Fats hidden in thousands of foods can harm a woman?s chance of having a baby, scientists said yesterday.
They can increase the risk of fertility problems by 70 per cent or more.
Eating as little as one doughnut or a portion of chips a day can have a damaging effect.
The scientists behind the study advised women who want to have a baby to avoid the fats, known as trans fats.
They are used in thousands of processed foods, from chocolate to pies, as well as take-away meals.
They have no nutritional value but are included simply to extend the shelf life of food.
It is very difficult to know the precise amount of trans fats in any food as it does not have to be put on the label.
Nutrition campaigners said the research provided ?considerable new weight and urgency? for trans fats to be banned.
The fats are found naturally in some red meat and dairy products, but most are produced artificially in a high-temperature process called hydrogenation which turns liquid oil into solid fat.
Previous studies have shown they can be linked to artery-blocking ?bad? cholesterol, which can lead to heart attacks and strokes.
Processed and fast foods are already implicated in Britain?s obesity crisis.
One in five Britons is obese and another two-fifths overweight.
Infertility is also a growing problem, with one in six couples having problems on how to get pregnant.
In the study, researchers from the Harvard School of Public Health in Boston looked at 18,500 women trying to conceive and found 438 cases of ovulatory problems