Study analysis · The Journal of clinical endocrinology and metabolism · 2023
Young male runners who don't eat enough to fuel their training may be sabotaging their bones — even though running is supposed to strengthen them.
In a small study, male runners with lower energy availability had weaker spine and shin bones than non-runners, while those who ate enough had stronger hips.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
In simple terms
This study is like a snapshot of male runners at one point in time. It shows that runners who eat less relative to exercise tend to have different bone measurements, but it can't prove that low eating caused the bone changes. We can only say they are linked, not that one causes the other.
What’s the bottom line?
Scientists studied 20 male runners and 19 non-runners. They checked how much energy the runners had left after exercise and looked at their bones with special scans.
How strong is this study?
The study used advanced bone scans and compared runners to non-runners, which is good. But it only looked at a small number of people at one time, so we can't be sure the results apply to everyone. It's a helpful clue, but not final proof.
75 / 100
- COI disclosure+40/40
- Data availability+35/35
- Code availabilitycode not shared
23 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=39)+3.5/20
- Follow-upno follow-up reported
100 / 100
23 / 100
- P-values+15/15
- Effect sizeno effect size reported
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
This design cannot establish causation — the findings describe an association, not a cause. Cross-sectional design measures exposure and outcome simultaneously, so temporal sequence cannot be established. Potential residual confounding, small sample size, and lack of incident bone stress injury data further prevent causal inference.
No Conflicts
No conflicts of interest identified
No conflicts of interest identified in the provided text. The excerpt lacks a funding or COI statement, and author affiliations are academic or government institutions.
The provided text is a partial excerpt (ending mid-Methods) and does not include the article's funding or conflict of interest declarations, which are typically located at the end. Author affiliations include Massachusetts General Hospital, Harvard Medical School, Boston Children's Hospital, Spaulding Rehabilitation Hospital, US Army Research Institute of Environmental Medicine, and Oak Ridge Institute for Science and Education, with no apparent industry ties. Absence of a COI/funding section in this excerpt prevents a definitive assessment.
Key takeaways
- 01
Runners who had less energy available had lower spine bone density: BMD Z-score −1.5 vs −0.8 in controls.
- 02
Runners with more energy available had higher hip bone density: Z-score 0.3 vs −0.4 in controls.
- 03
About 26% of runners (5 out of 19) had low energy availability.
- 04
These are absolute differences in BMD Z-scores, not relative risks.
- 05
The study did not report how many runners actually got a bone injury, so the absolute risk of fracture or bone stress injury per 1,000 runners is not known.
- 06
The 26% low-EA finding means about 1 in 4 runners in this small sample had low energy availability.
Surprising findings
- Running mileage was positively associated with bone at the hip, tibia, and even the non-weight-bearing radius, but low energy availability seemed to cancel those benefits.Many people assume more running either helps or harms bone depending on site. This study suggests the real switch may be whether you eat enough to match training.
- Estradiol, not testosterone, was positively associated with tibial failure load in male runners.Testosterone is often thought of as the main male hormone for bone. But in this study, estradiol and lean mass were linked to bone strength, while testosterone was not.
- Runners overall had lower lumbar spine BMD Z-scores than controls, but that difference disappeared after adjusting for BMI and calcium intake.It suggests the lower spine bone density in runners may be partly explained by lower body weight and calcium intake, not running itself.
- Higher serum sclerostin was associated with higher tibial and radial failure load in runners, even though sclerostin normally inhibits bone formation.Sclerostin is usually thought of as bad for bone, but in athletes it may reflect higher bone mass or a braking mechanism after repetitive loading.
Practical takeaways
If you're a male runner, avoid chronic large energy deficits. Aim to match your calorie intake to your training load, especially during high-mileage weeks.
This study is cross-sectional and cannot prove that eating more will prevent bone injuries. Energy availability was self-reported and only measured in runners. Absolute injury risk was not reported.
medium confidenceDon't assume that running alone protects your bones. Consider strength training and adequate muscle mass as part of a bone-health strategy.
The link between lean mass and bone strength is correlational. The study cannot prove that gaining muscle directly increases bone strength.
medium confidenceWatch for signs of low energy availability in young male runners: unintended weight loss, low body fat, fatigue, or performance decline. About 1 in 4 runners in this sample had low EA.
This was a small sample (n=39 total) and low EA prevalence was based on 19 runners with complete data. The study did not measure bone stress injury outcomes.
low confidenceIf you're a coach or parent, talk about fueling and bone health with male runners — not just female athletes. Low EA may impair bone microarchitecture at the tibia, a common stress injury site.
