Yoyo dieting benefits health and can be compared to going to the dentist, according to a scientist whose research appears to support the extreme slimming method.
US biostatistician Dr David Allison found repeated crash diets did no harm to obese mice.
In fact, serial dieting animals lived longer than those that remained obese.
He questions the widely held view that yoyo dieting is harmful and should be avoided.
Dr Allison, of the University of Alabama in Birmingham, said: "If you go the dentist for your six-month evaluation, they find there's some plaque around your teeth and scrape it off, and then they give you a toothbrush and piece of string and send you out and say keep up the good work.
"And six months later, guess what, the plaque is back on. Just like weight loss. Nobody says dentistry is a failure. They say that's OK."
Speaking at the American Association for the Advancement of Science annual meeting in Boston, Massachusetts, he added: "We think it's probably not a bad idea to lose weight even if you are going to gain it back and redo it every few years."
Leading nutritionist Susan Jebb, professor of diet and population health at Oxford University, said it was better to try losing weight than to do nothing.
"I agree with the notion that losing weight is generally worthwhile, even if you put the weight back on again," she said.
"We have good evidence from long-term follow up studies after controlled intervention studies in humans that there is a benefit."
But Professor Tim Spector, of King's College, London, author of The Diet Myth, spoke out strongly against yoyo dieting.
"Data in humans shows that yoyo dieting makes you gain weight long term. In our study of 5000 twins, the yoyo dieter was usually heavier long-term than the identical twin who didn't diet," he said.
A recent Israeli study in mice had linked yoyo dieting to a massive change in gut microbe population that permanently altered energy regulation, Prof Spector said.
The bugs caused obesity when transplanted into other mice.
"So the evidence for me shows crash calorie restriction dieting is to be avoided at all costs," Prof Spector said.
