RED-S in Male Athletes: The Clinical Differential Most Sports RDs Are Missing

A 32-year-old male cyclist walks into the consult. He has been training 14-18 hours per week for three years. His weight has been stable at 68 kg on a 178 cm frame. His FTP has plateaued, then dropped 8% across the last six months. His resting heart rate has climbed from 42 to 51. His sleep is fragmented. His libido is "basically gone." His PCP ran a total testosterone six weeks ago, got 380 ng/dL, said "low-normal, you're getting older," and offered no further workup.

The lab report is technically correct. The clinical interpretation is wrong. This athlete is in male Relative Energy Deficiency in Sport — RED-S — and the testosterone reading is a downstream marker of chronic low energy availability, not a primary endocrine pathology. He doesn't need TRT. He needs an additional 600-800 kcal/day for 12-16 weeks and a training-load adjustment.

The missed-diagnosis pattern in male RED-S is structural. The IOC consensus statements have evolved to explicitly include men, but the [LEAM-Q questionnaire](/blog/screening-athletes-for-low-energy-availability) wasn't validated in men until 2021, the screening tools most RDs use were built on female-athlete data, and the symptom presentation in men diverges from the textbook female phenotype in ways that look more like "overtraining" than "energy deficiency." The male athlete in front of you doesn't have amenorrhea. He has dropped libido, dropped morning erections, dropped power output, and a quietly creeping resting heart rate.

This post is the male-RED-S clinical workup I run when the intake history surfaces the pattern. The symptom cluster the LEAM-Q catches but the standard intake doesn't, the four-biomarker primary panel, the differential against primary hypogonadism and overtraining syndrome (because mis-routing the case to a urologist for TRT is a common failure mode), the energy-availability prescription, and the monitoring cadence to confirm reversal.

Why male RED-S gets missed

Three structural reasons.

The female phenotype dominates the published case literature. RED-S grew out of the Female Athlete Triad framework — low energy availability, menstrual dysfunction, low BMD. Men have no menstrual function to lose, so the most visible clinical biomarker of the syndrome doesn't apply. The IOC's 2018 and 2023 consensus statements explicitly include men but the symptom checklists in most clinical references still read as female-default.

Male symptoms cross over with overtraining syndrome and primary hypogonadism. Dropped libido, fragmented sleep, decreased motivation, elevated resting heart rate, and performance plateau show up in three different syndromes the male endurance athlete might land in: RED-S, non-functional overreaching / overtraining syndrome, and primary hypogonadism. Differentiating them requires the energy-availability assessment the GP isn't trained to run.

Total testosterone in a male athlete is interpreted against a sedentary reference range. The lab reports "normal" at 300-1000 ng/dL. An endurance athlete's testosterone should sit in the mid-upper portion of that range — typically 500-800 — to support the training adaptation and recovery the sedentary number doesn't capture. A reading of 380 in a 32-year-old cyclist is a clinical signal even though the lab flag says it isn't. Without the [SOAP-note documentation](/blog/soap-notes-for-sports-dietitians) that captures the trend from a baseline reading 18 months earlier, the directionality gets lost.

Documenting male-RED-S risk as a standalone differential, distinct from "low T workup" or "overtraining workup," is the structural fix.

The male-RED-S symptom cluster

The LEAM-Q (Low Energy Availability in Males Questionnaire, Lundy 2022) is the closest thing to a validated screening instrument and the items it surfaces are the symptom checklist worth running through:

Reproductive function. Libido (decreased from baseline, not absolute level), spontaneous morning erections (frequency drop is the actionable signal), erectile function with partner, fertility concerns (most RD-stage athletes haven't tried to conceive, but if they have, time-to-conception and semen-analysis history matter).

Sleep. Time to fall asleep (often shortened paradoxically as cortisol drops), but more importantly: sleep fragmentation, early-morning waking, time-in-bed not equaling time-asleep, dropped sleep quality scores on wearables.

Mood and cognition. Decreased motivation to train (distinct from injury-related dread — this is global anhedonia toward training the athlete used to love), decreased concentration, increased irritability, mild depressive symptoms.

GI function. Constipation, bloating, decreased appetite (paradoxical — the energy-deficient athlete often has suppressed hunger cues, which compounds the problem), early satiety.

Thermoregulation. Feeling cold persistently (especially extremities — hands, feet, nose), wearing layers when peers are comfortable, dropped core temperature.

