Diet and hair

Key takeaways

• Severe under-nutrition clearly causes shedding; ordinary diets rarely do. Crash dieting, very low protein and rapid weight loss are recognised triggers of telogen effluvium, a diffuse shedding that starts about 2-3 months after the trigger and usually regrows. Goette 1976 Hughes 2024
• Weight-loss surgery and drugs matter. Hair loss was reported in about 57% of people after metabolic and bariatric surgery (pooled), more in younger women and those with low zinc, folate or ferritin. Zhang 2021
• For GLP-1 weight-loss drugs, a 2026 review reports hair loss in roughly 3-5% of treated patients in pivotal trials (pooled risk ratio about 3.3 versus placebo), mostly telogen effluvium from fast weight loss. Bridges 2026 A 2026 matched cohort found higher odds of telogen effluvium with semaglutide and tirzepatide. Katragadda 2026 Reviewers suggest 1.2-2.0 g/kg/day of protein, an expert opinion rather than a trial result.
• There are no diet-intervention trials for hair loss. A 2023 systematic review of nutritional interventions in people without known deficiency found no diet-based studies that met its criteria. Drake 2023
• Observational data are weak but consistent. A 2026 review of 17 studies (97% women) linked higher vitamin D and iron to less alopecia and higher alcohol and sugary-drink intake to more hair loss. Gomes 2026 A 2024 scoping review lists unhealthy dietary habits, smoking and high BMI among reported risk factors for early-onset pattern hair loss. Liu 2024
• In mice, a high-fat diet pushed follicle stem cells to differentiate early and the follicles shrank. This is animal data. Morinaga 2021
• True deficiencies are less common among people with shedding than marketing implies. In 90 women with chronic telogen effluvium versus 90 controls, only zinc (lower) and selenium (higher) differed; ferritin, B12, vitamin D and thyroid tests did not. Durusu Turkoglu 2024 Other meta-analyses do find lower ferritin and vitamin D in telogen effluvium. Ahmed 2026
• Test, do not guess. Reasonable first labs for diffuse shedding are ferritin, thyroid function and a blood count, plus vitamin D and B12 where there are risk factors. Rushton 2002 Correct what is low; extra does not help and some excess harms (vitamin A, selenium, zinc).

The science

Follicles are among the fastest-dividing tissues, so they react to an energy or protein shortage by pushing growing hairs into rest. In crash dieters, 25-50% telogen counts appeared 2-5 months after starting and hair regrew within months. Goette 1976 About 15% of scalp hair is normally in the resting phase; after a significant stressor roughly 70% of growing follicles can shift to rest. Hughes 2024

Micronutrients are linked to hair loss in association studies: vitamin D, iron, zinc, folate and B12. A systematic review of micronutrients and pattern hair loss concluded deficiencies may be modifiable factors but the evidence is inconsistent. Wang 2024

What it means by hair profile

• Women with heavy periods, vegetarians and vegans: higher risk of iron and B12 shortfalls; test ferritin and B12 before supplementing. Most diet-and-hair studies are in women.
• Men with pattern loss: diet will not stop DHT-driven miniaturisation; see DHT and pattern hair loss.
• Anyone starting a GLP-1 drug, weight-loss surgery or a very-low-calorie diet: expect possible shedding and plan protein and micronutrients.
• Curly and coily hair: no diet-specific data; breakage from handling is far more common than nutritional loss.

Myths and facts

• More protein grows hair faster: only if you were short of protein.
• Biotin and collagen fix thin hair: see biotin and collagen peptides.
• Vegan diets cause hair loss: no hair-specific trial found; the risks are iron, zinc and B12 shortfalls that can be tested and fixed.
• Sugar causes hair loss: a review reports association with sugary drinks, not causation.

Practical recommendations

• Eat enough energy and protein across the day and avoid crash diets.
• Ask for ferritin, thyroid, vitamin D and B12 tests if shedding lasts beyond 3 months.
• Supplement only measured gaps and avoid stacking vitamin A, selenium and zinc (hair supplement blends).
• On weight-loss drugs, treat protein and slow loss as part of hair care, and see a clinician if shedding lasts beyond 3-6 months.

Bottom line

Eating enough is the diet advice that has real support. Test before you supplement, and expect hair to lag behind any change by months. Discuss with a doctor.