Women's small intestines are 30 centimetres longer than men's

Women’s small intestines are longer than men’s, with this added length probably helping them to better absorb fat and other nutrients if needed for pregnancy and breastfeeding.

“The small intestine is all about absorption, absorption, absorption,” says Amanda Hale at North Carolina State University. “It’s where you get the vast majority of your nutrients from everything you eat.”

Students in anatomy classes aren’t often taught about individual differences and instead focus on organs that follow textbook descriptions, says Hale. But these differences could help to inform healthcare decisions, she says.

“There’s a sort of formulaic approach centred on what’s average or what most people experience,” says Hale. “That’s versus individualised medicine, where you see if a person has specific features about their digestive system that might be contributing to what’s going on and which doesn’t meet the status quo.”

Concerned that important differences could be going undetected, Hale, Erin McKenney – also at North Carolina State University – and their colleagues measured the digestive organs of 21 female and 24 male human adult cadavers that had been donated to Duke University, North Carolina.

They found that, on average, the male cadavers’ small intestines were slightly over 4 metres in length, while those of the female cadavers were 30 centimetres longer. A statistical analysis suggests that this difference wasn’t a chance finding.

“If [women’s small intestines] are longer and there’s more surface area, that means they can pull more from everything that they eat,” says Hale. “That might be related to reproduction, and it most likely is.”

However, this anatomical difference probably doesn’t entirely explain why some gastrointestinal conditions are more common in one sex than the other. For example, Temple Health in Pennsylvania reports that women are more likely to develop Crohn’s disease – inflammation of any part of the digestive system, from the mouth to the anus – but men are more likely to have ulcerative colitis – inflammation of the large bowel, from the colon to the anus.

Sex-related differences in our immune systems and genetics probably play important roles in these conditions, says McKenney.

The researchers also found that the lengths of other organs differed among the cadavers, but there was less of a clear signal in variation occurring between the two sexes. For example, the cadavers’ gall bladder lengths ranged from 5.5 to 12.5 centimetres, while their appendixes spanned from 1.4 to 12.7cm.

Some of the cadavers also had colons – the longest part of the large intestine that removes water and some nutrients from partially digested food – that were more than twice as long as the others.

In general, the organ lengths weren’t related to the cadavers’ heights, which ranged from 149 to 184 centimetres, nor the size of their other organs. For example, having a longer gall bladder didn’t necessarily correlate with a longer appendix.

Overall, the study points to the importance of taking people’s unique anatomy into consideration when diagnosing and treating them, the researchers write in their paper.

“It helps cultivate an awareness of and appreciation for the vast amount of variation that there is, and how all these different clinical conditions would manifest in a variety of ways if our bodies are so inherently different,” says McKenney.

The study was made up of a relatively small number of subjects, but the researchers say that could strengthen their findings. “It is worth noting here that we found such variation even though we measured just 45 human cadavers,” they write.

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