Fatty liver and bowel cancer

Fatty liver affects more than the liver. Alongside heart disease, cancers outside the liver are one of the main health risks for people with MASLD, and bowel cancer is the one with the most consistent evidence. In 2026 a panel of 35 liver and bowel cancer specialists from 24 countries, including Australia, published an international consensus statement on this link in the journal Gut. They reached agreement on all 17 statements they considered.

What the evidence shows

Large studies from Asia, Europe and North America find that people with fatty liver are more likely to develop bowel cancer than people without it. Most of the big pooled analyses put the increase at somewhere between 15 and 40 per cent. The link remains after allowing for weight and diabetes, so fatty liver seems to be telling us something about bowel cancer risk on top of those factors. For any one person the extra risk is modest, but across a third of the adult population it adds up to a lot of cancers.

• More metabolic problems, more risk. In a study of almost 10 million people, each additional feature of the metabolic syndrome raised the risk a little further, and people with all five had about a 50 per cent higher risk of bowel cancer before the age of 50 than people with none
• A normal weight does not rule it out. Fatty liver in people who are not overweight still carries a raised bowel cancer risk, and one review found it higher in this group than in people with fatty liver who were carrying extra weight
• Younger adults. Newer studies, mostly from Asia, link fatty liver with bowel cancer and advanced polyps before the age of 50, which matters given that bowel cancer is rising in younger Australians
• After a diagnosis. In people who already have bowel cancer, more severe fatty liver is linked with poorer outcomes and a higher chance of the cancer spreading to the liver

Why the two are connected

Fatty liver and bowel cancer grow from the same soil. With insulin resistance the body makes more insulin to keep blood sugar in check, and insulin also acts as a growth signal for the cells lining the bowel. Excess fat tissue releases inflammatory chemicals, and the balance of fat hormones shifts, with more leptin and less adiponectin. The gut bacteria and the bile acids they produce change as well. The liver sits in the middle of all this because its blood supply comes straight from the gut, which is why doctors talk about a gut-liver axis.

What it means for bowel screening

• Do the free test. In Australia the National Bowel Cancer Screening Program offers a free home test every two years from 45 to 74. Kits are mailed automatically from 50, but people aged 45 to 49 need to request their first one, through the program website or their GP.
• Starting earlier is under discussion. The consensus panel suggested that people with fatty liver, particularly those who also have obesity or type 2 diabetes, could start screening from 40. This is expert opinion and is not part of Australian guidelines. Separate modelling estimated that people with diabetes or the metabolic syndrome reach the same level of risk three to four years earlier than everyone else. If you are in your early 40s with fatty liver and diabetes or significant excess weight, it is reasonable to raise this with your GP.
• Fatty liver on its own is not a reason for colonoscopy. The screening test is the usual first step. Colonoscopy is for a positive screening test, symptoms, a strong family history or previous polyps.
• Symptoms come first at any age. Bleeding from the bottom, a change in bowel habit lasting more than a few weeks, low iron or weight loss you cannot explain should be checked by your GP. Do not wait for a screening test.

The same changes help both

The steps that improve fatty liver are also linked with a lower risk of bowel cancer.

• Steady weight loss. Losing 7 to 10 per cent of body weight over a year improves the liver, and planned weight loss has been linked with fewer obesity-related cancers. Weight loss that happens without trying is different. It can be an early sign of cancer and should be reported to your doctor.
• Less red and processed meat. Both are linked with bowel cancer. More vegetables, fruit, legumes and whole grains help the liver and the bowel.
• Good blood sugar control. In a large study of people with diabetes, an HbA1c below 7 per cent was linked with about a 28 per cent lower bowel cancer risk, and the risk climbed as HbA1c rose.
• GLP-1 based medicines. In observational studies, people with type 2 diabetes taking these medicines had less bowel cancer than those on older diabetes treatments. This has not been tested in trials and is not a reason to start one on its own, but it is reassuring for people who already use them.
• Weight loss surgery. For people with severe obesity, bariatric surgery was linked with about a one-third lower risk of bowel cancer in a nationwide study of around a million people.

Most of this evidence comes from observational studies, which show links rather than proof of cause. The practical message does not depend on that distinction: look after the metabolic health that drives fatty liver, and do not skip bowel screening.