SupplementsHair, skin & nailsFoundational
Before any branded “hair, skin and nails” capsule is worth discussing, one boring fact settles most cases: hair is roughly 90% keratin, a structural protein, and the follicle is one of the most metabolically demanding tissues in the body. Starve it of protein or energy and it downs tools. This is the page to read first — and for a lot of people it is the only one that matters.
Key takeaways
- Hair fibre is almost entirely keratin — you cannot build it without dietary protein and the sulphur amino acids that cross-link it.
- Under-eating protein or energy (crash diets, illness, appetite loss on GLP-1 drugs) triggers telogen effluvium — a diffuse shed that shows up 2–3 months after the trigger.1
- The RDA of 0.8 g/kg is a floor to prevent deficiency, not an optimum — if you are active, dieting or older, 1.2–1.6 g/kg is a saner target.
- No pill outperforms simply eating enough. A “hair vitamin” taken on top of an under-eating diet is treating the symptom and ignoring the cause.
Why protein comes first
Keratinocytes in the hair bulb divide faster than almost any other cell in the body, and each new fibre is spun from amino acids — cysteine, methionine, and the rest. Nails and the skin barrier (which is built from keratins and collagen) draw on the same supply. When intake falls short, the body triages: vital organs keep their protein, and non-essential projects like growing hair get paused. That is not a vitamin problem you can supplement around; it is a raw-materials problem.
How under-eating shows up as shedding
The classic pattern is telogen effluvium: a stressor — a crash diet, a bout of illness, surgery, rapid weight loss — pushes a big fraction of follicles prematurely out of their growth (anagen) phase into resting (telogen). Because resting hairs sit tight for weeks before releasing, the shed lands two to three months later, which is why people rarely connect it to the diet they started in spring. The reassuring part: correct the intake and it usually reverses over the following months. A newly relevant trigger is appetite suppression on GLP-1 medication — the hair loss reported by some users tracks the rapid weight loss and low protein intake, not the drug itself.1
How much, and from where
Aim for protein at most meals rather than one big hit — roughly 20–40 g per meal, landing near 1.2–1.6 g/kg body weight a day if you are training, losing weight or over sixty. Complete sources (eggs, dairy, fish, meat, soy) supply the sulphur amino acids keratin needs; a well-built vegetarian or vegan diet gets there too, but it takes deliberate combining of legumes, grains and soy rather than luck.2
Who this is actually for
The people who benefit most are the ones least likely to be sold a capsule: chronic dieters, anyone recovering from illness or surgery, older adults whose appetite and intake have quietly dropped, vegans and vegetarians who have not paid attention to protein, and people on appetite-suppressing medication. If you are shedding and eating like a bird, fix that before you spend a penny on biotin.
References
Adult research summary for education, not a prescription. These are food supplements, not treatments for disease.
- Guo EL, Katta R. Diet and hair loss: effects of nutrient deficiency and supplement use. Dermatol Pract Concept 2017;7(1):1–10. pubmed.ncbi.nlm.nih.gov
- Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The role of vitamins and minerals in hair loss: a review. Dermatol Ther (Heidelb) 2019;9(1):51–70. pubmed.ncbi.nlm.nih.gov
This article summarises nutrition science for education. It is not a substitute for individual medical advice; consult a professional before starting a supplement, in pregnancy, or alongside medication.