Diverticulitis is usually relatively straightforward to diagnose and treat.

About 1% of the UK population is likely to be hospitalised in their lifetime due to the condition. But scientists don’t know what causes it

John Slater, a former railway worker who lives in Boston, Lincolnshire, was 40 when he first went to the doctor with gut problems. Along with “colossal” lower abdominal cramps, he had started passing blood from his rectum. His doctor thought he had irritable bowel syndrome (IBS) and then, when the bleeding worsened, an ulcer was suspected. It wasn’t until Slater ended up in A&E, after 12 years of debilitating symptoms, that a colonoscopy revealed adhesions in his bowel lining. “The walls were fused together,” is how Slater puts it.

The cause turned out to be a rare and extreme form of diverticulosis – a complication arising from the formation of pouches in the bowel lining known as diverticulitis. The presence of such pouches usually affects westerners over 50, with the incidence increasing with age.

A section of Slater’s small bowel had to be removed, along with his appendix. “There’s now a mesh attached to my spine to hold the bowel up,” he says. But two inoperable pouches remain. “I’m just waiting for one of them to suddenly wake up and then it will start again. I’m living day to day.” Meanwhile, he still has intermittent bleeding and is on medication for pain and to help his bowel function, along with a medium-fibre diet with plenty of fresh fruit, and wants to raise awareness of the condition.

While Slater’s case is unusual, diverticulosis is very common, says Robin Spiller, professor of gastroenterology at the University of Nottingham. “If you do postmortems on people, 40% of 65- to 74-year-olds will have diverticulosis, and many of them will never have had any symptoms.” Some people “have one little pouch which, of course, doesn’t do anything, while others can have 20-100 of them”. Most people remain blissfully unaware they have the pouches at all.

Trouble can occur when the pouches get pellets of fibrous material, known as fecaliths, lodged in them. This can be harmless, but will in some people lead to infection and inflammation and, in rare cases, perforation of the gut, causing intestinal waste to leak into the abdominal cavity.

Calculating how many of the 40% with diverticulosis will experience any trouble is difficult, Spiller says, “but it’s probably something like one in 10”. Hospitalisation will only be necessary when serious complications occur. “About 1% of the (UK) population could expect to be hospitalised with diverticulitis in their lifetime,” he says.

‘There are people who get pain every day, which lasts a few hours, maybe precipitated by food …’

Much of the time, fecaliths lurking in diverticular pouches aren’t remotely sinister. The trouble occurs, Spiller says, “if food residue gets stuck in there and puts pressure on the lining, which is very thin. Then it might cause a break in the lining and that might let bacteria in and cause inflammation.” Sometimes the pouches bleed and the worst-case scenario, he says, is if the walls burst. That condition, known as peritonitis, can be life-threatening.

Diverticulitis is usually relatively straightforward to diagnose and treat, says Spiller. “You’ll get a fever, a raised white blood cell count, pain and tenderness – similar symptoms to appendicitis.” You might be hospitalised, but most cases can be treated with antibiotics. Infection can recur intermittently: “A quarter will get another attack in the next year.”

What is more difficult to diagnose is when patients have pain related to the diverticular pouches, but no infection. “There are people who get pain every day, which lasts a few hours, maybe precipitated by food. This is very difficult to distinguish from IBS,” says Spiller. In such cases, it may be that another underlying problem, such as “incoordinate contractions”, is causing both the pouches to form and the pain. Contractions in the bowel, Spiller explains, “are carefully controlled to move things along or hold them back. But if you have damage to the nerves, from ageing, for example, then these coordinations fail and that puts the pressure up.”

Part of the reason the risk increases with age is that connective tissue weakens. While on the outside this leads to skin wrinkles, says Spiller, “internally, a weaker colon wall can lead to pouch formation”.

Diverticulosis is a peculiarly western affliction, but Spiller says none of the theories about why this may be are proven by scientific study: “Many of them are probably wrong.” However, it is almost certainly linked to diet or environment. Diverticular disease is rare in Africa and Asia and studies have shown that the longer people from these areas live in North America or Europe, the higher their risk grows.

“Something has made our colons not as strong as they should be,” Spiller says.

A diet lacking in fibre gets most of the blame, but Spiller says the evidence is weak. The most-quoted study looked at data from 43,881 male healthcare professionals, but it only shows associations rather than causation. The study found that both consumers of high-fibre diets and dedicated exercisers had the lowest diverticular disease risks. “You could say these people were more health-conscious overall and most of their diseases are less,” says Spiller.

There are other elements of the western diet that could be weakening our guts. “It could be high fat,” says Spiller. “Some have argued that the bacteria are different in people with diverticulitis, but there’s very little evidence on that at the moment.” There may even be other, non-dietary aspects of the western lifestyle that have an effect.

The precise cause, he says, could only be established through long-term randomised trials with subjects consuming either a high-fibre or a low-fibre diet and then followed for 10-20 years – but this would be prohibitively expensive and unlikely to attract many participants. Meanwhile, this common condition, which Spiller says “can seriously impair the quality of life of elderly people, is neglected because it’s not an easy problem, and the fact that it doesn’t affect young people works against it. But I do think we need to raise awareness and more work should be done. It’s important.”