Women who eat just one baked potato a week are a fifth more likely to suffer diabetes during pregnancy, a major study has found.
Consuming the vegetable in any form before conceiving significantly raised the risk of developing the condition when they are expecting, a ten-year project involving 15,000 women found.
When potatoes were substituted for other vegetables or pulses such as beans, lentils and peas, the risk dropped by around a tenth.
The study team, which included scientists from Harvard Medical School, suspect that the readily-absorbable starch in potatoes may be to blame.
Women eating a potato a week before conceiving ‘are 20 per cent more likely to develop diabetes’. Scientists suspect the absorbable starch in potatoes may be to blame
A study published in the British Medical Journal found that women who ate one serving of potato a week were 20 per cent more likely to suffer diabetes in pregnancy – known as gestational diabetes – even when their weight was taken into account.
Those who ate two to four servings a week had a 27 per cent increased risk.
The figure rose to 50 per cent among those who had more than five servings a week.
One serving included one baked or boiled potato, 237ml of mashed potatoes or 113g of chips.
In the study of more than 21,000 pregnancies, 854 were affected by so-called gestational diabetes – which usually disappears after the birth but can lead to the more serious Type 2 condition.
The authors stressed that the study did not prove that potatoes caused diabetes.
They said potato consumption before pregnancy ‘was significantly associated with an increased risk’ of the condition – but found no specific link for eating chips alone.
They added: ‘Though potatoes are rich in vitamin C, potassium, dietary fibre and some phytochemicals, unlike other vegetables they can have detrimental effects on glucose metabolism because they contain large amounts of rapidly absorbable starch.’
High potato consumption had already been associated with insulin resistance and an increased risk of Type 2 diabetes.
The NHS estimates that up to 18 per cent of women giving birth in England and Wales are affected by gestational diabetes.
Women are screened in pregnancy as there are often no symptoms – but the condition can increase the risk of stillbirth, miscarriage and premature labour.
Swapping potatoes for vegetables, or pulses such as beans, lentils and peas, reduces the risk
It usually develops in the third trimester (after 28 weeks) and usually disappears after the baby is born.
However, women who develop the condition are more likely to develop Type 2 diabetes later in life.
Emily Burns, research communications manager at Diabetes UK, said the findings need to be investigated further.
Dr Louis Levy, of Public Health England, said: ‘Our advice remains the same: base meals around a variety of starchy foods, including potatoes with the skin on, and choose wholegrain varieties where possible.’
And Dr Michael Heard, a spokesman for the Royal College of Obstetricians and Gynaecologists , added: ‘Most women with gestational diabetes will have healthy pregnancies and healthy babies.
‘While this small study found an increased risk of gestational diabetes for women who ate potatoes, there are a number of limitations to the study design, including that potatoes were included as a vegetable rather than a starchy food, and that gestational weight gain was not measured.
‘Importantly it does not show a causal link between eating potatoes and increased risk of gestational diabetes.
‘Women should not be alarmed by this study. Potatoes are a valuable carbohydrate and our advice continues to be that women should eat a healthy balanced diet including five portions of fruit and vegetables a day, starchy foods, lean protein and fibre-rich foods.’