Those trying for a baby are advised to eat only one portion of carbs a day.
The British Fertility Society says the food group increasingly appears to play a role in conception and egg quality.
It follows evidence that a low-carb diet can almost double women’s chances of pregnancy, while too much stodgy food may stop them ovulating.
The latest advice came from British experts at the European Society of Human Reproduction and Embryology in Geneva.
Dr Gillian Lockwood, of the Midland Fertility Clinic in Tamworth, Staffordshire, said couples are advised to follow a ‘fertility diet’ of one carbohydrate group a day, unlimited lean protein and leafy vegetables.
She added: ‘I tell my patients that if they are going to have toast for breakfast, then that is their carbs for the day. They cannot then have a sandwich for lunch and pasta for dinner.’
Private clinic Leeds Fertility has also launched a pilot scheme to teach couples about nutrition, including a cooking class with a major focus on carbohydrates.
White bread and pasta are banned in favour of wholemeal versions, while muesli or porridge, live natural yoghurt or eggs should replace processed breakfast cereals.
SUGARY DIET PUTS BABY AT RISK OF ASTHMA
Eating a sugary diet while pregnant can increase your child’s risk of asthma.
Research found sugary diets seemed to increase damage to the lungs, making allergic asthma – which accounts for about half of asthma cases – more likely.
Researchers from Queen Mary University London, Bristol University and others used data from 9,000 mothers who were pregnant in the early 1990s and their children. The findings, in the European Respiratory Journal, said mothers who ate the most sugar were 101 per cent more likely to have children with allergic asthma than those with the lowest intake.
The team believes a high intake of the sugar fructose causes inflammation in the baby’s lungs, making allergic asthma more likely.
Children with a sugary diet were not at any higher risk, suggesting the lungs are more vulnerable in the womb.
The lunchtime sandwich should be ditched for a salad – with biscuits and cakes allowed only as an ‘occasional’ treat.
Foods like white bread are refined carbohydrates, which are simple molecules that break down more quickly in the body, causing a sharp rise in blood sugar.
Over time the body becomes less able to process sugar, leading to possible damage to cells including sperm and a woman’s eggs.
The Society was told that the ‘lightbulb’ moment for experts came following research in 2013 that found a low-carb diet raised women’s chances of having a child. A team led by the Delaware Institute for Reproductive Medicine studied 120 women undergoing fertility treatment.
Those whose diet consisted of less than 40 per cent carbohydrates had a pregnancy rate of 63.2 per cent – almost double the 33.8 per cent rate for women with a higher carbohydrate intake.
Carbohydrates are also believed to make the lining of the womb less receptive to an embryo.
This applies to slender women as well as those who are overweight.
Professor Adam Balen, chairman of the British Fertility Society, said: ‘We know that diet has a major impact on the chance of conception and on egg quality and increasingly it seems that carbohydrates play a particular role.
‘When trying to conceive, men and women should have individual checks on their diet, and on levels of vitamins, minerals and nutrients.’