Yo-yo dieting is still beneficial for health, new research suggest, after a study showed serial slimmers live longer than those who simply remain fat.
Experts found those who dropped large amounts of weight, only to regain it later had similar life expectancies to moderate dieters.
Around nine in 10 diets end in failure, but researchers said that people should not be disheartened because a cycle of weight loss and gain is still beneficial than not dieting at all.
Dr David Allison, a biostatistician at the University of Alabama at Birmingham, said people should view dieting like a trip to the dentist.
“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,” he told the American Association Annual Conference in Boston.
“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.
“A concern with obesity is that you lose the weight and you gain it back within two to five years. And if you do this repeatedly, perhaps you’re harming yourself.
“We just finished a study in mice and what we found is that when mice who are obese keep on repeatedly losing and gaining that weight, they live longer than the mice that are allowed to stay obese.
“So 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.”
Around two in three British adults are overweight or obese, which increase the risk of type 2 diabetes, liver disease and cancer.
Susan Jebb, Professor of Diet and Population Health at Oxford University said: “I agree with the notion that losing weight is generally worthwhile, even if you put the weight back on again.
“We have good evidence from long term follow up studies after controlled intervention studies in humans that there is a benefit.”
However other experts cautioned against yo-yo dieting for health.
Professor Timothy Spector, of King’s College, London, author of The Diet Myth: “Data in humans shows that yo yo dieting makes you gain weight long term. In our twin study of 5000 twins the yo yo dieter was usually heavier long term than the identical twin who didn’t diet.
Although mice and men are different , a recent Israeli study in mice found that yo yo dieting causes a massive change in their gut microbes that permanently alters energy regulation. These microbes cause obesity when transplanted into other mice.
“So the evidence for me shows crash calorie restriction dieting is to be avoided at all costs.”
Experts also warned that obesity can be contagious, and said socializing with people who were gaining weight puts others at greater risk of becoming fat as well.
Conversely, if friends like spending time in the gym, it encourages more healthy behavior.
Dr Allison said: “One way people have thought about manipulating these social networks is through intervention programmes – maybe we should not treat people individually, but maybe we should have buddy programmes.
“So you and your buddy come in and get the treatment together.