The Effects of Being Underweight

Updated November 21, 2016

There is a lot of talk about the adverse health effects of being overweight, but being underweight has many unhealthy side effects as well. Being underweight probably means that you are not getting all of the nutrients you need to sustain your body, and eventually you may experience unhealthy side effects.

Body Mass Index

Everyone has a different height and bone structure, so how much you weigh is not always a good indicator of what is considered underweight. Body mass index (BMI) is a measurement used to gauge how much fat you have on your body. Women who have a BMI of less than 18.5 are considered to be underweight, according to the Weight-Loss-Center.

Lower Immune System

If you are underweight, you might find that you get colds and flu more often because of a weakened immune system from lack of nutrients.

Muscle weakness and fatigue are side effects of being underweight. You may also lose muscle mass if you are too thin, because your body starts to use your muscles as fuel.

Hair Loss

Hair loss is a side effect of being underweight, because your body does not have enough nutrients to grow healthy hair.

Being underweight lowers your blood pressure. If your blood pressure is too low you might feel tired, have dizzy spells and actually faint, according to MSN.

Osteoporosis and Heart Failure

The most dangerous health effects of being too thin are irregular heartbeats and possibly heart failure and death.

Osteoporosis, or loss of bone mass, is more common in very thin women. Those who don't eat enough might be low in the nutrients calcium and vitamin D, which are necessary for strong bones.

Irregular Menstrual Cycle

Irregular menstrual periods and difficulty getting pregnant are side effects of being underweight, because your hormonal system is disrupted from lack of nutrients.


Being too thin, especially if you are approaching middle age, will age your face, according to the New York Daily News. When you lose weight, you also lose the fat in your face that reduces the appearance of wrinkles.

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