Yes. Runners who lose a lot of weight often need smaller or narrower shoes.
The clearest numbers come from bariatric surgery. Sleeve gastrectomy is weight-loss surgery that removes part of the stomach. In 212 patients, mean reported European shoe size fell from 41.5 to 40.5 one year after surgery, according to the Turkish Journal of Surgery study.
Medical information disclaimer: This article is for general educational purposes only and does not provide medical advice, diagnosis, or treatment. Always consult a physician or other qualified health professional about symptoms, medications, tests, or treatment decisions.
Table of Contents
- How much can shoe size drop?
- Why does width change more than length?
- What will you feel on the run?
- When should you get refitted?
How much can shoe size drop?
In that same Turkish study, starting weight shaped the drop. Patients with BMI over 50 had a larger mean decrease than patients with BMI under 40. They also more often dropped at least two full sizes.
Small running-fit changes were likely missed. The study recorded shoe size by verbal report at 12 months and ignored half-size changes. For runners, that means small but important fit shifts are understated.
Why does width change more than length?
In a foot-shape study from Chinese University of Hong Kong authors, heavier adults had wider feet at the same length. They showed larger breadth and girth, altered forefoot length, and different height measures. Those differences change which last fits best.
A last is the foot-shaped mold used to build a shoe. Extra load also flattens the arch. Obesity is strongly linked with low-arched planus posture, pronated motion, and higher peak pressures while walking, according to the Springer Medicine review. A Frontiers in Pediatrics study found the same link in children, which supports arch rise as load falls.
What will you feel on the run?
Shoes may feel looser around the midfoot and heel. Arches sit higher and roll inward less. Peak pressure under the foot drops as load drops.
Forefoot width often shrinks before length changes. You may see extra space at the sides or toes sliding forward on downhills. Heel slip on climbs is a sign the volume no longer matches.
When should you get refitted?
These fitting checks follow Harvard Health Publishing tips. Get remeasured standing after major loss and always fit the larger foot.
Use afternoon fit as your buy signal. Replace the pair when the heel slips or the midfoot feels loose.
- Measure standing, both feet
- Fit the larger foot
- Shop in the afternoon
- Keep about a thumb's width ahead of the longest toe, with snug heel and midfoot