The study is observational and small. The authors call for larger longitudinal studies before making strong clinical recommendations.
medium confidenceWhy this study matters
Low energy availability hit 1 in 4 male runners
Among the 19 runners with complete diet/activity data, 26% (5 out of 19) had low energy availability, defined as less than 30 kcal/kg fat-free mass per day. That means about 1 in 4 young male runners in this sample were under-fueling relative to their exercise energy expenditure. The study did not report absolute risk of bone stress injury, so we cannot say how many actually got hurt.
Most people think low energy availability and RED-S are mainly female athlete issues. This shows it may be common in young male runners too.
Low-EA runners had lower lumbar spine bone density
Runners with energy availability below the median (<38 kcal/kg fat-free mass/day) had a mean lumbar spine BMD Z-score of -1.5 versus -0.8 in non-athlete controls (ABSOLUTE Z-score difference, P=0.028). This is not a relative risk; it is an absolute difference in standard-deviation units. It suggests their spine bone density was about 0.7 SD lower than controls.
The spine is not a weight-bearing site during running, so running alone may not protect it — especially if you're under-fueled.
High-EA runners had stronger hips than controls
Runners with energy availability at or above the median (≥38 kcal/kg fat-free mass/day) had higher total hip BMD Z-scores: 0.3 vs -0.4 in controls (ABSOLUTE Z-score difference, P=0.002). This suggests that when male runners eat enough, running may still give them a bone advantage at the hip.
It flips the narrative: running isn't bad for bones — under-fueling may erase the benefit.
Tibial bone microarchitecture was impaired in low-EA runners
After adjusting for calcium intake and weekly running mileage, runners with energy availability below the median had lower tibial total and trabecular volumetric BMD, trabecular bone volume fraction, cortical porosity, and apparent modulus compared with controls (P<0.05). The tibia is a common site for bone stress injuries in runners, so this is clinically relevant — but the study did not measure actual injuries.
Shin bone stress injuries are a runner's nightmare. This gives a possible mechanism: low energy availability may degrade bone quality at the shin.
Estradiol and lean mass — not testosterone — tracked with tibial strength
Among runners, appendicular lean mass (R=0.73, P=0.0002) and serum estradiol (R=0.45, P=0.046) were positively associated with tibial failure load, an estimate of bone strength. Testosterone was not associated. These are correlational findings, not proof of causation.
People often assume testosterone is the key male bone hormone. This study suggests estradiol and muscle mass may matter more for bone strength in male runners.
Want the whole report?
Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.
Overview
What the study found
The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists studied 20 male runners and 19 non-runners. They checked how much energy the runners had left after exercise and looked at their bones with special scans.
Research results
Runners who had less energy available had lower spine bone density: BMD Z-score −1.5 vs −0.8 in controls. Runners with more energy available had higher hip bone density: Z-score 0.3 vs −0.4 in controls. About 26% of runners (5 out of 19) had low energy availability.
What this means - more context
These are absolute differences in BMD Z-scores, not relative risks. The study did not report how many runners actually got a bone injury, so the absolute risk of fracture or bone stress injury per 1,000 runners is not known. The 26% low-EA finding means about 1 in 4 runners in this small sample had low energy availability.
Cross-sectional study asking whether male runners with lower energy availability (EA) have impaired bone mineral density, microarchitecture, and estimated strength compared with nonathlete controls.
In 39 men ages 16–30 (20 runners, 19 controls), runners with EA below the median had lower lumbar spine BMD Z-scores and, after adjustment, lower tibial total/trabecular volumetric BMD, trabecular bone volume fraction, cortical porosity, and apparent modulus vs controls. Runners with EA at/above the median had higher hip BMD Z-scores vs controls. About 26% of runners (5/19) had low EA (<30 kcal/kg fat-free mass/day). The study reports mean differences and correlations, not relative risks; absolute risk of bone stress injury was not reported.
Methods Used
Cross-sectional study at a clinical research center. Participants: 20 male runners (≥30 miles/week for ≥6 months) and 19 nonathlete controls, ages 16–30. Measures: DXA areal BMD, HR-pQCT tibial/radial volumetric BMD and microarchitecture, microfinite element estimated failure load, serum hormones, leptin, sclerostin, and 4-day food/activity records to estimate EA.
