Question 1

What is RED-S and why does it matter?

Accepted Answer

**Relative Energy Deficiency in Sport (RED-S)** is a syndrome caused by **low energy availability** — not eating enough to support both training and normal bodily function — with consequences across many body systems.

**The core concept: energy availability.** This is dietary energy intake minus the energy expended in exercise, leaving what remains for basic physiological function. When that remainder falls too low, the body **downregulates** systems it can survive without in the short term.

Crucially, this can happen **without an eating disorder and without being underweight**. Someone eating what appears to be a reasonable amount while training heavily can be in significant deficit, and athletes frequently are without realising.

**Why the terminology changed.** RED-S replaced the earlier **Female Athlete Triad** — low energy availability, menstrual disturbance and low bone density — because research showed the effects are far broader and **affect men as well**. The IOC introduced the term in 2014 and has updated the consensus since. The older framing led to men being overlooked entirely.

**What is affected:**

**Endocrine function.** Reproductive hormones fall — producing menstrual disruption or loss in women, and reduced testosterone in men. Thyroid function is suppressed.

**Bone health.** Reduced bone mineral density, and a substantially elevated risk of **stress fractures**. This is often the presenting problem, and damage can be permanent if it occurs during peak bone-building years.

**Metabolic rate** falls, which frequently confuses athletes trying to lose weight.

**Immunity**, with more frequent illness.

**Cardiovascular** and gastrointestinal effects.

**Psychological effects** — low mood, irritability, poor concentration.

**Performance**, which declines — endurance, strength, coordination, training response and recovery all worsen. This is the irony: under-fuelling to improve performance impairs it.

**Who is at risk:** endurance athletes, weight-category sports, aesthetic sports, and anyone increasing training without increasing food.

**Warning signs:** recurrent injury, frequent illness, stalled performance, poor recovery, disrupted sleep, and menstrual changes.

**Seek specialist help** — sports physician and dietitian.

Question 2

Does cardio interfere with strength and muscle gains?

Accepted Answer

It can — the phenomenon is called the interference effect — but the magnitude depends heavily on how much, what type, and how it is scheduled, and for most people training recreationally it is small

Question 3

How does sleep affect training, recovery and appetite?

Accepted Answer

More than almost any other recoverable variable. Sleep restriction measurably degrades performance, adaptation, appetite regulation and injury risk simultaneously, and it is the recovery input people

Question 4

How does the menstrual cycle affect training?

Accepted Answer

Measurably for some people and negligibly for others — and the honest summary is that the individual variation exceeds the average effect, which is why cycle-based training programmes are promoted

Question 5

How does exercise affect bone density?

Accepted Answer

Bone is living tissue that responds to load — it adds material where it is stressed and loses it where it is not, which makes the right kind of exercise one of the few things that genuinely builds

Question 6

Why does weight loss slow down even when you keep eating the same?

Accepted Answer

Because the target moves. A calorie deficit is the difference between what you eat and what you burn, and the amount you burn falls as you lose weight — so the same intake produces a progressively

Question 7

Is running bad for your knees?

Accepted Answer

The evidence says no — and in fact points the other way. Recreational running is associated with lower rates of knee osteoarthritis than a sedentary lifestyle. What the research found. Multiple

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