It is the perfect excuse to push aside that salad and pat yourself on the slightly rounded tummy. Scientists have shown it may be better to stay fat than go on diet after diet. A study of thousands of obese men and women found that more than one in three were perfectly healthy or had only slight health problems.

Contrary to the much-publicised message that one has to be thin to be well, they were no more likely to die at any given time than someone of an ideal weight. Indeed, they were less likely to be killed by heart disease. They were also in better health than those who had fought a constant battle with their weight by repeatedly dieting, only to pile the pounds back on.

The researchers say there is more to good health than how a person tips the scales – and some people classed as overweight are fine as they are. Rather than try to shed their excess pounds, something that can do more harm than good if repeated time after time, they should simply concentrate on not putting on any more weight.

The advice comes from researchers at Toronto’s York University who tracked the health of more than 6,000 obese men and women for an average of 16 years.

They underwent medical and physical tests and their results were compared with those of thousands of people of normal weight. This clearly revealed that being slim isn’t always superior, according to the journal Applied Physiology, Nutrition and Metabolism.

Those who are overweight but healthy may also exercise more and eat better than thin people who smoke to suppress their appetites. And a stressed-out, sedentary person of normal weight may be in worse shape than a plump person who exercises and keeps stress levels under control.

The Canadian researchers said that rather than using body mass index, or BMI, a measure of weight compared to height, to judge whether a person needs to lose weight, doctors should look at overall health.

A previous study found that pensioners who are slightly overweight live longer than those of a normal weight.

The Australian researchers said a bit of extra padding may give someone the reserves needed to recover from illnesses. It is also possible that concern about the health of the overweight means that problems are spotted and treated earlier.