Hair loss after weight loss or dieting: why it happens

Losing weight can improve health in many ways, so it is frustrating when your hair starts falling out a few months into a diet. This is a well-recognised pattern. In most cases it is temporary shedding, and there are sensible ways to reduce the risk.

Why weight loss can cause hair shedding

Growing hair is one of the most active processes in the body, and it needs a steady supply of energy, protein and nutrients. When the body is under strain, such as during rapid weight loss or a sharp drop in food intake, more hairs can shift into the resting phase. They are then shed together a couple of months later.

This is called telogen effluvium. Weight loss, unusual diets and nutritional deficiencies such as low iron are recognised triggers ¹. The extra hair fall is usually noticed two to four months after the trigger, then gradually tapers back to normal over the following months.

What studies have found

Crash dieting

This link was described decades ago. A 1976 report described nine people who had heavy hair loss two to five months after starting a vigorous weight loss programme, in which they lost between about 12 and 25 kg. The hair grew back within several months. The authors thought severe calorie restriction left the hair root without enough energy ². Some had the same experience each time they dieted strictly.

Weight loss surgery

Hair loss is a common complication after bariatric (weight loss) surgery. A 2021 review and meta-analysis of 18 studies with 2,538 patients found that about 57% reported hair loss after surgery. Hair loss became less common with longer follow-up, and it was more common in younger women and in those with low levels of zinc, folic acid and ferritin (the body's iron stores) ³. This is one reason why people who have weight loss surgery are followed up with blood tests and advised on supplements.

Weight loss medicines

GLP-1 medicines, a newer group of injections used for diabetes and weight loss, have become popular. Researchers have begun to study whether people taking them are more likely to report hair loss ⁴. Rapid weight loss itself is a likely contributor. If you are using one of these medicines and notice shedding, talk to the doctor who prescribed it rather than stopping on your own.

Signs it is shedding from weight loss

• Hair fall starts a few months after you began losing weight, rather than straight away
• Shedding is spread across the whole scalp rather than in patches
• Shed hairs have a small white bulb at the root
• You feel otherwise well, and your weight loss has been fairly fast

If you notice gradual thinning at the crown, temples or parting instead, pattern hair loss may be involved. Rapid shedding can make it more visible.

How to protect your hair while losing weight

• Lose weight gradually. Slower, steady weight loss puts less strain on the body than crash diets
• Eat enough protein. Include protein foods such as fish, eggs, beans, tofu, poultry and dairy in your meals, following a balanced eating pattern ⁵
• Do not cut out whole food groups without advice. Very restrictive diets are more likely to cause deficiencies
• Watch your iron. Red meat, chicken liver, legumes, tofu and dark green vegetables provide iron, and women with heavy periods are at higher risk of running low. See anaemia and hair loss
• Follow your surgical team's advice after weight loss surgery, including blood tests and supplements ³
• Be gentle with your hair during shedding: avoid tight styles and harsh treatments ⁶

Do supplements help?

If a blood test shows low iron, zinc, folate or another nutrient, correcting it makes sense and may help hair recover. Taking extra vitamins without a deficiency is not proven to prevent or stop shedding, and some, such as excess vitamin A or selenium, can actually cause hair loss. See vitamin deficiencies linked to hair loss.

How long until it recovers?

Once your weight and eating pattern are stable and any deficiencies are corrected, shedding usually settles and new hair follows ¹. Because hair grows only about a centimetre a month, it can take many months for the length and fullness to return. Short new hairs along the hairline are a good sign.

When to see a doctor

See a doctor if:

• Shedding continues for more than six months after your weight has stabilised
• You notice bald patches or scalp problems
• You feel very tired, dizzy, cold or unwell
• You have had weight loss surgery and develop new hair loss
• You are losing weight without trying, which always needs checking. See hair loss as a sign of illness

The bottom line

Hair shedding after weight loss is common and usually temporary. It is most likely after rapid weight loss, crash diets or surgery, and low nutrient levels can make it worse. Losing weight steadily, eating enough protein and iron, and getting blood tests when needed all help. Most people find their hair recovers once their weight and diet settle.

Frequently asked questions

Why does my hair fall out after losing weight?

Rapid weight loss and strict diets can trigger telogen effluvium, a temporary shedding that starts a few months later ^{1 2}.

Is hair loss after weight loss surgery common?

Yes. A review of 18 studies found about 57% of patients reported hair loss after bariatric surgery, and it became less common over time ³.

Will my hair grow back after weight loss?

Usually, once weight and diet stabilise and any deficiencies are corrected ^{1 2}.

Can weight loss injections cause hair loss?

Researchers are studying this. Talk to the doctor who prescribed them rather than stopping on your own ⁴.

Educational content. Not medical advice.