Researchers with the U.S. Centers for Disease Control and Prevention spent two years following more than 800 patients with tuberculosis. They gathered information about the patients from the time they were diagnosed with TB to see which medications helped them and what other factors might prevent them from getting TB again.

Awal Khan is an epidemiologist who studies nutrition at the C-D-C. He says TB patients are usually malnourished by the time they are diagnosed with the disease. "They have reduced weight, they have reduced body fat and they are always underweight at TB diagnosis," he points out. Khan compared patients' weights at the time of their diagnosis. He followed those who were far below their ideal body weight to see how often they got diagnosed with the disease again after treatment.

He found that skinny patients who didn't gain back their weight relapsed more often. "The patients who are underweight and did not gain weight...are (at) 2.4 times higher risk of having (a) relapse, compared with those who gained at least 5% of their body weight during the two months of treatment," he explains.

Khan says patients were defined as relapsing if they finished treatment and were diagnosed with TB again within two years. Normally, about 5% of all patients relapse. But Khan says really skinny patients who didn't gain weight relapsed about half the time.

Weighing patients is more easily done than lab tests or X-rays. Khan says this could become a low-cost way for doctors in what he calls "resource-limited countries" to target recovering TB patients at risk for relapse. The research is published in this month's issue of the American Journal of Respiratory and Critical Care Medicine.