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Women who eat less red meat have a lower risk of developing endometriosis, a 22-year-long study has found.

Endometriosis occurs when tissue from the womb spreads to other places like the bowel or ovaries. It affects one in ten women of reproductive age and can cause severe pain and infertility.

No one knows exactly what causes the condition, but it is thought to relate to excess levels of the hormone oestrogen.

at the Fred Hutchinson Cancer Research Centre in Washington and her colleagues wondered if eating red meat, which is thought to influence oestrogen levels, may play a role.

To find out, the team followed a group of more than 80,000 premenopausal women across the US from 1991 to 2013. Participants completed a questionnaire about their diet every 4 years, and the researchers noted any cases of surgically-confirmed endometriosis.

They found that women who ate more than two servings of red meat per day had a 56 per cent higher risk of developing endometriosis than those who ate no more than one serving per week.

Cutting down

Unprocessed forms of red meat like steak and pork chops had a greater effect than processed sources like bacon and sausages. In contrast, consumption of chicken, fish, shellfish and eggs was unrelated to endometriosis.

The reason why red meat increases endometriosis risk is unclear, but its effect on oestrogen may play a role, says Harris. Previous studies have found that eating red meat increases women’s oestrogen levels, and that high levels of the hormone promote endometriosis.

The latest findings hint that cutting down on red meat could protect against endometriosis and reduce symptoms in women who already have it, but more research is needed, says Harris.

Previous studies have found that switching from a diet high in animal fat to a plant-based Mediterranean diet can reduce oestrogen levels by . Others have found that eating lots of , and staying away from is protective against endometriosis.

Harris and her colleagues are now studying whether adolescent girls who eat a healthy diet rich in fruit, vegetables, whole grains, nuts and seeds are less likely to develop endometriosis as adults. They are also planning to test whether dietary changes can reduce symptoms and improve quality of life in women who already have the condition.