Recovery and training response. Elevated resting heart rate trend (10+ beats above baseline), dropped heart-rate-variability trend (the wearable signal is real and earlier than the resting-HR signal), increased perceived exertion at familiar workloads, slower recovery between sessions, plateau or regression in benchmark workouts.

Bone and connective tissue. History of stress reactions or stress fractures, recurrent tendon or ligament strains, bone tenderness on palpation of the tibia or femoral neck during clinical exam (RD scope is screening, not diagnosis — refer for imaging if positive).

A male endurance athlete checking 4+ of these clusters has a meaningful pre-test probability of RED-S. The biomarker panel confirms or excludes.

The four-biomarker primary panel

Order: total testosterone + free testosterone + LH/FSH + fasting morning cortisol. Add IGF-1 and free T3 as second-tier markers if the primary panel is equivocal.

Total testosterone. Athlete-appropriate target: ≥500 ng/dL for general training in adult male endurance athletes; ≥600 ng/dL for the 18-30 cohort. Below 450 in an under-35 endurance athlete is a clinical signal even if the lab reports "within reference range." Draw fasting, between 7-10 AM, on a non-training day to control for the diurnal variation.

Total testosterone alone is interpretively limited. SHBG can drift with caloric restriction and the bound-vs-free distribution can mask functional deficiency. Always pair with free testosterone or calculated bioavailable testosterone.

Free testosterone. Athlete-appropriate target: 80-200 pg/mL by direct assay, or calculated bioavailable testosterone via the Vermeulen formula using total T + SHBG + albumin. The direct-assay method is interlab-variable; the calculated method is more reliable across labs. Below 80 pg/mL with low-normal total testosterone is the signature of functional hypogonadism downstream of low energy availability — distinct from primary hypogonadism, which presents with elevated LH/FSH compensating for testicular failure.

LH and FSH. Athlete-appropriate target: low-to-mid reference range (LH 2-7 mIU/mL, FSH 2-7 mIU/mL). The pattern that matters: low or low-normal LH/FSH alongside low testosterone is hypothalamic-pituitary suppression — the RED-S signature. Elevated LH/FSH alongside low testosterone is primary testicular failure — the urology / endocrinology referral pathway, NOT a RED-S diagnosis.

This differential is the most important interpretive distinction in the workup. The TRT pathway is appropriate for primary hypogonadism. The energy-availability prescription is appropriate for hypothalamic suppression. Mis-routing a hypothalamically-suppressed athlete to TRT "fixes" the testosterone number but doesn't reverse the underlying energy deficit, leaves bone-mineral-density risk unaddressed, and creates iatrogenic dependence on exogenous testosterone for a problem that would have resolved with a sandwich-and-a-rest-day prescription.

Fasting morning cortisol. Athlete-appropriate target: 10-18 mcg/dL drawn at 7-9 AM. Elevated cortisol (>18) with the other signs is the chronic-stress-axis activation that accompanies sustained low energy availability. Suppressed cortisol (<8) is the late-stage HPA-burnout pattern — refer for endocrinology workup including ACTH stimulation if suspected.

Second-tier markers when the primary panel is equivocal

IGF-1. Athlete-appropriate target: mid-to-upper reference range for age. Suppressed IGF-1 in a male endurance athlete supports the energy-deficit differential. IGF-1 is a downstream marker of growth-hormone signaling and is sensitive to chronic caloric restriction.

Free T3. Athlete-appropriate target: 3.0-4.4 pg/mL. Suppressed free T3 with normal TSH and normal free T4 is the "euthyroid sick syndrome" / low-T3 syndrome pattern that accompanies sustained energy deficit. This is a metabolic-adaptation signal, not primary thyroid pathology — don't refer to endocrine for thyroid replacement.

Bone turnover markers (CTX, P1NP) and DXA bone density become relevant after 12+ months of suspected RED-S. Earlier-stage cases are caught and reversed before bone markers shift meaningfully. For the chronic-case athlete with stress-fracture history, the DXA reading + the bone-turnover ratio (P1NP/CTX) clarifies whether bone is in active deficit (low P1NP, normal-to-high CTX) versus stable.

The interpretation matrix

The four-biomarker panel produces a six-quadrant differential:

1. All four in athlete-appropriate range. RED-S is excluded as the dominant pathology. If symptoms persist, consider overtraining syndrome (workload + recovery audit), primary sleep disorder (refer for polysomnography), or psychiatric workup. Recheck biomarkers if training load changes.

