Harm of "yo-yo" dieting

"Yo-yo dieting" - repeatedly losing, then regaining weight - may harm a woman's immune system. The study by the Fred Hutchinson Cancer Research Centre also found that maintaining the same weight over time appears to have a positive effect on a woman's immune system, according to one of the researchers.

Researchers in the study, published on Tuesday in the Journal of the American Dietetic Association, interviewed 114 overweight but otherwise healthy sedentary, older women about their weight-loss history during the past 20 years. The women had to have maintained a stable weight for at least three months before joining the study. The study, which found that long-term immune function decreases in proportion to how many times a woman has intentionally lost weight, measured natural killer cell activity in the women's blood. Natural killer cells are an essential part of the immune system, killing viruses and leukaemia cells, said Cornelia Ulrich, senior author and an assistant member of the Hutchinson Centre's Public Health Sciences Division. Low natural killer cell activity has been associated, reports news24.com According to bbc.co.uk For instance, those who reported losing weight more than five times had about a third fewer natural killer cells.

The doctors said further research is needed to confirm these findings.

However, they said the study appeared to suggest that yo-yo dieting was bad for health.

"There's clear evidence that weight loss is beneficial for your health," said Cornelia Ulrich, a research assistant professor at the centre.

"What we're concerned about is this pattern of weight cycling where women go up and down."