By Dr. Asnat Raziel, bariatric surgeon specializing in obesity treatment, metabolic health and healthy longevity; Director of the Multidisciplinary Center for Obesity Treatment, Assia Medical, Assuta Ramat HaChayal, Tel Aviv
Hair loss during weight loss: what happens to your hair
Hair loss during weight loss is common, and it frightens many of my patients. Usually the shedding is temporary, and the hair grows back. Sometimes, however, it signals a nutritional deficiency that is worth finding and correcting. In this article, I will explain why it happens, which blood tests to consider and what really helps.
Here is something important to know: a healthy person typically loses 50 to 100 hairs a day. So a few hairs in your brush are no cause for concern. By contrast, whole clumps on the pillow, in the shower or while combing do call for a closer look.
Why hair loss during weight loss happens
Every hair has a life cycle. Most hairs are in a long growth phase that lasts for years. A small share moves into a resting phase, and at the end of it the hair falls out. According to the dermatology website DermNet, about 15% of follicles are in the resting phase at any given time.
A stressful event for the body upsets this balance. Rapid weight loss, an extreme diet or a nutritional deficiency pushes many hairs into the resting phase at once. This is called telogen effluvium, meaning diffuse shedding of hairs in the resting phase. It does not leave bald patches. Instead, it thins the hair overall.
The confusing part is the timing. According to DermNet, the shedding usually starts two to four months after the event that triggered it. That is why many patients notice it just as their weight is leveling off. The American Academy of Dermatology also lists losing about 9 kg (20 pounds) or more among the causes of this type of shedding.
Who is at higher risk
The risk rises when weight comes off quickly and the diet is poor. Examples include a very low-calorie menu, regularly skipping meals or cutting out entire food groups. In addition, women with heavy periods, vegetarians and vegans, and patients after bariatric surgery are prone to certain deficiencies.
Some medications also play a role. For example, metformin and acid-reducing drugs can interfere with vitamin B12 absorption. So it is important to tell your doctor about every medication you take.
Which blood tests to consider
There is no single “hair loss panel” that fits everyone. Your doctor chooses the tests based on your diet, how fast you are losing weight, any underlying conditions and your medications. Still, these are the tests that come up most often.
Iron and iron stores
Iron deficiency is one of the well-known causes of hair loss. That is why doctors usually check a complete blood count and ferritin, a marker of the body’s iron stores. According to the US National Institutes of Health fact sheet on iron, women with heavy periods, frequent blood donors and people with bowel disease are at higher risk.
Vitamin B12
Vitamin B12 comes naturally only from animal foods. According to the fact sheet on vitamin B12, groups at risk of deficiency include older adults, vegetarians and vegans, patients after stomach or bowel surgery, and people taking metformin. A long-standing deficiency also causes fatigue and nerve damage, so it is worth catching early.
Zinc and vitamin D
Zinc helps the body make proteins and DNA, and it supports the immune system. However, the direct link between zinc and hair loss in adults is weak. According to the fact sheet on zinc, too much zinc over time can lead to copper deficiency. In other words, a supplement taken “just to be safe” can do harm. Vitamin D is often checked as part of a general workup, but the evidence linking it to hair loss is limited.
Thyroid and other tests
At your doctor’s discretion, a TSH test may be added. TSH is the hormone that regulates the thyroid gland. In some cases, doctors also check blood protein and general nutrition markers. Your doctor reads the results together with your dietary history, not as a single number.
Hair loss during weight loss on weight-loss injections
Many patients ask whether the drugs themselves cause hair loss. The label for Zepbound, which contains tirzepatide and is the US counterpart of Mounjaro, reports hair loss in 4% to 5% of patients, compared with 1% on placebo. According to the label, the shedding occurred mainly in women and was tied to weight loss.
On the Wegovy (semaglutide) label, 3% of patients reported hair loss, compared with 1% on placebo. In most cases, then, the shedding reflects rapid weight loss and a restricted diet rather than direct damage to the follicle from the drug. You can find more in my guide to eating well on weight-loss injections. Either way, do not stop the drug or change the dose without talking to your doctor.
How to reduce hair loss during weight loss
Hair is made mostly of keratin, which is a protein. Therefore, getting enough protein is the foundation. The right amount depends on your weight, age, activity level and health, and a dietitian calculates it for you personally.
- Protein at every meal: eggs, fish, dairy, legumes, tofu or chicken.
- Small meals: when you feel nauseous or have little appetite, it is better to split your protein into several small portions.
- Don’t skip fat: olive oil, nuts, avocado and fatty fish provide essential fatty acids.
- A reasonable pace: gradual, supervised weight loss beats a crash diet.
- Protect your muscle: protein and strength training also preserve muscle mass, as I explained in my article on preserving muscle mass during weight loss.
It is also wise to treat your hair gently during this period. For example, avoid tight hairstyles, cut back on straightening and coloring, and lower the heat on your blow-dryer and flat iron. These steps won’t prevent the shedding, but they will reduce breakage of the hair you have.
Supplements: when yes and when no
The temptation to buy a “hair supplement” is strong. However, a supplement without a proven deficiency usually doesn’t help, and sometimes it harms. Excess iron causes digestive problems, and a high dose is dangerous for children. According to the American Academy of Dermatology, too much vitamin A or selenium can also cause hair loss. So the rule is simple: test first, then treat in a targeted way. When there is a deficiency, your doctor decides on the type of supplement, the dose and the length of treatment, and then retests later on.
When to see a doctor about hair loss during weight loss
According to the American Academy of Dermatology, hair usually regains its fullness within six to nine months after this type of shedding. So it is worth getting checked if the shedding lasts longer than that. In addition, see your doctor if you notice distinct bald patches, itching or pain in the scalp, or symptoms such as extreme fatigue, paleness and heart palpitations. In such cases, the cause may be something else, and your doctor may refer you to a dermatologist.
A dietitian works at our clinic. In addition, when needed, I refer patients to a multidisciplinary mind-body team. It includes dietitians, psychologists, holistic coaches, naturopaths and complementary medicine practitioners, as well as Pilates and yoga instructors and stress-reduction experts.
The bottom line
Hair loss during weight loss is usually a temporary response of the body to rapid change. It appears a few months after the weight starts coming off, and most patients see their hair grow back. The keys, then, are a protein-rich diet, a reasonable pace of weight loss and targeted blood tests instead of taking supplements blindly.
This article provides general information and is not a substitute for personal medical advice.
Questions and answers
Does hair loss during weight loss go away?
In most cases, yes. Once the cause is addressed and your diet is balanced, the hair grows back gradually, usually within six to nine months.
Should I stop weight-loss injections because of hair loss?
Not on your own. Usually you can continue treatment, improve your diet and check for deficiencies. Any change in treatment should be made together with your doctor.
Which blood tests should I get?
Most often a complete blood count and ferritin, plus vitamin B12, and if needed vitamin D, zinc and TSH. Your doctor tailors the list to you.
Should I take biotin or a “hair supplement”?
Only if you have a proven deficiency. Without one, supplements usually don’t speed up regrowth, and some may even be harmful.
Sources
Do you have hair loss or hair shedding?
Telogen effluvium (hair shedding)
Iron – Fact Sheet for Consumers
Vitamin B12 – Fact Sheet for Consumers
Zinc – Fact Sheet for Consumers