2. Low total + free testosterone, low-normal LH/FSH, ± elevated cortisol, ± suppressed IGF-1/T3. Classic male-RED-S signature: hypothalamic suppression downstream of energy deficit. Energy-availability prescription is the treatment.

3. Low total + free testosterone, elevated LH/FSH. Primary hypogonadism. Refer to endocrinology / urology. NOT a RED-S diagnosis. The RD's role is the nutrition-adequacy backstop while the workup proceeds.

4. Low-normal testosterone, low-normal LH/FSH, normal cortisol, normal IGF-1, no LEAM-Q symptoms. Constitutional low-normal endocrine status without clinical RED-S phenotype. Monitor; don't intervene.

5. Normal testosterone, elevated cortisol, plateau performance, fragmented sleep. Overtraining syndrome differential. Workload and recovery audit is the lead intervention; energy-availability assessment runs in parallel because the two syndromes overlap.

6. Mixed signals, ambiguous panel. Repeat in 4-6 weeks under standardized draw conditions (same morning window, same fasting state, same training-load state) before committing to a differential. Single-draw biomarker interpretation in male athletes carries meaningful test-retest variance.

The energy-availability prescription

The IOC consensus and the male-RED-S literature converge on >40 kcal/kg fat-free mass/day as the energy-availability threshold for adaptive male athletic function. Below 30 kcal/kg FFM is overtly suppressive. The 30-40 range is the gray zone where individual variation determines outcome.

For a 68 kg cyclist with 12% body fat (≈ 60 kg FFM), the math:

• Current intake (from food log audit): ≈ 2800 kcal/day
• Training expenditure (from validated power-meter data, not the wearable estimate per [estimating exercise energy expenditure](/blog/estimating-exercise-energy-expenditure-when-wearables-lie)): ≈ 1100 kcal/day average
• Energy available: ≈ 1700 kcal/day = 28 kcal/kg FFM
• Target for restoration: 40+ kcal/kg FFM = ≥ 2400 kcal/day energy available = ≈ 3500 kcal/day total intake at the same training load

The prescription is a 600-800 kcal/day intake increase, sustained for a minimum of 12 weeks, with the increase distributed across the day rather than dumped into one mega-meal the athlete can't tolerate. Carbohydrate intake gets the largest absolute increase because chronic LEA athletes are typically more carbohydrate-restricted than protein- or fat-restricted, and because the muscle-glycogen replenishment that drives training adaptation is the most carb-dependent recovery process.

Training-load reduction is a parallel lever. Cutting 15-25% of weekly volume for the first 4-6 weeks of restoration speeds the biomarker reversal without sacrificing the long-term training base. Pure intake-increase without training-load adjustment works but takes 50-80% longer to reverse.

Monitoring cadence

Week 0: Baseline four-biomarker panel + LEAM-Q + body-composition reading via the [body-composition-reports-as-bayesian-priors](/blog/body-composition-reports-as-bayesian-priors) protocol.

Week 4: Symptom recheck (LEAM-Q items expected to start shifting: libido, morning erections, sleep quality, training motivation). Biomarkers not yet expected to fully normalize but trend should be visible. Compliance audit on the intake prescription via the [member compliance auditing](/blog/member-compliance-auditing-in-sports-nutrition) protocol — under-eating the prescribed increase is the most common failure mode.

Week 8: Repeat four-biomarker panel. Expect testosterone to be moving toward target; LH/FSH should be normalizing; cortisol should be dropping if previously elevated. If no movement at 8 weeks under documented compliance, escalate to endocrinology referral — the differential may have been misclassified.

Week 12-16: Full panel repeat. Target: all four primary biomarkers in athlete-appropriate range AND symptom resolution AND performance trajectory reversed. Athletes restored to this state can typically resume full training volume with periodic monitoring every 6 months.

When to refer out

Elevated LH/FSH with low testosterone at any panel → endocrinology / urology for primary hypogonadism workup.

No biomarker movement at 12 weeks under documented intake compliance → endocrinology for occult pathology screen (pituitary imaging, prolactin, ferritin if not yet drawn, celiac if not yet ruled out).

Suspected eating disorder phenotype (LEAM-Q items combined with body-image distortion, food-rule rigidity, exercise compulsivity) → behavioral-health referral. The energy-availability prescription doesn't reverse without the upstream psychiatric piece, and the RD's nutrition counseling alone is insufficient.

Bone tenderness or stress-reaction symptoms → sports medicine for imaging.

