March 6, 2006 -- The eating disorders anorexia and binge eating may run in families, according to two new studies.
Both studies appear in the Archives of General Psychiatry. The first study showed that genetic factors accounted for more than half of anorexia cases among more than 31,000 twins in Sweden.
"We were able to show for the first time that there is a substantial genetic component to anorexia nervosa," researcher Cynthia Bulik, PhD, tells WebMD.
The second study showed that binge eating tends to run in families. Genes might be at work, but the study doesn't prove that.
"Basically, what we're finding out is that eating disorders are familial disorders," says Bulik, who worked on both studies and is an eating disorders expert at the University of North Carolina (UNC).
Bulik, who led the anorexia study, directs the UNC Eating Disorders Program. She is also the William and Jeanne Jordan Distinguished Professor of Eating Disorders at UNC's psychiatry department and a professor of nutrition at UNC's School of Public Health.
"For a long time, people have viewed anorexia nervosa as a disorder of choice," Bulik says. "People thought that these were people choosing to lose a lot of weight and diet down to some thin ideal."
She adds that people have also blamed parents and parenting styles "for far too long" for causing anorexia.
Her study included 31,406 twins in Sweden who were screened in 2002 for anorexia and other problems. A total of 1.2% of the women and 0.29% of the men had anorexia.
Anorexia and Genes
Genes appeared to be a big influence on the odds of developing anorexia.
"The way I say it is that 56% liability for developing anorexia nervosa is due to genetic factors and the remaining is due to the environment," Bulik says. "Environment" means factors besides genes.
However, "this is not a one-gene disorder," Bulik says. "We will never find one gene that causes anorexia nervosa. It's a complex trait, and that's a real scientific term which means it's influenced by multiple genes and multiple environmental factors."
Environmental influences -- like cultural emphasis on thinness -- still counts. "I think what this genetic research will lead us to is a better understanding of who is more sensitive to the environmental triggers," Bulik says.
Anorexia's Warning Sign
The Swedish twins had also been studied in the early 1970s, when most of them were teens. That data let the researchers check, in hindsight, for anorexia's warning signs.
The researchers checked BMI (body mass index), physical activity levels, gastrointestinal problems, and neuroticism. Only neuroticism predicted anorexia, the study shows.
Neuroticism is "the tendency to be anxious or depressed, and also a tendency to be emotionally reactive," Bulik says.
"What that means is things that might be like water off a duck's back for someone who is low on neuroticism, [for] someone who's high on neuroticism they're like emotional Velcro," she explains. "So things just stick to them and impact them more, emotionally, than for other people for whom they can just brush it off and move on."
"It's really that tendency towards being anxious and depressed that seems to be the core that predicts the later onset of anorexia nervosa," Bulik says.
Taking It Seriously
"If you have eating disorders that run in your family and especially if you have a child who's starting to show some of these anxious and depressive traits, you should be alert for any signs of eating-disordered behaviors," Bulik says.
"Take them seriously, and if they do become concerning, head right toward early detection and early intervention," she says. "Because we do better when we can detect and intervene earlier [with] anorexia nervosa."
She lists these possible warning signs:
- Falling off the growth curve (losing weight needlessly)
- No longer eating with the family
- Saying things like "I hate my body" or "I feel fat"
- Being very anxious or depressed
- Going on a diet needlessly
If a child is "normal weight and they come home and say they're going on a diet, take that seriously, just as if your child would come home and say, 'I'm going to smoke my first cigarette.' It should be just as much of a red flag," Bulik says.
Bulik also worked on the binge-eating study, along with other experts.
The study included 300 overweight or obese Americans -- half of whom had binge-eating disorder -- and their families. In binge-eating disorder, people consume unusually large amounts of food in a short time (usually less than two hours).
The researchers interviewed the family members. They found that 20% of those with an immediate relative with binge-eating disorder had ever had the same problem, compared with 9% of those whose relative didn't have binge-eating disorder.
The study doesn't show why binge-eating tended to run in families. Genes and environment could both be factors, but it's not clear how much either contributed, write the researchers, who were led by James Hudson, MD, of the psychiatry departments at Harvard Medical School and McLean Hospital in Belmont, Mass.
Checking the Family Tree
"I always ask people, 'Has anyone in your family ever had funny eating habits?' or 'Has anybody in your family ever been really underweight or really overweight?' and then the stories start coming out," Bulik says.
She recalls talking to a black woman whose mother used to vomit after every dinner. The woman said her mother, who was born in the South in the 1940s, always blamed "greasy food" for her vomiting but was very thin and nagged her kids about their weight.
"I said, 'You know, that's really interesting, because I'll bet back then, nobody was diagnosing bulimia nervosa,'" Bulik says. Bulimia nervosa is an eating disorder in which people deliberately throw up their food.
"I think the more we broaden our questions, the more we can capture some of these folks in families who really did have problems but never received a diagnosis," Bulik says.