Well, that's other way to see it. The effects of carcinogens at low doses are increase in cancer probability, and is almost definitely linear (as it is added to existing mutations, and you are effectively dealing with a small piece of a mutation vs cancer risk curve, at a non-special point).
You have to be careful what you mean by carcinogen. I suspect what you're saying is true for some chemical carcinogens and ionizing radiation in single burst exposures, but not for other time varying patterns of ionizing radiation exposure.
It hasn't been confirmed in humans, but ionizing radiation exposure most certainly doesn't have a linear dose response with in vitro cell lines. Well, it does for single doses- but initial doses to be protective against future doses (hormesis): http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1533272/?tool=pmcentrez
Nutrition is a case where we have to try to make the best possible use of the data we have no matter how terrible, because we have to eat something now to sustain us while we plan and conduct more experiments.
I want to apply Bayes theorem to make rational health decisions from relatively weak data. I am generally wondering how one can synthesize historical human experiences with incomplete scientific data, in order to make risk-adverse and healthy decisions about human nutrition given limited research.
Example question/hypothesis: Does gluten cause health problems (ie exhibit chronic toxicity) in non-coeliac humans? Is there enough evidence to suggest that avoiding gluten might be a prudent risk-adverse decision for non-coeliacs?
We have some (mostly in vitro) scientific data suggesting that gluten may cause health problems in non-coeliac humans (such as these articles http://evolvify.com/the-case-against-gluten-medical-journal-references/). Let's say for the sake of arguing, that I can somehow convert these studies into a non-unity likelihood ratio for gluten toxicity in humans (although suggestions are welcome here too).
However, we also have prior information that a population of humans has been consuming gluten containing foods for at least 10,000 years, without any blatantly obvious toxic effects. Is there some way to convert this observation (and observations like this) into a prior probability distribution?