Kalantar-Zadeh noted that the mortality risk for underweight patients might be connected to the disease causing weight loss rather than weight loss leading to more deaths.
Younger patients were also at greater risk if they were obese. They were 1 1/2 times more likely to die than older obese patients and had a 50 percent greater chance of dying in seven years than young people of normal weight.
In populations with chronic diseases "something called the obesity paradox protects older obese patients," said Kalantar-Zadeh. Researchers "have looked at different age groups and have found older populations (among the chronically sick) in whom obesity is not bad. But if you're young, in your 30's or 40's, you're back to the situation where obesity plays against you."
The "nutritional reserves" of obese people may stand them in good stead when they become old and sick, he said.
Hoogeveen said the most important message from the study is that "young obese dialysis patients have a lower survival rate" than same-age patients of normal weight. "It is important to strive for normal weight in this age group," she said. "Maybe this can improve their life expectancy."
Because both studies were presented at a medical meeting, the data and conclusions should be viewed as preliminary until published in a peer-reviewed journal.
Find out more about chronic kidney diseases at the National Kidney Foundation.
SOURCES: Kamyar Kalantar-Zadeh, M.D., Ph.D., M.P.H., professor, medicine, Harbor-UCLA Los Angeles Biomedical Research Institute, associate professor-in-residence, medicine, pediatrics and epidemiology, UCLA David Geffen School of Medicine, and UCLA School of Public Health, Los Angeles; Ellen Hoogeveen, M.D., Ph.D., nephrologist and epidemiologist, department of nephrology, Joeren Bosch Hospital, Den Bosch,
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