Fighting the flab? well take heart it could all be down to your hormones - or it seems down to one in particular.
Most serious dieters will have experienced that seesaw of losing the pounds only to pile them all back on again later.
Now doctors at Columbia University Medical Centre in New York, have discovered why it is so hard to maintain weight that loss.
The researchers examined the effects of the hormone leptin, which apparently plays a key role in regulating our metabolism and tells our body when it has had too much food.
They found that when weight is shed , the levels of leptin also fall, making it harder to burn off the calories and making the weight creep back up.
They believe their findings could explain why 85 per cent of dieters fail to adhere to their target weight and could also pave the way for new leptin based dieting drugs.
Dr Michael Rosenbaum, who led the research says the key to maintaining weight loss is to keep the leptin levels high.
Rosenbaum says that anyone who has ever tried to lose weight realises that you never lose as much as you should for what you are eating, and, even when you reach a weight you are happy with, you are never able to sustain that level of thinness.
He says that Leptin fools the body into being happy with a lower weight, but won't help you lose weight but it should help you keep weight off once you have lost it.
In their study Dr Rosenbaum's team looked at the effects of leptin on ten healthy volunteers and discovered that as the men and women lost weight, their leptin levels also fell.
They found that giving them leptin allowed them to maintain to their new weight.