Weight
Signs of Being Underweight in Women: Causes and When to See a Doctor
Quick answer
Common signs of being underweight in women are low energy, frequent illness, hair fall, dry skin, feeling cold and irregular or missed periods. A body mass index (BMI) under 18.5 is generally considered underweight. Unexplained weight loss, or worry about eating and body shape, should always be checked by a doctor.
Last reviewed NariCareLife editorial team · 5 sources
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What is Being underweight?
Being underweight means your body weight is lower than is considered healthy for your height. Doctors often use body mass index (BMI) as a first check, although it does not tell the whole story about health.
Some women are naturally slim and healthy. Others are underweight because they are not getting enough energy and nutrients, or because of an underlying health problem, stress or an eating disorder. Being underweight can mean missing out on vitamins and minerals, which may affect immunity, bones and periods.
The signs vary with how low your weight is, how quickly it has changed and what is causing it. Unplanned weight loss is different from a steady, lifelong slim build and always deserves a medical check.
Common symptoms of Being underweight
Tiredness and low energy
Feeling weak or drained, as the body may not be getting enough fuel for daily activity.
Irregular or missed periods
Very low body weight or eating too little can disturb hormones and cause periods to become irregular or stop.
Getting ill often
Frequent colds, infections or slow recovery can happen when nutrition is poor.
Hair fall and dry skin
Thinning hair, brittle nails and dry skin can reflect low intake of protein and other nutrients.
Feeling cold
Feeling cold more easily than others, as there is less body fat and energy to keep warm.
Dizziness
Feeling light-headed, especially on standing, which can also point to anaemia and should be checked.
Loss of muscle and strength
Arms and legs may look thinner, and everyday tasks may feel more tiring.
Clothes feeling loose
Clothes, bangles or rings becoming looser over time can be a sign of ongoing weight loss.
What can cause Being underweight?
- Not eating enough to match your energy needs, often from skipped meals, a busy routine or low appetite.
- A naturally fast metabolism or a family tendency towards a slim build.
- Health conditions such as an overactive thyroid, diabetes, coeliac disease, digestive problems or ongoing infections.
- Stress, anxiety or depression, which can reduce appetite.
- Eating disorders, such as anorexia nervosa or bulimia, which are serious but treatable mental health conditions.
- Very high levels of physical activity without enough food to match.
How is Being underweight diagnosed?
A doctor usually starts by measuring your height and weight to work out your BMI and asking about your eating, periods, energy, mood and any recent weight change. They may examine you and arrange blood tests, such as a blood count, thyroid function, blood sugar and tests for coeliac disease or nutrient levels. If there are signs of an eating disorder, they can refer you to specialist support in a kind, confidential way.
When to see a doctor
See a doctor if you have lost weight without trying, if your periods have become irregular or stopped, or if you feel tired and unwell most of the time. It is also important to seek help if food, weight or body shape is causing you worry or distress; eating disorders can affect anyone, and people do recover with the right support. If you are worried about a friend or family member, gently encourage them to speak to a doctor. Discuss any supplements or weight-gain products with your doctor before using them.
Get medical help promptly if you notice:
- Losing weight without trying, especially over a few months.
- Fainting, a racing or irregular heartbeat, chest pain or severe weakness. Seek urgent medical care.
- Periods stopping for several months without pregnancy.
- Weight loss with ongoing diarrhoea, blood in stools, night sweats, fever or a persistent cough.
- Fear of gaining weight, restricting food, making yourself sick, or using laxatives or exercise to control weight. Please speak to a doctor; help is available.
In an emergency, call 112 or go to the nearest hospital.
How nutrition and lifestyle may help
Food does not cure or treat Being underweight, but everyday habits can support your overall wellbeing alongside the care your doctor recommends.
Eat regularly
Three meals and two or three snacks a day may help you take in more energy without feeling overly full.
Add healthy, energy-rich foods
A spoon of ghee on dal or roti, nuts on poha, or peanut chutney with idli can add nourishment in small portions.
Include protein at each meal
Dal, paneer, curd, eggs, fish, chicken, soya or sprouts can be part of meals that support muscle and strength.
Choose nourishing drinks
Milk, lassi, banana or dates smoothies and ragi malt may help when appetite is small. Avoid filling up on water or tea just before meals.
Build strength gradually
Gentle strength exercises may help build muscle rather than only fat. Check with your doctor first if you have been very underweight.
Aim for steady, gradual gain
Slow, steady weight gain from balanced foods is healthier than relying on sugary snacks, fried foods or crash diets in reverse.
Indian foods to include
- Ghee with dal and roti
- Peanuts, almonds and walnuts
- Paneer and full-fat curd
- Banana and dates
- Ragi malt or ragi porridge
- Eggs, fish or chicken if you eat them
- Rajma, chole and soya
- Sweet potato and potato
- Milk, lassi or dry fruit milkshakes
- Sesame (til) and peanut chikki in moderation
Key takeaways
- Signs of being underweight include tiredness, frequent illness, hair fall, feeling cold and irregular periods.
- A BMI under 18.5 is generally considered underweight, but BMI is only a starting point.
- Unplanned weight loss always deserves a medical check.
- Eating disorders are serious but treatable, and reaching out for help is a strong first step.
- Regular, balanced Indian meals with protein and healthy fats may help support gradual weight gain.
Being underweight: frequently asked questions
You may be underweight if your body mass index (BMI) is under 18.5. You can check it with a BMI calculator using your height and weight. BMI does not measure muscle, bone or overall health, so a doctor or dietitian can help interpret it alongside your energy, periods, eating habits and any recent weight change.
Yes, being underweight can make periods irregular or stop them. When the body does not get enough energy, it may reduce the hormones that control the menstrual cycle. Missed periods can also have other causes, including pregnancy or thyroid problems. If your periods have stopped or changed, see a doctor to find the reason.
Being underweight can be harmful when it means your body is missing out on energy, vitamins and minerals. This may lead to a weaker immune system, fragile bones, low energy and irregular periods. Some naturally slim women are healthy, so a doctor can help work out whether your weight is a concern for you.
Losing weight without trying can be caused by stress, low appetite, digestive problems, an overactive thyroid, diabetes, infections or other medical conditions. It can also be linked to an eating disorder. Unplanned weight loss should always be checked by a doctor, especially if it continues or comes with other symptoms such as fatigue, fever or changes in bowel habits.
Warning signs of an eating disorder include strong fear of gaining weight, strict food rules, skipping meals, making yourself sick, using laxatives, over-exercising and feeling distressed about body shape. Eating disorders are serious mental health conditions but people do recover. If this sounds familiar for you or someone close to you, please speak to a doctor.
The healthiest way to gain weight is gradually, through regular balanced meals and snacks with enough protein, whole grains and healthy fats, plus some strength exercise. Foods like dal, paneer, nuts, ghee in moderation, milk and bananas are good choices. Avoid relying on junk food, and see a doctor first to rule out a medical cause.
Sources & references
- Healthy ways to gain weight — NHS
- Malnutrition: symptoms — NHS
- Eating disorders: overview — NHS
- Eating Disorders — National Institute of Mental Health
- Malnutrition — World Health Organization