Main Finding
Male runners with lower EA had impaired skeletal integrity despite weight-bearing activity. Runners with EA below the median (<38 kcal/kg fat-free mass/day) had lower lumbar spine BMD Z-score (−1.5 vs −0.8 controls, P=0.028) and lower adjusted tibial total/trabecular volumetric BMD, trabecular bone volume fraction, cortical porosity, and apparent modulus vs controls (P<0.05). Runners with EA at/above the median had higher hip BMD Z-score (0.3 vs −0.4 controls, P=0.002). Appendicular lean mass and serum estradiol were positively associated with tibial failure load (R≥0.45, P≤0.046), but testosterone was not. Absolute risk of bone stress injury was not reported in this study.
Confidence Level
Limited by cross-sectional design (no causality), small sample size (n=39) and likely underpowering for HR-pQCT outcomes, self-reported diet/activity, no incident bone stress injury data, and no correction for multiple comparisons across many bone endpoints. No retraction or correction noted.
Study Flags
Red Flags
- •Cross-sectional design cannot prove causation
- •Small sample size (n=39) and likely underpowered for HR-pQCT outcomes
- •Self-reported diet and exercise; no incident bone stress injury outcomes
Surprising Findings
Running mileage was positively associated with bone at the hip, tibia, and even the non-weight-bearing radius, but low energy availability seemed to cancel those benefits.
Many people assume more running either helps or harms bone depending on site. This study suggests the real switch may be whether you eat enough to match training.
Practical Takeaways
If you're a male runner, avoid chronic large energy deficits. Aim to match your calorie intake to your training load, especially during high-mileage weeks.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Human Cross-Sectional
Subject
Moderate probability
on the GRADE evidence scale
This study is like a snapshot of male runners at one point in time. It shows that runners who eat less relative to exercise tend to have different bone measurements, but it can't prove that low eating caused the bone changes. We can only say they are linked, not that one causes the other.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Use of high-resolution peripheral quantitative computed tomography (HR-pQCT) and microfinite element analysis
- Inclusion of a non-athlete control group
- Comprehensive assessment of bone density, microarchitecture, and estimated strength
Weaknesses
- Cross-sectional design cannot establish causality
- Small sample size and underpowered for many outcomes
- Multiple comparisons without correction
Methodology
Evidence Keywords
Statistical Reporting
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
Scientists studied 20 male runners and 19 non-runners. They checked how much energy the runners had left after exercise and looked at their bones with special scans.
Research results
Runners who had less energy available had lower spine bone density: BMD Z-score −1.5 vs −0.8 in controls. Runners with more energy available had higher hip bone density: Z-score 0.3 vs −0.4 in controls. About 26% of runners (5 out of 19) had low energy availability.
What this means - more context
These are absolute differences in BMD Z-scores, not relative risks. The study did not report how many runners actually got a bone injury, so the absolute risk of fracture or bone stress injury per 1,000 runners is not known. The 26% low-EA finding means about 1 in 4 runners in this small sample had low energy availability.
Cross-sectional study asking whether male runners with lower energy availability (EA) have impaired bone mineral density, microarchitecture, and estimated strength compared with nonathlete controls.
In 39 men ages 16–30 (20 runners, 19 controls), runners with EA below the median had lower lumbar spine BMD Z-scores and, after adjustment, lower tibial total/trabecular volumetric BMD, trabecular bone volume fraction, cortical porosity, and apparent modulus vs controls. Runners with EA at/above the median had higher hip BMD Z-scores vs controls. About 26% of runners (5/19) had low EA (<30 kcal/kg fat-free mass/day). The study reports mean differences and correlations, not relative risks; absolute risk of bone stress injury was not reported.
Methods Used
Cross-sectional study at a clinical research center. Participants: 20 male runners (≥30 miles/week for ≥6 months) and 19 nonathlete controls, ages 16–30. Measures: DXA areal BMD, HR-pQCT tibial/radial volumetric BMD and microarchitecture, microfinite element estimated failure load, serum hormones, leptin, sclerostin, and 4-day food/activity records to estimate EA.
Main Finding
Male runners with lower EA had impaired skeletal integrity despite weight-bearing activity. Runners with EA below the median (<38 kcal/kg fat-free mass/day) had lower lumbar spine BMD Z-score (−1.5 vs −0.8 controls, P=0.028) and lower adjusted tibial total/trabecular volumetric BMD, trabecular bone volume fraction, cortical porosity, and apparent modulus vs controls (P<0.05). Runners with EA at/above the median had higher hip BMD Z-score (0.3 vs −0.4 controls, P=0.002). Appendicular lean mass and serum estradiol were positively associated with tibial failure load (R≥0.45, P≤0.046), but testosterone was not. Absolute risk of bone stress injury was not reported in this study.
