See what recent research has uncovered on this emotive health issue.
A yo-yo diet is better than no diet for someone who needs to lose weight, scientists have claimed.
New research suggest a U-turn on rollercoaster diets that have been criticised by many experts.
Shedding and regaining weight in a rapid cycle is generally viewed as unhealthy and psychologically damaging. But the new US research conducted on mice suggests it can have long term benefits and even extend life.
Animals that switched between a high-fat and low-fat diet every four weeks lived 25% longer than those which only ate a high-fat diet and remained obese. They also had better blood glucose levels, and lived roughly the same length of time as mice on a continuous low-fat diet.
In addition, preliminary findings indicated that yo-yo dieting mice had reduced levels of cytokine immune system signalling molecules linked to inflammation. Increased inflammation is a major risk factor for diseases such as diabetes, heart disease and cancer.
Study leader Dr Edward List, from Ohio University, told the annual meeting of the Endocrine Society in Boston, US: "If the conventional wisdom is true, it would discourage a lot of overweight people from losing weight.
"The new research shows that the simple act of gaining and losing weight does not seem detrimental to lifespan. The study adds to our understanding of the benefit of losing weight. I would hope that this encourages people not to give up."
Consultant dietician Sian Porter, from the British Dietetic Association, said previous research had shown that yo-yo diets could be "self destructive".
She added it was "not surprising" that yo-yo dieting mice lived longer than mice that were obese. The problem for humans was keeping weight control at a sustainable level.
"It's a good idea to be a healthy weight for your height, but mice aren't people. I think this falls into the category of very interesting but it would be more interesting if replicated in humans."better blood, british dietetic association, cancer study, health issue, heart disease, losing weight, low fat diet, yo yo