Does maintaining a healthy weight still help after a cancer diagnosis?
For most cancer types, a healthy weight after diagnosis is associated with better survival, but note: unintentional weight loss is a warning signal, and for a few cancer types the opposite pattern applies. Always discuss weight and muscle mass with your treating physician.
Obesity after a cancer diagnosis is associated with a higher risk of death in most cancer types. In an analysis of more than 6.3 million cancer patients, the likelihood of dying from cancer was 17% higher in people with obesity, and overall mortality was 14% higher. The risk of cancer recurrence was also 13% higher. These are associations, not proven cause and effect, but the scale and consistency of the findings are impressive.
There are, however, exceptions. In lung cancer, kidney cancer and melanoma, patients with obesity actually survive better than patients without. This is known as the 'obesity paradox'. Researchers do not yet know why this is the case. For these three cancer types, the usual advice about weight does not apply without qualification.
Importantly, weight loss after a diagnosis is not automatically good news. In women with breast cancer who lost 10% or more of their body weight in the 18 months following diagnosis, the risk of death was more than twice as high as in women without such weight loss. Weight gain, on the other hand, was not associated with worse survival. Unintentional weight loss is therefore more of a warning signal than a favourable sign.
Muscle loss is at least as important as the number on the scale. In cancer patients with severe muscle breakdown, median survival was 8.4 months, compared with 28.4 months in patients with good muscle mass. That difference held regardless of whether a person was overweight or underweight. BMI alone therefore tells only part of the story.
Protein-rich nutritional drinks containing omega-3 fatty acids can modestly slow weight loss and muscle loss during chemotherapy (on average nearly 2 kg more weight retained). Whether this also improves survival has not yet been demonstrated. Standard dietary counselling or regular nutritional drinks had no measurable effect on weight in these studies.
Based on a meta-analysis of 203 studies (n>6.3 million), supplemented by observational research in breast cancer (n=12,590), a cohort study in lung and gastrointestinal cancer (n=1,473), a large US cohort (n>900,000), a systematic review of RCTs on nutrition, and observational data in ovarian cancer. All associations are associative in nature; causal evidence from randomised studies is largely lacking.
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 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.
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 exercise lower my risk of cancer?
Regular physical activity is associated with a clearly lower risk of several cancers in large population studies. Alongside that, aim to reduce the number of hours you spend sitting during the day, and use sun protection if you do a lot of outdoor sport.
Does bowel cancer screening really help (less mortality)?
For people aged 45 to 75 with average risk, colorectal cancer screening is worthwhile and widely recommended. It demonstrably reduces the likelihood of developing colorectal cancer, although the evidence for short-term mortality reduction is less definitive than previously thought.
Does fasting or intermittent fasting help prevent cancer?
There is no evidence that fasting prevents cancer in humans; the animal results are promising but contradictory. If you want to address excess weight as a way of reducing risk, intermittent fasting can be a tool for that, but do not expect a direct cancer-preventive effect.