Confidence Level
Limited by cross-sectional design (no causality), small sample size (n=39) and likely underpowering for HR-pQCT outcomes, self-reported diet/activity, no incident bone stress injury data, and no correction for multiple comparisons across many bone endpoints. No retraction or correction noted.
Study Flags
Red Flags
- •Cross-sectional design cannot prove causation
- •Small sample size (n=39) and likely underpowered for HR-pQCT outcomes
- •Self-reported diet and exercise; no incident bone stress injury outcomes
Surprising Findings
Running mileage was positively associated with bone at the hip, tibia, and even the non-weight-bearing radius, but low energy availability seemed to cancel those benefits.
Many people assume more running either helps or harms bone depending on site. This study suggests the real switch may be whether you eat enough to match training.
Practical Takeaways
If you're a male runner, avoid chronic large energy deficits. Aim to match your calorie intake to your training load, especially during high-mileage weeks.
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
Human Cross-Sectional
Subject
Moderate probability
on the GRADE evidence scale
This study is like a snapshot of male runners at one point in time. It shows that runners who eat less relative to exercise tend to have different bone measurements, but it can't prove that low eating caused the bone changes. We can only say they are linked, not that one causes the other.
No conflicts of interest were detected in this study. No score impact.
Strengths
- Use of high-resolution peripheral quantitative computed tomography (HR-pQCT) and microfinite element analysis
- Inclusion of a non-athlete control group
- Comprehensive assessment of bone density, microarchitecture, and estimated strength
Weaknesses
- Cross-sectional design cannot establish causality
- Small sample size and underpowered for many outcomes
- Multiple comparisons without correction
Methodology
Evidence Keywords
Statistical Reporting
Scoring
How strong is this study?
The study used advanced bone scans and compared runners to non-runners, which is good. But it only looked at a small number of people at one time, so we can't be sure the results apply to everyone. It's a helpful clue, but not final proof.
75 / 100
- COI disclosure+40/40
- Data availability+35/35
- Code availabilitycode not shared
23 / 100
- Randomizationnot randomized
- Blindingblinding unclear
- Control group+15/15
- Sample size (n=39)+3.5/20
- Follow-upno follow-up reported
100 / 100
23 / 100
- P-values+15/15
- Effect sizeno effect size reported
- Confidence intervalsno confidence intervals
- Pre-registrationnot pre-registered
Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.
Where it sits
RCT reviewsReviews of RCTs (Meta-analyses)
Max 100Randomized TrialsRandomized Trials
Max 90Reviews of Cohort StudiesReviews of Cohort Studies
Max 85Cohort StudiesCohort Studies
Max 72Reviews of Case-Control StudiesReviews of Case-Control Studies
Max 63Case-Control StudiesCase-Control Studies
Max 58Cross-Sectional & Case SeriesCross-Sectional & Case Series
Max 50Expert OpinionExpert Opinion
Max 544 / 100
Probability of being correct
Snapshots of a population at a single point in time, or descriptions of small groups. Can identify correlations and prevalence, but cannot determine cause and effect.
This design cannot establish causation — the findings describe an association, not a cause. Cross-sectional design measures exposure and outcome simultaneously, so temporal sequence cannot be established. Potential residual confounding, small sample size, and lack of incident bone stress injury data further prevent causal inference.
No Conflicts
No conflicts of interest identified
No conflicts of interest identified in the provided text. The excerpt lacks a funding or COI statement, and author affiliations are academic or government institutions.
The provided text is a partial excerpt (ending mid-Methods) and does not include the article's funding or conflict of interest declarations, which are typically located at the end. Author affiliations include Massachusetts General Hospital, Harvard Medical School, Boston Children's Hospital, Spaulding Rehabilitation Hospital, US Army Research Institute of Environmental Medicine, and Oak Ridge Institute for Science and Education, with no apparent industry ties. Absence of a COI/funding section in this excerpt prevents a definitive assessment.
Standing
The people behind it
The researchers who wrote the study this analysis is built on.
Authored by
13 researchersIf this is your work, this is how we attribute it on Fit Body Science. Melanie S. Haines is listed as the lead author.