of it?”
Sometimes, that simple shift in perspective changes everything.