My teenager has lost a lot of weight from sports or dieting. Can it hurt their bones and muscles?

Last reviewed: September 29, 2026

It can.

The harm comes from training hard without eating enough for the amount of training. It happens in boys and girls. It is more common in running and other endurance sports, in sports judged on looks such as gymnastics and dance, and in sports with weight classes such as wrestling.

Bone is where the harm shows most. The teenage years are when the body builds its bone for life. A teen who does not eat enough builds weaker bone and is more likely to get a small crack in the bone from repeated pounding (a stress fracture). Girls who start dieting young also build less bone through their teen years, even if they do not play sports.

Muscles are affected too. Athletes who do not eat enough tend to have less power, speed and endurance, and they miss more days from illness.

Eating enough for the training is the main treatment. The body can recover once a teen eats enough, but bone recovers slowly and may not fully catch up. That is a reason to act early.

If the weight loss comes from strict dieting or a fear of gaining weight, it may be an eating disorder. Your teen’s doctor can check for this.

In general:

• Make sure your teen eats enough for the amount of training.
• See your teen’s doctor if the weight keeps dropping, or if your teen gets a stress fracture, is often sick, or is getting weaker or slower in the sport.
• Talk with your teen’s doctor before any diet to make weight or look leaner for a sport.

Drafted with AI assistance from published sources, reviewed and edited by Babak Sheikh, MD.

Sources:

• Gallant TL, et al. Low Energy Availability and Relative Energy Deficiency in Sport: A Systematic Review and Meta-analysis. Sports Med. 2025. https://doi.org/10.1007/s40279-024-02130-0
• Mountjoy M, et al. 2023 International Olympic Committee’s (IOC) Consensus Statement on Relative Energy Deficiency in Sport (REDs). Br J Sports Med. 2023. https://doi.org/10.1136/bjsports-2023-106994
• Papageorgiou M, et al. Reduced Energy Availability: Implications for Bone Health in Physically Active Populations. Eur J Nutr. 2018. https://doi.org/10.1007/s00394-017-1498-8
• Hohman EE, et al. Dieting Is Associated With Reduced Bone Mineral Accrual in a Longitudinal Cohort of Girls. BMC Public Health. 2018. https://doi.org/10.1186/s12889-018-6206-y
• Nazem TG, Ackerman KE. The Female Athlete Triad. Sports Health. 2012. https://doi.org/10.1177/1941738112439685
• Watkins RA, Guillen RV. Primary Care Considerations for the Pediatric Endurance Athlete. Curr Rev Musculoskelet Med. 2024. https://doi.org/10.1007/s12178-024-09883-1

This is general information about what published research shows. It is not medical advice and it is not about your situation. Reading it does not create a doctor-patient relationship with me. I am a retired orthopedic surgeon and I do not see patients. Talk with your own doctor before changing anything about your care. If something feels suddenly or seriously wrong, get medical care promptly rather than waiting.

This page is provided as is. I make no guarantee that it is accurate, complete or current, and medical evidence changes. Use of it is at your own risk.

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