Being overweight gets a lot of attention — and deservedly so. It’s a serious health risk for both adults and children, leading to soaring rates of type 2 diabetes, heart disease, and stroke, among other health problems. But being underweight can lead to just as many and just as serious problems as weighing too much.
Being underweight, according to the Centers for Disease Control and Prevention (CDC) is defined as having a body mass index under 18.5. It means you’re not getting the calories you need — and you may be missing out on key vitamins and nutrients your body needs, too. Weighing too little can lead to growth problems (especially in kids and teens), fragile or weak bones, a weakened immune system, anemia, fertility problems, and a host of other complications.
Also, a study published in April 2014 in the journal BioMed Central Public Health found that underweight individuals have an increased risk of dying from external causes, such as accidents or suicide, compared with individuals who were not underweight. The study followed more than 31,500 individuals, including 945 who were underweight, for 32 years.
This article breaks down everything that can cause people to be underweight, the health problems associated with being underweight, and ways to gain weight that are safe and healthy.
Being Underweight May Be About More Than Just Not Eating Enough
Being underweight can be a result of not eating enough calories, or it can be a result of other health problems, says Eric Feigl-Ding, PhD, nutrition scientist at the Harvard T.H. Chan School of Public Health in Boston. Some of those problems can cause an individual to lose their appetite, consume fewer calories, and lose weight, while other problems cause weight loss even if someone doesn’t change their eating patterns.
Some common causes of being underweight include:
Genetics Some people are born with a naturally speedy metabolism or small appetite, meaning they are less likely to be heavier than others.
Being Very Physically Active Lots of physical activity means you burn more calories than people who are not as active. If you’re an athlete, work out a lot, or work in a job where you’re very active, you likely require more calories on any given day to fuel your body than you would if you were less active.
Illnesses Many conditions, including thyroid problems, diabetes, digestive diseases — like Crohn’s disease or irritable bowel syndrome — and cancer, can cause individuals to become underweight. Your doctor can help identify other symptoms and make the right diagnosis if this is the case for you.
Some Medication Prescription and over-the-counter drugs may cause nausea and weight loss, or reduce appetite, which can lead to weight loss.
Stress Feeling stressed, overwhelmed, or constantly worried can affect appetite and weight loss. These feelings can be caused by work, relationships, or another life event.
Depression and Other Psychological Issues Depression, anxiety, and any mental health condition can interfere with healthy eating patterns and appetite — and affect weight.
Body Image Issues Body image fears and distortions can quickly turn into an eating disorder, which can lead to weight problems and nutritional deficiencies.
Smoking Smoking can dampen appetite, making smokers more likely to be underweight, Dr. Feigl Ding says.