Email to Your Friends

What Are The Health Risks Associated With Being Underweight?

High metabolism, physical exertion, diseases, mental instability and genetics can be causes for your bony structure. Liver issues can also leave your body ineffective in absorbing nutrients from food. Weak bones that easily suffer fractures, infections due to weak immunity, malnutrition, stunted growth in children, anemia and infertility can be health issues from being underweight.

Super slim, skinny, curvaceous – the fashion industry and the media of the world are often accused of distorting the way we perceive the human body. Along side, the obsession with the ill-effects of obesity and the clamor for weight loss have hit a crescendo today. Amidst all the body image battles raging across societies, lower body weight usually gets away with minimum scrutiny. Many even secretly condone it as a “good problem.” But the reality is that being underweight can bring its share of health risks and can even be symptomatic of an underlying disease.

So what constitutes “underweight”? A person is considered underweight if their body mass index (BMI, which correlates weight to height) is under 18.5 or if body weight is about 15% to 20% below the normal weight for their age and height group.1

Why Underweight?

A person could be underweight due to a host of factors.


Scientists have discovered that genetic factors can lead to extreme thinness or low body weight. If being thin runs in your family, it’s likely that you will also be underweight, which may be due to higher metabolism. You may also have a naturally small appetite. Research shows that people with extra copies of certain genes (a gene overdose) are also much more likely to be very skinny.2


Many prescription medicines cause nausea and reduction in appetite, leading to weight loss. Treatments such as chemotherapy can also reduce appetite and worsen weight loss caused by illness.

High Physical Activity

People who engage in high physical activity burn more calories than people who are inactive. These people tend to move around more, burning more calories than they take in. High frequent workouts can also affect your body weight.


Various health conditions such as thyroid problems, diabetes, gastrointestinal diseases, or cancer can affect your appetite, metabolism, as well the body’s ability to absorb nutrients from food. This may lead to sudden weight loss. People with liver problems may also be unable to absorb nutrients adequately.

Psychological Issues

Factors like stress and depression can disrupt healthy eating habits. Patients suffering from depression not only often have a reduced appetite, but may also lose weight at an alarming rate.

Health Risks Of Being Underweight

People who are underweight are typically not getting enough calories to provide energy to their bodies. They may also be suffering from malnutrition because of the insufficient intake of vitamins and minerals. Being underweight may greatly increase your risk for the following health disorders.

Fragile Bones

A healthy body weight is important for bone health throughout life. Studies show that being underweight raises the risk of fracture and bone loss, as weight loss is also associated with bone loss.3 Being underweight for your height increases your risk of bone injury and osteoporosis. A low body weight with a deficiency in vitamin D and calcium can also lead to weak bones.

Weakened Immune System

Severely underweight individuals may have a weak immune system, leaving them open to infection. This can be attributed to the insufficient nutrients in the body, which leads to an inability to restore energy and difficulty in fighting illness.4

Inhibited Growth And Development

Children who are underweight may have stunted growth and poor brain development, as their bodies do not get the recommended amount of nutrients for growth and healthy development.5


Being underweight increases the risk of anemia caused by iron, folate, and vitamin B12 deficiency. This condition can result in dizziness, headaches, and fatigue and may leave you feeling drained and tired.6

Fertility Issues

In women, low body weight can lead to irregular periods, lack of periods, and infertility. If you’re missing periods, you won’t release an egg (ovulate) during each cycle, which can lead to difficulty in conceiving. Women with BMI of between 20 and 25 are considered to have a greater chance of conceiving than women with a BMI below or above this range.7

What’s The Verdict?

Being underweight, in some cases, might just be the way you are made. If you are eating and feeling healthy, your weight is constant, and there are no indications of a medical problem, the alarm bells needn’t go off yet. But if lower body weight is a result of poor nutrition or some underlying health condition, you have a concern at hand that needs immediate attention. Either way, seeing a doctor or dietician for an evaluation is a good first step to understanding your body and what it needs.

References   [ + ]

1. Assessing Your Weight and Health Risk, National Heart, Lung, and Blood Institute.
2. Gene overdose’ causes extreme thinness, Imperial College London.
3. US Department of Health and Human Services. “Bone health and osteoporosis: a report of the Surgeon General.” Rockville, MD: US Department of Health and Human Services, Office of the Surgeon General 87 (2004).
4. Black, Robert E., Saul S. Morris, and Jennifer Bryce. “Where and why are 10 million children dying every year?.” The Lancet 361, no. 9376 (2003): 2226-2234.
5. Approach to the Underweight Child, The University of British Columbia.
6. Underweight adults, NHS.
7. How can I increase my chances of getting pregnant? NHS.
