Does a large belly increase my risk of cancer more than being simply overweight?
A large belly raises the risk of several types of cancer more than being simply overweight, especially in men. Having your waist circumference measured is therefore more meaningful than watching the scales alone.
In men, a large waist circumference is a stronger risk factor for cancer than a high body weight. Each step up in waist circumference raises the risk of obesity-related cancers by 25%, compared with 19% for BMI. In women the difference is smaller: waist circumference and BMI are equally good predictors, each with a risk increase of 13% per step, and waist circumference adds little extra information on top of body weight in women.
Why belly fat appears more dangerous than fat elsewhere in the body has a biological explanation. Belly fat is hormonally active: it causes a low-grade inflammation that never fully goes away, raises insulin levels, and disrupts the balance of growth factors and sex hormones. This encourages cells to keep growing and makes it harder for damaged cells to die off, which promotes the development of tumours.
The difference is clearest for certain types of cancer. For bowel cancer, waist circumference remains an independent risk factor in a study of more than 23 million people, even when BMI is taken into account, while BMI itself drops out as a predictor. People with the largest waist circumference have a 42% higher chance of developing bowel cancer than those with the smallest. For oesophageal cancer, a large belly is associated with a risk more than twice as high. For every 10 cm increase in waist circumference, the risk of lung cancer rises by 10%, which stands out because a high body weight actually works in the opposite direction there.
There is also a notable exception: for prostate cancer, a larger waist circumference is linked to a lower risk of cases detected early. This is probably not a genuinely protective effect, but rather a distortion caused by heavier men being screened less often. No link has been found for advanced prostate cancer or death from prostate cancer.
This answer draws on several large studies in people, including one with more than 23 million participants looking at bowel cancer. The associations have been consistently shown across multiple cancer types, but they are associations: the studies cannot prove that belly fat directly causes cancer. The evidence on how belly fat works is well supported but comes largely from laboratory and animal studies.
Does being overweight increase my risk of cancer, and if so, which types?
Excess weight increases your risk of at least 13 types of cancer, including uterine, colorectal, breast and liver cancer. Losing weight reduces that risk, although it remains unclear whether all methods of weight loss are equally effective for immune defence against cancer.
Does sitting a lot increase my risk of cancer, even if I exercise?
Sitting a lot increases your risk of certain cancers, even if you exercise. In addition to moving regularly, try to reduce your sitting time itself, because the two only partially compensate for each other.
Does eating a lot of sugar increase my risk of cancer?
Drinking large amounts of sugary drinks is associated with a noticeably higher risk of certain cancers, especially early-onset bowel cancer and liver cancer. The link is associative, but consistent enough to make cutting back on soft drinks and fruit juice a concrete priority.
Does poor sleep increase my risk of cancer?
Poor sleep, and sleep apnea and night-shift work in particular, is associated with an increased cancer risk. Whether you personally face a higher risk depends on which sleep problems you have; at the very least, have any apnea symptoms evaluated.
Does working at night increase my risk of cancer?
Night work probably increases the risk of breast cancer, and possibly of other types of cancer. If you have been working night shifts for years, it is worthwhile to discuss this with your doctor and to stay alert to population screening programmes.
Does eating burnt food increase your risk of cancer?
Burnt or heavily grilled meat contains substances that cause cancer in animal studies, but whether ordinary exposure measurably increases cancer risk in humans has not yet been proven. Those who want to limit the risk should more often choose boiling or steaming over grilling, and leave blackened pieces aside.