It's the one issue any father should know to leave well alone.

Now, new research backs up what the wise among us already knew - never comment on your daughter's weight.

Remarking on how your teenager looks can leave her unhappy with her size in later life, scientists discovered.

Women who recall their parents' comments about their weight are more likely to be fatter as adults.

They are also less satisfied with their size, the study revealed.

Women who recall remarks about their weight from childhood are more likely to be overweight and less likely to be satisfied with their size as an adult, a study by the Cornell Food and Brand Lab found (file photo)

The study's author, Professor Brian Wansink, of the Cornell Food and Brand Lab, said: 'Commenting on a woman's weight is never a good idea, even when they are young girls.

'If you're worried about your child's weight, avoid criticising them or restricting food.

'Instead, nudge healthy choices and behaviours by giving them freedom to choose for themselves and by making the healthier choices more appealing and convenient.

'After all, it's the choices that children make for themselves that will lead to lifelong habits.'

The study asked 501 women between the ages of 20 and 35 about their body image - as well as finding out how often their parents made remarks about their figure.

Both healthy and overweight women who could recall their parents comments were less satisfied with their weight as an adult, proving that any comments made to young girls can be damaging.

Those with a healthy body mass index (BMI) were found to be 27 per cent less likely to remember their parents comments than women who were regarded as overweight.

Comments made to young girls stick with them for life, researchers said. Rather than criticising daughters or restricting their food, nudge healthy choices and behaviours, they added (file photo)

In fact, research published last year reveals it is better not to mention weight at all.

A study found telling someone they are overweight is likely to make them eat more and continue piling on the pounds.

The stress of being made aware they are out of shape may be the trigger that stops them from adopting a healthier lifestyle.

Psychologists found that believing you are overweight is counter productive – highlighting a problem for doctors trying to combat the obesity epidemic.

They suggested that people who are unaware they are overweight may be better off being kept in the dark.