All the 2 percent want to do is gain weight

A physician can rule out medical issues that would impede weight gain or cause malabsorption.

Story highlights

  • Two percent of adults in the United States are underweight
  • Difficulty gaining weight can be a frustrating problem
  • Genetics play a big role in why some people are underweight
  • It may be more important to practice healthy habits than worry about weight
Like many 23-year-olds, Amanda Eang is self-conscious about her body. She constantly covers up and wears loose-fitting clothing to disguise her shape.
At five-foot-two, she weighs just 93 pounds, and for years she has tried to gain weight.
"There are a lot of shows about losing weight, but they really don't have anything for people who are underweight," she says. "It's just as frustrating for people who are trying to gain weight."
Eang, who lives in Toronto, says she has tried everything: eating junk food (which left her with high cholesterol), drinking supplements and doing resistance training. She'd like to reach 110 pounds, but she has never even weighed 100 pounds.
Fewer than 2% of adults in the United States are underweight, according to 2007 to 2010 data collected by the National Center for Health Statistics. To be considered underweight, individuals must have a body mass index of less than 18.5. A woman who is five-foot-six, for example, would weigh 114 pounds or less.
For some, difficulty gaining weight can be a frustrating problem and must be approached in a healthy way, experts say.
Ruling out problems
Before attempting to put on pounds, individuals who feel they are underweight should visit their primary care doctor for a complete physical examination, says Craig Primack, a medical obesity specialist and member of the American Society of Bariatric Physicians.
A physician can rule out medical issues that would impede weight gain or cause malabsorption, including celiac disease, lactose intolerance, bacterial overgrowth syndrome or B12 deficiency.
Genetics play a big role in why some people are underweight, Primack says. A high metabolic rate is usually a factor, he says
The rest is a mystery. Experts have done significantly less research about being underweight than causes of being overweight.
If individuals are slightly underweight, it might not be a sign of a problem. They may be in sync with their bodies' needs and avoid overeating, Primack says.
Being naturally underweight is different from an eating disorder, in which individuals consciously try to reduce their size and avoid eating through various means.
"If someone has a problematic relationship with food, that's an eating disorder, and it doesn't matter what your weight is," says Linda Bacon, a psychologist and researcher at the University of California at Davis and author of "Health at Every Size: The Surprising Truth About Your Weight."
In extreme cases, being underweight can lead to difficulty fighting diseases, and for women it could lead to amenorrhea, or inability to menstruate, says Rachel Begun, a registered dietitian and spokesperson for the Academy of Nutrition and Dietetics.
If individuals are underweight and also not getting enough nutrients, this could cause osteoporosis, anemia and other nutrient-related conditions.