Does eating heavily heated or burnt food increase your risk of cancer?

Heating starchy foods, such as chips, crisps, toast and biscuits, at temperatures above 120 degrees Celsius produces acrylamide. That is well established chemically. Whether that acrylamide then causes cancer in humans, however, is considerably less certain.

For most common cancers, including colorectal, stomach, lung, bladder and prostate cancer, no statistically meaningful association has been found. Relative risks are almost all close to 1.0, meaning: no measurable difference compared with people who consume little acrylamide.

There are two exceptions that stand out. In women who have never smoked and eat a lot of acrylamide, the risk of endometrial cancer is consistently elevated: a pooled risk of approximately 1.4 across four large cohort studies involving more than 450,000 women. A large French study also found an elevated risk of pre-menopausal breast cancer, particularly the oestrogen-sensitive form. For kidney cancer there is a borderline-significant signal (risk approximately 1.2), but this is not yet sufficiently substantiated. For ovarian cancer in never-smokers the signal is too uncertain to draw conclusions from.

An important caveat concerns measurement quality. Most studies estimate acrylamide intake through questionnaires, which is imprecise and may underestimate the true risk. Researchers have been pointing this out for more than twenty years, and the question of whether acrylamide genuinely causes cancer in humans has still not been definitively answered.

In practical terms: there is no reason for panic over an occasional fried or toasted slice of bread. But if you systematically eat large amounts of chips, crisps and heavily burnt food, the pattern for endometrial and breast cancer in non-smoking women gives sufficient reason to exercise moderation. Burning food less and not cooking at too high a temperature for too long already helps to limit acrylamide formation.