Your hair is a low-priority organ. When your body is short on nutrients, hair is among the first things deprioritised, which is why a rough few months of stress, restrictive eating, or illness usually shows up in the hair three to six months later. The shape of this problem is not philosophical; it is biochemical. Hair is mostly protein, and it is built from a small set of specific nutrients your body has to deliver to the follicle while also keeping every more-important system fed.

This is a practical guide to the dietary inputs that show up in the salon chair — what the hair needs, what the deficiencies look like, and what we actually recommend clients pay attention to. It is not a prescription. Talk to a doctor before supplementing. But the fundamentals are straightforward and worth knowing.

Protein is the foundation, and most clients do not eat enough

Hair is roughly 95 percent keratin, which is a protein. Without enough dietary protein, your body cannot build the amino acids hair follicles need, and new hair grows in thinner and weaker than it should. The recommended daily protein intake for an adult is 0.8 grams per kilogram of body weight, but for active women at altitude (a lot of our clients), 1.0 to 1.2 grams per kilogram is closer to the target. For a 150-pound woman that is 68 to 82 grams of protein per day. Most people we talk to eat half that.

Good sources: eggs, lean meat, fish, Greek yoghurt, cottage cheese, legumes, tofu, tempeh. Plant-based eaters often need to be more intentional about protein, because most plant sources are lower in density. Spread protein across all meals rather than loading one dinner; your body cannot store amino acids efficiently, so a steady supply is more useful than a feast.

Iron and ferritin — the hidden cause of thinning

Iron deficiency is the single most common nutritional cause of hair shedding we see, especially in women under 45. You can have normal hemoglobin and still be iron-deficient for hair purposes because ferritin — the body’s stored iron — has to stay above about 70 ng/mL for the hair follicle to function properly. Standard blood work usually does not test ferritin unless you ask for it.

If you are shedding more than usual, ask your doctor for a ferritin test along with your standard iron panel. Dietary iron sources: red meat, shellfish, spinach, lentils, pumpkin seeds, fortified cereals. Take iron-rich food with vitamin C (a squeeze of lemon or a handful of bell pepper), which improves absorption. Avoid coffee and tea within an hour of iron-rich meals; both block absorption significantly.

Biotin is overrated; B vitamins broadly are underrated

Biotin became a hair-supplement darling a decade ago and has never really left the conversation, but biotin deficiency is actually very rare in people eating a varied diet. Supplementing megadoses of biotin does not make hair grow faster if you are not deficient, and it can interfere with certain thyroid and cardiac blood tests. Skip the standalone biotin supplement unless your doctor has identified a deficiency.

What is worth paying attention to is B12 and folate, especially in people who eat little meat. Both are essential for cell division and affect hair growth directly. A B-complex supplement with a reasonable dose of B12 is cheap and well-tolerated.

Omega-3 fats for scalp and shine

Omega-3 fatty acids (EPA and DHA) are the nutrients most directly linked to scalp health and hair shine. The follicle sits in the scalp, and a dry, inflamed scalp produces unhappy hair regardless of what the strand is doing. In Denver, where dry air already challenges the scalp, omega-3 intake tends to matter more than it would in a humid climate.

Dietary sources that deliver a meaningful dose: wild salmon (two servings per week), sardines, mackerel, walnuts, ground flaxseed, chia seeds. Plant omega-3s convert to the useful form less efficiently, so if you do not eat fish, consider a quality algal oil supplement. Most clients who notice dramatically shinier hair after adjusting diet did so by adding omega-3 rich fish or an algae-based supplement.

Zinc, vitamin D, and the quieter deficiencies

Zinc is required for the hair growth cycle to run properly, and low zinc can produce diffuse hair loss. Good sources: oysters, beef, pumpkin seeds, chickpeas. Vitamin D deficiency is epidemic in Denver despite our sunshine (something about altitude, sunscreen, and indoor life), and low D is linked to telogen effluvium, a temporary shedding. Get a vitamin D test once a year and supplement if your level sits below 30 ng/mL; most Denver residents do in winter.

Selenium, copper, and silica also play roles but are more niche and usually well-supplied by a varied diet. If you are eating a reasonable amount of real food, these do not need special attention.

Restrictive eating and what it does to hair

Rapid weight loss, extreme calorie restriction, and highly restrictive diets (keto done carelessly, very low-protein plant-based, extended fasting regimens) all show up in hair within three to four months. The body shifts hair into resting phase when caloric or protein intake drops below what is needed for core functions. The good news is that it is almost always reversible once intake returns to normal. The bad news is that by the time you see the shedding, you are already several months into the problem.

If you are intentionally in a calorie deficit (for fat-loss goals, for instance), pay attention to protein first. Most diet plans under-specify protein, and hair is one of the first systems to feel it. 1.2 grams per kilogram stays the target in a deficit, not less.

Hydration and coffee — the Denver footnote

At altitude you dehydrate about 30 percent faster than at sea level, and dehydration shows up in hair as brittle, lifeless strands that will not hold a style. Aim for 2 to 3 litres of water a day. Coffee is fine — it does not dehydrate net-positive the way older advice suggested — but it does block iron absorption if consumed too close to iron-rich meals. Separate coffee from iron-rich foods by at least an hour.

Frequently asked questions about diet and hair

How quickly will diet changes show in my hair?

Three to six months for most changes to become visible in the hair you can see. Hair grows at roughly half an inch per month, so dietary improvements made today will show up near the scalp now and move down the strand slowly. Patience is the hard part.

Are hair-specific supplements worth it?

Usually not. Most hair-specific supplements are multi-ingredient megadose biotin formulations that are redundant if you are eating a varied diet. The exceptions: iron if your ferritin is low, vitamin D if you are deficient, and a B-complex if your diet is light on animal products. These are cheap. Doctor-tested and doctor-recommended beats general “hair vitamins” almost every time.

Does sugar affect hair?

Chronic high sugar intake contributes to systemic inflammation, which over time affects hair quality indirectly through scalp health. It is not a direct cause-effect like iron or protein, but clients who reduce refined sugar usually see improvement in both skin and hair over three to six months. Moderation, not elimination.

I am a vegetarian. What should I pay extra attention to?

Protein intake (plant proteins are usually less dense, so eat more volume), iron and ferritin (plant iron is less bioavailable — pair with vitamin C), B12 (a supplement is wise unless you eat dairy and eggs regularly), and omega-3 via algal oil or flax. These four cover the deficiencies we see most often in long-term plant-based clients.