Does a large belly increase my risk of cancer more than being simply overweight?
A large belly increases the risk of several cancer types more than being simply overweight, especially in men. Having your waist circumference measured is therefore more meaningful than paying attention only to the scales.
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 distinction is smaller: waist circumference and BMI are equally good predictors, with a risk increase of 13% per step, and waist circumference adds barely any extra information on top of body weight in women.
Why abdominal fat appears more dangerous than fat elsewhere in the body can also be explained biologically. Abdominal fat is hormonally active: it causes low-grade chronic inflammation, raises insulin levels, and disrupts the balance of growth factors and sex hormones. This stimulates cell growth and inhibits cell death, which promotes tumour formation.
For some cancer types the difference is clearest. In colorectal cancer, waist circumference remains an independent risk factor in a study of more than 23 million people, even when BMI is taken into account. BMI then drops out as a predictor. People with the largest waist circumference have a 42% higher chance of colorectal cancer than those with the smallest. For oesophageal cancer, the risk associated with a large waist rises to more than twice as high. For every 10 cm increase in waist circumference, lung cancer risk rises by 10%, which is striking because a high body weight actually works in the opposite direction there.
There is also a noteworthy exception: in prostate cancer, a larger waist circumference is associated with a lower risk of early-detected cases. This is probably not a genuinely protective effect, but rather a distortion caused by heavier men being screened less often. No association has been found for advanced prostate cancer or prostate cancer mortality.
This answer draws on several large human studies, including a study of more than 23 million participants on colorectal cancer. The associations have been consistently demonstrated for multiple cancer types, but they are correlations: the studies cannot prove that abdominal fat directly causes cancer. The mechanistic evidence (how abdominal fat works) is well supported but derives largely from laboratory and animal research.
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 sugar-sweetened beverages is associated with a noticeably higher risk of certain cancers, particularly early-onset colorectal cancer and liver cancer. The association is observational, but consistent enough to make reducing soft drinks and fruit juice a concrete point of attention.
Does eating heavily heated or charred food increase your risk of cancer?
Heavily heated or charred meat likely increases the risk of certain types of cancer, although the associations in humans are associative. By not charring meat and varying cooking methods, you can substantially reduce your exposure to these substances.
Does poor sleep increase my risk of cancer?
Poor sleep, and certainly untreated sleep apnoea, is associated with an increased cancer risk, but it has not yet been proven that sleeping poorly causes cancer. Have sleep apnoea checked if you have symptoms, and try to maintain a regular sleep schedule.
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.