The largest data set I’ve come across so far in nutrition studies and seems like they put a lot of effort into the data analysis to correct for other cancer promoting factors like age, gender, physical activity, smoking behavior etc. (Overall pretty impressive study in my opinion, although I’m not an expert)

Yet, for example, the group with the highest amount of ultra processed food in their diet contains 6% more smokers and 10% less physical activity. They correct for each factor individually but the combined effect of the two might lead to a higher risk than expected. To get these combined effects right you need a lot more data though and it’s probably hard to get good statistics on people which do a lot of sports don’t smoke and eat a lot of ultra processed food.

Which brings me to the question, why for these studies it is always so desirable to find out the increase in risk of a single factor. I would expect a statement like “if you neither smoke, do sports, and eat healthy food you have x% less chance to get cancer” to be more sound.