Women may be able to lower their risk of endometriosis by eating less red meat, according to Italian scientists.
Eating red meat more than seven times per week increased the risk
Endometriosis occurs when the tissue which normally lines the uterus is found elsewhere in the body, causing pain and sometimes infertility.
In the study, women who ate meat every day were up to twice as likely to have endometriosis than women who ate less meat and more fruit and vegetables.
Dr Fabio Parazzini's research appears in the journal Human Reproduction.
The study authors from the University of Milan interviewed 500 women with endometriosis and 500 healthy women of similar age and background but with no history of endometriosis.
They asked the women about their diet in the past year, including how often they ate meat, dairy produce and fruit and vegetables per week and how much alcohol and caffeine they consumed.
They looked at the responses, estimated how many portions of each food type the women had eaten each week and then ranked the intake as low, intermediate or high.
Foods the women were asked to quantify - low, intermediate or high
Milk - none, 0.5-6 portions or 7 or more portions per week
Meat - 0-3, 4-6 or 7 or more portions per week
Liver - none or 0.5 or more portions per week
Carrots - none, 1 or 2 or more portions per week
Green vegetables - 0-6, 7-12 or 13 or more portions per week
Fresh fruit - 6 or less, 7-13 or 14 or more portions per week
Eggs - 0, 1 or 2 or more per week
Ham - 1 or less, 2 or 3 or more portions per week
Fish - 0, 1 or 2 or more portions per week
Cheese - 2 or less, 3-5 or 6 or more portions per week
The women who had the highest intake of meat (beef, other red meat and ham) increased their risk of endometriosis by between 80 and 100%.
In comparison, women who ate lots of fresh fruit and vegetables lowered their risk of endometriosis by about 40%.
The other foods studied had no link with endometriosis.
Dr Parazzini and colleagues said their study was limited because they could only look at some foods people commonly eat.
Also, women who eat a healthy diet with lots of fruit and vegetables might be more healthy in general.
Dr Parazzini said: "Our study does suggest that there is some link between diet and risk of endometriosis and indicates that we now need a proper prospective interventional investigation to study these factors.
If the findings are confirmed, eating the right diet could cut the rate of endometriosis to around 3-4%, which would mean about 800,000 fewer women with the disease in Europe, he said.
"Endometriosis is a distressing condition that affects the quality of life for many women and if there are adjustments that can be made in the diet to lower the risk it is vital that we gain really firm evidence about which foods protect and which foods increase risk," he said.
Dr Janice Rymer, consultant in obstetrics and gynaecology at London's Guy's and St Thomas' hospital said: "It's interesting. There is no reason why dietary factors would not affect endometriosis because we do not know for sure what causes endometriosis.
"So dietary factors may be important," she said.
She said some of her patients with endometriosis had found dietary changes useful.
A spokeswoman from the British Nutrition Foundation said it was too early to draw any conclusions but the findings were promising.
"Endometriosis is an oestrogen-related disease. Diet has been shown to modify the risk of a number of oestrogen-related diseases such as endometrial and ovarian cancer.
She said diets high in compounds known as phytoestrogens - found in soya, dark green leafy vegetables, nuts and legumes - reduced circulating levels of oestrogen in the blood and appeared to be protective against these diseases.
"There have been few studies looking at the effect of diet on endometriosis, but animal studies do suggest that certain foods may offer protection such as omega-3 fatty acids found in oil rich fish.
"Diets high in saturated fats have been shown to increase concentrations of oestrogen in the blood," she said.