Common mistakes

Reading the testosterone alone and calling it "low-normal age-related decline." The reference range is sedentary; the directional change from baseline matters more than the absolute number; LH/FSH discrimination is non-negotiable.

Skipping the LEAM-Q symptom cluster. A biomarker panel without the symptom history is a snapshot. The symptom history is the differential.

Conflating overtraining syndrome and RED-S. They overlap but the lead interventions are different. Overtraining responds to load reduction alone; RED-S requires intake increase. Running the energy-availability calculation discriminates.

Routing male-RED-S to TRT. The exogenous testosterone normalizes the lab number but leaves the energy deficit, the bone-density risk, and the long-term metabolic adaptation untouched. It also creates iatrogenic dependence.

Prescribing the intake increase without auditing compliance. Athletes with sustained energy deficit often have suppressed appetite cues and food-rule rigidity that make a 600-800 kcal/day increase psychologically difficult. The compliance audit at week 4 is where most failed restorations get caught and rescued.

Drawing biomarkers post-training session. Acute exercise transiently elevates cortisol and shifts testosterone. Standardize draws to a non-training morning to remove the confound.

Skipping the contraception / supplement reconciliation. Some performance supplements (anabolic steroid contamination, prohormones, certain herbal stacks) confound the testosterone reading. The [supplement reconciliation](/blog/supplement-reconciliation-in-sports-nutrition-intake) workup catches this.

Where this lands in the SOAP

Objective section format:

```

Male-RED-S Differential Workup (drawn YYYY-MM-DD):

• Total testosterone: [value] ng/dL (target ≥500, ≥600 if <30yo)
• Free testosterone: [value] pg/mL or calculated bioavailable T: [value] ng/dL
• LH: [value] mIU/mL | FSH: [value] mIU/mL
• AM cortisol: [value] mcg/dL
• IGF-1: [value] ng/mL (if drawn)
• Free T3: [value] pg/mL (if drawn)
• LEAM-Q positive items: [count and cluster]
• Energy availability estimate: [kcal/kg FFM/day]
• Differential: [RED-S / primary hypogonadism / overtraining / mixed / excluded]

```

Assessment integrates the biomarker pattern with the LEAM-Q symptom cluster and the energy-availability calculation. Plan documents the intake prescription, training-load adjustment, monitoring cadence, and any referrals.

Where platform tooling helps

The bottleneck in male-RED-S charting is the multi-biomarker interpretation alongside the energy-availability calculation alongside the LEAM-Q tracking alongside the differential against overtraining and primary hypogonadism. The cognitive load of holding all four pieces in working memory while the athlete is in the consult room is the structural friction that drops the male-RED-S phenotype off the differential entirely on busy days.

The leverage is a male-RED-S module that ingests lab results, runs the four-quadrant differential automatically, surfaces the LEAM-Q symptom cluster from the intake history, computes energy availability from the food log + training-load data the athlete is already logging, and flags the case for the RD's interpretive judgment with the underlying evidence already organized.

The RD's job becomes the differential call and the conversation, not the data marshalling.

The bottom line

Male RED-S is real, prevalent in endurance and weight-class sport, and routinely missed by both PCPs and sports RDs because the symptom presentation diverges from the female-default phenotype and the biomarker interpretation requires comparison to athlete-appropriate ranges rather than sedentary reference ranges. The four-biomarker primary panel — total T, free T, LH/FSH, AM cortisol — discriminates RED-S from primary hypogonadism and from overtraining syndrome. The energy-availability prescription, sustained 12-16 weeks alongside a training-load adjustment, reverses the syndrome in athletes whose differential was correctly classified.

If the current intake captures "male athlete, no concerns" and moves on, the practice is missing the male endurance athlete who has been losing 8% FTP and his libido across the last six months while his PCP told him it was age. Add the LEAM-Q symptom screen, the four-biomarker panel, the differential matrix, and the energy-availability prescription, and the male-athlete workup catches the cases the standard reference range hides.

[Calsanova's Dietitian plan](/signup?role=dietitian) ships a male-RED-S module with four-biomarker lab ingestion (PDF or direct lab integration), automatic differential classification against primary hypogonadism and overtraining patterns, LEAM-Q symptom tracking integrated into the intake form, energy-availability calculation from food log + training-load data, and a 12-week monitoring cadence with auto-scheduled rechecks. Start your 30-day free trial and turn the male-RED-S workup into a clinical record that catches the cases the standard low-T workflow misses.