There is a WHO publication called "Food, Nutrition and Cancer" . It's about 3 inches thick, and comes out as revised edition every couple of years. It discusses every cancer known to man from the viewpoint of statistical analysis of deaths in each category.
The evidence is overwhelming. If you smoke, drink, or are obese, you have a much higher probability of dying of cancer. What is remarkable is while alcohol and tobacco are linked to a few very specific cancers, obesity is linked to almost every one of them. The message is quite clear - lose the beer gut.
My own hypothesis is that fat is an accumulator of toxins, inhibiting the body's ability to detoxify them. In point of fact, I could kill any drinker on this forum overnight by massive liver failure with several compounds, and it would be virtually undetectable.
Anyone who has seen the images from an electron microscope of bacteria and viruses would disagree with your hypothesis. Do you think the millions of dollars spent on Stage 4 biological laboratories is money wasted? Your theory says it is.