5 Health Problems Caused by Being Too Thin

woman on scale with doctor
Talk to a medical professional about whether your weight is an issue; together, you can develop a plan for gaining weight healthfully.
Keith Brofsky/Thinkstock

The United States is in the midst of an obesity epidemic. As a result, the media is full of stories about how to eat and exercise so that we can lose weight and avoid health problems such as diabetes, heart disease, stroke and cancer.

Because obesity is so prominent, we often avoid the people on the other side of the scale -- the underweight. And we're not talking about people with eating disorders or dangerous habits such as smoking that keep them thin; in this article, we're concerned about those who just can't put on any weight no matter how hard they try. We might write these people off and say they're lucky that they don't have to worry about their skinny jeans fitting, but as it turns out, people with a body mass index (BMI) of less than 18.5 have their own set of health problems to worry about.


5: Heart Disease and Diabetes

Heart disease and diabetes are usually thought to be problems for the overweight and the obese, but thin people aren't immune from these conditions. It's very easy to be thin yet unhealthy, as naturally thin people might indulge in fast food, skip the gym and think they can get away with it. No matter the number on the scale, though, blood sugar levels and bad cholesterol counts can be rising. Thin people might also skip out on the check-ups that can detect these problems because they think they're in good shape.

Additionally, the very factor that keeps people thin may cause diabetes. People who are naturally very thin are usually that way thanks to genetics, and a 2011 study revealed that these "lean genes" might work by placing fat very deep within the body. Rather than carrying a spare tire, these people might be carrying fat around the heart or the liver. According to the study findings, fat located at these spots might put a person at higher risk for diabetes than visible fat [sources: Naish; Park].


4: Lowered Immune System

woman blowing nose
We're all in danger when there's a cold going around, but very thin people are at risk of having a compromised immune system to boot.
Peter Dazeley/Photographer's Choice/Getty Images

The immune system is like a guard at the gate, ensuring that foreign and abnormal cells do not pass. This system needs fuel to take on invading infections, and unless an underweight person is eating very carefully, he or she could easily starve this disease defense guard. That means that very thin people are at extra risk for getting sick during cold and flu season, and they could be at risk for more serious conditions such as cancer, which begins with abnormal cell activity. If you're very thin, check with a doctor or a nutritionist about dietary supplements that might be necessary to keep you well year-round.

Nutritional deficiencies can also lead to the next problem on our list. What is it?


3: Anemia

Many underweight people find themselves feeling tired all the time. This lack of energy and fatigue is a classic symptom of anemia. Other symptoms of anemia include irregular heartbeat, shortness of breath, dizziness and headache. Anemia is a disease of the blood that occurs when there's a deficiency of red blood cells. These blood cells are responsible for transporting oxygen to the organs, and when they don't show up for work, the body doesn't receive the fuel it needs to energize the body. Anemia is caused by nutritional deficiencies of iron, B-12 and folate, which is another reason why underweight people should constantly check with their doctors about whether they're consuming enough of the right foods.


2: Fertility Issues

woman looking at pregnancy test with fingers crossed
Hoping for a baby? Ask your doctor if your weight will be a problem.

Being underweight can cause many reproductive issues for women. First, a woman's menstrual cycle often stops or becomes irregular when she is too skinny. While that might not matter to a young woman, that irregularity could become an issue when she decides to conceive. Not only is it harder for underweight women to conceive, it's also harder for them to sustain the pregnancy, as menstrual irregularities affect the uterine lining that supports a fetus. According to one study, underweight women who got pregnant were 72 percent more likely to miscarry during the first trimester [source: Naish].

Men aren't off the hook, either -- underweight men are 22 times more at risk for persistent sexual dysfunction such as erectile dysfunction, painful intercourse or inability to ejaculate [source: Goodman]. There may also be a link between a man's weight and the health of his sperm [source: Naish].


1: Osteoporosis and Broken Bones

While many of us worry about having too much body fat, we all have to have a little bit in order to keep our bodies healthy. One task that fat performs is producing estrogen. We associate estrogen with women, but both men and women need it for healthy bones. Without enough estrogen, bones become brittle and prone to breakage. That leaves both sexes at risk for osteoporosis, no matter their age. As a result, a simple fall or accident is more likely to cause serious injury or even death in an underweight person.

To avoid osteoporosis and the other conditions we've discussed in this article, people who fall below the body mass index of normal weight (18.5) should speak to a medical professional about gaining weight safely. For more on diet, exercise and other health matters, see the links on the next page.


Lots More Information

Related Articles

  • American Heart Association. "Common Misperceptions about Cholesterol." June 14, 2011. (July 11, 2011). http://www.heart.org/HEARTORG/Conditions/Cholesterol/PreventionTreatmentofHighCholesterol/Common-Misconceptions-about-Cholesterol_UCM_305638_Article.jsp
  • Aschwanden, Christie. "Fertility 101." Marie Claire via WebMD. Jan. 31, 2009. (July 11, 2011). http://www.webmd.com/baby/features/fertility-101
  • Bouchez, Colette. "Using Your Immune System to Stay Well." WebMD. Dec. 19, 2005. (July 11, 2011). http://www.webmd.com/cold-and-flu/features/using-your-immune-system-to-stay-well
  • Cleveland Clinic. "Amenorrhea." (July 11, 2011). http://my.clevelandclinic.org/disorders/amenorrhea/hic_amenorrhea.aspx
  • Goodman, Brenda. "Size Counts When It Comes to Sex." WebMD. July 7, 2011. (July 11, 2011). http://www.webmd.com/sex-relationships/news/20110707/size-counts-when-it-comes-sex
  • Kresser, Chris. "Think skinny people don't get type 2 diabetes? Think again." The Healthy Skeptic. Sept. 19, 2010. (July 11, 2011). http://thehealthyskeptic.org/think-skinny-people-dont-get-type-2-diabetes-think-again
  • Mayo Clinic. "Anemia." Feb. 19, 2011. (July 11, 2011). http://www.mayoclinic.com/health/anemia/DS00321
  • Naish, John. "Broken bones, depression and lung disease: Why being skinny is bad for you." The Daily Mail. July 5, 2011. (July 11, 2011). http://www.dailymail.co.uk/health/article-2011309/Broken-bones-depression-lung-disease-Why-skinny-bad-you.html
  • National Health Service. "Underweight adults." Sept. 28, 2010. (July 11, 2011). http://www.nhs.uk/Livewell/Goodfood/Pages/Underweightadults.aspx
  • National Osteoporosis Foundation Web site. (July 11, 2011). http://www.nof.org/
  • Park, Alice. "Why Being Thin Doesn't Always Mean Being Healthy." Time. June 27, 2011. (July 11, 2011). http://healthland.time.com/2011/06/27/why-being-thin-doesnt-always-mean-being-healthy/
  • Seeman, Bruce Taylor. "Skinny Isn't Always Healthier." Seattle Times. March 20, 2005. (July 11, 2011). http://seattletimes.nwsource.com/html/health/2002212024_healthskinny20.html
  • WebMD. "Understanding Anemia -- the Basics." (July 11, 2011). http://www.webmd.com/a-to-z-guides/understanding-anemia-basics