Signs That You Are Underweight

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Are you worried that you might be underweight? While many of the people around you might be concerned about weight that they are gaining, you might be concerned about weight that you are losing. So what are the signs of being underweight? There are several that you should pay attention to if you are very thin or losing weight quickly.

What Is Considered Underweight?

According to the Centers for Disease Control (CDC) if your body mass index (BMI) falls below 18.5 then you are in the underweight category. You can calculate your BMI using a simple formula. You'll need to know your height and weight to insert into this calculator:

Compare your numbers to standardized body mass index scores.

  • 18.5 or less: Underweight
  • 18.5 to 24.9: Normal Weight
  • 25.0 to 29.9: Overweight
  • 30.0 or higher: Obese

Keep in mind that body mass index is not a diagnostic measure. If your BMI falls below 18.5, you are not necessarily in harm's way because of your weight. BMI is only a classification system. Your doctor and other health organizations use it as a screening tool to assess your weight and your risk for a disease.

You can also use body fat percent measurements to assess your body size. In general, women should have a body fat measurement of at least 10–13% for essential body functions. Men should have at least 2–5% for essential body functions. Falling below those recommendations may not be healthy for you.

Government studies published by the National Center for Health Statistics in 2018 estimate that only about 1.5% of the population is underweight. Roughly 1.8% of women are underweight and about 1.2% of men are underweight.

So how do you know for sure if you are underweight? Your healthcare provider can evaluate your weight and determine if you need to gain weight to improve your health.

Symptoms of Being Underweight

If you are underweight, you may notice certain signs on your body. But some symptoms commonly associated with thinness may have other causes. For example, do veiny arms mean you're underweight? Some people who are very thin complain about veiny arms. But bodybuilders have veiny arms, as well. So veiny arms, alone, aren't necessarily an indicator that you are too thin.

Other people complain about joints that look too large. If you are underweight and carry very little muscle mass, your bones and your joints may appear more prominent. But again, having large bones or a more noticeable joint doesn't mean that you are definitely underweight.

Other symptoms of being underweight may include problems due to malnutrition:

  • Dizziness or fatigue from anemia
  • Fragile bones
  • Hair loss
  • Irregular menstrual periods or problems getting pregnant
  • Poor growth and development, especially in children who are underweight
  • Weak immune system

What Should I Do If I Am Underweight?

The best source of information if you think you are underweight is your doctor. There are many causes of low body weight and your health care provider can rule out conditions like cancer, thyroid disease, digestive problems, or medications. There are also behavioral causes of underweight, such as stress or depression .

But it is possible that you are underweight because of genetics, because of your activity level, or simply because you don't eat enough.

How to Gain Weight and Stay Healthy

If your doctor does find that you are underweight, he or she will probably recommend that you put on weight by eating healthy and nutritious foods. You can increase your calorie intake by focusing on good sources of protein, grains, and healthy fats. A registered dietitian may be able to help you build meals and snacks to help you gain weight to build a strong healthy body.

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3 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. Assessing Your Weight

  2. American Council on Exercise. Percent Body Fat Calculator: Skinfold Method.

  3. American Academy of Family Physicians. Healthy Ways to Gain Weight if You’re Underweight

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