Does Relative Energy Deficiency in Sport (RED-S) with iron deficiency, low cortisol, and normal ferritin levels make it hard to lose weight in a physically active 39-year-old woman?

Does RED-S Make Weight Loss Difficult?

Yes, RED-S with iron deficiency and low cortisol makes weight loss extremely difficult because the body's metabolic rate decreases as an evolutionary response to conserve energy during perceived starvation, creating a hypometabolic state that actively resists further weight loss. 1

The Metabolic Adaptation Problem

Your body is fighting against weight loss by lowering its resting metabolic rate (RMR). This is the core issue:

• Low energy availability in RED-S causes the body to reduce energy expenditure through metabolic adaptations, specifically decreasing RMR to conserve calories 1
• Female athletes with low energy availability (<30 kcal/kg fat-free mass/day) have significantly lower RMR compared to those with optimal energy availability (≥45 kcal/kg fat-free mass/day) 1
• Athletes with menstrual dysfunction have lower RMR than eumenorrheic athletes, indicating the severity of metabolic suppression 1

How Iron Deficiency Compounds the Problem

Iron deficiency worsens the metabolic slowdown in multiple ways:

• Iron deficiency impairs thyroid hormone synthesis (T4 production) and hepatic conversion of T4 to the active metabolite T3, further suppressing metabolism 1
• This shifts ATP production away from efficient oxidative phosphorylation to less efficient anaerobic pathways, reducing overall energy expenditure 1
• Iron deficiency suppresses growth hormone and IGF-1, which are important for maintaining metabolic rate 1

Important caveat: Your normal ferritin with iron deficiency is paradoxical. Ferritin is an acute-phase reactant that can be falsely elevated during stress or inflammation 2. Low TIBC typically indicates chronic inflammation rather than true iron deficiency 2. This suggests functional iron deficiency in the context of chronic energy restriction 2.

The Low Cortisol Factor

Low cortisol indicates severe hypothalamic-pituitary-adrenal (HPA) axis suppression:

• This represents advanced RED-S with HPA axis dysfunction from chronic energy deficiency 2
• Paradoxically, while acute energy deficiency typically increases cortisol, your low cortisol suggests the body has progressed to a state of adrenal suppression 2
• This further impairs metabolic function and makes weight loss physiologically counterproductive 2

Why Attempting Weight Loss Now Is Harmful

Attempting further weight loss in your current state will:

• Further suppress your already compromised metabolic rate 1
• Worsen hormonal disruptions affecting bone health, cardiovascular function, and immunity 1
• Increase risk of long-term health consequences including cardiovascular dysfunction and bone loss 1
• Potentially cause severe performance decline and further metabolic damage 3

The Clinical Approach

The priority is metabolic recovery, not weight loss:

• Increase energy intake to achieve at least 45 kcal/kg fat-free mass/day to restore metabolic function 1
• Reduce training volume temporarily to allow energy balance restoration 3
• Address iron deficiency with complete iron panel (serum iron, transferrin saturation, C-reactive protein) and thyroid function tests (TSH, free T4, free T3) 2
• Monitor RMR recovery as a marker of metabolic restoration 3

Critical pitfall to avoid: Do not interpret stable body weight as evidence that energy intake is adequate. Athletes with RED-S can maintain body weight while still having suppressed RMR and hormonal dysfunction 3. The goal is metabolic recovery, which paradoxically requires increasing energy intake despite concerns about weight 1, 3.