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What Are the Health Risks of Being Underweight?

Expertly reviewed by Chris Icamen · Dietetics and Nutrition

Written by Jan Alwyn Batara · Updated Sep 29, 2022

What Are the Health Risks of Being Underweight?

The health risks of being underweight is a topic that’s not often discussed. Most of the time, when weight problems are talked about, people think about being overweight or obese. However, being underweight can also be unhealthy, and can put someone at risk of serious health problems.

What Does Being Underweight Mean?

Before we get to the health risks of being underweight, we first need to define what underweight is.

Medically speaking, being underweight means that your BMI, or body mass index is below 18.5. You can calculate your BMI by dividing your weight in kilograms, by the square of your height in meters. The resulting number should be your BMI.

A healthy BMI is around 18.5 to 24.9. Going over that means that a person is overweight or obese, and going under means a person is underweight.

Doctors usually use the BMI to have an idea of whether or not a person’s weight is healthy or not. However, it is important to note that BMI does not always apply to everyone. This is because each person’s body is different, and the BMI does not account for those differences. Still, it can provide an easy way to gauge a person’s health based on their weight.

What Causes a Person to Become Underweight?

Being underweight can be caused by a number of factors. Some people are just naturally small or thin, and being underweight is the default for their bodies. While some people can have an overactive metabolism, and even if they eat more food, they still find it difficult to gain more weight.

In these cases, being underweight is not necessarily a bad thing, nor is it unhealthy.

However, there are also health problems that can cause a person to become underweight. These conditions can include the following:

  • Stomach problems
  • Cancer
  • Diabetes
  • Thyroid problems
  • Crohn’s disease
  • Anemia

Certain mental health problems can also cause a person to become underweight. In particular, some conditions can cause people to have eating disorders, which can affect their weight.

One common example of this is anorexia nervosa, or a condition that causes a person to eat very little, or avoid eating entirely, in order to stay slim. In more serious cases, people with anorexia might already look thin, but to the person with this condition, they still look overweight.

Here are some other mental health problems that can cause weight loss:

  • Anxiety
  • Depression
  • Low self-esteem
  • Too much stress

What are the Health Risks of Being Underweight?

Being underweight is more than a physical concern. It can also cause serious health problems, especially if not treated.

Here are some of the possible health risks of being underweight.

Health risks of being underweight: Nutritional deficiencies

Among the health risks of being underweight, the most common would be having nutritional deficiencies.

We depend on food for our nutrition, and to provide our body with energy. If a health problem is causing a person to not eat as much food, or is preventing them from digesting their food properly, they can suffer from nutritional deficiencies.

Nutritional deficiencies can affect people in different ways, depending on what nutrients they lack. For example, having a lack of calcium can cause a person’s bones to grow brittle and weaker, and thus they can easily break.

Health risks of being underweight: Weaker immune systems

Another possible health risk of being underweight is having a weaker immune system. Our immune system directly benefits from the vitamins and minerals that we get from the food we eat.

If a person does not eat enough food, then their immune system will start to suffer. This can make them more prone to serious illness, as their body will not have the ability to fight off disease and infection.

Health risks of being underweight: Fertility problems

Fertility problems can also be exacerbated by being underweight. A person’s reproductive health is tied to their overall health, so if they suffer from certain deficiencies, then it would be difficult for them to have a child.

This means that women might find it harder to get pregnant, and men might find it more difficult to have healthy sperm.

Health risks of being underweight: Slower wound healing

Another one of the health risks of being underweight is slower wound healing. If a person’s body lacks iron and protein, then their body might take longer to heal their wounds.

This is because these nutrients are important in repairing damaged tissues, so if there is a lack of these nutrients, then wound healing can suffer. It can also make a person more prone to bruising.

Health risks of being underweight: Increased risk of heart attacks

One serious health risk of being underweight is an increased risk of heart attacks. For the most part, people usually associate heart attacks with obese or overweight people. However, underweight people are also at risk of having a heart attack.

This is due to the fact that being underweight causes a lack of hemoglobin serum in the blood. Hemoglobin serum is important in the heart’s function, and having a significant lack of it can cause heart failure and other cardiovascular problems.

How can people avoid being underweight?

Here are some ways to avoid being underweight:

  • Try to eat more healthy foods. This can help you gain weight, and provide you with the necessary nutrients that your body needs. Try to focus on lean meats and proteins as well as fresh fruits and vegetables. Eating dairy can also help you gain weight.
  • Exercise can also help with weight gain. While exercise is commonly associated with weight loss, it can also help you gain weight. Exercise helps build muscle, which keeps you strong and can increase your weight.
  • If you suddenly become underweight, try to consult your doctor first. It could be a symptom of an underlying condition, and getting it treated should be a top priority.

Key Takeaways

While there has been greater focus on losing weight to achieve ideal BMI, there are others who find themselves needing to add on a few pounds to ensure that they are healthy. The key to achieving a healthier BMI is by eating a good, nutritious diet and exercising regularly. With any change in diet and lifestyle, it is best to consult a doctor.

Learn more about Other Healthy Eating Tips here


Hello Health Group does not provide medical advice, diagnosis or treatment.

Expertly reviewed by

Chris Icamen

Dietetics and Nutrition

Written by Jan Alwyn Batara · Updated Sep 29, 2022

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